My engine seems to be very noisy on the overrun, and unless I have some power on its noisey too. I whittled it down to the gaps being set a bit big and the cast iron amplifying the noise as it does, so checked the settings in the manual, 10 & 12 I think they are, anyway I've brought them down 2 each and it's still noisey.

I'm not too keen on making the gaps any smaller, could I ? but are there any solutions, it's run an awful lot quieter in the past. Started really after I stored the bike badly and the exhaust valve stuck open which is all sorted now.

email (option): Kit247@hotmail.com

Kit I think most of the clatter you get from these is the valve gear. There is that point where a valve reaches it's utmost position and the cam changes instantly from pushing to being pushed, for want of a better description, and any backlash in the cam gear teeth is taken up.
Apparently the engine builders at the BSA factory would hand pick cams and pinions to match them to give the minimum backlash of the teeth. Not an option that is readily available to most of us.
It probably answers why some engines are quieter than others, even if they have been rebuilt with brand new parts.

Ron

PS I run my tappets at 8&10 also. Never understand why the tappet clearances differ so much between similar
engines. Maybe the M20 gaps are to do with their valve overlap?

email (option): ronpier@talk21.com

I run my tappets at .008" and .008" with a 'slack' setting on the exhaust and a 'snug' one on the inlet.
If the crankshaft is not running true within the .002" concentricity limits, the engine will be noisy, even with brand new timing gear..Ian

I did set my tappets .008 & .010 yesterday and ended up with no compression after 25 km ride today. Compression recovered when engine cooling down. Now I have .010 & .012 again and no problems.

A M20 exhaust valve needs all the time on it's seat it can get as that's it's main chance to have some of it's heat conducted away.
Reducing the gap I would say could reduce exhaust valve life.

It's a long time (and 10s of thousands of miles) since I have run standard clearances on any of my M20s or 21s and certainly haven't suffered from any loss of compression as a result. I would be inclined to look elsewhere for the cause of this problem...Ian

Thanks Gents...

email (option): Kit247@hotmail.com