well have spoken to a couple of people so far today, possible cause is the fact it may have been running lean so a possible problem with the injector, could also be ecu related, the car was using a little bit of oil (bout 1litre every 1000 miles) so perhaps oil was getting past rings and causing a bad hot mixture of oil and petrol other possible cause is dodgy spark plugs... was using bosch super4, but the plug looks fine, dont really want to bolt my rebuilt 2l bottom end on for exactly the same the to happen! will take some pics when i get home tonight see what you all think
1 Is the hole down the side or in the piston crown ? If it is down the side it might have just cracked a ring which then breaks up and works its way out burning a hole as it goes. Did you grease the gaps between the piston and cylinder walls when you cleaned them to stop carbon getting down there ? 2 Blocked injector seems likely too but could also be the timing too far advanced at high revs causing inaudible high speed detonation. 3 Could also be poor coolant circulation causing that cylinder to run hotter than the others and also cause detonation on that pot only. No 4 is furthest away from the coolant inlet (the pump) and will always run fractionally hotter than the others anyway. 4 The oil burning theory is also valid. Oil in the mixture or a weak mixture burns slower than a clean or correct mixture meaning the whole cylinder gets hotter leading to detonation etc etc. Combine any or all of these......but going forward... Change the piston, rings (obviously), valve guide seals and hone the bore which eliminates No 1 and No 4 above. Check or change the injectors (might as well do all 4 to be safe) which eliminates No 2. Get the timing set up on a rolling road to elimante No 3. Go for a few beers and smile philosophically about your appaulling luck and what an expensive week it has just been.
Hole is in the crown of the piston.... not going to bother repairing the 1.8 block anyway, I have a rebuilt 2l block with new rings, bearings etc etc.... so that should hopefully elimante theory 1 & 4, i'll try and find some new injectors so that'll eliminate theory 2...anyone got any? and obviously would get timing checked on rolling road with a new engine anyway so eliminate theory 3 The head has done less than 20k miles so really shouldnt need valve guide seals doing again... should i?
Sorry mate, got sidetracked half way through the post and got my points wrong Hole on the crown is detonation without any doubt. Classic symptom. Rolling road will eliminate No 2 combined with an injector check / change. You will almost certainly need the ignition curves remapped if you are changing to a 2 litre lump and might need different injectors anyway. Try a separate post for a response on this specific. For No 3 it needs a good rad flush and a check of the water pump and thermostat if you are refitting the old ones. If the thermostat is missing it can have drastic effects on the way coolant circulates even when the engine is hot and the thermo should be wide open. I would probably chuck a new pump on anyway for what they cost unless you know yours is recent. Agree the valve seals should be fine unless the engine has overheated at any stage (you didn't say it had). Every cloud has a silver lining. It'll be different motor when you get it finished
