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R51/3 crankshaft endplay?

alkis
Posts: 20
Joined: Thu Mar 28, 2013 9:50 am

Re: R51/3 crankshaft endplay?

Post by alkis »

I agree with this but isnt it strange that BMW states a very specific endplay in the gearbox shafts and has the appropriate shims to adjust it ? I mean that the gearbox also has roller bearings just like the crankshaft. Mabe it is because the crankcase is all in one piece and it is machined as one while the gearbox is two pieces machined seperately and then matched so there may be a difference between two complete gearboxes concerning their internal dimensions...

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caker
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Location: Haddonfield, NJ, USA
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Re: R51/3 crankshaft endplay?

Post by caker »

My $0.02:

The only axial forces acting upon the crank is when the clutch is engaged (other than the worble / harmonics of a running engine). The position of the crank is still critical - on these /3 motors, the crank is pulled forward and "bottoms out" against the front bearing carrier.

Positioning of each shaft in the transmission is also important. But, the axial thrust forces inside a multishaft gearbox that has helical gears (4th gear only, in this case) - the shafts are literally trying to walk themselves past each other - so endplay clearances and thrust are critical considerations.

*shrug*!!

-Chris

scottiesharpe
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Re: R51/3 crankshaft endplay?

Post by scottiesharpe »

There is NO endplay on a crankshaft. The crankshaft is held rigidly by the front bearings and does not move fore nor aft in relation to the engine case. The rear crankshaft bearing locates its own position in the carrier. In other words it can walk fore and aft as the steel crankshaft and aluminum engine case expand at different rates. If you have any fore and aft crankshaft endplay--e.g., if your crankshaft visibly moves forwards when you engage the clutchrod--then...either 1) your front crank bearing is worn and should be evaluated and/or 2) your front bearing is loose in the carrier. BMW produced several bearing carrier cover plates (the part with the oiler tube in it) for shimming this fit. Alternately, as we do here at Scottie's Workshop, you can use a surface grinder to adjust the thickness of 11 21 0 016 244 which is 1.0 mm in thickness. Hope that helps.
Scottie Sharpe, Proprietor
Scottie's Workshop, 3282 E Hwy 4, Murphys CA
Full Service Workshop for vintage and classic BMW Motorcycles http://blog.scottiesharpe.com

alkis
Posts: 20
Joined: Thu Mar 28, 2013 9:50 am

Re: R51/3 crankshaft endplay?

Post by alkis »

Than you very much.
You have all been very helpfull
cheers

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