Oil Leak Cylinder Head 1971 750

Hello. My '71 750 was rebuilt by the previous owner, and sold to me when he gave up because it was smoking badly on one jug after the rebuild. I rode it a few times and the smoking is vastly improved, so maybe just rings not seated. It smokes a tiny bit on start up, and sometimes on down shifts now, but is livable. However, after a short ten mile ride there is oil on the side panels and it seems to be coming from the front of the engine around the exhuast nuts at the front of the cylinder head. Any ideas? The guy that rebuilt the engine told the previous owner that he should check valve clearance and re-torque the head after 100 miles, and I have probably put about a hundred miles on it now. Does that sound like possible cause? Any thoughts on this? Thanks in advance!

I had a front weep. I didn't believe I would seal it up by simply torquing the head, but it did. In my case, about 3,000 miles after rebuild and I have no info on whether it had been retorqued after the rebuild.

I did 2 other things at the same time:
1. Cleared some blockage out of the drain hole in the head (bottom E guitar string IIRC), access via the rear valve cover;
2. Relived pressure in the motor with a reed valve (Kawasaki XS650) added into the breather pipe.

A very noticeable improvement in how happy the motor felt when I added the reed valve. 5,000 miles on and I still feel I dodged a bullet.

ok thanks. encouraging to hear the retorquing worked for you. I have already added a reed valve crank case breather from Colorado Norton Works . Will try retorquing and your guitar string trick!

Valve lashes should be checked after the head is retorqued

Have a good look where the oil is coming from first, sometimes oil will come out of the lower valve cover studs and think its coming from the head gasket, what head gasket it have copper or the fiber gasket as the fiber ones need to be retorqued more than the copper gaskets before they settle down.

definitely not coming from valve covers or spindle covers. Thise are bone dry. Thanks for the suggestions though, worth a look.

My Cdo had a slight oil staining at the front of the cylinder / head junction. Found the three head studs had pulled out of the aluminum head. Pulled the head and repaired the three studs and refitted with a new head gasket. All dry now. Try a head re-torque and hope. Cheers

I had a slight leak on my 1974 Commando from the head gasket in the area under the drive side exhaust valve cover. Similar results to what you experienced, oil on left side panel. I replaced the head gasket (annealed copper gasket) as part of another project (intake valve seals), and leak disappeared. I have also installed the NYC Norton breather kit. My bike has been leak free ever since. I’d try the head bolts first and check the gasket as a second step. Good luck.

Because of manufacturing imperfections caused by antiquated machine tooling , many of the threaded bores for the front head mounting studs were bored slightly too deep and broke through the thin wall into the push rod tunnels. Oil will migrate up the stud threads and result in a leak that appears
to be a leaky head gasket but is just below that juncture. The cure for that is quite simple if the head is off. Remove the two studs, apply a sealer to
the bottom of the bore and use thread sealer on the studs. I would think that the reed valve by itself would almost eliminate this condition. This condition, though, would have nothing to do with the engine smoking.

Smoking on downshifting. Suggests leaky valve? Ditto on start up.

Mart UK said:

Smoking on downshifting. Suggests leaky valve? Ditto on start up.

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That makes sense. It used to smoke badly all the time when I first got it, a little on start up and then lots of smoke when it warmed up. Now it’s just a little on start up and on down shifts. Maybe rings seated, and now only left with the valve issue. Will take a look at valve seals.

Big Red said:

That makes sense. It used to smoke badly all the time when I first got it, a little on start up and then lots of smoke when it warmed up. Now it’s just a little on start up and on down shifts. Maybe rings seated, and now only left with the valve issue. Will take a look at valve seals.

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Hard to inspect seals with springs in plalce.
Note there is a procedure for changing seals with head insitu on bike, see this post and thread: