Morris Minor Owners Club

I’m going to do the valve clearances this week myself. First time I’ll have done the job. I’ll be using a combination of a helpful YouTube video, which has taught me the rule of 9, and my workshop manual. It looks straightforward.

Now, both of them say to use 12 thou...but I’m aware from previous threads on here thuat 15 thou is advocated by some owners...and possibly by MG when unleaded fuel came in?

The car is a 1098cc unleaded conversion.

So, should I opt for 15 thou? (Apologies if this is going over old ground).

Yes, the manual says 12 thou for all valves. But there is a school of thought that says 12 thou on inlet valves and 15 on exhaust valves, to allow for unleaded fuel burning hotter. Others say 15 thou on all valves works well. So you have choices!

The valve clearances for use with unleaded fuel are inlet valves 0.012" and exhaust 0.015".
It has to be remembered that the 0.012" for both inlet and exhaust was predetermined for use with leaded fuel. The valves can run especially the exhaust valve a lot hotter with unleaded fuel so reducing the valve to rocker clearance.
Oil seals especially top hat seals should not be fitted to the exhaust valve guides as the exhaust valve stem needs all the lubrication it can get.
I have found that when the valve clearances are set at 0.015" for both inlet and exhaust the engine runs better though with a little bit more noise.

Excellent - thanks for your help.