Piston pin fit

[mark]

I am working on my 62xlh .i heated the piston in the oven but cannot get the pin to go in .i have new pistons and pins .i checked the old pin and it fits the piston.i checked the size of the old pin it was. .7910 the new pin is .7913 .is this enough for it not to fit.




Mark
Amca#8993

[Tom Lovejoy]

Those who know will be along, but sounds to big to me. What's the hole size? How about the rod bushings - what size are they? or do Sportsers have em? Good luck, could you use the old pins/ anything wrong with em?

[Knotthed]

Not to state the obvious, but yes that could make it too big to go into the hole without heat and/or cooling or both or the use of force.

"fits" can vary greatly and I do not know the specs for your application. The specs would be the first place to start.

Hopefully this will help you a little bit, with some definitions. I just googled them to find some quick definitions for you.

1) Clearance fits for when it may be desirable for the shaft to rotate or slide freely within the hole, this is usually referred to as a "sliding fit."
2) Interference fits for when it is desirable for the shaft to be securely held within the hole, this is usually referred to as an interference fit
3) Transition fits for when it is desirable that the shaft to be held securely, yet not so securely that it cannot be disassembled, this is usually referred to as a Location or Transition fit.

Within each category of fit there are several classes ranging from high precision and narrow tolerance (allowance) to lower precision and wider tolerance. The choice of fit is dictated first by the use and secondly by the manufacturability of the parts.

[ricmoran]

Wrist pin to rod fit? Tight or does the wrist pin slide into the rod and rotate within the spec called for?

[Carl Olsen]

Hone the pistons to fit, your piston has to expand across the pin because it is cam ground. I like a sliding fit at room temp.
Carl

[mark]

Piston pin fit

The rod bushing were reamed for the new pin.the book said a light hand press fit at 70 f. For the piston and pin fit .i heated the piston in the oven to more then 70f and the pin went right in .that was on the first piston .the next piston is the one that I was having trouble with .i lapped the pin with 600 grit and wd40 heated the piston again and it went right in.so Carl do you think this will be to tight.do the pins need to move in the piston?
Thank you guys for the help

Mark

[ricmoran]

No, pins do not move in the piston, but if required to, the fit should be correct to allow some minor movement such as a hand tight fit to be able to slide in or tapped in with a wooden doll and mallet or a brass mallet without being driven like a nail into wood>

I've used a brake cylinder hone to releive psitons before but you have to be really careful when doing this to insure a straight hone is done and doen at low speed and interval to check to see ho wclose your getting to the right fit.

So what is the ring to piston clearance like? Did you gauge that too to be sure there is enough room for the piston to expand without biting the rings and causing cylinder gouge?

[mark]

Yes ricmoran I did check the side clearance and also ring end gap all is good thanks again for your input



Mark