Hi all,

Mahle have finally got back to me saying that my pistons have cracked all in the same place due to there being too much compression. I have measured the head and have found that it is 0.5mm smaller than a standard one. Would this raise the compression too much for the pistons to cope?

Cheers
Dave

 

Generally speaking, No way.
What they actually mean, is too much DYNAMIC compression.. IE: Boost

 

Wierd. I was only running 5psi of boost as i wanted to run the car in properly. I'm getting the pistons sent back to me. Do you know of anywhere I can get them tested too see if there was a fault with the actual pistons or is that unlikely?

Cheers
Dave

 

So this happened in run-in... Were the pistons oversize and the block just bored? Were the piston rings broken too?

 

I had done about 500 miles before they went. The pistons were 0.5 oversize and the block was re-bored and honed. The piston rings were fine. The only damage was the pistons being cracked in between the ring lands. I've posted up a pic of the damage. No sign of detonation either.

Thanks for the input so far.

 

did u have the checked over before you started running it in, ie the fueling, doubt there are faults with the pistons, havent heard of it before, next time you buy some if u can strech the extra cash get sum forged pistons to be safe

 

No, thats one of the things i'm regretting. I set it up as per the haynes manual and websites. Got a mobile cryton tuner to to have a look at it and he didn't know where to start.

 

maybe you were running very lean or rich, proberly lean, think they are around 1.0 - 1.5% co2 on a standard engine with standard boost, but i would run it at a bit more using only optimax fuel, what oil are you using to run it in?

 

I've seen this happen on RST's Mahles and it always seems to happen right after rebuild or then not at all. I for one am giving all the death (det, +30psi, high comp, ...) to my pistons as I can and they are holding just fine even though they have done over 200 000km.