I set the inlet tappet clearance to 0.004 inch on my 1932 BSA W32-6 500cc side valve. I tighten everything up then use my feeler gauge to check that it is still 0.004 inch, however after I turn the engine over a few times by using the kick start, the gap has closed up. What is happening and how do I solve it?
Thank you Ron, for your suggestion to read the manual. Reading the manual revealed that I need to use a special cone spanner applied to the flat of a bolt that sits below the locking nut while turning the head up or down. I thought that setting the tappets would be a simple operation, but it turns out not as obvious as you may think.
Normally I always read the manual before attempting any mechanics but on this occasion I regarded the task as to trivial, hence I missed a step.
Mark. I'm sure Ian will agree that you can tighten them down to 8 & 10 thou. But depending on the lash between the teeth on the timing gears, you can still have a clattering timing gear train. The clatter will occur at the point where the cam reverts from pushing open the valve to suddenly being pushed down by the closing valve. Ron
The correct positioning of the cams for tappet adjustment is critical because these BSA cams have very long opening and closing 'ramps' to (ironically) make the valve operation less noisy..Therefore they are only in the fully closed position for a very short duration during the cams rotation..
Regarding the 'click' caused by the timing gears by far the greatest contributor to the noise is not wear in the gear teeth but a lack of concentricity in the flywheel set up...It is important that the runout of the mainshafts is within the laid down limits..Beyond that and the shaft and crank pinion are running too eccentrically, giving too little gear tooth clearance at one point and crucially, far too much at another..It is the take up of the 'slack' that Ron describes that is often at its worst during the exhaust cams closing phase...
As for tappet clearance I ran some experiments on one of my bikes and found a 'tight' .008" on the inlet and a 'slack' .008" on the exhaust will run without any detrimental effects and does help to reduce noise..I've run these settings for many thousands of miles....Ian
