wrist pin variance of 30 grams

[pampadori]

I had assumed that my piston wrist pins would be pretty similar and close in weight from one to the next. Nope.
#1 117g
#2 137g
#3 142g
#4 113g
#5 142g
#6 142g

pistons removed, cleaned up and wearing their new rings weighed much closer to one another. All within 2-3 grams.

Not sure why the wrist pins have such a large delta. THere are a few different numbers stamped on them, so maybe the experts will know something more. Pictures are below.

Should i try to drill/grind/machine out up to 29 grams from these or look to replace?

[Lyle O]

I wonder if the factory matched pistons with wrist pins to a combined weight target, recognizing that there would be variation. But it seems like there are two weight families: ~115g, and ~140g wrist pins. There must be similar weight class pistons, then, if my theory holds...

Can't wait to hear the experts weigh in on this one.

[DRACO A5OG]

Intersting, I have Rods and Pins a Ollies to be trued, straigtened and polished. I will ask them if they will weigh/grind them to match.

[stownsen914]

That's a pretty large range. And they have visibly different wall thicknesses. Has the engine been rebuilt before? Your result makes me wonder if whoever had it apart wound up mixing and matching wrist pins ...

[prschmn]

That is scary! Definitely a potpourri of bits from different engines assembled badly. I'd be very
careful and check EVERYTHING to make sure you aren't building a bomb.

[pampadori]

Originally Posted by stownsen914

That's a pretty large range. And they have visibly different wall thicknesses. Has the engine been rebuilt before? Your result makes me wonder if whoever had it apart wound up mixing and matching wrist pins ...

Yes, it has been rebuilt at least one time. Maybe more!

Some of the pins appear to say K+$ while some others have random characters (alphanumeric and shapes like a triangle?)

Related question, were there different weight groups for the rods used? How much did they vary?

[tom1394racing]

The wrist pins should be replaced. The variation of combined wrist pin and piston weight will be much too large.

I can probably provide a pair of 140 gram wrist pins. PM me for details if you would like to follow-up.

[prschmn]

Nine weight groups of 9 gm variance.
Look at the last two numbers on them-should be 51-59

[chris_seven]

Weigh the pistons

If the pistons, rings and pins weigh to within 2-3 g then the piston weights must vary so matching the pin weight will 'unbalance' the pistons.

Have you checked the rods end to end? and overall?

[Lapkritis]

Originally Posted by pampadori

Yes, it has been rebuilt at least one time. Maybe more!

Some of the pins appear to say K+$ while some others have random characters (alphanumeric and shapes like a triangle?)

Related question, were there different weight groups for the rods used? How much did they vary?

K+S is kolbenschmidt.

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