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Beemer54
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VBMWMO #8832
Joined: 09/07/2014
Posts: 64

Having rebuilt one R12 recently I'm now working on a friend's engine. There are slight differences between the two breather systems but nothing major. One thing though has got me puzzled and I'm not sure whether to correct someone else's adaptation or whether this was, in fact, a factory modification.

On my bike the oil from the cam chain oil feed pools in the crankcase 'bath' under the chain and then drains back into the engine sump through the front brearing, then the slingers and out through the crankpin into the big ends. On this second engine, however, two holes, about 1mm diameter, have been drilled through the crankcase oilbath under the timing chain, thus allowing some of the oil to drain directly back into the sump. The holes don't look like factory items - they are not drilled centrally or in line with anything. Picture attached.

My guess is that some time in the past the engine has been blowing too much oil out of the breather and so this modification has been done. It's an easy job to fix this whilst the engine is stripped but I don't want to 'fix' something that was in fact done at the factory.

Any thoughts?
Geoff

  • drains.jpg
Darryl.Richman
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VBMWMO #6285
Surf City, USA (Santa Cruz, CA)
Joined: 10/27/2006
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No holes in mine

My R12, which is a 1941 wartime model, doesn't have these holes. The front chamber doesn't have any drain back to the sump. But my case also doesn't have the hole that's visible in your photo at the top, in the opening for the plug.

Does your breather exit at the bottom of the crankcase, like the older models do? Mine has a plug with a banjo fitting for the breather exit. The banjo has a copper tube that leads off under right side frame rail.

  • p8221469.jpg
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Darryl.Richman
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VBMWMO #6285
Surf City, USA (Santa Cruz, CA)
Joined: 10/27/2006
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OTOH...

My R52, which has an earlier development of this engine, does have a drain hole (just visible in the attached photo). It's not clear to me how critical this detail is, as I have put over 10,000 miles on the R52 without any lubrication problems.

  • p5090862.jpg
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Beemer54
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VBMWMO #8832
Joined: 09/07/2014
Posts: 64
My R12, which has an engine

My R12, which has an engine delivered to the Luftwaffe in 1943, doesn't have a breather like this at all. The vertical hole you can see in the picture leading down the crankcase to a vent underneath the bike, hasn't been drilled on my bike. Instead, like yours, it has a plug with a banjo union to a side vent. The engine I'm working on now has actually got both!
Thanks for the photo of your R52. Interesting. It looks to me like this is a much larger and clearly factory-drilled hole and, on my friend's engine, someone has tried to copy it by amateurishly drilling these two small holes.

geoff

Ian R11
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VBMWMO #8148
Yorkshire uk
Joined: 10/22/2011
Posts: 202
With the correct bung the

With the correct bung the breather hole in the lower casting doesn’t matter.

I have an R17 engine case with the hole allowing breathing at the bottom. It had a bung blank to the bottom hole in the casting and breathed through the front banjo fitting. It would breath through the bottom if a bung with aligning holes like the earlier bikes was fitted and wouldn't need the banjo.

If my slightly failing memory is correct, the oil feed on this bike feeds the pool and not directly onto the chain, so no drainage hole like the earlier engines that had an oil feed directed onto the crank gear.

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