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Old 04-08-2014, 09:19 AM   #1
drjason OP
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Lighter oilhead wrist pins in an airhead

I googled this and searched the forum and I couldn't find anyone having discussed this yet, but it seems like it is worth considering:

Success: Soaking piston in carb cleaner removes carbon very well.
Failure: Soaking wrist pin (gudgeon pin) in carb cleaner removes chrome very well.
Solution: Call re-psycle for a good used wrist pin. 11 25 1 335 474 GUDGEON PIN - 22mmOD X 13mmID X 74.31mmL

What arrived happened to be what I figure is an oilhead wrist pin. 11 25 1 341 365 GUDGEON PIN - 22mmOD x 17.5mmID x 74.31mmL.

It looks like it would fit just perfectly. The original wrist pin is 147grams, the oilhead wristpin is 83grams. Weight savings of 64g of reciprocating mass per piston.




Now I need to decide whether to send this back and order a proper airhead wrist pin, or keep it and ask for another for the other side.

Question#1: Is there a heat/stress reason that the oilhead wrist pin shouldn't be used in an airhead?

Question #2: Why hasn't this been discussed before (or is my Google-Fu just not up to snuff)?
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Old 04-08-2014, 02:07 PM   #2
Cogswell
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I think the airhead pistons are quite a bit heavier than the oilhead pistons, no ? There would be more stress on the thinner wrist pin.



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Old 04-08-2014, 08:25 PM   #3
BOETJE
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That weight difference would be worthwhile I think ! .

According to some info I dug up, the weight of a piston for a R100 airhead is
570 gr (http://www.zeebulon.de/Mot/bmw_allg.htm#Kolbenbolzen) , and the one for an 1150 GS is 585 gr....(http://www.advrider.com/forums/showthread.php?t=836329)
Mind you I did not measure myself.
But that would be not too big a difference in stress if you are not constantly bouncing of the rev-limiter.....
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Old 04-08-2014, 09:23 PM   #4
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seems like a good enough idea. :hmmm
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Old 04-09-2014, 04:43 AM   #5
bmwrench
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That looks to me to be an aftermarket lightweight pin for an Airhead. It's been a while since I had an Oilhead apart, but my memory is their pins are heavier than the one in the picture.

As far as I know BMW wristpins are not chromed. Are you sure yours is unusable?
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Old 04-09-2014, 05:06 AM   #6
chasbmw
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Carb cleaner may be aggressive, but I don't think that it can remove chrome.

There was a craze for fitting lighter wrist pins some years ago and many claims were made about the results, however some of the wrist pins had a habit of breaking.

Nowadays you can get the same result by fitting lightweight pistons, but without the breakages!

I would suggest that you review what you have got
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