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Post by henri on Nov 7, 2014 10:18:42 GMT
blimey guru ,hard question ,its a long time since ive worked out an co-efficent of expansions , in its free state the ali barrel would expand more than a steel conrod ,length wise tho in use expansion is choked by barrel studs/nuts ,an also if i remember right the cross section area has a inverse effect as in a big block of ali will expand slightly less than a smaller 1 over the same temp range ,its minimal an usually ignored when calculating expansion distances .but is part of the reason for piston/bore clearances as aswell as being hotter the piston is of thinner construction =less sectional area an expands more/quicker than a ali barrel.piaggio with there aero experience used a low-expansion grade of ali for pistons , mallossi dont hence the "slapper" nickname. but its not just the expansion that squish gaps are maintaned for , the stretching of a high tensile steel conrod thats hot n being put through a accel/deccel cycle is quite amazing to think off,well for me anyway. even tho a piston an pin/bearings weigh grams ,force=mass x velocity ,at piston speeds some very high forces are generated ,add in were talking of repeating the cycle upto 10,000 times a minute , more on some engines an i'm constantly amazed something ive put together works an isnt just a "pretty grenade" , tho ive blown a few engines they was all jap bike 1's so dont count. sorry wandered off then, but the stretch of conrod is more critical than expansion . all these gearing/porting/calculaters apps n software are pretty slick an almost tempt me to get dremmelling again , lot easier than a stub of pencil n back of fag packet , but its puters ,ya got to remember GIGA , garbage in =garbage out , not sayin anybodys talkin garbage just ya need to be careful of what ya measure n record or all the fancy puter software wont help ya . but it is pretty an will admit to throwing a few numbers in just to see ,mostly it just said "are you joking" but in puter speak ,H
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Post by sime66 on Nov 7, 2014 13:37:46 GMT
ya got to remember GIGA , garbage in =garbage out , not sayin anybodys talkin garbage just ya need to be careful of what ya measure n record or all the fancy puter software wont help ya . but it is pretty an will admit to throwing a few numbers in just to see ,mostly it just said "are you joking" but in puter speak ,H H, 'GIGA' is EXACTLY why I wanted to start my calcs from scratch, not use fancy software until I knew the 'WHY'; you've got to know where the numbers come from first. Which leads me on to last night's ponderings, and a bit of Youtubing early this morning; I'm going to start another thread on precise measuring tools and techniques because I haven't got a clue how we might measure to this degree of accuracy in the first place, and some experienced guidance there would be mightily appreciated. Here is that thread: vespa.proboards.com/thread/4506/precise-measuring-tools-techniques
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Post by vespasco on Nov 8, 2014 3:55:17 GMT
Giga for sure! It sounds odd but this is why i actually post these figures, to check im right. Glad i did! And to give something to work with for the purpose of this thread. Thankfully i never relied on any figures i wasnt sure of, inc corrected ratios in any of my previous work. Now i understand more im happy as i believe i can safely get a bit more out of my motor, by raising compression Safely! Ive spotted the 60.38mm now you pointed it out. I aimed for stock 200 compression (uncorrected at least) after i decided i wanted it bullet proof, low compression, like the stock 200 motor. and keep it as close to/better than stock as possible. I probably would have never considered upping the corrcted compression to as much as 8:1 tho' (not that i knew how to work it out properly anyway! until now). Its v valuable info which will get put to good use Im with you on the squish. The more i think about the expansion of the conrod the more i think it doesnt you know! Not to what we could measure anyway! It is 'high tensile' after all There maybe minimal allowance in the bearings but again , for us, difficult to measure. The piston expands the most for sure, out of the 3 (cylinder, piston, conrod). Especially the crown, the conrod is also getting cooled by incoming fuel and is better protected from the extreme heat by the piston. So, until i get my motor back together and measure deck height, then i/we can work out an ideal/happy medium. Giga - guineapig is gaining atonement?
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Post by vespasco on Nov 8, 2014 23:24:57 GMT
Here are my final figures! No more editing! Top of Exhaust port to top of cylinder - 37.3mm - 170.21° - ideally ° would be more Top of Transfer port to top of cylinder - 47.3mm - 127.06° - ideally ° would be less Blow Down duration - 21.57° - ideally ° would be more Exhaust port height - 23.3mm No base gasket 0.6mm Deck Height Squish gap 1.6mm - 60.6mm to bottom of ports (60mm stroke); With 25cc Combustion Chamber volume Uncorrected compression ratio - 9.98:1 Corrected - 6.49:1 Existing head is 26cc Take out 1cc = 0.4mm of the head Giving a new squish gap of 1.2mm Perfect?! All measurements are taken from the top of the Dykes ring (its a pinasco 225)
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Post by pxguru on Nov 9, 2014 4:44:35 GMT
As you already know these numbers are are not so good. That 0.6 static deck and 47.3mm transfers changes everything! 0.5mm out and it's a totally different story. It will perform ok ish but not exactly like it could and probably not so well in 4th. If your exhaust port is classed as oval (and yours is!) the blowdown will be really too short. With a full square exhaust port blowdown can be shorter. With the blowdown under the minimum requirement (and yours is!), power will be lost at high rpm (+6000rpm) which will be part of what you were seeing last time it ran. The whole issue is that this barrel of yours is ported to suit a 57mm crank. Same everything with a 57mm crank would be in limits but a little too boring (even for a tourer) and leave you with squish like a standard 200 but even lower compression. With the new seal and bearings and higher compression it really could run ok like this and you might not even notice the power loss that you never had Probably though it will go really exceptional through the gears rev right out in 3rd and drop dead in 4th at high revs. This is the fun of 2 strokes, they are just all or not so much! I'm sure the 60mm crank is definitely staying, so the options to fix it and keep the 60mm crank with a 0.2mm base gasket are any of the following; 1. Get someone to raise the exhaust port by at least 1.5mm (across the full width) 2. Fit a really decent expansion exhaust 3. See option 1 If you run it as it is now as an experiment, then you might as well fit the 0.1mm base gasket, as it makes hardly any difference to the numbers.
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Post by sime66 on Nov 9, 2014 8:54:51 GMT
Thanks for the numbers vespasco; I’ll play with those later. Looks like you’ve confirmed the issue without finding a simple answer though; I’ll be interested to see what you decide – probably not crank or pipe, so the exhaust port or leave it and see how it is .................. ............and then the exhaust port?
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Post by vespasco on Nov 9, 2014 21:27:07 GMT
So now you can see the dilemma i had when i first build the engine!! Although my understanding of port timings is much clearer now it doesnt really help the fact that the pinasco has weird timings for 57 or 60mm cranks I first tried the 57mm crank, noticed the massive deck height and the exhaust port not covering the piston rings...(try punching the numbers in, with a 57mm crank,allowing 1.5mm extra deck height)! My way of thinking was to fit a long stroke, giving perfect clearance at exhaust port and perfect deck height!!! It was just a matter of fitting a stock 0.2mm base gasket and sorting the compression in the head and hey presto, it looks so much better! (At least I now know i can raise the compression a touch without going overboard, using stock p200 specs as a guide) Now with the port timing guides it appears i need to, as guruji suggested, raise the exhaust port by approx 1.5mm, which being nikasil lined is not something i wanted to do, so bolted it together knowing at least the rings were covered at BDC and thinking if that lines up, so will the other ports! And by jove it did actually work pretty well for 1000s of miles, attaing the same revs in 4th as i did in 2nd and 3rd (7300rpm).
Ive had a long weekend and didnt get a chance to finish building and fitting the engine. Ill also have a read through your post gaz , when I've more time!
With refernce to measuring... Ive measured to top of Dyke's ring, which i considered accurate as i could get the vernier depth gauge right on top of the ring and right on top of the cylinder, with a light up the exhaust i measured exhaust port and double checked by using verniers inside barrel, as pic above in previous post. I also measured to top of crown....which was not so accurate. But if you want to play with some more figures.... Deck height becomes 0.0mm with 0 packer, 0.1mm with 0.1mm pàcker etc... Which makes a difference but unless someone tells me otherwise, the top of dykes ring is the place to measure for me (as this is what opens/closes ports). Id be interested in comparing the stock like? pinasco port timings to the polini and malossi and stock for that matter if any one has some figures. My previous readings of 0.38mm deck height must have been a happy medium! Ill keep you posted as i progress! Thanks again for your inputs!
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Post by sime66 on Nov 10, 2014 8:22:35 GMT
I’m going to get a vernier when a decent one comes up. I’m hestitating because I’m still not convinced the even modified jaws will fit down my (smaller) barrel, so I’m checking jaw sizes; and I see a big margin for error at the junction between edge of crown and top of chamfered port if trying to measure using the vernier depth gauge only there if jaws don’t fit. I understand that it wasn’t a problem for you with a dykes ring. I am not questioning your method; just making sure mine will be equal to it.
I’ve played with your numbers, so I’m happy with that; just need to read back above about your breakthrough with corrected/uncorrected compression to make sense of it – I lost track there before, and just need to spend some time on it to catch up, but like you I’ve had a busy weekend.
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Post by pxguru on Nov 10, 2014 9:28:22 GMT
Vespasco, If you are saying the static deck to the top of the dykes ring is now measuring 0.0mm or 0.1mm, then this is better but still not quite enough. When I said you needed at least 1.5mm on the exhaust port, I meant as a minimum. It would need to be raised 2.5mm to be ideal. It will run like it is, and probably go fine but the sums say the power will tail off early at high rpm.
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Post by henri on Nov 10, 2014 9:30:58 GMT
if worried about fitting a vernier down your barrel without altering it ,a blued feeler gauge an right angle scribe can be used to measure the distance your checking, slide the feeler into position an mark with scribe the 2 points you want to know distance between , bring feeler back out into the light an then use verniers where its easier to see . its a bit of a 3 handed double jointed neck job whatever you use ,torches/dentist mirrors/measuring stuff down bore an you peering up the exhaust port or in tother end .a glass table with a strong light underneath to sit barrel on was a idea of mine once ,but i could only get a 80's chrome n smoked glass one at the time ,an the smoked effect spoilt it . H
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Post by vespasco on Nov 10, 2014 10:05:26 GMT
The static Deck height @ 0.0mm I mentioned was measured (uncorrectly) from the edge of the piston crown (not the dykes ring), theres a 0.6mm difference between top of dykes ring and the inaccurate reading to top of piston/crown. Inaccurate because the edge of the piston/crown where you would normally measure from is actually (approx) 3mm smaller in diameter than the piston itself, due to the dykes ring. I thought id chuck those figures out there for the record but i will be using to top of dykes ring for accurate measuring purposes. Yes, the long stroker will defo stay So will the mild expansion of the SIP road. So will the stock si24 Its a matter of making them work together the best they can .
Without a gasket the transfer duration would be as low as i can get it without machining or swapping cranks...127°...thats got to be my datum point! If i was to raise exhaust port height by 1.5mm for eg, then the exhaust timings would be much better @ 176° giving much better BD duration @ 24.5° Ill put that on the list of things id like to do for now!!!
Also, a little piece of 6mm (or thicker) glass would not cost you much at all. Ask your local glass supplier for an off cut. Smooth the edges with emery cloth.
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Post by pxguru on Nov 10, 2014 14:22:19 GMT
That makes it a lot clearer Vespasco. You are correct, with a dykes ring the port measurements are taken from its edge and forget about the piston (unless calculating compression). This also makes your problem a bit worse ;( with 127 TD you are going to need about 180 exhaust duration to achieve full power. This means raising the exhaust port 2.5mm With this amount of TD and with well below the absolute minimum blowdown, mid range will be lost, as well as high rpm power. As said it will run but won't perform anything like it could. If you are keeping the SIP road and the 60mm crank then get the port moved. Nikasil can be ported really easily without re-plating. Just need the right type of diamond bit and carefully do the chamfering with a fine drum sander. There will be someone near to you that can do it for you. A bit pointless putting it back together like this.
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Post by vespasco on Nov 10, 2014 14:32:29 GMT
I hear what youre saying guru ji I must decide what to do, and soon!!
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Post by sime66 on Nov 11, 2014 8:19:53 GMT
Now, a little ahead of planned purchase, but I can’t resist a bargain; new listing overnight - I bought two sets of 150mm Mitutoyo Absolute Digimatic Calipers on Ebay this morning, with a view to re-selling one of them to recoup the cost. These are very good quality ones; £80 new in UK, so if anyone is interested PM me. I’ll take some better photos of jaws etc. when they arrive, and leave on here for one week in ‘For Sale’ before putting one set back on Ebay. www.mitutoyo.co.uk/small-tool-instruments-and-data-management/calipers/500-171-30
Might also be interested in swaps for other quality measuring tools – calipers, dividers, scribes, rules…. that kind of thing to the value of about £30 if anybody has anything, or any suggestions.
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Post by henri on Nov 11, 2014 9:05:47 GMT
as pxguru says vespaco, best to get somebody with experience of nicasil bores ,if ordinary/normal iron barrel porting burrs are used they have a tendency to snag an tear the lining ,that in the person is use to iron bores its very easy to take too much off from a ali 1 , H
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Post by vespasco on Nov 11, 2014 9:54:36 GMT
Someones getting tunititus but seriously sime, thats a good move,,being able to measure accrately the parts you buy will fit the parts you have accurately without hoping or guessing! And knowing which parts to buy (shims for example) when yours are wearing out. Thanks h . id be quietly confident of doing it myself on a cast iron barrel but its the nikasil lining that puts me off letting anyone do it...! because if ports are altered/ground you would see the join between barrel and the lining, whereas, at the moment , the lining bleeds over into the port, no visible join. Im sure people do it all the time and the lining is well stuck onto the ali but it is still a concern of mine. Unfortunately there aint many people i trust to do a decent job of anything nowadays Ill wait until the right person to do it comes along!! Upto now my plan is......(but could change)!! Fit without any base gasket, keeping transfer duration down to a minimum. Ride it. Note power bands rpms and speeds. If it does no more than 6500-7000rpm in 4th then i will try a 0.5mm packer under barrel..such a leap from 0 to 0.5mm packer will (hopefully) help me easily 'spot the difference'! If i still cant get it to ride how it used to then i will seriously consider raising the top of exhaust port, a little at time., as i dont know exactly how big the port area is,... I think its wider than a malossi for eg, and having a wider port may compensate for a short exhaut duration?!! So i dont want to solely rely on the height of exhaust port alone to give me the desired durations.
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Post by pxguru on Nov 11, 2014 12:59:32 GMT
Porting Nikasil is pretty easy with the right tools. The plating doesn't come off unless its chipped and even then it can be sanded back to a good bit if its somewhere that is not so important for sealing Little choice with the plan. It will go as least as well as it did originally. With those numbers it won't be as well as it could go. Do you think the 0.5mm packer will make it go better or worse? When it comes to ports height is worth far more than width (oh er! ). As yours is an oval port its only the centre that matters here. If you put the dykes ring in the barrel and uncover 1.0mm of the exhaust port and check the width uncovered. How wide is the section of uncovered port?
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Post by henri on Nov 11, 2014 16:27:30 GMT
as pxguru says ,but then everythings easy with the right tool , ive always steered clear myself but those i know who do do nicasil have always advised the specific tools for the job ,but even if a total hash is made of it re-plating is possible an not terribly more than a rebore last time somebody mentioned a price to me , but then he lived in the midlands in a industrial area ,H
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Post by vespasco on Nov 11, 2014 21:06:02 GMT
Ill edit in the pics as i want to make sure i have this correct.... Pics now edited in! *Edit - i re read your post guruji...i think the measurement you need is above the Dykes ring yeh!?..... Whch is hard to be accurate, but for arguments sake/as close as i can get its 20mm... I guess this is to help work out the extra area that would be gaind by raising the top of the port?? These are all taken measuring the arc, which i just realised is wrong too isnt it? .. So measuring flat across/ chord = (approx) top of Dyke's - 17.5mm (bottom of Dyke's= 30mm) It aint 100% accurate as i have no calipers and had to draw, then measure it. Whats more i no longer have my Eclipse tungsten tipped scriber...the was my most used/favourite tool at one stage! (I was going to scribe the exhaust port onto the piston)!!!!!! 'Kin up a good barrel is not an option!! What i did spot , which I never had before, was this..... This could do with a bit of work surely!!!!.... This is effectively @ BDC !!!!!
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Post by vespasco on Nov 11, 2014 21:50:57 GMT
I seemed to have kidnapped your thread sime!! I hope you have learnt something about cranks, thick gaskets and squish too?
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Post by sime66 on Nov 11, 2014 22:00:25 GMT
You go ahead mate; I'm following it all with interest, and I'll chip in if I have anything sensible to add. You recording it so well enables me to catch up in my own time, which I haven't had too much of the last few days.
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Post by henri on Nov 12, 2014 9:39:14 GMT
a picture of the piston out the barrel will show how much meat theres is to "carve",but without seeing the skirt length below the transfer i'd say the bottom edge could be matched better , wouldnt get tempted by the lip on left tho as your getting into the support for wrist pin/gudgeon area .give it a swipe with a cd marking pen in situ an give us a piccy of it then outside the barrel ,can get a better idea of whats poss , H
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Post by vespasco on Nov 12, 2014 9:46:45 GMT
Nice one I try to add as much (useful) info as possible as in 5 years time i may have forgotten most of it? !!! So will want to read back and make sense of everything again!! And to answer your earlier question guru ji..... Am i expecting it to go faster /slower with 0.5mm gasket?? From what weve learnt here, i would expect the 0.5mm to raise the transfer duration too much , also making the BD too little, which will very likely have an effect on performance, for the worst. However, from my previous set up, im (only) 90% sure i used to have a 0.5mm base gasket , im still hunting for it in the bin (only so the rings would be covered @ BDC)... This would open the exhaust port a little more at least. BD would still be very short tho'. .... I do remember suffering from blow back when i first set it up but a bigger exhaust (sip road) and air filter/timing modifications smoothed it out a little. I do also remember noting at the time (rightly or wrongly) that i could/would raise the cylinder even more on my next rebuild!?!?!?! Now i have become enlightened a little more im going to go the opposite way and try without base gasket!... Which accrding to the figures would be better than packing it more. BD would also be (only) slightly better altho' still not enough. If im lucky, i may even bolt it all together today,,,,depending in how long it takes me to skim the head.... And i have a choice of two.... Ill try the one ive been using first...then the other, similar head.... I have lots of options..... Do i try and set it up how i had it (yes id like to!!) as it was fast, powerful and reliable....even although i was not getting 100% out of the kit. Or do i (yes please) try and get the most out of the kit (without swapping pipe and carb) , probably by raising exhaust port.... Time an experimenting wil tell!! Bascally, i have lots of setting up to do!!! Which is a little annoying as i only wanted to do all this once (when i first built ages ago) ... Replacing anything like for like to retain the set up i had.... But thats what happens when you learn something new.... You have to try and test it out for yourself, try and prove its right, (to try and prove it wrong even)! to believe it for yourself and take another step closer to Nirvana. Im still lovin' this thread!
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Post by pxguru on Nov 12, 2014 11:22:16 GMT
Good work on the 1mm measuring on the exhaust port. Shows it perfectly. The area covered by the dykes ring is about what is missing. If the port were even 10mm wider you would still not add anything like this area above the ring in the 1mm zone in comparison to what is missing. With a full flat square port would be better but still not enough. There is a lot of area missing and its really going to notice! I think the same, raising the barrel 0.5mm is going to make it run terrible. The TD is already too much and that would be way over. All you would notice is that it drinks loads of petrol and doesn't perform well across any of the rev range. You should fix the piston port line up. Those Pinasco transfers are small enough anyway. A bit of the skirt could do with cutting out there too. If you're feeling brave, try moving the window with small fine drum sander. The Niaksil don't matter where the rings don't touch
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Post by vespasco on Nov 12, 2014 16:05:47 GMT
Here you go..... I see what you say about the gudgeon pin h. Its pretty close. I think theres plenty of tolerance at the bottom of the skirt.
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Post by henri on Nov 12, 2014 17:38:17 GMT
as i thought earlier ,leave the pin an get it matched below on bottom line , theres plenty skirt there to keep a "ring" that will stop excessive expansion at piston bottom ,will get rid off that step,it maybe only there a split second but for "pure" gas -flow smooth is the watchword eh, that an as ya know radiused corners . seems to be a shadow from base gasket on transfer port opening , nit-pickin maybe but the "devil is in the detail" eh, an as for "only wanted to do this once" ,i aint buyin that line,not even for a dollar, your as bad as me ,H
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Post by vespasco on Nov 13, 2014 10:04:16 GMT
What shadow do you speak of h? Are you referring to the base gasket not being matched to the port? (Which ive not done yet)
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Post by pxguru on Nov 13, 2014 12:53:23 GMT
There is a lot that could be done with those transfer ports with a couple of days demelling Put some ally filler in the cases to line up the ports smoothly. Open it all right out to match the piston ports. Easy increase to the mid and high end power.
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Post by henri on Nov 13, 2014 17:39:05 GMT
yep,thats what i thought i'd spotted ,a mis-match on the base gasket ,guessin thats a sacrificial 1 to get measurements from n not bothered matching it . an px guru , what do ya mean by " ali filler" , jb weld /chemmy metal or other ,whats your recomendation to use , H
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Post by vespasco on Nov 13, 2014 18:24:17 GMT
Its back together! Work done that was different to last time: (cases have already been opened to match the small inlet) Ive filed out the bottom of the piston No base gasket. Skimmed the head a little too (about 0.3mm - my arm aches!),,,but i forgot to check the actual squish band upon assembly. Doh! I do need to double check the squish as my figures didnt quite add up) Flowed the ports a little more 1/2 heartedly (as i know its so hard) sanded the top of the exhaust port as much as i could (<0.1mm) Every little helps!!! Test run tomorrow, plus the usual tweaking...fingers crossed all will be well!
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