Sympton - My engine is creating a lot of smoke on start up, which, once cleared, disappears. The engine sounds sweet as a nut when running. My oil consumption is minimal, and I have good pressure. Knowing the amount of knowledge out there in Elanland, can anyone tell me what the symptons would be for a car that has been run on unleaded fuel for the last 5000 miles on an engine that has not been converted to U/l petrol? Could it be associated with the sympton above? I add lead replacement additive every fill up and don’t run the engine at high revs. Thanks for replies
Possibly slightly worn valve guides? When the engine is switched off, oil sits on top of the head around the guides in a pool. On startup, this pool gets sucked down the guides (or perhaps drains down while it is stationary? - unlikely unless the guides are REALLY worn) into the cylinders giving the characteristic ‘smoke screen’. If oil consumption is good, ‘don’t worry, be happy…’ 
Matthew
I agree with Matthew, UNLESS you have a brake booster and the smoke is very white in which case it could be inhaling brake fluid as my Plus 2 did. Watch the level in your master cylinder closely.
I would say that it sounds like valve guides. Probably related to running on unleaded gas with guides not being upgraded or lead substitute used for the 5K mi. indicated.
Rob
Another thought - is your oil breather pipe from the cylinder head connected to the airbox (as original) 
Matthew
Hello tyasman,
Read my story. It might be interesting to understand your problem.
My S3 engine (May 1966) was rebuilt about 2 years ago. After it was still smooking as badly as before the rebuild.
The symptoms were similar to yours. A lot of smoke when starting but also a little cloud after staying at idle (at a traffic light for example).
After enquiry (partly through this forum) I came to the conclusion that the drainage of the oil on top of the head was not good enough. And if you search on this forum you will find topics about this.
Now it is important to know that the early twin cams had this poor oil drainage. Newer one not.
And as ppnelan mentions oil sits on top of the head and slowly drips along the valve stems.
In your case if the problem only appeared recently (after 5 000 miles) it is maybe different. Indeed if the reason of your problem was the one I mention, I don’t understand why the problem did not appear right from the beginning.
As a conclusion if I was you I would check and make sure oil drains easily.
Olivier.
the lack of oil seals causes this ----the oil seeps down into the piston and smoke s at at start up ----[-its the --'they all do that ] syndrome --dont worry about it -ed
With out strict adherence to the specified valve guide to stem clearances you get excessive oil down between them and a smoky exhaust. You also really need to be at the low end of the clearance specs or put in valve stem seals to avoid “they all do that” situation.
The most leakge and smoking occurs when running at high engine manifold vacuum (idle and overrun situations).
They also smoke on startup due to the above from oil that was splashed in the area and has dripped down the stems while shutdown.
The other situation that makes it worse is if you park the car with the nose up hill so that oil sits in the back of the head on the exhaust side above the level of the top of the valve guides and much more then leaks down. The rear of the head on the exhaust side had no drain point orginally so the oil had nowhere to go. Later heads had a cross drilling to drain from the exhaust side to the inlet side at the rear to help prevent this problem. However the negine is tilted to the exhaust side to provide carb clearance and if the place the car is parked is also tilted to that side you can still end up with the rear of the head not draining perfectly.
Synthetic oil produces less smoke when it burns so also helps reduce the problem.
Park it on the level or slightly nose down and drive it until the smoke gets to bad in normal use then it time for a head rebuild and when you do the head get the builder to use top quality guides and valves and set them up to the middle to bottom end of the specification range.
cheers
Rohan
Yes ditto that, there’s no substitute for getting valve stem clearances right, as I found out the hard way. Eventually I had it all properly set up by someone who knew what they were doing (ie not me), using new big valves (from Ebay USA, cheap as…) and new guides. Oh and a newly bored 1600 block and piston rings. Problem solved. But I’d try the head first.
The old trick to tell if it’s valves is to go down a long long hill on override and then plant your foot at the bottom. If you suddenly feel like James Bond in the DB5, that’s valves.
Robert
Thanks to all for replies, it looks like the problem is probably leaky valve guides, but Matthew raises an interesting point. When I bought the car the breather pipe was not connected to the airbox - and it didn’t smoke. I re-attached the pipe and the problem started. I’m not sure if the smoking started straightaway, but it sure is a co-incidence. I’ve taken the airbox off and there are signs of oil on the trumpets. Question. What happens if I disconnect the oil breather pipe? Why does it connect into the airbox? Will it do any harm if I leave the pipe disconnected? Sorry, that’s three questions!
Thanks for answers - I’ll post a reply if I solve the problem
Best regards
Smoky Robinson
The early cars did not have the tube into the airbox, they had a “road tube” , which simply ran down to the bottom of the chassis. Good for lubing the highway as you drive. 
This arrangement is not exactly enviro friendly, thus the tube to the airbox.
I did not like either way, so I went the way of the racers, and routed the tube into a plastic catch bottle. No oil in the airbox, and ummmm, less oil on the road. 
The effects of oil blowing out the breather can be greatly decreased by adding a second breather on the cam cover ( I did this also). Again, this is done by racers. I have both tubes to one catch bottle, and see very little residue inside.