Daz-E

My Feedback: (9)

Can someone explain Pinch please to me ? Thanks !

46u

My Feedback: (3)

Welcome to the forums. The engines we run do not have rings so the top of they sleeve is pinched to make it smaller to help keep the air fuel and compression from leaking around the piston.

Daz-E

My Feedback: (9)

So how do you know when you have good pinch ? Is it the resistance the engine has when turning it by hand ?

bentgear

Don't confuse pinch and compression. On the two stroke engines we run the sleeve is made with a taper at the top. When new this causes an interfenence fit between the sleeve and the piston as it approachs the top of its travel. When running at correct temperature the sleeve will expand so that the clearance with the piston is closer to what it should be.

Part of the break in process sizes everything to the correct clearance.

If you want to check pinch take the glo plug out and turn the crank. On a new engine it is very hard to go past top dead center (TDC). On an engine that is broken in completely, that has very little if any pinch, if you left the glo plug in place what you would feel would be the compression generated.

Ed M.

574kman

My Feedback: (1)

there are also several companies offering pinch restoring services and kits for the hobbiest to do this themseleves has anyone out ther tried this if so what were your results. no need to say your sorry for asking a qustion. everybody has something they need to learn!

46u

My Feedback: (3)

The pinch tools some sell like the ring with a screw is not worth the money. Really good pinch tooling is expensive and unless you do a lot of engines you are better sending it off and letting them do it. As long as the plating on the sleeve is in good shape and you send it to a reputably person re pinching works out fine.