Thanks for the answers, you're all right. I don't think it's anything major - I'm just a bit OCD (you should have seen me whenever a warning light popped up on a CX, and it's the main reason I got rid of my C5). Started this morning with no smoke, so probably the rings lining up. I'll try and sort the sender though.

My main shame is it only did 1500miles between MOTs!

Update time.

Oil pressure switch came back to life, was just dirty connections. The smoke is down to leaking pushrod seals.

so how does the oil leaking out of the engine via the pushrod seals ( classic CPD failure symptom BTW) cause the puff of smoke on start up?

As the man said "Just like that!"...

I am wondering about that too? Co-incidence or Tommy Cooper?
Anyway in typical sod's law fashion the thing didn't puff smoke after I'd called the garage to book it in.

It's going back together now and Pete's going to give ecas a call and see whether he can get a cpd valve.

Maybe Richard meant valve stem seals, which can give smoky starts. I am surprised no one suggested these before (or they did and I missed it?).

No idea - as everyone can tell, I'm more of a point to a problem and pay someone to fix it

Thanks god for saurus

Valve guide seals 100%

normal on new especially (1990 year ) engines i have done loads of them

fit a rubber type for good results

so stop pissing around with oil pressure ideas and think in a logic way

Pony

There's no need to be rude.
Oil pressure switch changed as sometimes it lit and sometimes not. Co-incidental with oil / smoke issues not causal. For £7.50 it's hardly a great expense.

It seems the long cylinder head studs at the back were not as tight as they could be. No idea why they were working loose though. Tightened up, new seals and gaskets and heads lapped just to be sure. New CPD valve ordered from Roy, again just to be sure.

I hadn't noticed any oil leaking, but it was very clean so looking on the ground didn't show any marks. But there was enough around apparently to coat the crossbox.

Any oil leak is blown around by the engine fan that together with forward motion tends to coat large areas. I've a leak or at least I get some oil blown around the engine bay,but even after the long 2 up well loaded blasts from Staffordshire to SW France the oil level has hardly dropped so I'm not worried.Yes there's the odd drip under the car but not enough to cause me any concern. Mind having owned british bikes oil drips/puddles are something you learnt to live with