Classic Bike (UK) - - Classic Workshop -

Jonathan Holmes makes his own alu­minium tanks and sug­gests a leak-test­ing method I could have used to check my Norvin tank when I was strug­gling with it. He fits the cap and tapes over the breather hole, then lightly pumps in com­pressed air through the tap, shut­ting it smartly be­fore all the air can es­cape, then im­merses it in a dust­bin of wa­ter, seek­ing give­away bub­bles. Thanks, John, but I’m not so sure that would have worked for me in

this case. My leak was only re­ally ap­par­ent with a full tank; it was fine with half a gal­lon, so it was more a seep.

I have used the bub­ble test to re­pair a Scott ra­di­a­tor; it was great for lo­cat­ing orig­i­nal leaks. Af­ter sol­der­ing I blocked off all out­lets and blew through the ra­di­a­tor breather pipe – no sign of bub­bles. But on the first ride, it leaked again. The heat seemed to find leaks the air missed. Air seems to take longer to es­cape than hot or volatile flu­ids, so I’m a bit wary but thanks any­way! .


Nigel Lan­don had a prob­lem with his 1970 Triumph Bon­neville jump­ing out of gear – any gear, any time – mak­ing the bike al­most un­ride­able. New se­lec­tor springs didn’t help, but dis­man­tling fur­ther he found wear on the se­lec­tor cam­plate. Order­ing a re­place­ment, he was sur­prised to find it was sig­nif­i­cantly dif­fer­ent, with no notches in be­tween gears as on his old one. “Are th­ese older, pre-unit gear­box parts?” he asks. “Are they in­ter­change­able and if it’s a com­plete early gear­box, will that cause fur­ther prob­lems?” My own ’68 TR6 has an ear­lier gear­box be­cause it has in­ter­nal speedo drive gears, used prior to 1966 when the drive moved to the rear wheel – but that aside I wasn’t sure about parts in­ter­change, so I spoke to Arthur at Triumph spe­cial­ists Rocker­box in Farn­ham, Sur­rey (01252 722973). Arthur said that four-speed unit and pre-unit gear­boxes are in­ter­change­able, but it’s best not to mix parts as there are slight vari­a­tions over the years. Arthur also pointed out that 1970 was the year of the short-lived cam­plate leaf spring in­stead of the more fa­mil­iar de­tent plunger; many own­ers have bored out the gear­box shell to fit a sprung plunger and prob­lems arise if it hasn’t been done ac­cu­rately.

Nigel’s prob­lem turned out to be sim­ple – his bike just pre­dates the leaf spring, the cam­plate he or­dered is for the leaf-type, so his notched orig­i­nal is cor­rect for his bike al­though the two plates are in­ter­change­able. The bike wouldn’t stay in gear be­cause the de­tent plunger spring was about ½in too short; fit­ting a longer one sorted it. As he said “All that time and ex­pense just for a $1.50 spring!” We’ve all been there, Nigel…

You’ve got to be care­ful when order­ing Bon­neville cam­plates

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