AJS & Matchless Owners Club

I know this is an old chestnut and I thought I knew this BUT.. on lightweights do the valve clearances get bigger or smaller when the engine heats up? The reason I ask is that I can't seem to find a definitive answer and whilst from my listening experience of my bike the tappets seem noisier when the engine is hot (set correctly at nil clearance, only spinning clearance when warm) and generally speaking with most vehicles this is the case, I seems from reading some of the old threads that actually it is the opposite and they in fact get less clearance when hot? Thanks

Hi Paul, my and it is "my experience " that the clearance gets smaller, going back many years to when I rode a pre war ex army Norton 16H side valve. The tappets were very loud so I lessened the clearance, it ran and sounded fine for few miles then spluttered to a stop, give it five minutes to cool it would start again, so my way of thinking is the valve stem increases in length with the heat and then fails to close.

Others may have their view.

Colin

PS overhead or side valve will be the same

Hi

I also believe the clearance diminishes, the increase in 'noise' is due to the oil warming up, reducing in viscosity and hence the cushioning effect diminishes.

The engine is designed to run hot and in this condition the tappet clearance should be very close to zero.

Regards Mick

It is not just tappets that cause noise when oil thins as it warms up. I have pre war bikes that have no oil to the top end. They have grease nipples, mainly to the rockers. When the old bikes get noisy, greasing quietens them very noticeable.

Thanks everyone.. I will leave it as it is then..

A noisy tappet is better that a totally silent one. I learned that from a chap who had a big 4 cylinder kawasaki on which adjusted his tappets to make them quiet. He suddenly had a Kawasaki with a full set of bent valves. As you may have guessed, he was more inept than even me and never thought to slowly manually turn the engine over to see if everything was OK before pushing the starter button.

You have prompted me of something Janet.
Some time ago I brought a 64 G12 CSR unfinished restoration project. The engine claimed to have been rebuilt by Joe Frances. ( A long established London motor cycle dealer. ) The engine pumped out more oil from the front crankcase joint, than it returned to the oil tank. I got John Bolton who had his workshop at Kettering HQ to fix it. He found other faults.
A new set of push rods was also required as those fitted were bent.