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Autor Thema: R 26 alloy connecting rod  (Gelesen 1083 mal)

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jeffr

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R 26 alloy connecting rod
« am: 08 Juli 2019, 22:29:21 »

New member here, Jeff in Upstate New York. Trying to bring a R 26 back to life bought it sight unseen so lots of unpleasant (expensive!) surprises.

 This bike came with alloy connecting rod the big end of which is quite damaged from banging on the journal. Journal likewise damaged. My question is does anyone have experience with machining out the damaged area to oversize, pressing in a bushing (plain bearing), and honing the repaired rod to receive a BMW supplied journal?

I also have a NOS piston in the box stamped 68 45 on the crown. Comes with wrist pin and cir clips. This is the standard size that was in the bike when it left the factory. Price on the box is $ 24.90! I would like to trade for a second, third or fourth oversize piston in like condition.

Thanks in advance.
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R 26 alloy connecting rod
« am: 08 Juli 2019, 22:29:21 »

cledrera

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Re: R 26 alloy connecting rod
« Antwort #1 am: 08 Juli 2019, 22:41:36 »

Moin (= Morning) Jeff,
welcome to the show.
Please write a few posts, than you can show us a few foto`s.
I do not beleave in a bushing, but first let us take a look.

Clemens
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Taz

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Re: R 26 alloy connecting rod
« Antwort #2 am: 09 Juli 2019, 01:41:52 »

Hello Jeff.

Welcome to the forum and good luck with that project of yours....

Re. the connecting rod and the crank shaft....before spending good money here please make sure that the balancing weights of the crank shaft are the correct ones (i.e. right shape, see https://monos.bmw-einzylinder.de/#kwelle_EN for details) for the aluminum rod, otherwise all effort will be in vain...after some 60 yrs you might be well advised to not take anything for given as for a reasonably long time people had to be incredibly inventive with what was available in order to keep them wee beemers on the road.

Your plan to take the crank shaft apart, have the bearing surfaces machined down to a good state and then fit bushings of sleeves (or whatever it takes) to enable it for re-use...IMHO the wider end of the connecting rod will be seriously weakened by this action so it might be worth considering to get hold of a refurbished crank shaft (or at least a less worn set) in order to avoid spending quite some money and effort on a part that won't be able to take the strain afterwards anyway.

Please forgive my bluntness.

Kind regards to New York, Taz
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OldsCool!

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Re: R 26 alloy connecting rod
« Antwort #3 am: 09 Juli 2019, 08:27:24 »

Hey Jeff! A warm welcome in one of the world's best community  ;D

Unfortunately there is no reasonable way to refurbish the alloy con-rod, although it is the best fit for the R26. In later R26 series and as replacement, only steel rods with needle bearing were used with a modified crankshaft (bigger crankwebs due to heavier steel rod). Be sure to get such a one and not a refurbished old alloy crankshaft (smaller webs) with attached steel rod. This will shake the bones out of your body :o
The crankwebs of a steel rod crankshaft should look like the ones of R25/x (Mushroom shape).
Keep it up! It's worth it!

Best regards,
Steffen
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jeffr

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Re: R 26 alloy connecting rod
« Antwort #4 am: 12 Juli 2019, 22:53:00 »

Thanks to all for taking time to reply. Have not given up on trying to refurbish crank with alloy connecting rod but options for success are dwindling! I will post again if I meet with good results.

Jeff
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