Reply To: Ethanol in Petrol, engine coolant and tyre pressures

That sort of damage usually suggests a valve that hasn’t seated properly and is being eroded, although most of the examples that I have seen have just one segment missing rather than this strange formation.

It is amazing how engines will carry on with quite extensive internal indigestion. A friend has a Mercedes SL, which although it ran well after being recommissioned after a lengthy hibernation, developed a tapping noise in the engine, which defied all diagnosis, and eventually he bit the bullet and took off the head. No 5 cylinder had some battlescars on the piston crown, so he delved further and found that the con rod was bent such that it was several mm shorter than standard overall and the tapping was the piston skirt hitting the crank.

How had this happened? They concluded that the  hydraulic timing chain tensioner had been slow to react in the initial startup, sufficient slack being present in the valve timing for the piston to hit the valves. Miraculously, apart from a few impact marks on the piston crown, there was no other visible damage to valves, etc. and only one cylinder was affected.