Commando top end oil leak finally fixed!

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Jan 13, 2008
My '74 Commando has always had an oil leak coming from the front of the engine around the head gasket area. While I was doing a recent top end job on it I read about the likely cause for the leak in the Norton Tech Digest. It seems that the two 5/16 studs that screw into the front of the cylinder are the cause. The threaded holes for the studs are drilled in such a way that they protrude into the push rod tunnel cavety. This allows oil to work its way up the stud threads and eventually out to the atmosphere. I did as the Digest recommended and reinstalled the studs with gasket sealer on the threads. Problem solved. I highly recommend that anyone with a Commando obtain this Tech Digest from the INOA, lots of useful tips. Cheers!
I found the same thing with my own Mk2A. I went to the Norvil/Fairspares shop in Burntree for some new studs as the old ones were very loose in their threads. While I was there the young lad who served me told me about the way the oil creeps up the thread just as you describe. When I tried the new studs they were just as loose in the barrel as the old ones. Doesn't inspire confidence that all will be well when you torque them up does it? Also I noticed that the threaded hole was twice as deep as the thread on the studs. I simply made some new studs out of some old Trident headbolts with twice the length thread on them. I then used blue hylomar when I fitted them. They torqued up a treat and the head is still oiltight several years later. Don't know why Norvil or someone don't make these studs with longer threads as a matter of course.

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