CASTING OFF
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 (loctite.co.uk); 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.