Piston pin fit. How tight is too tight.

[Johan1963]

I'm rebuilding the 6-cylinder flathead out of my 1953 M37 but I have a question about the piston pins. The rod ends bushings were burnished to fit the pin. I'm having to use a hydraulic press to push the pins into the pistons. I've never had piston pins that are this tight before. I assumed they would be a thumb pressure push fit. Which is right?

Thanks

 

[SturmTyger380]

That’s not right. M37 pins are supposed to be the floating type.

I had a machine shop install new piston bushings and then size them by reaming to the right size.

After that you could push the pins in with not much force at all.

 

[GopherHill]

Try warming the pistons in a hot water bath. The pins should go in without undue force.

 

[Johan1963]

I cleaned them up with a green pad and tapped them in with a rubber hammer. They were originally packed in cosmoline. I had to soak them for a day in gasoline to unravel all the packing. I still had to press them out of the piston with a press. Must have been some cosmoline around the pin. I think this is the last time I use NOS pistons and rings. I'll buy new stuff next time.

Thanks for the help.

 

[Valley Rock]

Your pins should NEVER be tight in the piston, only the small end of the rod .

If you have full floating pins they will be tight nowhere and held in by clips in the pistons .