Morris Minor Owners Club

Hi chaps. I have a query. I bought 69' traveller back in August and have been using it every day. Recently I have suspected that
it had developed a 'sticking valve', more so when the engine had got to working temperature. I have had it in my local garage ( someone I put a lot of trust in ) and after doing all the necessary elimination tests ie : compression / spark / fuel etc. he took the rocker cover off as one pot was showing around 80 per cent compression, with the other 3 pots at 120 per cent.
The diagnosis was right and one of the valve ''stems'' was sticking. It's now freed off and has been running - will try a proper run out with it tomorrow.
My query is this : I have been reassured by the chap that sold it to me that the car had a reconditioned engine ( WITH unleaded head ) fitted app. £8k miles ago. Is it advisable to add a drop of ''additive'' say - every other fill up just to be on the safe side and what additive is best ?

i dont understand the figures did he mean 120 psi rather than percent ,they are a bit low as for additive some say do some say dont .

Sorry Dale, it should have read psi. and not per cent. If 120psi. is 'low' - what would ''good'' compression normally be ?

120 is desperately low - should be 160/170 psi on a good engine - test done with hot engine and a good battery of course. Sticking valve is possible...but a bit unlikely. Look at the guides - if the exhaust guides have been (foolishly) fitted with rubber seals - cut them off! The exhaust guides need to get some oil... Other (not unknown but not common either) possibility is weak or broken springs - which can't shut the valve properly...have a good look at them when you have the rocker cover off. Some 'reconditioned' engines are , let's just say ' less well reconditioned' than others.... Some are not much more than a new set of gaskets and a coat of paint.....and offered at high cost on ebay.... No need for additives! Do set the exhaust valve gaps to 15 thou, and check/reset every 3000 miles.

Many thanks for the comprehensive reply. Much to study - cheers !