Q Why is my Tri­umph T’bird Sport knock­ing?

Motorcycle News (UK) - - Garage -

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.

There could be some teeth rat­tling around in your en­gine

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