How to / DIY > Engines

wristpin/piston/connecting rod fit

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wrightkiller:
 Upon disassembly  I found the piston to have clearance slop , and the wrist pin was pulled out from the piston with my little finger :o    the wristpin put in the rod had slop ,  and when I put the wristpin in one side of the piston it had slop ,,and when I put it in the other side it was nice and tight .......this would account for the knocking noise when the engine  was test run by me   .......  also when I tryed to push the wristpin through the piston ,the loose side was ok till it got to the other side ..the bore is off a little ..like who ever drilled it did one side and fliped in over and drilled the other side   :-\ >:(  is this normal for this type of engines?/  auto engines I have rebuilt have been nice and tight.this is my first diesel engine to go through    yes i am hooked on it now.  I got lister fever   WRIGHTKILLER

aqmxv:
If yours is a normal 6/1, 8/1, or 10/1 listeroid, the pin should go in like every other slip-in wrist pin in the world.  Mine is a stiff slip fit in the piston and a .003" or so fit to the rod bushing.

Clean everything thoroughly if you haven't already.  There's probably a black gunk on the inside of the piston head that needs to be removed, and there may be lots of crud in the middle of the wrist pin.  I had a thin coating of the black gunk, but my pin looks like it came out of an airplane engine.  Check carefully for burrs in the wristpin bore of the piston.

I suggest you mic everything.  Parts are cheap and available, so if you need another piston or pin, they can be had.  They're all generic for IDI listeroids of the same size. IDI engines need different pistons and may have other odd parts.

cujet:
As a very general rule, the con rod to pin should be about 0.001 inches. Three thou is really too much. The piston should fit the pin fairly tightly. A tight slip fit is a good description. Maybe 0.0005 clearance. Anything loose will knock and produce plenty of wear.

Chris

aqmxv:
To be honest, I haven't measured a thing yet.  I'm still removing paint and applying surface finishes to rough contacting parts.  Once I get to the assembly stage, I'll check clearances everywhere during rough assembly.  For the record: my wrist-pin to rod clearance felt OK.  It could be .001", it could be .003"  With the thick, dirty oil that was there, it was impossible to tell without measurement.  The wrist pin to piston measurment also felt OK.  I'd believe .0005" - it was quite stiff at room temp.

snowman18:
The Petter shop manual says to submerge the piston in hot water before installing the wrist pin.

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