I have an 850 Mk 2A, first registered on 1/3/74. I am addressing the tacho drive that has just started leaking after some years trouble free running. I have bought the garter seal from Andover Norton as it seemed a good idea at the time, but maybe not as regards tacho drive shaft lubrication? (Must remember to pack the housing with grease!)
Whilst doing the research I came across a lot of writing about excessive crankcase pressure that forces oil through the tacho housing, which makes sense - but I thought the breathing problems were all to do with earlier engines? I have found no specific reference to breathers to fit to a 1973/74 engine, or am I just not searching hard enough?
I have used the bike a lot this Spring, including the inevitable motorway mileage, and wonder whether I should be looking further than a new O ring on the tacho drive?
Don't over-grease the drive…
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Thank you very much for your…
Thank you very much for your prompt response which has put my mind at ease. It never ceases to amaze me how far up cables - and even wires, that oil can travel when you'd rather it didn't.
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high temp
You're correct to be concerned about tacho drive lubrication.
I had it machined and fitted a lip seal, then a few years later a horrible squealing noise was heard from the tacho drive area.
Removed it and found it to be partially seized, since then I pack it with high temp grease annually.
BTW
Holland Norton Works do a nice PCV valve which is unobtrusive and seems to work ok for me.
Scroll down to item #H14
https://www.hollandnortonworks.eu/?lang=EN&page=10
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Which is actually an EGR…
Which is actually an EGR valve off a Chinese bike that you can pick up for a tenner.
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EGR = exhaust gas…
EGR = exhaust gas recirculation, a technique on diesel engines where some of the exhaust gases are directed into the inlet manifold to reduce NOx emissions. Not related to crankcase breather.
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Don't over-grease the drive cable as grease can work it's way up into the tacho itself.
850 mk2A and mk3 crankcase breathing is fine but can be improved with a one-way valve, aka positive crankcase ventilation (PCV) valve. Lot's of discussion if you search the forum. But that mostly addresses too much oil going up the breather pipe. The oil seal tacho drive housing should fix your immediate issue.