Oil from breather

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Oil from breather

Postby dig » Mon Mar 01, 2010 6:22 am

1939 BSA Silver Star is loosing large amounts of oil from breather,it has done 3000+ miles after the cylinder was sleeved,new piston and rings fitted,have fitted breather hose with a one way check valve and connected hose to catch bottle. The engine performs great with no smoke from exhaust at any time.There are two small vents in the rocker box cover, little or no oil is coming from the vents but lots of blow-by.Exhaust valve guide to valve stem is clearance is a bit large,could this be the problem? or a cracked head? or could it be a ring problem?? It has good compression. :250 :203
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Re: Oil from breather

Postby Tman » Mon Mar 01, 2010 9:25 am

.
Exhaust valve guide to valve stem is clearance is a bit large,could this be the problem?
In theory slack exhaust guides shouldn't be a problem as the piston is rising when the valve is open, so the "pressure" is going "out" of, rather than "in" to, the combustion chamber. The caveat here is that if the guide is *sufficiently* slack that the valve head can slightly tilt or rock in it's seating, compression can be lost into the rocker box, and cause breathing problems as you quote. Probably find that the effect wouldn't be noticeable when the engine is static as when doing a comp test though. Does it smoke on the over-run?
Rings should be easy enough to check.
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Re: Oil from breather

Postby dig » Mon Mar 01, 2010 9:52 am

no smoke on the over run in fact it never smokes, am using Pennzoil HD-50,now could this be synthetic or is it mineral? mineral i think
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Re: Oil from breather

Postby Welsh Wizard » Tue Mar 02, 2010 8:45 am

is the oil scavenging from the cases properly?
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Re: Oil from breather

Postby dig » Tue Mar 02, 2010 9:51 am

I have had the pump out,it had no gasket behind it,the amount of oil that came out a pone removal seemed about right. Even with a new gasket it still passed oil out the breather,the amount of oil returning to the tank at an idle seemed a bit small but on revving it to about 2000rpm it was streaming out the two holes in the return pipe. I have removed the long breather hose and check valve and refitted the BSA breather,with the engine running no air comes out the breather but plenty coming from vents in rocker cover,the flapper disc is free as it works fine by blowing and sucking on it.A test run tamora will tell me if all is well or not :250
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