KV6 loss of compression on No4 cylinder

[Geoff130]

Thanks for all the helpful comments here, I always find it frustrating to search for a subject and not get an answer from the original poster. I now have the answer, the misfire is due to a chunk missing from one of the inlet valves on cylinder 4, although there is no sign of why it happened. The seat appears ok at first glance and the valve operates still. There is also no sign of any contact with the piston and no sign of any damage from the missing part.

[SD1too]

Originally Posted by Geoff130

I now have the answer, the misfire is due to a chunk missing from one of the inlet valves ...

Fault diagnosis is not an exact science!

Simon

[bl52krz]

Glad you found out what it was. Just a little story comes to mind. I had a Daimler V8 250 Saloon in the 70s. 40 mph not far from home. Big loud bang from engine area. Signs of large money changing hands. But, I purchased a second hand engine, stripped it down, and had the block bored first size oversize. Renewed all seals, checked everything twice that had to be done. Borrowed a works manual from the Jaguar garage in Birmingham for one day to get the timing definitely right. Assembly complete and away we went to fit it at a mates garage. Everything ok. Started and ran like a sewing machine.The punch line was that the top of one of the pistons had broken off, bent a valve and ................had disappeared I know not where.I drove that car TWP 606F for approx 12 months while I got the other engine up to spec. Kept to 40 mph and it never burnt any oil even with the piston top missing.I sold it for the same as I bought it for to a young enthusiast with 99,900 miles on the car, 20,000 on the new engine. Wish I had it now.