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Post by oldgeek on May 11, 2015 22:44:03 GMT -5
Sadly the Streetrace kit is still sitting in the living room floor. No time for it due to work and other scoot projects.
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Post by thatcrazyguy on May 11, 2015 22:47:00 GMT -5
Sadly the Streetrace kit is still sitting in the living room floor. No time for it due to work and other scoot projects. I can put it to good use down here in Tampa Bay  |
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Post by oldgeek on Oct 14, 2015 9:55:06 GMT -5
Last night I finally pulled the motor from this scoot and started working on it. I have decided not to split the cases, because I have searched thoroughly for the missing piece of the piston ring and it is nowhere to be found in the crankcase.
I have been thinking about this rebuild and am now contemplating whether I should use the new 70cc Streetrace kit I have, or not. There have been several reports of rings getting hung on the exhaust ports of these kits lately. I don't know the specifics of what happened to the others, but in my case it is clear to me the locating pin for the top ring somehow got pushed all the way in allowing the ring to rotate and get snagged on the exhaust port. To me this points to a problem with the piston itself, not the cylinder. IMO looking at the piston, it does not appear to have gotten hot enough for the pin to have been pushed into the piston. I think what happened is the hole for the locating pin was drilled too deep allowing it to work its way into the piston too far.
Anyway I decided to check out an Autotech 70cc cast iron kit I have on the shelf to see how it matches up. I ended up trying a bunch of combinations using the autotech piston and both cylinders, along with 3 different heads. The streetrace piston is going on the shelf for the time being.
Lately, I have been trying to set up the cylinder with enough base gasket to make the top of the piston flush with the bottom of the transfers, and then use a head and gaskets to attempt to get a decent squish. Not an easy task sometimes!
After getting to that point I check durations to see what I have to work with. I am having trouble getting a squish below 1mm with any combination I try using the parts I have. I will either need a head with a bigger step cut, or have to settle for the top of the piston not quite flush with the bottom of the transfers. There is always some compromise I guess.
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Post by spaz12 on Oct 14, 2015 14:50:21 GMT -5
I have an mhr rep head that you can have if you think that you can use it? I have no idea if it'll help ya, but it's just sitting here gathering dust and I'll never use it.
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Post by oldgeek on Oct 14, 2015 17:56:35 GMT -5
I have an mhr rep head that you can have if you think that you can use it? I have no idea if it'll help ya, but it's just sitting here gathering dust and I'll never use it. Thanks, but I think I found the winning combination earlier today. Using the streetrace jug, the autotech piston, the step cut streetrace head, and various spacers and gaskets, the piston height is near perfect at the bottom of the transfers, and squish is .72mm. A little copper spray, and fully torqued head bolts should put me just about right. Now I gotta look at the durations so I can see what pipe it may like. I also need to check piston to cyl clearance and ring end gaps before I go much further, I could be wasting my time if those are way out. |
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Post by 190mech on Oct 14, 2015 18:51:37 GMT -5
Thats the right way to do a setup oldgeek!Keep moving stuff around till the numbers look good,make them better if possible,then select a pipe for THAT build!!  |
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Post by oldgeek on Oct 14, 2015 19:41:58 GMT -5
Thats the right way to do a setup oldgeek!Keep moving stuff around till the numbers look good,make them better if possible,then select a pipe for THAT build!! I am slow to learn, but I am finally starting to catch on... I think! It also helps to have great teachers  I sincerely appreciate the knowledge that flows freely here, not much of that left in this world today. THIS FORUM ROCKS! |
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Post by tsimi on Oct 14, 2015 20:56:29 GMT -5
So you would say that Stage6 kits have problems with their pistons and are therefore not reliable?
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Post by oldgeek on Oct 15, 2015 13:34:53 GMT -5
So you would say that Stage6 kits have problems with their pistons and are therefore not reliable? Stage 6 makes good products. The Stage 6 Streetrace kit with the 12mm pin appears to be having problems IMO. Despite that, I may be buying another streetrace kit soon. See my reason for that in my next post! |
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Post by oldgeek on Oct 15, 2015 13:58:27 GMT -5
Well I screwed up royally today, but it should still work.  I was checking durations using the usual copper pipe spacers and nuts to hold the cylinder in place. The exhaust duration was 193 and the transfers were at 136. I wanted to see what the durations were with the cylinder torqued to spec, but you cannot torque the copper pipe spacers because they are soft and deform under much pressure. So I found some brass inserts from some old variator rollers, and decided they would work as spacers. I torqued them up evenly, got to 13ftlbs and SNAP! I think what happened is the spacer I used where the fin broke has a larger ID than the others and I tightened it up off center which allowed it to put too much pressure on the fin instead of the cylinder wall. If I had used the odd sized spacer on one of the top studs, I think it would not have happened because gravity would have put it closer to the cylinder wall. I am still going to use it because it should seal fine the way it is but damit! So let this be a lesson for you, maybe it will save some embarrassment for you one day!  |
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Post by spaz12 on Oct 15, 2015 14:39:29 GMT -5
Aw man, that's terrible when crap like that happens. Makes ya sick to your stomach. If it's any consolation, I dropped an almost new mhr rep off my balcony and destroyed it.
I would bond that back together with something so that those fins are still cooling that area. But I'm sure you already know that.
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Post by Corrosion on Oct 15, 2015 16:13:21 GMT -5
That must have been a sick moment. Sorry to see that!
I would be tempted to Braze that back together. Flat file it and try it.
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Post by moofus02 on Oct 15, 2015 19:02:56 GMT -5
I've got a trophy cylinder that looks like that. Didn't seam to hurt the way it ran
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Post by tsimi on Oct 15, 2015 19:13:26 GMT -5
oldgeekOh snap! Man so sorry to see this! The second something like that would happen to me I would probably pass out. And after I wake up and look at it again, pass out again. How can you fix that? Since some of you guys say it still can run.
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Post by 190mech on Oct 15, 2015 19:52:23 GMT -5
Got lots of head gasket seal area left,,would likely need a steel spacer in the broken area to share the clamping load of the other 3 studs,,Fit would be critical,heck I'd try it!!!
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I sincerely appreciate the knowledge that flows freely here, not much of that left in this world today. 
