16-09-2018, 12:39 PM
I had exhaust valves Nos 3 & 4 sticking a couple of years ago. Initially it happened after a long haul up hill in 2nd (3 speed box). The car would run badly once back in top for a short while then settle down. This got worse and worse over quite a few miles (100+) until it happened every time high revs had been used in 2nd and very badly affected performance.
It took some time to work out what the problem was and I found both valves had a carbon deposit on the stem. I guessed that the valve had got very hot with sustained high revs and expanded more than usual allowing the tappet to close and combustion gasses to reach the stem. After cleaning the valves and running a reamer down the guide I reassembled with a slightly wider clearance. That fixed the problem.
Since then I have reset the tappets to standard gaps and the problem hasn't recurred after 6000+ miles.
It took some time to work out what the problem was and I found both valves had a carbon deposit on the stem. I guessed that the valve had got very hot with sustained high revs and expanded more than usual allowing the tappet to close and combustion gasses to reach the stem. After cleaning the valves and running a reamer down the guide I reassembled with a slightly wider clearance. That fixed the problem.
Since then I have reset the tappets to standard gaps and the problem hasn't recurred after 6000+ miles.
Jim