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ALBANY VINTAGE & CLASSIC MOTORCYCLE CLUB
OCTOBER 2001 CLUB NEWS
ADJUSTING the valve clearances on your motorcycle engine is often a frustrating experience. Access to inlets in particular is very difficult; the carbs are in the way etc.
More often than not when you have completed the task they sound noisy and is seems a total waste of time.
Once again there is an easier way!
train wear usually is the culprit, and if you look the valve stem, wear
forms a hollow, which is often more than the clearance specified.
Try adjusting them without a feeler gauge. How is it done? - Let me explain.
Remove a tappet adjuster nut and measure its thickness with a calliper. Count the number of threads in the nut and divide it into the thickness measurement. You now have the pitch of the thread. For example a 6mm thick nut with 12 threads would have a pitch of 0.5mm.
If the inlet clearance specified was 0.25mm, one half a turn would be an accurate clearance unlike the one done with a feeler gauge. Just remember to lightly seat the adjuster screw and back if off the calculated part of a turn.
all the early Honda single cam fours I do the inlets 1/2 of a turn and the
exhausts 1/3 of a turn.
It was worked out about 30 years ago.