oversize piston pins

[paolomarks]

I got a brand new set of German SM pistons for my AAZ.  I brought them to my machinist and he told me the pins are loose. They should be a push fit and these slide in and out too easily and knock slightly as you push them through the bore.  Can I get some oversize pins?  Supposed to be 26 mm, so maybe 26.002?  What do you think.?  Paolo

[theman53]

New bushings in the rods would probably be best

[RabbitJockey]

are you missing the clips that hold the wrist pin in to the piston?  your machinist should know what you need to do, if not i would no longer use them.

[paolomarks]

Hello , thanks for the quick response.  Let me clarify.  I'm talking about the fit between the wrist pins and the piston.(not the con rod)  Does any one have a numerical value for this clearance? My Machinist uses the term "push fit" and said mine would work but might lead to piston knock sooner down the road than normal.  I'm not sure whether it's the pin that's too small or the holes that are too big.  I'm thinking the issue is probably with the holes and that an oversize pin could be the answer.  Any one out there ever dealt with this issue?  Thanks, Paolo

[theman53]

The pins are not a press fit they will be held in by clips.

on the small end of the rod inside is a bronze bushing...

New bushings in the rods would probably be best

[paolomarks]

Yes I'm having my machinist install new con rod bushings as my old ones were worn out, but the issue still remains of the clearance between pin and piston. He says it's on the loose side. Does VW have a clearance spec on this.  How about oversize pins? did VW make them. Can I find some other slightly larger pin and have my machinist turn it down to size.  Any suggestions would be helpful , Thanks, Paolo.

[theman53]

The pins should come with the pistons and fit perfectly. I would wait and see if the slop is still there when the new bushings are installed.

[rabbitman]

I am not aware of oversize pins for VWs.  As has been said, the pins all come with pistons new and the bore wears out long before the pin or bushings do so I can't see there ever being a call for them unless there was a manufacturing defect.  FWIW, the pins should slide easily in the wristpin bore in the piston but they should not clunk around.  They are not a press fit.

X2

If you can push the pin halfway through the piston and have it rock around or even just click then I'd return them. They're supposed to be snug but easily push in with your finger.

Never heard of oversize pins.

[paolomarks]

Thanks for all the good advice, still on the fence though about what to do. They definitely have more play than other pins I have seen. Hate to have them knock before their time.  We'll see.  Paolo

[sdwarf36]

I guessin' here-but when the machinist is saying "push fit" ,he means you need a slight push to get them to slide thru. Picture turning your piston so the pin is facing up+ down--letting go of the pin, it falls thru. A push fit would require a slight push with your finger to get it going.
 It is possible to have wear in the piston-- unlikely on the pin. (most likely on the bushing-that why its a serviceble piece).
 According to the Bentley-in a bath of oil at 140*, a slight push with your finger will allow the pin to slide.
Pin me down to a number-i'd say that translates to .0003 to .0005.

[clarkrep]

 According to the Bentley-in a bath of oil at 140*, a slight push with your finger will allow the pin to slide.
Pin me down to a number-i'd say that translates to .0003 to .0005.

I agree(assuming you mean .0003-.0005 clearance not press fit)