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chauffeur
08-28-2010, 8:55 PM
Hi all...
New to this site but been riding old British bikes for years.At present a Triumph speed twin 1950,....problem with excessive build up of crankcase pressure....oil forced into mag and genny and leaks....breather vave been rep[laced but hasn't helped....Any suggestions greatfully appreciated...thanks.Vic

Torch
08-29-2010, 7:07 PM
Hi all...
New to this site but been riding old British bikes for years.At present a Triumph speed twin 1950,....problem with excessive build up of crankcase pressure....oil forced into mag and genny and leaks....breather vave been rep[laced but hasn't helped....Any suggestions greatfully appreciated...thanks.Vic

Excessive pressure is the sign of a well worn engine, what breather valve did you replace?
the 1/4 time crankcase breather valve is located inside the intake cam bushing and requires the crankcase to be split and the cam be removed.
If you did that why didn't you rebuild the engine?

chauffeur
08-29-2010, 11:14 PM
Thanks for your reply...the engine has done about 5000 miles scince complete recondition...the breather valve was replaced at this time....bike does not smoke or use oil.I believe there is a modification that can be done???.Question "If I were to drill a small hole from the crankcase leading into the primary chaincase would this affect the bikes performance or impact adversly on the inner engines lubrication...would the hole need to have a valve? how important is crankcase pressure?" thanks in advance..any suggestions or advice appreciated.Vic

Torch
08-30-2010, 8:19 AM
yes you will end up loosing a lot of engine oil, it is hard to separate the oil from air witch is what a good breather does and as you know the pressure will play hell with the magneto and generator, rather than modify the engine if it was me I would go after the cause of the pressure. If you have that much pressure on a stock engine then I would pull the top end off and look at the ring gap and piston to cylinder clearance. on a stock motor the stock breather should be enough to handle the normal crankcase pressure.
high compression motors build up more pressure and we have modified several modified pre-units with different breather ideas, and have still have not found the perfect breather,
a simple thing you can do if your pressure is caused by valve guide wear is drill and tap a vent hole and put a tube fitting in your tappet caps , if that doesn't help you can always change them back to stock.