Melted Pistons...why?

[R33]

Guys, I am posting this here b'coz I "virtually" know some of u here and I trust your advice. Ok...my frind has an Evo7 and had modded the car recently with big turbo/cams/forged pistons/conrods etc.
Sent it for retuning last week (as he was gonna take part in a sprint this weekend)...received news yesterday that his mechanics had apparently managed to melt one piston!

a) what are the possible cause(s) of that...overboosting/lean AF mix?
b) apart from the melted piston, what other consequence(s) can a melted piston cause to the engine...scratched block/broken conrod/unbalance crank?
c) will it ever be the same again for the engine...power and reliability wise?

I am posting these questions just to help him out. The mechanic will surely be blaming the mishaps on something and will never admit they have fu**d up big time. As it is, they hv already blamed the problem on the fuel pump which according to them did not deliver sufficient fuel...which makes me wonder...there are 2 fuel pumps (Bosch) installed at THEIR recommendation!

Any advice will be appreciated.

[RazorGTR]

Too melt any piston takes heat, lots of it! Odds are and this is only speculation without actually seeing the piston it sounds as though they ran it way too lean, got detenation backed it off a wee bit but was still too lean. This could be the result of a few things.

- Poor petrol, low grade or contamination
- too much boost
- too much ignition timing
- lack of fuel caused by a faulty fuel pump, filter, or pressure regulator

If they were tuning it, and from what you have just discribed they messed up. Now I am not sure on how things work there but I know 99% of the tuning shops here make you sign an endeminty form saying if it goes bang, your out of luck unless it is sheer neglagence. That is hard to prove though.

See if you can get some pics so i can see them mate.

[R33]

Thanks Razor for the reply. My friend says he will e mail me a pic of the piston. Will put it up here when received.
Mechanics over here are not that advance...legally...so no indemnit was signed. They have apparently opened up the engine and 2 pistons are destroyed. The conrods and crankshaft are ok but the block has a bit of scratch. How is my friend to know whthere the cranks n block are actually okay?

[SkylineUSA]

Its the big CYA time.

Like Razor mentioned there could be host of reasons why, but in the end when buidling an engine to get the most out of it, there are always a chance something can go wrong.

[Moppie]

Vince pretty much hit the piston on the head with the how and why.

Haveing rebuilt two engines with melted or cracked pistons then depending on why they melted the either could apply:

If it was from over heating in the compustion chamber from to much boost or a cooling system failure then the head will need to be pulled down and crack tested, if its hot enough to melt a piston its hot enough to crack a head.

The crank and rods should be perfectly alright, remember it would be soft melted steel from the piston that would have had any contact with them, but if your are really concerned get the affected rods crack tested as well.

The cylinder walls may or may not be alright.
It depends on how the piston melted, if it was just a hole through the middle then chances they will be perfectly ok.
But if the piston collapsed or melted through one side, then you need to check them carefully for scoring, and if nessacry get them honed, or if badly damaged re-bored. No biggy since your going to need new pistons anyway.


The most important thing is to accertain EXACTLY why the pistons melted.
Even if it means letting the shop get away with fucking up because they dont want to admit that it was simply because they leaned it out to much.
But if it was something more serious like a blocked oil line, or cooling passage then when you rebuild the engine there is a high chance it will simply happen again.