Melted Piston!
 

My mates 1999 standard UK Turbo has 'melted' no:4 piston. He has stripped it down and there is no bore damage but the piston is 'goosed'! Why has it done it???? Running weak? Running hot? Ignition timing? It seems every time an Imprezza has a problem it's with number 4! What causes it? Cheers.

Sorry to hear about the loss of the engine,I know what it feels like.
There will bwe someone along shortly to tell you that this is very rare,I hope someone can give you a deffinate answer,but its near impossible without actually looking at it and running through all the possible causes.

Ive never heard of no 4 going before,no 3 yes,all the time,and I had a no 2 once (i saw a post not so long ago with no 2 aswell).
I cant understand how the bore managed to escape without getting scored.???

There are a lot of things to go through,for a start:

what fuel was being used?

when was the last time the MAF was changed?

Was there any other problems with the way it ran prior to failing?

Was there any safety devices in place ie knock link?

Is there any modifications?

How many miles has it covered?

How often was the oil changed,what procedure was followed in changing the oil,what grade/make of oil was used?

How was the car being driven when the when the failure happened?
(ie was it being thrashed? did it see the red line often?was it being held at high speed/revs?)




Its more than likely a dettonation failure,caused by lean running (IMO),more than likely MAF related.
More info would be helpfull.

Get your mate to get intouch with David at API engines,he will be very helpfull in explaining the failure and probably the best person to speak to about a rebuild.

I'm here if you need me. David. API Engines / APi Impreza

01926 614333

If he needs a cheap solution I have an engine which the big ends have let go the bore,pistons,rods are all fine though. Let me know if he wants it.