primary fountain

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Mar 13, 2005
Here's one for you, I've just cured the oil leak on the timing side (new crankshaft seal is all) but not the primary drive is like a fountain! Check the breather I thought & did so clean as a whistle. So what might be causing this? 1972 Combat engined Interstate, 11,000 miles from new and untouched since the bearings were done by the factory in '73. I'm wondering if all the seals should be repleced as the rubber may have begun to give way? any thoughts?

Your Commando might be suffering from Positive pressure within the crankcase. When the rings start to wear then blow by pressures increase. You end up chasing then replacing all the weakest seals. You could try to cure this problem by creating a negative pressure within the crankcase. Modify by either putting a Power Brake check valve (Motormite, part # 80190) or a reed valve ... ory_id=4.7 used from a Yamaha XS 650 could be a solution for you. Do a search on crankcase venting on this site. This is not new to the vertical twin Nortons.
Alpha said:
I've just cured the oil leak on the timing side (new crankshaft seal is all)

Sorry, but I don't see how you could cure a timing side leak by replacing the crankshaft timing side seal? Do you mean the camshaft (points housing) oil seal?

Starting the engine with the sump full of oil that has drained down from the oil tank over a period of time can blow the primary seal due to increased crankcase pressure?
Are you saying you have a blown primary seal? Or is it just a bad leak from the primary crankcase joint?
Whoops ok camshaft! my mistake. the leak is all round the joint between the inner & outer chaincases
Alpha said:
the leak is all round the joint between the inner & outer chaincases
I've re-written my reply as I misunderstood slightly:

The leak is from the large rubber band seal? So the rubber seal needs replacing. Check that both case joint faces are flat.
As Les says, check that the chaincase faces are flat. Then check that the inner cover is properly shimmed. When the inner cover is bolted to the crankcase, the central fixing stud shoulder should be shimmed so the inner chaincase rests against the shims with no warping.

Use a new chaincase o-ring (proper sized vacuum tubing can substitute in a pinch) and lay a thin bead of RTV silicone in the channel. Allow it to set briefly, then push the o-ring into the groove. Use a thin smear of RTV on the outer chaincase mating surface and bolt it together.

Add just enough ATF (or your favorite primary lube) to reach the bottom run of the primary chain.
I chased oil leaks for years on my 72 Combat. Tried the Motormite valve with moderate success on a fairly fresh engine. Unfortunately, the Motormite give up after a couple of thousand miles and never did eliminate the oil leaks. It is designed to be a vacuum check valve. I went to the Yamaha XS 650 crankcase breather valve. Voila! No more oil leaks.

Why Norton got rid of the rotary breather, I'll never know. They then compounded the problem by locating the breather at the bottom of the crankcase. Brilliant (not). Do the crankcase mod per Old Britts and use the XS 650 valve and you will have straightened out a lot of things. You'll be amazed how oil tight a Norton can be once the positive crankcase pressure is eliminated. An added benefit is the increase in horsepower. Say about 25 more HP. Only kidding, probably more along the lines of 1 or 2 HP. I do know race engine builders spend a lot of money eliminating positive crankcase pressure.
But, from what Alpha has actually told us so far, his problem appears to be due to the primary case seal leaking.
Nothing he has said suggests there is any sort of problem with the engine breather at all?
I must admit to an abysmal lack of knowledge about why she's leaking, a friend suggested the breather which is why I looked at it.
I think you're right in that she was left far too long & probably dumped a fair amount of oil in the sump which then migrated to the primary drive (does this sound feasable?)
I've a week off work so will drain the lot & start again & see what happens, thanks for all the help.
Let me get this straight. You fixed a leak from the timing side of the engine by replacing the oil seal in the timing cover at the camshaft. Now it is leaking at the primary cover, but no longer from the timing side of the engine.

Does there appear to be pressure building in the primary? The only place it could come from is the crank seal. This can be changed without splitting the cases. Check the oil level in the chaincase. If it is above the level hole, then the crankseal is likely the culprit.
Alpha, in answer to your question about the likelyhood of motor oil getting into the primary case if the bike is left to lie for an extended period of time (particularly parked on the side stand). This is extremely common and may not necessarily be the fault of the crank seal, over time it can also leak through the three bolt holes where the inner primary case is bolted to the crankcase, as these are a coarse thread. I would drain the sump and put the oil back in the oil tank - failure to do this can in extreme cases result in the oil pump running dry until the scavenge system delivers enough oil back into the tank to supply the feed side - then drain the primary case and refill up with the appropriate volume and type of oil. Start the beast and see how it goes. If the oil contamination in the primary case has been serious you may have to remove the clutch plates and clean the oil off.
How embarresed am I? Drained the sump, then cracked open the primary drive, yep loads of oil in there. Checked for flat, cleaned it all out. Now (for the moment!) oil tight. Thanks for all the advice.

primary fountain
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