XtremeAir125
Member
- Jul 5, 2001
- 120
- 0
Originally posted by Mudboy
As for those saying "an hour isn't enough of a break in" that just isn't true on a 125 two stroke. I put a new top end in my 250, warmed it up for five minutes, then revved the crap out of it riding sand dunes. If you've installed everything right and jetted it right, there really is nothing more than a little warm up required before you twist away!
Originally posted by Anssi
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My guess is on imsufficient warm-up after you took your little break.
If the tip of the plug was melted awat, it was either very lean, or detonating badly for some reason, possibly both, the pinging could have been caused by lean jetting. The short wamr up time you described can certainly seize a piston, new or not, and it's much more likely with a new piston, especially a forged one, but that would not melt the plug. After repairing it, I would jet much richer before riding it again, and jet it a step at a time after break-in ( which needs to be more than one short warm up). Why did you rejet anyway? Did it run rich or lean before? How much did you change the jetting? If your engine is basically stock other than the exhaust, you shouldn't have to change it very much, and my experiece with aftermarket pipes is they require you to make the main one or two sizes richer, not leaner. I'm sure some bikes are the opposite, but none that I have owned.Originally posted by Yamamoto
well that will not melt spark plugs
I have to disagree. the running time is not the issue, it is heating-cooling cycles that a new piston needs to relieve the trapped stresses in the metal from the manufacturing process. Without this, it is just a guess if it will run or blow. If it is a forged piston with tight tolerances, it will most certainly seize this way.Originally posted by Mudboy
As long as you're getting a good seal with the rings and have it jetted right, it's either going to work or it won't.
The answer to this is no. The heat cycles release the frozen stresses in the metal that are left over from the manufacturing process. We performed an experiment in Tech school on this subject. We took two pistons, one brand new, and one used, and put both of them in a 500 degree oven for twenty minutes. The used piston came through this test unscathed, but the new piston was distorted beyond recognition. The heating cycles during break-in help to relieve the stresses, while the cylinder keeps the piston from distorting. Since the piston is trying to change shapes during this process, rushing the break-in and trying to push the piston too hard too soon will allow it to distort enough in the cylinder to seize. I also believe that the heat produced by the combustion is not the only factor at work, you also have the huge forces placed on the piston by the acceleration and decceleration that occurs at the end of each stroke, and by the extreme pressure rise that occurs at the moment of combustion.Originally posted by motopuffs
Heat cycles: isn't or couldn't this be already done at the factory? Couldn't I do it in the oven before ever assembling?
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