WRIST PIN FIT?

CFD244 said
Hi Folks

So I tore into a 1970 340 that I picked up knowing that is was .030 over TRW 2332P. The bores were pretty nice with no wear, and the rod and mains were .010.

Unfortunately, the main and rod bearings looked like ****, but the crank looked ok (to be determined).

What I found, regarding rods was that whoever built this thing used pressed in pins, and I found 2 rods with different forging numbers. 1 of the assemblies looked really good. The rod rocked back and forth between the skirts, and the pin slid sideways back and forth to the point where the piston contact with the small end stopped the movement. On the other 7 however, all of the ends of the pins were bluish from heat and the rod/pin would not slide back and forth in the piston, and it took a lot of effort to rock the piston from skirt to skirt.

My question is.....how are the pins supposed to fit in the pistons? I know that they are pressed into the rod, but should they be a "slip fit" in the piston? Even without a rod, the pin needs a light press to remove them from the bare piston.

I am hypothesizing that the builder may have ruined the piston holes on a press while trying to assemble everything.

What are your thoughts?

Thanks

There are two kinds of wrist pins, floating and press fit...

Floating pins have a clip on each side to keep the wrist pin in position, and the rod can slide from side to side between the piston ears on the wrist pin...

Press fit pins are press fit to the rod and can't move in the rod, but the pin can slide to where you can touch the rod between the ears of the piston....

Either one the wrist pin should be able to slide side to side in the piston... When installed in the engine, the crank journal and bore position keep the rod form sliding side to side in the piston...

With either wrist pin, the piston should be able to be rocked back and forth (Gently by hand) where you can touch one piston skirt to the rod, then the opposite skirt to the rod with no resistance.... Otherwise there will be too much friction when the engine runs and may cause galling in the pin bore of the piston and possible breakage....

If the rod has turned blue, it has been overheated above 520° and weakened the microstructure of the rod....