Once again. Thank you olds 97 your help has been cherished I was getting on forum to ask you those exact questions its people like what's here on this forum that s making this "new hobby" a lot less stressful. Another question: when I got into this hobby I ran into a old friend he had 2 tmaxx's one ran good one ran not so good looked fun so I bought one from him, yes I bought the one that ran not so good, I h a d. A lot of issues I'd fix well now I have 16 various models. This normal I'm always working on several. Can I get a compression tester so I know when a motor is worn out?
The easiest way to see if the pinch is gone is to take the engine apart, orient the piston in the sleeve in the same direction it would be if it was in the engine, then with light pressure, push the piston up in the sleeve. If it reaches the top of the sleeve, it's worn out. When the piston/sleeve are room temp, the sleeve should be shrunk enough at the top to bind the piston a bit above the top of the exhaust port. When it gets up to running temp, the sleeve expands and you end up with the right gap to keep compression without blow by.
Thank You very informative , I've looked all over web for those parts found 2 of them everywhere. They are back ordered.thinking about buying a another engine do you have a favorite ?The easiest way to see if the pinch is gone is to take the engine apart, orient the piston in the sleeve in the same direction it would be if it was in the engine, then with light pressure, push the piston up in the sleeve. If it reaches the top of the sleeve, it's worn out. When the piston/sleeve are room temp, the sleeve should be shrunk enough at the top to bind the piston a bit above the top of the exhaust port. When it gets up to running temp, the sleeve expands and you end up with the right gap to keep compression without blow by.
The sleeve is built with a taper in it so it gets smaller as you go up the sleeve. When the "pinch" is gone, the sleeve expands too much when it's up to running temp and allows the compression to get past the piston.
Examples of worn piston/sleeves I've had re-pinched:
You can see how the piston comes out of the top of the sleeve on two of those.
Then after I got them back from being re-pinched:
That is as far as I could push the piston by hand without overdoing it.
I'd never replace a piston/sleeve. Just isn't worth it for most engines I own. At most, I'd get it re-pinched to get 2+ more gallons out of it. You can get one re-pinched a few times before it's too worn. Depending on who you have do it, the price is around $25.
For what a TRX 3.3 would cost new, I'd probably just replace the entire engine with a new one. By the time the pinch is gone in one of those, the composite carb is probably worn/prone to binding up, the bearings are worn and the con-rod is worn. Not really worth paying retail to fix all that individually.
I've had OSRocket and RayARacing pinch mine in the past. Just ask for a medium pinch so they don't overdo it and cause excess strain on the con-rod/pull-start. After getting it back, you just need to run it a bit rich the first few tanks, but since the "break-in" was already done, your just running it rich to loosen it up a bit.
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