Classic Bike (UK) - - Classic Workshop -

Af­ter rid­ing Nor­tons on and off for 40 years, John Ebert in Texas has had the fun of dis­cov­er­ing a new prob­lem. Hav­ing just recom­mis­sioned a low-mileage 1974 MKIIA Com­mando, he wasn’t pleased to find oil leak­ing from the head gas­ket. He was even less pleased when re­plac­ing the gas­ket didn’t cure the prob­lem.

Close in­spec­tion re­vealed that one of the cylin­der bar­rel stud holes had day­lighted into the pushrod tun­nel. Al­though re­search in­di­cated that this is a com­mon prob­lem, eas­ily reme­died by Loc­tit­ing the stud into the hole, this didn’t work for John and the joint still leaked. “Do you have any ideas?”john asked. “It’s a shame to scrap the bar­rel if it can be fixed!”

In­deed so, John, but I didn’t know what to sug­gest. Blow­holes, ‘bub­bles’ in the casting, are not un­com­mon and in more pros­per­ous times dodgy cast­ings would have gone for scrap, but to­ward the end Nor­ton were prob­a­bly be­ing more fru­gal. In a sit­u­a­tion like this, where seal­ing the stud should have cured the prob­lem, you have to con­sider why it didn’t and I see three pos­si­bil­i­ties: a) the sealant hadn’t stuck, maybe be­cause the area is dif­fi­cult to ef­fec­tively de­grease – I sug­gested a good poke about with cel­lu­lose thin­ner or ace­tone on a smoker’s pipe-cleaner; b) it was the wrong sealant – Loc­tite make a vast range, well be­yond the usual Diy-store se­lec­tion and have an in­for­ma­tive web­site (loc­; or c) there was an­other cause of the prob­lem, pos­si­bly a pin­hole or crack as yet un­de­tected.

John cleaned ev­ery­thing scrupu­lously, dropped a ball of JB Weld into the bot­tom of the hole and wound in the stud, coated in Per­ma­tex high-temp red thread­lock (which he says comes in gel form). Af­ter tight­en­ing it home, he smoothed off the JB that squeezed from the hole and re­assem­bled the en­gine with a new and an­nealed head gas­ket. This time the oil leak had gone, which goes to show that just be­cause a re­pair fails doesn’t mean you’ve used the wrong method; maybe you just need to try harder.

Com­mando oil leak solved with JB Weld and thread­lock

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