oversize piston pins?

[paolomarks]

Can you get oversize piston pins for our engines.  I've got an AAZ.  Thanks, Paolo

[libbydiesel]

I don't know.  I've never had a need for them.  If you are rebuilding your engine, then I would assume you are replacing the pistons and getting the rod small ends re-bushed, no?  If so, then standard pins should fit perfectly.

[paolomarks]

I bought some new pistons and the pins seem a bit on the loose side.  They fit real close and don't wobble, but they fall out if I turn the piston sideways.  Maybe this slight clearance is OK?  When I heat the pin to say 150degrees and put it in a cold piston then It feels right to me, ie push fit but stays there when tilted sideways.  I'd say the difference is a less than .0005.  Think I'm being too picky.?  Paolo

[rallydiesel]

Hmmm that doesn't really seem right. Did the pins come with the pistons? They should. Normally you have to heat up the pistons and freeze the pins to get them to slide in.

[theman53]

If you got pistons from Prothe then that is the way of it. Mine were very easy to get in and out. My stock bore KS pistons that came out with however many hundred thousand miles were tighter than his brand new. Same with my new KS .020" over pistons, very tight. The new ones said to oil and they should barely slide in, and that is what I had to do.

If you have another MFG than what Prothe has I would call them.

[paolomarks]

I got my pistons from German Ebay. They're German made SM((Schoettle Motorenteile).  Do I have to worry about this?  Has anyone found that after many miles  the piston pin bores or the pin(on the ends) wears at all?  I've taken a few engines apart and seen wear before in the rod small end bushing and middle of the pin , but that's all. What do you think?  paolo

[Gizmoman]

I'll be watching this post closely as well. I haven't bought my pistons yet and was planning on going the Prothe route as the price is good and I've heard they are fairly good. I have also heard that the pins that come with them are thinner so I was going to use my current ones if they fit well.

I realize the pistons you bought aren't Prothe (unless he has added "Schoettle Motorenteile") to his list of sites , but I believe if there is any play at all, it can only increase, and sooner than you'd want it to.

I think I'll go the high road and add some bucks for better quality - like KS.

[theman53]

I actually didn't notice them being any worse after the 40,000 miles on them...except the 3rd piston, but it ate the precup LOL. I wouldn't worry too much, unless it is measurable.

[paolomarks]

    Sorry to hear about the pre cup!  Did you peen them in the head?  Seems like this happens quite a bit with these engines.  I still don't quite understand it since it appears that the pre cups are "trapped" by the mating surface of the block when the head is bolted on.  Do they crack into smaller pieces and then fall into the cylinder?
      Any one else want to chime in about piston pin wear over time?  Thanks,  Paolo

[theman53]

Yes I peened them in, and they were pressed in tight before I peened them. The precup is tougher than the aluminum and if it expands it pushes the aluminum out, eventually the aluminum doesn't come back and it gets sloppy in there.