Originally posted by Jesmol
..... noticed that the front 3 cylinders had a reddish residue all over the are within the combustion chamber. The back 3 cylinders had a greyish colour, with a very smell amount of red material.
Never seen anything like this before. Anbody got any clues??
I've seen this on some taxi's running on LPG. It sounds like you might be suffering from a bit of valve recession (this can happen on gas) The red deposit is probably small (minute) bits of iron oxide (rust) from the erosion of the valves and their seats. Check (and keep track of) your tappet clearances to see what's happening, they'll close up with recession.
The only reason I can think that it's different from your front and rear cylinders is that the mixture might be different from the front to the rear and some cylinders are running hotter.