main bearing oil seal

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Sep 8, 2007
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Do you need to split the crank cases to replace the left side main bearing oil seal or can it be done by removing the inner primary cover? '73 850
You're in luck !

The change can be done from the outside with a bit of care.

My preference is for a seal with a steel outer and a drop of Loctite.
I used to change oil seals on a somewhat regular basis on my 72 Combat. Even went to a special $25 CR seal. All to no avail. When I finally got a decent crankcase breather valve installed I had no more crankshaft seal problems. If you're not stopping the crankcase from filling up with air on the upstroke, you're pi--ing into the wind fitting new seals. An added benefit with a proper valve is you will gain power, as well as eliminate the crankcase from oozing oil. I know racecar engine builders spend a lot of attention to crankcase breathing.
I see that Steve Maney

offers a rubberised crankshaft oil seal, which "stops oil leaking from crankcase to chaincase." I assume he is referring from around the shoulder. The interference fit on the crankcase shoulder on my crankcase is not very good and it is hard to positively locate the seal, so next time I come to replace my crankshaft oil seal, I will try one of these and see if it is any better than the metal shouldered oil seal, although they are not cheap at £7.99, but if it saves me messing around with loctite and similar products trying to get an oiltight seal, then maybe worth the extra?

Just out of interest, has anybody on this site tried out his 1007cc conversion? :?:
I am forever having trouble with this seal because I run a dry primary and you really notice leaks from it. This is mainly because some previous owner held the crank in a vice and marked the juornal.
The interference on mine is not good and I can push the seal in by hand. Loctite did not work and the metal rimmed seal pops out when the engine's hot.
I have found the rubber rimmed ones stay in better and they don't need loctite.
You can buy them from any bearing shop, you don't have to pay Steve Maney's inflated price.
I can't remember the seal size, but it is an imperial sized seal running on a metric sized crank!
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