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Post by sime66 on Dec 6, 2016 12:18:25 GMT
Crank has arrived, and in the meantime I’ve had a few thoughts: I wonder if, with this scheme we still want 125/65 (for a 57mm crank). I think a skim of barrel and/or head is inevitable to get squish and compression better. I’m not sure if/how that head can be skimmed; if the channel for the ring would be cut again or done away with. There is 1mm in the barrel that could be skimmed before going into the fin, so perhaps there is the better idea. I think the chap who did my fragile DR barrel would be able to do this fairly easily. I’ve measured the crank timing as 108/6°, so it would be a fair cut of the I.c. to get /65 if that’s still what’s needed. I have no problem doing the cutting if it doesn’t mess up the balance of the crank; it’s quite a lot of metal to remove. At some stage I will check the crank on a jig too.
I quickly put the crank, piston, casings and barrel together. With no base gasket the Deck Height is indistinguishable from zero, so the base packer will be the deck height. From previous calcs I wanted 0.3mm, but I’ve had no comment on those figures, so don’t know if I was on the right lines or not with those. I guess I’ll make a copper base gasket, so making the right size should be fairly straightforward, depending on finding required thickness.
I wonder if I might find a better solution to port timing now that it seems a skim is needed anyway, and that’s what I’ll look at next, but for now I think I can box all this up again and use the measurements I have.
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Post by pxguru on Dec 6, 2016 15:36:59 GMT
I take it the 57mm crank is usable? I didn't see your edit. A lot of useful information.
0.3mm total of base packer will be ok but no more. A little less will be better if you need to adjust something to get the compression better.
This malossi barrel is extra safe in standard form isn't it? 9:1 Compression is c**p for a kit. As this is to be a lower rpm motor. For the compression, I would aim for trapped compression of near to 7:1 and a squish of 1.0mm if it can be done. if any metal needs to come off this can be from the head. No need for the rubber ring, they are just for babies staying in the shallow end of the pool.
The only issue with going for lower blowdown duration, is that if it doesn't rev high enough, there is no room for increasing the packer, as the blowdown will go too short. Will have to grind the exhaust port up before increasing the packer. I am sure you won't need to but just saying.
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Post by sime66 on Dec 6, 2016 18:14:08 GMT
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Post by pxguru on Dec 7, 2016 8:37:15 GMT
0.2mm will be better, as you will need a little on the exhaust for cleaning it up. Chances are it will end up a little over but with the conservative numbers it will be no issue.
Not over happy about not getting rid of the groove in the head. Would be ideal if it were a screamer with 60mm crank and bigger base packer. If you end up with a groove that the rubber doesn't fit into it will be ok but not ideal. If GLM is doing the skimming he could put the groove back in? The only issue with leaving the groove empty is the heat, having the cavity full of air might cause it to leak more. Not keen on skimming the barrel and having the piston sticking out the top. The other option is reprofiling the head to have less squish %. Would mean the volume would change and more could be skimmed off.
If you are really un interested on high rpm power, the crank could be cut less ATDC. Not sure how much. I'll have a think about it.
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Post by sime66 on Dec 7, 2016 9:31:06 GMT
0.2mm it is then; I’ll revise everything to suit, so we have a set of numbers and sketches that all tie in together. 0.1mm to tidy exhaust does make good sense. I can easily make a spot-on 0.2mm copper base gasket to match our barrel wizardry. I’m sure GLM can re-cut the groove if needed, or I can see if the ‘O’ring will squash down, or I can get a Ø1.5mm ‘O’ring (I found a good place when I was getting spare rubber for my split-tubeless rims). I see several solutions, and no problem with the groove. The crank has cleaned up lovely; I might have a play with making a jig over the holiday; and in January I will talk to GLM about the head, and ask him about checking the crank at the same time. Motorcycle racing is their game, so I expect his standards are high; just as long as he doesn’t laugh at my crank and tell me to bin it! Might as well name him now, rather than GLM; he did a splendid job on the other barrel after all: www.gibbsperformance.co.uk/workshop-services.aspx‘Uninterested’ is a strong word (though I concede I might have used it before). This now has Transfers at 123.5°, so max power slightly higher than The Beast, so that sounds good to me. I’m happy we have the Inlet in the casings wide open again, (though we may decrease Inlet timing a bit), and I see we’ve reduced Blowdown to keep torque high. Two matters I mentioned before are still important: I would like to get on top of my 4th gear, but not by putting too much emphasis on high-end power that it compromises my low-end power/torque, because that is the other matter that is important to me; I think not-worse-than The Beast would do, but better if possible, and certainly not any more low-end losses than before. So I would say interested, but not at the expense of other factors, more important to me - I'd rather have both!My Internet is slow today, so instead of getting annoyed with it, I'm off to do some real work; I'll try it again this evening........... Edit:
Internet back, so crank and revised numbers:
And these are the current measurements, calcs and dimensions
If the big ATDC on the Inlet Timing gives me more high rpm power without messing the low, then I’ll do the crank cutting as above sketch, or change if when you’ve had a think; I'm easy.
Edit: 125/58:
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Post by pxguru on Dec 8, 2016 10:35:19 GMT
That is a lot to cut off the crank and it isn't going to affect a low revver so much. How about 125/58? That means 10 degrees off the port and 10 degrees off the crank for ATDC. Should be plenty.
Any thoughts on reprofiling the head while its getting skimmed?
That crank will need the flywheel bearing ring changed. Any rusty oil run out of the big end? It is in really good condition otherwise, if only it had been greased up and wrapped in a plastic bag for storage.
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Post by sime66 on Dec 8, 2016 14:07:10 GMT
125/58°– no worries; I’ve added revised sketch above with the rest to keep all the current stuff together. I’d have cut the ring off anyway, and used the new one with the flyside bearing I buy; I did that before, and made myself a little 1mm spacer for the job – no worries. Nothing nasty dripping out of big-end bearing; it was quite dry, and loosened up easily with just a squirt of WD40. I’ll grease the bearing and bag it. Reprofiling head: I don’t know very much about this, but always keen to learn. The only work I did inside the head before was cleaning up the poor casting of the DR head whilst keeping an eye on the volume, and then taking a bit more out to after-skim to get the volume spot-on. I remember checking the %ge of bowl volume against head volume; I’ll have to read back. I’d prefer to do stuff myself, rather than add to the lathe bill, but I’m curious what you’re thinking, and open to suggestions. I’ll be having a chat with them in January, so can add it to the list if I understand what we’re after. I will have a read-up later to see what I can find for myself too – I suspect something to do the width of squish band, or the %ge volume of the bowl itself?
I meant to say ID66 x 1.5mm ‘O’rings, are no problem in Viton(200°C & chem) or Nitrile(120°C); I reckon that would squeeze into the 1.3 x 2mm wide groove nicely, so I don’t think I need to worry about that at skimming stage. (2x2mm groove = 4mm², Ø2mm = 3.14mm²; and 1.3 x 2mm groove = 2.6mm², Ø1.5mm = 1.76mm²).
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Post by pxguru on Dec 9, 2016 9:36:39 GMT
Have you found out what changes would suit that head?
Those malossi 166 heads are quite decent already better than standard format anyway. Centre squish and near to centre spark plug. And probably near 50% squish band by area, which is said to be ideal for general use. Everything to do with two stroke tuning is a compromise, as it gets nearer to optimum. That being the case, there are ways to make this head give more torque with a slight loss of power. Interested?
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Post by sime66 on Dec 9, 2016 15:26:30 GMT
I didn’t read anything last night because I was playing with my prototype home-made crank jig, for which current best scheme is sitting it in a 100x100x50 galvanised steel electrical box, which I’ll keep rigid by keeping the corners when I cut the sides out, and which can be firmly fixed down to my kitchen hob with some strong magnets I have from dead computer hard drives; so here’s a little Friday afternoon deviation:
(Metal box: £4, nuts & bolts: £6, magnetic-base stand and DTI gauge about: £20, and four surplus Chinese bearings, so it’ll be about £30 total).
Now to the more sensible subject of head reprofiling; yes absolutely I’m always interested – in the learning definitely, and the doing of it too, depending on what I find out, what the compromise is, and whether it’s something I can do myself. I’ll also keep my eye out for spare heads in case we want to try options (there was one recently, but I didn’t bother – I should have, but was on a self-imposed spare parts embargo). I’d rather keep my stuff local and I don’t really want to give Gibbs another couple of hours work either; because that makes their job more expensive than the kit. I see Reedspeed offer Malossi 166 head reprofiling for £48, (Taffspeed, £45 + p&p skim and reprofile) - but I haven’t found out what they actually do (Reedspeed before, wanted to tell me what I needed, rather than let me tell them). I’m also keen to keep this build job interesting, so anything different or extra to The Beast build, (if for a good reason and sensible cost), is worthwhile.
In the mean time, to get things rolling; checking the ring-bowl area is pretty straightforward for starters, so I’ll do that – 48% squish band by area, I’ll do the bowl volume too if needed – the total volume and profiles as the previous page, but I can add detail and get piston profile if needed:
I forgot to mention yesterday, but as we’re back to thinking about the head; the kit comes with a 0.5mm copper head gasket. If I should be using it I need to allow for that and increase my skim to suit (and the depth of the ‘O’ ring groove will reduce also reduce – to 0.8mm).
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Post by pxguru on Dec 9, 2016 18:58:59 GMT
Crank tool looks like it will do the job just fine. I take it that the bearings move around to set it up. How did the new crank look on the jig?
To change the head squish band to aim for a bit more torque and slightly less max rpm power, a little dremelling is required. It doesnt need to be perfect but can look ok with a little polishing. If you look at the head the transition between the squish band and the bowl has about a 1mm radius curve. This is fine for top end but not great for mid range or less. With a spare hour, a sanding drum in a Dremel and a radius gauge, this radius can be changed from 1mm to 5mm. Will probably change the squish percentage to about 35% and increase the head volume by 1 or 2 cc. Even if it doesnt look pretty after it will still work ok and give a bit more torque for the change into 4th gear.
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Post by sime66 on Dec 9, 2016 20:15:51 GMT
That radiussing of the change between squish band and combustion bowl sounds like a perfect little job for me to tackle; I’ll do that for sure. Makes good sense too. I’ll have to give myself some time to picture the difference in volume and then compression ratios (which are good now), but I’m sure you already know the consequences of it before I squirrel away and work it out – maybe in the morning – (I quickly added 1cc to measured head volume just to get a feel, and it gave me CCR=6.8:1, so looks like I should take out as little as possible). I’ll draw your attention to the question I asked above about the copper head gasket that comes with the Malossi kit; do you think I should use it and allow for it in the skim or not? Details in post above. My Crank jig is still on the drawing board and ordering bits stage, so no measuring yet - I’ll knock it up over the holidays. When I have the box, which is bought but not here yet, and get a definite internal dimension (it’s quite crucial to get as much crank on the bearing without the bolt-head fouling the web; I’m using shallow dome-head bolts), I’ll finalise the nuts and bolts and cut the box up to suit exact dimensions. The ID of the bearing is 12mm; not sure if I’ll use a big bolt or a shoulder bolt or a sleeve – still looking for best option, though M12 is drawn precisely, and works. I’ve thought-through how to spin the bearings and adjust the height though; that plan won’t change: The bearings are 1mm apart, and 2.5mm thick washers hold the inner race tight and space the bearings off the case, so the outer ring of bearing spins free. The washers also stiffen the holes I’ll make in the case. I think one pair of bearings will be permanently fixed, and the other will be run in a vertical slot to give a bit of adjustment for different cranks, possibly also horizontal adjustment with washers. (I also want to check the web and axle sizes of a few other cranks, eg. a 200, to see if they’re different and can be accommodated – I think they’re the same because the bearings are the same, but I don’t know about the web widths and diameters). A little plan and section of the bearing, bolt and washer arrangement to explain:
Warm and wet this weekend, so might get some daylight hours on The Beast too.................................
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Post by sime66 on Dec 14, 2016 23:28:12 GMT
I made my Crank jig, and did some tests, which show the crank is good to use. I’ve noticed a few things, which I’ll improve for my own satisfaction, but with the film as it is, I think the Crank passes. Here’s the box: I checked dimensions for all the cranks I could find (for ‘P’ range anyway – there are some specials); all Crankside webs are Ø97.9mm, so my box will work for 200s too. Both bearing surfaces are Ø25mm, so the only adjustment needed was for if a flyside inner bearing race was present or not, so I made one pair of bearings adjustable, in a slot, by 2mm, so it works with or without the race. This first film shows that I have a problem with lateral movement of the Crank in the Jig; I made some wire guides, but I need to improve on what I had, so scrapped them until i have a better idea. It particularly distorts mearurements on the taper, which creep as the Crank moves sideways. The magnetic base on the DTI stand is excellent, but I need a more secure method for the box, and for them to be fixed to the same object; that fine adjusting arm is very sensitive, so getting it spot-on zero is quite tricky (but not actually that critical because I can see total movement on the film). I do have a better DTI coming, but probably don’t need it for this (DTI will work for TDC too when I’ve made a little bracket). I carried on with the measurements anyway, although I reckon I can improve my method and this Crank moving issue, and I think I’ve recorded enough data to show the Crank is good to use: That’ll do; I think this engine project has gone as far as it needs to for now. I was going to see if we could decide gears, but maybe I don’t need to yet. I have an ongoing issue with The Beast, (still the same, and not just jetting), which I’m not going to tackle until after Christmas, so I reckon I’ll ease-up with the scooter obsession now for a couple of weekends. I’ll update Beast thread when I’m in the mood to tackle it………………….
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Post by pxguru on Dec 15, 2016 9:05:43 GMT
Well that works really well. Stable enough for a home made jig. Will tell a bad crank from a good one. Usually the first time when problems are identified its because the flywheel keeps spinning the key or the fly side bearing burns out too quickly. this does the job well. That crank looks like better than most too. Agree, the build is far enough before any building. Gearing might go 22/68 but probably 21/68 will work the best. Need to see how it pulls into 4th on the road with 21/68 before making any decision. Next thing will be to get the barrel ported and that will take time and concentration....and a few more tools. might get some for Christmas
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Post by sime66 on Dec 16, 2016 19:43:57 GMT
As I’m on here anyway, posting some Wav stuff on your Tourer thread, I thought I’d post this too because it’s ticking over at the back of my mind, and I sketched it out last night. I’m trying to picture the piston ports and the barrel ports alignment at TDC and BDC to try to highlight where I need to tweak – obviously aware that it’s all getting opened-up anyway, but as a start-point for me to try to remember what I did before (as far as aligning them is concerned). Does this tell us anything useful? I know we’re going to open the channels in the piston, and they don’t show on the rubbing, but I’m aware of where they are too. Whilst posting, and following on from your last post; what size shank do you use for your long carbide burrs? I ask because my Dremel only goes up to ⅛” - 3.2mm, and I’m having trouble finding any that aren’t ¼” – 6.4mm. If you use 3.2mm, I’d really appreciate knowing the source. If you use 6.4mm ones then I need to rethink my Dremel, and won’t bother with the 90° adapter until I’ve got a tool with the right size chuck. There’s just these few things nagging me before I put it away for the holidays.... ....last one; I’m still trying to find out if the copper head gasket is part of the sealing system or is an optional LS/timing/volume/squish tweak; opinion seems to be divided on other forums. I see that Wasp say (for mk3 kit) that the copper head gasket isn’t used, but it’s still part of the gasket set they sell for Mk1 & 2. Malossi is decidedly ambiguous in its instructions. Do you have an opinion on it? I’d have thought metal-metal and something to fill the 'o'ring groove would do. I’d like to decide before I speak to Gibbs in the New Year - it changes the skim if i use it.
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Post by pxguru on Dec 17, 2016 8:12:10 GMT
Going to take you a while to move theose transfers but will be worth it in the end. www.amazon.co.uk/gp/product/B018LT5U42/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=AMSIYUYCK400XBurrs like these are plenty long enough for this job. The really long 3mm ones are hard to find but not often needed. The last one I got was on ebay, can't find any now. The opposite will be more relevant, for doing the transfers you will need to cut some short ones in half. I don't like head gaskets if they can be avoided. Had a copper one blow out on a dual carridgeway once and it put me right off. Was quite happy when I realised it was only the gasket. I though I had holed the piston. Was lucky I impatiently took the head off in a lay by to look before phoning the AA, took the blown gasket off and rode home without it
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Post by sime66 on Dec 17, 2016 9:35:52 GMT
Yes indeed, lots of delicate cutting, but I don’t mind – I’ll probably whinge at the time, but that will pass. I’m wondering if the lower transfer ports should keep the relative height difference, or if they all go to 45.22mm. I was also interested to see that the blanked-off central boost port aligns with the little square cut-out in the piston, which makes an extra channel through piston to combustion chamber there (if I’m reading it right). I know there are plans for that area that I don’t have info for yet anyway, but it’s interesting to see as it is intended too. I think I’m widening the exhaust by 2mm either side as well, but didn’t show it yet. I have a set of those burrs already, so that’s another £50 (on long burs) I won’t need, and can stay in the kitty for my meaty clutch. I note about cutting some burrs shorter; I’ll have the 90° and the flexi head too; I’m sure with care it’ll be OK. I’m happier without the head gasket; I couldn’t see why it was needed, in fact I don’t really follow the reasoning for this gasket and ‘o’ring head junction at all. Best just to keep it simple. Anyway, happy days! Maybe I can let this one rest for a bit now, but it’s still ticking over at the back of my mind.
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Post by pxguru on Dec 17, 2016 14:13:44 GMT
I wondered when you would mention the relative height differance between the transfers. First you need to work out why they are like this and whether you want that or something else. See what you can find out and we can determine what is most appropriate. That centre boost port is not as naff as it first appears. This kind of port is ingenious actually. There are two very big benefits doing it this way. It reduces the load on the boost port transfer tunnel, so the other two ports will get more. And most importantly for me, it keeps the trapped mixture under the piston crown moving, which reduces the piston temperature a little while maintaining continuous oil delivery to the small end bearing. Clever (so we will be keeping that but making it work properly).
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Post by sime66 on Dec 17, 2016 18:28:04 GMT
I will have a read, but I reckon I’ll have a stab at it first as well. Those boost transfer ports are lower, so open later and close earlier; they’re also in a ring opposite the exhaust. I reckon the main side transfers fill the combustion chamber first, then the boost, which are under and around/behind, push it up, over the spark and towards the exhaust. Probably a better flow than filling from all directions at once, less turbulence, and emptying more efficiently before filling. The other thing I’m thinking, although I need to look at the specific timings relative to the exhaust to see if it makes any sense or not, (maybe a quick look at the angles of the ports too) is that maybe these later boost ports are late enough that they are helping the combustion gasses out. I’m sort of picturing my port-timing wheel with another ring for the boost ports, with shorter timing, which interacts differently with the exhaust timing than the main transfers do. I’ll stop guessing now, and have a read and a scribble in the morning instead; I reckon it’s to do with controlling how the gasses pass through the combustion chamber though; they’re either helping the shape of the flow, or helping the filling and clearing. When I noticed that central boost port channel it reminded me of something you said elsewhere about some imaginative barrel/piston arrangements to make a third boost/transfer in 2-port casings; I imagine it’s a similar solution. I also hadn’t thought about the small-end bearing, but it all makes good sense now. Edit(A bit more of a look at the cylinder and port timings) With the 123.5° TD now set, and if I kept the secondary and boost ports 1.5mm lower, the Transfers would open at 118.2° ATDC, and the others 4° later at 122.3°. At 118.2° the Main Transfers fill the chamber; those ports are horizontal and point towards the rear of the cylinder, away from the Exhaust (which opened at 95.5° = 22.7° earlier). At 122.3° the Secondary and Boost ports open, the Secondaries still point backwards (maybe slightly upwards), and the Boost ports point upwards at the back. I reckon this will force the uncombusted gasses firstly away from the Exhaust at 118.2°, and then up the back at 122.3°, then over and into the combustion chamber as it compresses, and then towards the exhaust. It’s sort of making a circular-path across the piston, up the back, over the spark, and down and out. My first guess is that we should try to keep it, or maybe you have an idea to improve on it. I’ll still have a read on the Internet, but that’s what I see from having a quick look at the barrel and the port timings.
Shabby sketch, but it shows what I'm trying to explain
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Post by pxguru on Dec 18, 2016 8:19:30 GMT
This is the subject that tuners argue about the most. Not all of the information you find will say exactly the same ideas. Any barrel with 5 transfers or more will have the same concept of getting the mixture in and the exhaust gas out (Scavenging Process), the transfers open and fill from the bottom to the back, up to the sparkplug and over the top to the exhaust port. This part is all the same, the difference in opinion is about the phasing of the transfer port opening, shape of the transfer port window and direction they point to. 2 strokes have been around a long time now and a lot of porting information is now public knowledge.
The compromises that have to be considered are all to do with what the engine is for and where it needs the power and torque. The basic concept that the sooner a port opens the more mixture can be transferred at high rpm, is better for top end power but the sooner a port opens the more likely that mixture is to go out of the exhaust port at low rpm is terrible for torque. When considering port shape, it will cause the flow from the port to twist and with port direction will cause port interaction, then it starts to get complicated. Factor in the exhaust port shape and style (like the 3 Ex ports in your DR) and its affect on getting the exhaust out to pull the mixture in but closing early enough to not let too much mixture out of the cylinder. Its all a compromise but where is the key.
See what you come up with and we can decide what to do with your Malossi ports.
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Post by sime66 on Dec 18, 2016 8:20:45 GMT
I had a good read-round last night, which I’ve started to tidy up and think about this morning, so here’s an update, but I’m still thinking it through….
This first port timing bit is to help me understand what’s happening better; it’s nicked from somewhere else, but tailored to my port timings:
TDC 0 – 95.5° ATDC: Power Stroke – Crank Case pressure increasing, Inlet still open 58° ATDC: Inlet closes – Crank Case pressure increasing 95.5° ATDC; Exhaust opens – Power Stroke ends, Blowdown starts (“The pressure in the cylinder must blowdown below the pressure in the crank case so that the unburned gasses passinto the Transfers during scavenging phase”). 118.2° ATDC: Transfers open – Blowdon ends, Scavenging starts [Here comes the relevant bit – but I’m still scratching around with it] 122.3° ATDC: Secondary & Boost Transfers open ; the unburned and the fresh gasses are flowing out of the transfers and the boost ports are helping the gasses flow up the back of the cylinder, and are pushing the burned exhaust gasses out. [“It is critical that the burnt gasses are scavenged from the combustion chamber, in order to make room for as much unburned gasses as possible. That is the key to making more power in a two-stroke engine. The more unburned gasses you can squeeze into the combustion chamber, the more the engine will produce.”] The unburned gas mixture flows into the exhaust header section, but aren’t lost because a compression wave is reflected from the end of the exhaust header pipe to pack the unburned gasses back into the cylinder. BDC 125° BTDC: Inlet opens – piston moving up is drawing in fresh mix through carb and crank. 122.3° BTDC: Secondary and Boost Transfers close 118.2° BTDC: Transfers close 95.5° BTDC: – Exhaust closes, Compression phase 18° BTDC: - Ignition
I found one reference to the lower height of secondary transfers giving a wider power band; that sounds interesting……: “and you can widen power bands by staggering the porting as the smaller ports will flow under less pressure hence 'stretching' the pipes range.”
I found a lot of disagreement over best height (+ & - relative to main transfers), and roof angles, and it’s difficult to know who is correct when there isn’t agreement. (Other forums with unknown contributors aren’t the best source, but the reference books are hard-going and prone to being out of date, but I’ve had a good look round).
Bell goes into the history of the development of the Transfer ports nicely, but I found no reference to Secondary or Boost Transfer port heights. There’s a lot to read though, and it was getting late, so it needs a better study.
This is from Wikipaedia; it explains Schnuerle Porting / Loop Scavenging: “Gas flow within the two-stroke engine is even more critical than for a four-stroke engine, as the two flows are both entering and leaving the combustion chamber simultaneously. A well-defined flow pattern is required, avoiding any turbulent mixing. The efficiency of the two-stroke engine depends on effective scavenging, the more complete replacement of the old spent charge with a fresh charge. Apart from large diesels with separate superchargers, two-stroke engines are generally piston-ported and use their crankcase beneath the piston for compression. The cylinder has a transfer port (inlet from crankcase to cylinder) and an exhaust port cut into it. These are opened, as the piston moves downwards past them; with the higher exhaust port opening earlier as the piston descends; and closing later as the piston rises. The simplest arrangement is a single transfer and single exhaust port, opposite each other. This "cross scavenging" performs poorly, as there is tendency for the flow to pass from the inlet directly to the exhaust, wasting some of the fuel mixture and also poorly scavenging the upper part of the chamber. Before Schnuerle porting, a deflector on top of the piston was used to direct the gas flow from the transfer port upwards, in a U-shaped loop around the combustion chamber roof and then down and out through the exhaust port. Apart from the gas flow never quite following this ideal path and tending to mix instead, this also gave a poorly shaped combustion chamber with long, thin flame paths. In 1926, the German engineer Adolf Schnürle developed the system of ports that bears his name. The ports were relocated to both be on the same side of the cylinder, with the transfer port being split into two angled ports, one on either side of the exhaust port. A deflector piston was no longer required. The gas flow was now a circular loop, flowing in and across the piston crown from the transfer ports, up and around the combustion chamber and then out through the exhaust port. With Schnuerle porting, the piston crown may be of any shape, even bowl shaped. This permits a far better combustion chamber shape and flame path, giving better combustion, particularly at high speeds. Loop scavenging As Schnuerle porting encourages flow in a loop, it is termed "loop scavenging".”
So I know what we’re trying to do, but I’m not yet certain about whether to keep the relative heights as they are, or how best to modify them, or quite what changes will make what differences.
-- you've just done a post - I'll leave mine as it is, but have a good read of yours now and see where that leaves us.........
....OK, I did see some diagrams last night, going into detail about where the ports are pointing (sweet spot?), and the shape and angles of the top of the ports - so I'm thinking as much to do with precisely where they're pointing as just the timing, which is where I thought we were going. I also see the compromise between port height for power and torque losses too, and a compromise which may be helped by the staggering. I've made a mental note about port interaction as well, but this isn't something I'm going to find a single answer to overnight. It seems to me the aim needs to be precise, so a lot of measuring of what is there, and very careful changes. Not much point me writing more now; I have a few clues there, and will concentrate on those when I have my next reading session.
There's some good Youtube computer models of gas flow through cylinders too, but maybe more of a distraction than actually relevant: I'll look again though to see if any are worth sharing; they gave me a better picture of what's happening anyway.
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Post by sime66 on Dec 18, 2016 19:35:03 GMT
I’ve read Jennings’ chapter on Cylinder Scavenging, and made a sheet of notes, which I’ll tidy; I don’t want to re-write it all here, and it will take a few reads to let it all sink in. I picked up quite a lot of stuff that didn’t mean as much on first reading as it does now, but for this bit I’ll just concentrate on the question. Before that I also thought it best to measure, as best I can, what I already have from Malossi, so I’ll start there. Here is a more studied sketch of the Transfer ports, showing which corners are radiussed, which tops are sloped on the cylinder face, and the angles of the roofs of the ports as best I can (which was making little moulds from strips of plastic. It’s sometimes hard to tell what is poor casting and what is deliberate, but I think the secondary transfer is deliberately sloped from the height of the Main transfer to the height of the Boost transfers; I think this is connected with keeping a wide power band at the expense of peak power - if they were all at the Main Transfer height. The Main Transfers are horizontal, the secondaries are at about 67°, and the Boosts are at about 37° – I think the Piston Boost is a little steeper-still, but it’s not easy to be precise (which is something I’m coming to later; a first hint of a concern). I’ve also tried, as best I can until I think of a more precise way of doing it, to work out the angles of the vertical walls in plan, to decide where the ports are pointing. This is what I have – I think the Secondary Transfers aim further back that the Main Transfers, partly because of the distance from the Exhaust port and also the location of the stud – these dictate the wall in the Transfer there:
If the Secondary is sloped, then the progression of transfers is that they point further back and get steeper in order: Main ->high-end of Secondary Transfer->low-end of Secondary Transfer->Boost
I found in Jennings that steeper port roofs improve the Scavenging efficiency, which improves power-range and torque, but at the expense of peak power. I imagine Malossi was more interested in peak power than me, so that’s worth bearing in mind for later. I also found that pointing further towards the rear wall also improves Scavenging efficiency, with the same effects on Power and power-band:
Now I know my Main transfers want to rise by 2.2mm and remain horizontal. I suspect that, if it was intended, that slope on the Secondary Transfer should be kept (giving Malossi some credit for getting it right). Here, I wonder if an increase in the roof angle might take up some of the necessary height increase needed, and at the same time, increase Scavenging efficiency to improve power-band and torque? I doubt the same can be done with the Boost ports because they are already steep, but a combination of changing the angle and raising them to achieve the same relative height increase seems best.
*So, I think the shape of the tops should stay the same, but maybe the angle inside the Secondary Transfers could be steeper.* (Having the Main Transfers horizontal (under) and pointing away from the Exhaust first, also seems to get the bulk of the volume in the chamber early for power, but pointed away and below, to keep it away from combusted gasses and, probably more importantly, the exhaust port itself; then the smaller Transfers, which are later, start to aim it up the back and draw the main charge with it).
I read, and made a big note to myself, what Jennings said about asymmetric changes to angles of aim or roof angles (due to inaccurate work) having a seriously detrimental effect on Scavenging efficiency and power loss, so that bothers me a bit. Clearly you are already aware of that and we wouldn’t be doing it unless you thought it was doable, but just thought I’d mention it. (Jennings says don’t mess about unless you have to, and just raise the barrel instead). [but we’ve done that before].
Jennings also wrote this little gem, which actually tells me very little, but I feel he was close to revealing something important: “Some designers have obtained best results by either advancing or delaying slightly the opening of the auxiliary transfers, with respect to the main transfer port timing” (p124)
I’ve got a load of other notes to work through – some interesting stuff on shape and size of exhaust, radiuses and minimum distance to Transfers for example. I think I can improve my angle-measuring with a bit of thought and care. – Even sleeping on it all will probably give me some subconscious working it out in my mind, but I’m beginning to see that this bit is the special part of the porting-work that you chaps guard so carefully.
It was reading SS90 on kiwibiker, on the link below, that put me back on the Jennings (which was safely gathering dust), that then stole a couple of hours of my life and gave me a migraine, just to find a morsel of understanding of where I think you are steering this little conundrum.
www.kiwibiker.co.nz/forums/showthread.php/155906-ESE-s-works-engine-tuner/page28
I hope not all of this post is nonsense, but I do realise there’ll be big holes in my understanding (or identifying the important bits) until I’ve had a few reads and sleeps on it. Posting this tonight so I can forget it for a bit, but might well edit it in the morning……..
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Post by pxguru on Dec 19, 2016 10:16:02 GMT
I think you have covered quite a lot of ground already. The trick here is working out what you already have and why it is like that. Then from all the new information, work out what is old ideas that have been disproved, what is a great idea if only you had 6 gears and what is relevant to the scooter you are trying to create.
Like you have summerised, looks like Malossi did a really good job. All the little radiused parts and port angles. All thought about and carefully considered. They are doing some twisting flows, which I always find quite cool. Just a shame they make them so tame, compared to what they could be. Its not even all about economy, as you can see from the Beast build that a little tuning can actually give more power and more economy.
What I think is keep all of what Malossi did, all the angles and radiusing the same but set the top of the main transfers to 123.5 duration. Then, move the secondary ports up so that the low side of the sloping roof is level with the top of the main transfers. Then move all the boost ports up to the high level of the scondary transfers. Can you theorise why I think this?
Do you have a BHP figure for a bolt on Malossi 166? Just for the before and after comparison. It is possible that after these few careful changes in the porting we might see double the power and torque.
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Post by sime66 on Dec 19, 2016 19:32:43 GMT
From your post I did myself a list of seven questions, and I think I’ve tackled five of them here, and left a couple for the morning; it was quite a lot to tackle in one go. Firstly I need to clarify/correct what I said I already have. A more careful study of the Secondary Transfers, with the piston in place to use as a guide, and some photos, shows them to be slightly different to how I sketched yesterday (and actually slightly different to each other now I’ve looked at both – but that can be fixed). I’d say there is a slope, but it isn’t for the whole length of the top; I’d say the first 2/3 is horizontal, and the last 1/3 is sloped - (maybe I can make one slope when I raise them). The horizontal roof is lower than the top of the Main Transfers (by about 1.5mm), and the end of the slope seems to be intended to match the boost ports about another 0.6mm lower (though the left-hand boost port is higher than the others, which looks like it needs correcting. I’ve revised my sketch to show it. From that I’ll interpret your suggested mods below, later in this post. Here’s a photo and the revised sketch first (some dimensions are not precise because they vary from either side):
I think what I want from my engine is emphasis on efficient Scavenging, for high torque and a good range of power rather than peak power. I think that means staggered Transfer port tops (like we have). I think the change in the timing of the Transfer ports you suggest makes the band above the intended timing of 123.5°, rather than below it. Possibly efficient scavenging is more important in a smaller displacement cylinder too. I’ve had a bit more of a bash at explaining my ‘theory’ below; there’s quite a lot of other stuff to get through from your post as well…. I think the gasses will have less friction/turbulence in a radiussed port corner than a square one, so will be faster; so I think an edge with one radius and one square corner will cause a twisting flow. I also think that adjacent ports with radiussed corners might also make a twisting flow. I think twisting flows are probably easier to direct and less easily subject to other turbulence in the cylinder (like a spinning rugby ball through air). I think this sketch below illustrates your suggested mods; I think I do understand why, because I had a similar notion, but mine was to still keep the difference, as you have, but do it by having the Main Transfers higher, and the low part of the Secondaries and the Boosts at 123.5°. My thinking being if we are going to have a good range, then the lower limit of it should be 123.5°, not the upper limit. I think the extra 0.61mm (shown below & still T.B.C.) makes the Secondary and Boost Transfers at 44.61mm, which is 126.75° (9,000rpm!?); seems like a max power revs increase to compensate for the power loss for the port staggering to give better Scavenging efficiency. Why you think it is better to change the order of the ports opening is something I’ll think about a bit more. Maybe your method clears a turbulent-free path/space for the main charge to pass through behind it; using the Boost and Secondaries to Scavange, and create a less-turbulent area, more controlled path, before the Main Transfer (bulk of the volume) charge passes through it? Here’s the sketch, the only important dimensions for now are the height of Main Transfer, which is for 123.5°, and the higher Secondary and boosts, which end up higher by the difference between the lower and higher end of the Secondaries, which is about 0.6mm. I’ve said ‘about’ because I have a discrepancy between what I measured carefully before (which concentrated on the Main Transfer for the port timing calcs) and what I’m getting in this drawing – they were done on opposite sides of the cylinder though, and there is a bit of a difference; I just need to have a much more careful measure. Basically though, the Secondaries move up by the 2.2mm (for 123.5°) + the difference between them and the Main Tranfers + the difference between the high and low ends of the roof (= approx 2.2 + 1.7 + 0.6 = 4.5mm!!):
Unlike the DR, I don’t think the Malossi kit tends to be bolted on without some reference to the instructions, which cover case-matching and Inlet timing, but not Port timing, so I think BHPs I might find will include that work. Malossi do not state any figures (too many unknowns, I suppose). I’ll look round for a general consensus, but on this forum Joey stated 12-13BHP here: vespa.proboards.com/thread/1719
There’s a couple of other questions in your post, which I haven’t answered yet; they need quiet reading, which I haven’t been able to do today, but will try to have a bash at those in the morning.
((I have a hunch the emphasis on symmetry might be out of date (now with twisting flows, and because I know the 200 cylinder is not symmetrical with the offset Transfer)).
((I’ve read some reference to what we could do with more gears, somewhere in the load of stuff I’ve waded through in the last few days, I haven’t been able to find it again this evening, and I’d rather find it again than guess, especially as I've gone a bit brain-dead now this evening, so I’ll leave that one for now. I suspect it would mean there’d be less need for a wide power-band, and so a higher (narrower) max power revs could be aimed for, with all the ports the same height, but that’s more of a hunch than a formed theory until I find the text again)).
((I’ll spend more time interpreting what Malossi have given us and comparing it with my needs when I’ve had another good read too - we like the twisted flows due to the radiusses, we like the roof angles and we like the staggered ports - though we're changing the order of it)).
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Post by pxguru on Dec 20, 2016 9:26:19 GMT
The secondary port slope is not a great concern. The part sloped window will flow more and work the same. The porting I have suggested does move the secondary’s a long way but will give you a lot of metal to practice on (check the outside of the barrel to be sure there is metal). If the boost port angle ends up steeper, to slide up the back wall of the bore this isn’t a bad thing either. If you check the burn pattern on the original head look for the bare aluminium parts, these are where the old exhaust gas gets trapped. You won’t be getting anywhere near 9000 rpm as there is not the blowdown for it. Opening the secondaries earlier will make it scavenge better at all rev ranges. Like torque for nothing. You have drawn it correctly. I think this is the best balance for what you are trying to achieve. I am not sure a bolt on 166 (with or without any matching) is 12-13BHP. That would make it quicker than a standard 200 and a little quicker than a T5. Don’t think so. The symmetry part is still correct. The 200 barrel is offset opposite on either side. Still balanced. A bit c**p but balanced.
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Post by sime66 on Dec 21, 2016 6:48:24 GMT
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Post by pxguru on Dec 21, 2016 8:24:47 GMT
That's a whole load of measuring! Going by the last diagram, it will be ok. As long as there is at least 1mm of metal left. There is little stress or pressure involved and its only for the width of the port. On the main transfer, if you take the back of the port radius to follow on for a while and just go flat for a few millimeters, this will help a lot.
Do you think the Beast problem my just be the weather not getting on with the over rich jetting?
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Post by mijapxman on Dec 21, 2016 9:53:46 GMT
☺
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Post by sime66 on Dec 21, 2016 11:17:26 GMT
The measuring got more precise as I realised how close this was going to be to a problem. I am reassured you think it will be OK; I will reassure myself more by some more measuring! (casting, fins and barrel wall) and a redraw around the Tranfers (I won’t subject you chaps to more diagrams; just satisfy myself!). I'd cut these Transfers first, so that the only loss would be the investment of my time on this particular work (and only £35 for the barrel) if I did break through and junk it; on that basis it's probably a fair risk. I looked at piston head burn patterns yesterday, and may post something later if there is a natural lull in this thread when we’ve finished working out the Transfers. Also, concerning a natural break in this thread, which we nearly reached before we went on to Transfers, which has been a real eye-opener; when this thread dies down, that will give me the ideal opportunity to get back into sorting The Beast before Spring. I don’t think it’s just jetting, but what I need to do first is clean up the engine, find my leak (the filthy engine could be mud, oil, fuel or a c**ktail of the three – but there is definitely a leak of some sort and a patch under the scooter - into a pot for inspection, since I noticed it); I’ll do an oil change (for volume and contents) and a pressure test, and redo all my torques. At that stage I’ll either have found the cause, or I’ll decide she’s better indoors for a proper investigation. Without you chaps advising me otherwise, my inclination would be to split it indoors in a clean environment where I can concentrate undisturbed, check everything (including crankcase seal and crank bearing seal), and restore it (with the old 0.2mm spacer and new rings, which I have a few sets of – I know you’d suggest not; I’m saying what I’d do if left to my own devices) restore it to how it was pre-seize in June 2016, when it was really splendid, and where I think I should have been satisfied with it, rather than pushing it further. How it was then, I can ride it to my complete pleasure and satisfaction, and not be putting it near its limits at all. I don’t think it has been the same since the seize, and I don’t think the problem now is just jetting (although I acknowledge that your recent progress would probably be an improvement on mine too, but not the cause of the current problem). I will revive the Beast Update thread when I get back to it, but that won’t be until the New Year (two weekends at least I am not even planning to look in the garden to lift the scooter cover, or think much about that matter at all). Back to this briefly, and your other points yesterday, which I did note, but didn’t reply to: I found another few Malossi set-ups and Bhp claims last night, which I’ll post later (been concentrating on this barrel yesterday). I was wondering if new thinking might deliberately make slightly asymmetric paths to create swirls, but I’ll forget about that now you’ve said symmetry is still important. I also have some interesting photos of other people’s porting work, which I will add later when I have time to get all those outstanding bits together and tidy to post.
Thanks for posting mijappxman; I always hope it’s interesting for others, but wonder if it’s just boring if you’re not into the detail. It’s pxguru’s expertise and experience, and my tendency to detail with measuring, sketching, photographing and filming a record of it all as I learn more. I made my last build threads into a single PDF file, which I have on disc as a full record of it all for myself. This thread, so far, has been a lot more to the point than the previous tuned build, which went on for about 50 pages in two big threads. I did mean to post on your thread because whilst going into crank measuring business, I found myself at the chap you’d previously linked to on Youtube, and I had a better look at his other films too; he’s well worth a look – but you need the Pause button to read the captions to follow it all. So a belated welcome to the forum.
(I can’t say coĉktail – someone turn the Nannying Monitor off, please!!)
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Post by mijapxman on Dec 21, 2016 14:11:12 GMT
😉
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Post by sime66 on Dec 22, 2016 18:14:14 GMT
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