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Post by 90GTVert on Aug 5, 2012 8:50:59 GMT -5
I'm thinking about setting the cylinder up for around 10,000RPM using base gaskets/shims and seeing how the MRP works without the timing advance. As I said a while back, I think it may work and hit better if I could use light rollers. I just can't now becasue it doesn't pull higher. I suspect the MRP would be good for more than 9500RPM if it had a cylinder that supported it. Only issue right now is that I'm gonna have to sand the heck out of a head to get compression right after spacing the cylinder up somewhere near 1mm. Don't really wanna screw up the current setup, so even though I don't like the other head with less cooling fins I 'd use it I guess. I'm mainly curious because I don't recall ever seeing specs for the MRP exhaust. The Leo stuff I can find specs and dynos.
The reason I don't wanna screw up the current setup, even though I'm about done with the stock jug, is that when it's all over I'd like to try lean pre-mix ratios with AMSOil Sabre. It was discussed elsewhere on the forum and how the moped folks use 100:1 without issue. I ran 80:1 when I first started using AMSOil and had seizes till I went to 50:1. Maybe that was a fluke or maybe our engines just aren't created equal? I'd try it before the 70cc, but I don't wanna risk any other parts. Hoping to use the setup as it was with the GP to get good performance, but have something I can ride a bit that doesn't wake the neighbors. Not sure how much it matters though. If I try 100:1 I'm gonna try to get someone to follow me in a truck at first. That's how well I think it will go based on my very minimal past experience with lean ratios.
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Post by 90GTVert on Aug 5, 2012 11:17:53 GMT -5
I raised the cylinder 1mm using a shim sandwiched between the original and one additional base gasket to get 191° exhaust / 135° transfer. Should be good for 10,000RPM+ if the pipe wants to do it. Now I just gotta figure out what cc I need the head to be to keep the same corrected compression ratio and sand it till I get there.
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Post by 90GTVert on Aug 5, 2012 17:11:38 GMT -5
I shaved the other head down till it was 3.6cc.   Stuck it back together and set timing back to stock. Put in 5g sliders instead of 6g. Haven't even left the garage, but I can tell it's struggling to hit. It's really windy and gonna storm so I'll work towards tuning it tomorrow I hope. I think I'm gonna end up needing a stiffer contra, since 5g are my lightest sliders, and probably 2000RPM clutch springs. |
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Post by reveeen on Aug 5, 2012 19:00:51 GMT -5
Brent: I know you like your sliders, but you might get a, well, smoother "hit" with rollers. I could not get sliders to work consistently here with a 50cc ported motor.
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Post by 90GTVert on Aug 6, 2012 11:37:07 GMT -5
2strokd suggested I try swapping on another silencer when I mentioned waking my neighbors with the MRP exhaust. I gave it a shot. It's a little bit quieter and it does tame some raspy sound. Doesn't make a difference in performance. I'm thinking the MRP's thin steel may be a big cause of the volume. It's pretty light.  I tuned the CVT and ended up using 4g rollers (no sliders that light) to get it to rev. I saw max revs of just over 10,700RPM before the contra spring started to fade. The problem is, it makes no more power now than when it was revving to 9,500RPM. I see no sense in all the extra RPM if it's not accomplishing anything, since it causes more stress to the engine. After riding around at 10,400-10,500RPM for a bit, I started hearing a rattle I've never heard before. Not sure what it was, but I didn't really like it. Prob just something from the different harmonics at that RPM. It seems the MRP is comfortable anywhere from a low 9,000RPM to at least mid 10,000RPM. Making it rev higher helped the pipe to hit a little faster than before (stock timing), but not much. What you gain from being able to use light rollers and stiffer clutch springs is partially lost from the even greater lack of low end power. I made a vid since over the years I've heard so many people say stock ignitions can't do over 10,000RPM. I know they can, because I've done it. I've showed T1 plenty doing 10-12,000RPM with it's 103cc and stock ignition, and now here's a 49cc with a stock ignition past 10,000RPM. I'm sure some of the aftermarket stuff is a lot better, but it can work. I'd imagine I could do 11,000RPM... but I only have .5g lighter weights and I really don't have a desire to push it when I'm not accomplishing any more power. Also another note of the fuel economy since step asked. I am at 39.99 miles on the trip odometer from filling it to the top. When I looked in the gas tank I can only see a tiny bit left at the bottom corner of the tank. I came fairly close to running out of gas once again.  I'm gonna have to think a little more when I look at the odo before leaving and fill it back up if there's any doubt. |
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Post by 90GTVert on Aug 6, 2012 15:23:23 GMT -5
Remember I said I heard a rattle after running for a while over 10,000RPM? (If not go back a page and read and watch the vid of it revving.) I took the engine out this afternoon to install a BBK and found out what the rattle was. I removed one circlip as usual. Then I looked at the other side and the circlip was at the edge of the piston. I touched it with the needle nose pliers and it fell out. I removed the piston. Let's start out by looking at one side of the piston, what it should look like....   Alright, now check the other side out...    I looked at the cylinder...  "Well, that's not so bad", I thought. Just a piston kit. I shouldn't be so hasty. After being quite happy at how I had probably narrowly avoided anything major, I removed the wrist pin and needle bearing. They seemed fine... until I removed them from the connecting rod. The needle bearing was only held together because it was sandwiched between the wrist pin and the conrod.  Small nicks on the wrist pin.  Okay, still not horrible. A piston kit and a new needle bearing. Wait... if the wrist pin is nicked... what about the other part of the needle bearing sandwich?!?  Oh,  . The silver parts are where the bearing started eating into the conrod. I measured the ID at 16.10mm, but where it's been chewed on it goes up to as much as 16.25mm. If I put a new bearing in and spin it, of course it sorta grinds on the imperfections. I don't think I can try to hone it out, because it would be too big. I tried to find a service limit, but everything I found is for 10mm pin. I think I'm going to have to buy another crank. Don't really wanna try replacing the conrod either, assuming I even knew where to get one. I may try opening it up and see how the bearing fits, but I don't expect it to work. Only reason I really would try is I have nothing to lose. The rest of the engine is fine. The big end is good to go as far as I can tell. No bits and pieces came off and got banged around or anything like that. Keep the revs down on the stock stuff. It's not just the crank you have to worry about apparently. |
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Post by palezu on Aug 6, 2012 17:56:12 GMT -5
There is one thing in engine design which I absolutely hate. Those piston pin circlips. You can never be sure if the clip is gonna stay there unless you use the very rare spiral-lox (?) circlips with a circlip groove without the side slots. I have had a circlip failure before and it ruined my piston and cylinder..you have had too and here it was again close. One thing I noticed. Judging from your picture it seems that the circlip almost fell out from the variator side of the piston. That was in my case too. Maybe the direction of the engine rotation or something else in the design causes the wrist pin to rub and push the variator side circlip outwards, and after some time the groove gives away and there goes the circlip. Or is it just random which side it fails  ? Some time ago I changed the crankshaft of my friends yamaha aerox and the engine was never opened before and the Original circlips were some sort of glued to the grooves. They were very hard to get out and the clip bent before it snapped out. I want that glue too. Heat-resistant thread locker or something like that? Btw a Piaggio 50cc connecting rod should fit if you want to replace it. |
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Post by reveeen on Aug 6, 2012 18:07:25 GMT -5
palezu: if you noticed the Yamaha clips did not have any "ears" (for want of a better word) on either end of the clip. Extra mass is not a good thing on a pin clip. Red Locktite will hold the clips in.
What came first.... the chicken, or the egg?
Did the clip shifting ruin the bearing?
Did the bearing cause the clip to shift?
Did rpm "do" the bearing, or was it that 20 degrees BTDC timing?
My vote is: timing
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Post by 90GTVert on Aug 6, 2012 19:00:39 GMT -5
The timing was stock and I had this thing apart last night and all seemed fine. Timing was stock because I wanted to see if just using rollers light enough to make it rev would make it hit off the line. It never made any noise until after riding for a while in the mid 10,000RPM range. I think it was the RPM that killed the bearing, and then the circlip, but I dunno that any of us can say for sure. I've had many circlip failures. Every time the clip came out and scarred the walls and busted up and got bits of it embedded in the piston skirt or crown and damage to the head at times. Every time was with those easy to install clips that let you squeeze two tabs with pliers and pop them right in. This was a different kind of circlip, the ones I have not had fail, at least prior to this. I have tried the red loctite before. Hard to know if it saved anything, since by then I quit using the clips that failed. Didn't hurt anything. I smoothed out the conrod, but I think it's too big. It's 16.3mm now. Seemed like too much play with a bearing and pin in there. I measured 2 stroker cranks with 12mm pins and they're 15mm ID. Gotta love Chinese stuff. The bearing for one 12mm pin engine may not even fit in another. Isn't that great? Here's a selection I have. Short and tall are for 50, 70, and 90ccs.   |
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Post by 90GTVert on Aug 6, 2012 19:28:00 GMT -5
If anyone knows a good, but cheaper, source for a 12mm pin crank please let me know. Best I can find ATM is $80 at Scrappy + $10 shipping. I can find the 10mm for $50, but that won't do me any good.
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Post by 90GTVert on Aug 6, 2012 20:20:28 GMT -5
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Post by tygertung on Aug 7, 2012 3:25:38 GMT -5
If I get those easy to install circlips I always clip off the ears with some side cutters and file the cut smooth. I read in many books never use the type with the ears as they tend to fail in service.
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noday
Scoot Enthusiast
Posts: 149
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Post by noday on Aug 7, 2012 5:57:36 GMT -5
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Post by 90GTVert on Aug 7, 2012 6:33:41 GMT -5
First, I can't find the right rod. They're all 14mm ID for a 10mm pin. The Piaggio rod says 17mm on the small end. They're half the price of a new crank. Considering the threads have stripped once too, I don't think it's worth me attempting the rod. I say attempting because I'd be surprised if I actually could do it. I do not have a press. The one in that vid is not homemade, or if it is it looks just likes ones they sell. Maybe not this one exactly, but you get the idea... www.harborfreight.com/20-ton-a-frame-industrial-heavy-duty-floor-shop-press-37999.htmlThe sad part is I can get a stroker crank with bearings and seals for the same cost or less than the 50cc crank. |
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noday
Scoot Enthusiast
Posts: 149
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Post by noday on Aug 7, 2012 6:47:45 GMT -5
just wishful thinking on my part, I guess.
I found a shop in Tampa that will do cranks, had to look for motorcycle & marine. they still want $100 for the labor.
yes, that looks like the same press.
and it still amazes me that you can buy a new quality part made in Taiwan & shipped to the US for less than machine shop cost here to repair an old one.
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