|
Post by pxguru on Dec 2, 2014 20:07:57 GMT
If they were just 15mph over then it would be easy. My last one was spot on to GPS at 40mph. Yet by 60mph on GPS it was reading 70mph on the speedo. And this was a good one!
|
|
|
Post by pxguru on Dec 2, 2014 8:36:45 GMT
I just paid the £6.24 so I would hope its the full version! I'll do a run later and get a sample to play with and we can take it from there
|
|
|
Post by pxguru on Dec 2, 2014 6:56:56 GMT
You guys have been pretty busy I downloaded MD on my phone. Can you summerise what I need to know and I'll give it a run when its not raining!
|
|
|
Post by pxguru on Nov 23, 2014 11:22:45 GMT
Nice job fpb how does it go on the road?
|
|
|
Post by pxguru on Nov 13, 2014 13:27:12 GMT
Can you post a picture of your Pinasco head? Any idea on the volume of it?
|
|
|
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.
|
|
|
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
|
|
|
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?
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
Post by pxguru on Nov 8, 2014 13:12:02 GMT
Thx Gaz, I don't think we are going to get into grinding barrels here. Too easy to make mistakes and ruin them. And when you are learning you do ruin a few! I spend weeks/months grinding my own kits to get them just right, far beyond what the "professionals" have time to do My Polossi is still going strong and been running 2 years at least but I have a Malossi 210 I am doing at the moment and another PX200 tourer to do soon (might do the same as Vespasco on that one. We'll see). For here, I am just happy to help with the blue printing exercise, getting engines set up right and jetted in properly really makes a lot of difference. Not that they were not generally ok before but a few tweeks here to set them up to how you use them can make the whole experience that much better My Mrs just brought me a 2 stroke leaf blower. That's getting tuned soon too!
|
|
|
Post by pxguru on Nov 8, 2014 12:43:59 GMT
Sounds like it might just be the head not tightened down properly. Take the barrel cover off and re torque the head before going any further.
|
|
|
Post by pxguru on Nov 8, 2014 3:15:23 GMT
Easy to get carried away with all the measurements. Accuracy of 0.1mm is enough for what I do. If you can get this kind of linearity across the width of a port ground by hand then you are doing pretty well. Ports heights should be measured a 2 mm back from the barrel wall. The thing I use most for ports is a cheap digital vernier similar to Gaz's. To get it to measure on the edge of the port I took a saw to it and cut the back off and a little off the nose. Now it fits in fine I don't consider a degree wheel is accurate enough for porting, as you have to guess where the port is open after the port chamfer is visible. A degree disks only real use is for checking rotary inlet timing, where it's the best thing ever.
|
|
|
Post by pxguru on Nov 7, 2014 3:28:11 GMT
Exhaust port height i measure @: (at the moment) 61.5mm - 37.3mm = 24.2mm = 6.15:1 corrected = 26cc C.C. (combustion chamber) That 61.5 should be 60.38. Still works out very similar though. A little skimming to do, especially if you stay with the 124 TD. While on the compression subject 6.5:1 for corrected compression is still not so much. 6.5:1 is the same value for a standard PX200 as it came out of the factory. So not going to strain the engine very much On an air cooled scooter tuned just for speed there could be 8:1 corrected compression and the same engine can still take it long term with a decent crank. Next point is the squish clearance; the less clearance there is, the less mixture compressed in the squish and less likely to detonate at the outer edge. So go as close as you dare to avoid mechanical contact. The books all say 1.2mm is safe for a 200. What they don't tell you about is the detonation risk. There is actually far more damage done from detonation with a wider squish clearance as there is more fuel at the edge to go bang! The ideal for racing is 0 mm, when expanded at full temperature (and someone else is paying the bills). On my own road scooters I usually set to less than 1mm, never had an issue. With all the issues there are to fix it might be ok with the 124 TD. If it pulls 4th then 124 would actually be faster in the end. With the passing seal, casing leaks and low compression sorted it should just about make it Edit: Without an expansion type exhaust giving some "supercharge effect" the 6.5:1 corrected compression can be even higher!
|
|
|
Post by pxguru on Nov 6, 2014 6:03:28 GMT
I would fit a 0.1 base gasket and leave it at that. The only reason you are reducing the transfer duration is to lower the power band. If I cant do that then I just raise the revs and increase the power a bit to balance it out. That way it can rev higher in 3rd to close the gear gap. Without porting the barrel you can just raise the compression or fit a long length expansion with a lower rpm power band. You are in a muddle with the trapped compression. Typical confusion from the Lammy camp with their engines that run backwards The exhaust port height is the height of the exhaust port (23.8mm in your case) not the height to the deck (37.3mm) Try it again. I work yours out as 6.28:1. So there is some head skimming to do (The squish needs closing up anyway) Question for H. Would this ally barrel grow in height more than the conrod would lengthen?
|
|
|
Post by pxguru on Nov 5, 2014 16:43:35 GMT
wow, you have all been busy. Vespasco, 123 sounds like plenty. 24 degrees is about minimum blowdown and is all you need for yours. Don't worry too much about the dykes ring, as long as there is a little static deck above it.
Swept volume compression numbers on a 2 stroke don't mean a great deal. See what you can do with your head to keep the trapped compression over 6.5:1 (pretty much the same as a standard P200).
|
|
|
Post by pxguru on Nov 4, 2014 12:04:00 GMT
|
|
|
Post by pxguru on Nov 4, 2014 10:39:59 GMT
On 22/68 gearing your set up could make over 75mph on a GPS read out (about 90mph on a vespa speedo). If you have the power A standard DR177 will make loads of power at low revs but top out and not go any faster. Trust me don't change the gearing just find more high rpm power (without losing the low range!).
|
|
|
Post by pxguru on Nov 4, 2014 6:38:49 GMT
Q1, there is no definitive data but all the tables you will find agree within a few degrees, so it must be true. I would only recommend that you measure what you have. Then after some analysis you will decide where you want to be and what you can practically change. The weakest part of any PX engine in generally good condition is the clutch and this is the limiting factor of increasing the power. A banded CosaII is good for 15 bhp without doubt. Q2, The existing rpm for max power can be estimated by the speed/rpm it goes at when faced with a mild hill or into light wind. That being the case adjusting the engine to how slow you want to go is one way of looking at it. The higher the transfers the higher the peak power but the later the power comes in, so again the bottom of the power band is the limiting factor. On a scooter with only 4 gears every single porting technique to widen the power band must be used to achieve maximum usable power Once you measure where you are, calculate what you need to improve against what you can achieve with your facilities and skill available you will probably decide to just fit the 1mm base packer and be done with it
|
|
|
Post by pxguru on Nov 4, 2014 5:37:45 GMT
Interesting to note that is doesn't go much faster with the higher gearing. It is just going as fast as the power you have. It probably only feels like it is screaming as it doesn't rev that high. For example, some of my motorcycles rev to 15,000rpm and cruising along at 9,000rpm feels like tickover. 22/68 is usually ideal for your set up. If you want it to go faster you will need more power first
|
|
|
Post by pxguru on Nov 2, 2014 12:49:15 GMT
It is possible to make improvements on a set up like yours to whatever you want to do with it. It takes barrel work though and you're not allowed to use power tools anymore Just tweeking the transfer duration to suit your needs isn't going to mean you need a BGM clutch like Vespasco It would be drawing more air so will need to be up jetted. The rest of the engine won't break if you dont wheelie it (too often). The 120 degrees at 6000rpm in that chart refers to where maximum power is, not how high it revs. Yours could typically be max power at 4500rpm or so. Also less open transfers, means less fuel in and that means less power out and peaking too early.
|
|
|
Post by pxguru on Nov 2, 2014 12:20:28 GMT
Looks like its all going fine. Any pictures of the blown seal? If it was leaking past the outer edge as it wasnt bonded then probably nothing to see.
I think the clutch spacer is no issue. It can only be caused by the crank or the bearing. If neither need changing just put it back together like that. Your not using the autolube anyway.
Be sure to repeat the pressure test before it goes back in.
|
|
|
Post by pxguru on Nov 1, 2014 16:15:13 GMT
Sime66, You got me going for a sec there. I didnt think I got it wrong. Your little calculator is upside down. Duration is either side of BDC not TDC. Try it again and it will work out to about 1.1mm Don't worry too much about compression or squish clearance until the rest is set up.
|
|
|
Post by pxguru on Nov 1, 2014 12:27:02 GMT
This simplification pretty much sums it up. These durations are a bit high for road scooters but they do serve to demonstrate there is only 6 degrees between a 6000 rpm plodder and a 9000 rpm screamer. In milimeters this 6 degrees is about 1mm. A DR kit bolted straight on out the box will be nowhere near 120 degrees. If you are happy with it now just imagine how it could go, maybe something for the Spring The "ported to 8700rpm" on my Polossi means that it revs to 8700rpm in gear. Never seen it rev past 8200rpm in top (Need to lay off the pies for quite a while before that happens) but very happy with it as my road scooter.
|
|
|
Post by pxguru on Oct 31, 2014 13:49:50 GMT
You are certainly right about the not that easy. That Jennings book was actually published in 1973. It does contain good stuff but is has quite a few misleading old ideas thrown in amongst the good stuff and mor importantly the overlooked areas. You are getting a bit to far into conceptual tuning than just coming up with a figure to set your barrel to. Was trying to keep this simple and practical As H said earlier. Might be easier if you find out where you are set to and decide how good it is.
|
|
|
Post by pxguru on Oct 30, 2014 11:21:06 GMT
H's way is accurate but here is the laziest way there is to check the squish clearance. This is just a rough check but good enough. Get some solder that's about 1mm diameter. Reel off about a foot and fold in half and twist together. Take out the spark plug. Turn the flywheel clockwise by hand until half inch from the TDC (or you can see it with a torch) . Insert solder until it touches the bore on the far side. Turn fly wheel past TDC. Measure with vernier or similar. Job done.
|
|
|
Post by pxguru on Oct 30, 2014 10:51:58 GMT
You have both pretty much got to the crucial detail now. If you are someone who just gets stuff out of boxes and bolts it on then what we are discussing here doesn't really concern you and your scooter will have the performance that luck will provide. I have said this is a few threads before but when it comes to porting there is no luck. The point of this thread, is that the number one priority when fitting any new barrel to any new engine is to have the transfer degrees set to where they should be. The engine tolerances all add up and are not under the control of DR (or any kit) and are really very important to the performance and should not be left to chance. In practical terms a kit should be dry fitted, measured and adjusted. With kits it generally means how many base gaskets to fit. Once the transfer ports are set up, then everything else should be set and adjusted from this datum. As you say this is not tuning but it is just a part of blue printing process. Things like squish clearance and compression are very relevant but not the first or second priority. Exhaust choice, carb choice, gearing and rotary inlet timing are also on the list but not right at the top of it. The big question is what should the transfer duration be? (and on standard DR this is not 124 degrees!)
|
|
|
Post by pxguru on Oct 29, 2014 17:40:10 GMT
Really very close to the point now. You have the idea though. Adjusting the base gasket to set up the transfer duration to where you need it to be for your purpose or set to just where it is supposed to be on the manufacturers design. Measuring the static deck height is necessary for the calculations to be accurate. Head off, clamp the barrel down, hold the piston at TDC, then ram feeler gauges into the top of the piston until you feel a smooth transition with the top of the barrel. With practice this can be done with only two hands To us degrees and time are the same thing. When it comes to transfer ports, plus or minus a few degrees really notices and this is no big distance. What Sime is nearly on to is not about spending money to achieve but just free power that was always available
|
|
|
Post by pxguru on Oct 28, 2014 17:50:43 GMT
Last time this happened to me I made one on a lathe. Worked fine for years! ps. you know the picture is a front brake
|
|