main bearing oil seal

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brf1957

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May 15, 2009
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Hi all, I have fitted 2 seals to the main bearing now and still there is leakage, as the bike is running with belt drive i would like to get this problem sorted, both seals came from hemmings and i dont know how good these are, does anyone know where i can get the best quality seals Brian
 
Which bearing.. engine or gearbox?

The gearbox mainshaft oil seal rides on a spacer behind the sprocket. The spacer eventually gets a groove worn into it by the seal, and will leak even with a new seal.

The engine oil seal leaks if you have positive crankcase pressure.
 
hi maylar and rich, i think he,s talking about the engine main bearing seal as he,s concerned about oil contamination on the belt drive
 
brf1957 said:
Hi all, I have fitted 2 seals to the main bearing now and still there is leakage, as the bike is running with belt drive i would like to get this problem sorted, both seals came from hemmings and i dont know how good these are, does anyone know where i can get the best quality seals Brian
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If it's the crankshaft seal you are referring to the fix is to relieve the crankcase pressure. I've changed those seals until I was dizzy and still had a leaker. Finally, I installed a decent crankcase breather valve. Viola! No more leaks.
 
Hi what is this breather valve you speak of sounds as though this is what is required
 
http://www.mikesxs.net/products-40.html#products Reed type PVC Valve

main bearing oil seal
 
Same with me. My original seal came loose on my first hot run, last October (70+ miles at 80-90 mph). I replaced the seal and installed the cheap Motormite check valve at the highest point on the vent line (right at the top of the oil tank where the line reduced in size. Perfect for the 90 degree fittings on the valve).

I've had no issues since (a further 5000 miles)
 
Hi, thanks for all replies, one other thing i should mention is in the breather hose coming from left side crankcase to the top of the oil tank there is a brass coloured unit about 2 inches long incorporated in this hose if anyone can identfy this there is also a sucking noise when you switch bike off would this be anything to do with restricting breather and causing seal to leak . Brian ps bike is 1970 750
 
brf1957 said:
Hi, thanks for all replies, one other thing i should mention is in the breather hose coming from left side crankcase to the top of the oil tank there is a brass coloured unit about 2 inches long incorporated in this hose if anyone can identfy this
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That sounds like the Norvil (Norvil Motorcycles) one-way breather, so should have a spring and ball bearing inside?



brf1957 said:
there is also a sucking noise when you switch bike off would this be anything to do with restricting breather and causing seal to leak .
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I doubt it, but check the one-way breather is connected the right way, so that the valve operates to vent air pressure out of the crankcase?
 
hi brian,that sounds like you already have a check valve installed but maybe its not working, try removing it and see what happens,your original breather from the left crankcase is a timed breather (disc valve) are you sure your sucking noise is not a blowing noise,ie excess pressure trying to escape?
 
Hi chris, there does seem to be oil and air mixed blowing into oil tank after you switch off engine is this normal and what is the purpose of check valve , and do you think it would be better removed Brian
 
hi brian,if you look up previous threads on crankcase breathers you will get a much better understanding,but basicly they are fitted to create a negative pressure in the cases,i cant think why one would be fitted to your 70 model with the timed breather on the end of the cam,i would certainly remove it and see what happens ,it cant do any harm
 
Out of curiosity... if my `71's timed breather (disc) is working correctly, should (shouldn't) I be able to feel an air "beat" coming out of the end of the breather hose in the airbox rear plate?

...and how strong should that beat be ? (since the flow I do feel is very faint)

(I ask this since my right cylinder is apparently pushing about a quart of oil every 500 miles past the rings, while still maintaining a balanced 160psi compression between the two cylinders)
 
brf1957 said:
Hi all, I have fitted 2 seals to the main bearing now and still there is leakage, as the bike is running with belt drive i would like to get this problem sorted, both seals came from hemmings and i dont know how good these are, does anyone know where i can get the best quality seals Brian
Click to expand...

I finally got mine to seal using an all rubber type seal rather than the type with outer metal. The metal type I removed was loose in the crankcase. Local club members tell me the metal type need to be installed with locktite.
 
In all probability, once the crankcase pressure problem has been addressed, the seal no longer is trying to keep oil in the engine. It's purpose then, with a crankcase vacuum, is to prevent contaminates from entering the crankcase.
 
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