Q Why is my Triumph T’bird Sport knocking?
My 2002 Triumph Thunderbird Sport has started to make a strange knocking noise from low down in the engine. I’ve had a look through the paperwork that came with the bike – I only bought it recently – and it had a new sprag clutch fitted just before I did the deal. Could the noise be related to that? Tom Dawson, Leamington
Answered by A Adrian Clancy, Total Triumph Quite possibly! Your bike has one of the last T3 engines which had weak sprag clutches and could have the same issue as a 1998 Trident I had in the workshop a couple of years ago which also had a knocking sound from the engine’s bottomend. I removed the clutch assembly to check the basket and plates, but they were all OK. However, when I was having a look around the engine with the clutch removed I found the culprit – two teeth missing from the primary gear on the crankshaft.
Basically, the sprag/ starter clutch had been playing up for a couple of months but the owner had ignored the problem. Eventually the primary gear had had enough of the sprag clutch sporadically catching and slipping every time the bike was started and two teeth sheared off. The primary gear is part of the crankshaft in that engine, so I had to pop it out, replace the sprag clutch and the crankshaft, and find the two broken teeth. It wasn’t cheap but she’s still running like a dream.
So don’t ignore that noise, and make sure your battery is in good nick, because if it isn’t turning the engine over energetically enough on start-up, the backlash will kill the sprag clutch.