Cylinder oil leak

Yorkie

Yorkie

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My 72 Commando has developed an oil leak from the front of the cylinders - see picture. I’ve checked the torque in the nuts and they are tight. I was thinking if simply loosening the nuts and lifting the head and cylinders as a complete unit so I could add a little Yamabond sealant to the crankcase and barrel interface. My dear old Dad (RIP) would accuse me of bodging the job and he is correct of course but it’s hot in the garage right now and I’m feeling lazy. Is this possible or do I bite the bullet and pull off the whole top end?
Cylinder oil leak
 
It's not clear to me where the leak is - could you please spell it out?
The only oil I see is around the base of the tacho cable outer.
Cheers
 
Apologies. It’s flowing from the front where the cylinder sits on the crankcase face. Primarily it’s on the left side of the crankcase half. It’s as if the oil that accumulates where the followers sit is leaking out.
 
That drop is from a previous leak at the valve cover. The one I’m referring to is a to cylinder base gasket to crankcase joint. What I want to confirm if it’s possible to lift the cylinders and head up 1/2” to allow some sealant to be added at the base gasket
 
Nah - your Dad's right.
I'd do it properly (...and think of what else I should do while it's apart)
Cheers
 
Yorkie said:
That drop is from a previous leak at the valve cover. The one I’m referring to is a to cylinder base gasket to crankcase joint. What I want to confirm if it’s possible to lift the cylinders and head up 1/2” to allow some sealant to be added at the base gasket
Click to expand...
I understand your question. Give it a try, let us know. Seems plausible. Be careful the pushrods go into position as you come back down.
Good luck.
I would have like to do it on my '74, but the SHCS's holding the cylinder down made it impossible.
 
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I think it's worth a try.
Interested to see how well the barrell breaks away from the CC with head insitu.
Let us know how it works out.
 
My bike had a couple of leaks at block base to crankcase...I "bodged" it by thoroughly degreasing with brake clean etc several times. Used a bit of "Seal All" along the boundary after taping off surrounding areas. Has worked fine for past 8k miles and did not discolour anything.
 
I have had mild success degreasing with brake clean lots of times and using 690 wick in loctite. Might try the Seal All next time, thanks.
 
Yorkie said:
Apologies. It’s flowing from the front where the cylinder sits on the crankcase face. Primarily it’s on the left side of the crankcase half. It’s as if the oil that accumulates where the followers sit is leaking out.
Click to expand...
Are those standard crankcase to barrel studs? If so there’s too much thread showing and the nut could be tightening on the unthreaded part of the stud and not clamping the barrel flange to the crankcase mouth.
And with less thread into the crankcase I’d also be concerned it would be pulling out.
IMG_2029.jpeg
 
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The furthest stud looks like it could be the correct Unified thread as it appears to have the first thread removed, the other two do not so could be the earlier type studs, however, the marks on the corners of the nearest nut could make it Unified, nevertheless they all look to be too far out as mentioned by Mark Savage.

andover-norton.co.uk

Andover Norton - CYLINDER BASE NUT 5/16

CYLINDER BASE NUT 5/16
andover-norton.co.uk
 
I wouldn't try to tighten the studs further into the case, unless you're sure the crankcase holes were cleaned and blown out and dry before the studs were wound in. A mate cracked his crank case (on a Suzuki 2T). He thinks he cleaned out threads in his case, finishing with a spray degreaser and forgot to blow out one of the holes, creating enough hydraulic pressure to crack the case.
 
I guess it's a 750. Not feasible with through bolts.

I would pull it all anyway, fit new studs and confirm fully wound in.

1184 is the stuff, Yamabond if you have it, but I wouldn't fit a gasket anyway.

Good opportunity to check out head and bore. Look for the positives.

And listen to your dad!
 

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