UNUSUAL ENGINE KNOCK

[Keith Clements]

More from the camshaft search.Jowetteer1983-02

UNUSUAL ENGINE KNOCK - (All Twins)
A loose rear camshaft bush or loose rear camshaft bush blanking disc can cause an unusual knock. The rear end of the bush and the blanking disc can be felt with the fingers if the hand is placed between the rear of the crankcase and the flywheel vhen the engine is running.
Should the camshaft bush be loose, replacement is the only satisfactory cure, but a temporary cure can be effected by tightening down the locating screw which is fitted in the top of the crankcase immediately over the rear camshaft bush.
A loose blanking disc can be caul ked by the use of a long punch operated over the flywheel.
In cases where it is possible to deal with t his trouble fairly soon after the symptoms occur, the following remedy may be found effective.
Remove the locating stud and drill into the camshaft bearing 3/16" diameter to a depth of 1/8 to 3/16in Turn the end of the locating stud down to 3/16" diameter for 3/16in of its length. A slight taper on this spigot will be found an advantage.

[Tony Fearn]

I remember that I posted something about an engine knock on my pre-war 'Flying Fox' back in April 2013 when Alan was sorting his car out:-

"A slight knocking on my Flying Fox engine turned out to be the wrong-sized split pin holding the camshaft sprocket nut in the timing case. It was too thin (should have been 1/8") which allowed too much end-float as the nut unwound a fraction".

Tony.

[Keith Clements]

How often do we sacrifice the correct tightening torque to get the split pin in? That is if we have a value for such a torque of course.
It is only with experience of materials and tensile strengths, thread shape, pitch and bolt dimensions that one can estimate what the correct torque value might be. This is way beyond most people's competence and probably most people's torque measuring device that is usually no more than their strength.
As we get older we get weaker when we are young we have too much strength and we break fixings. As modern 'mechanics' have little knowledge and use impact drivers at will they stretch our Jowett fixings to breaking point. Care and sympathy of our old cars is required.