RGraves

iTrader: (37)

Please explain what people are talking about when they talk about the "pinch" of a engine. I am still trying to learn the lingo

Duster_360

iTrader: (21)

The piston and sleeve in a nitro engine are tapered. Near top dead center (where piston is at highest point in the cyl), there is very very little or no clearance. This fit at TDC is what is being referred to as pinch. This condition is what gives a nitro engine its momentary seal in the cylinder so that when the mix explodes, this seal allows a power stroke to take place, otherwise with no seal, the pressure would just leak by, past the piston and you'd have no power.

When engine is new, you can take glow plug out and it will be very hard to turn thru top dead center - you can feel the pinch. The pinch wears with running and will disappear as the piston and sleeve wear in together. Now the difficulty turning thru TDC is due to compression, take plug out and you can turn it over by hand easier. Seal now is partly close fit and a film of oil from fuel between piston and sleeve.

JeromeK99

iTrader: (3)

Now that Duster explained the concept. +1

Some folks will take the motor's sleeve and "Pinch" it when it wears out to regain that compression seal. It does work and you'll get some more life out of the motor.. save some $$$


Jerome