21 replies to this topic

[silvertop]

Due to a recent trip to the goldy this was the result



But what really worries me is the wash marks on every piston


Does anyone have any idea on what could be the cause?
I appologies for the noob questions

[Hyper_Mike]

[silvertop]

Once again sorry I was unable to make it Mike, would have been good to meet up with you

[Hyper_Mike]

No worries man, just sucks about your car

[Geo&Kez]

Cam timing maybe? Too much back pressure. Just a guess. Interesting result, whatever it is.

[vr401]

Detonation melting valves and pistons.

[silvertop]

Apparently pistons are fine as per the mechanic

[silvertop]

It's just the wash marks on the pistons that I'm not sure about

[vr401]

Is it on exhaust on inlet side?

[Benzo4gT]

How was the power before it took a dump on itself? Usually wash is an over fuelling thing so you might have noticed an increase in fuel use or decrease in power or both perhaps? It might have been doing it for a long time so you might

 

not have noticed.

 

Did the oil blacken fast?

 

It could well be more complicated. The hole in the exhaust valves spins me out, I've never seen that before

[vr401]

If the car is pinging then it will slowly chew the hole somewhere.

[Benzo4gT]

If the car is pinging then it will slowly chew the hole somewhere.

 

Very true. Makes me have an increased amount of respect for those pistons

[blackvr]

I would like to see the underside of the piston, and how the bearing shells clip ( or fall !!) out of the conrod big end. This usually gives a clue. if the bearing shells fall out... indicates heavy detonation. Pinging and detonation create huge loads on the piston and consequently squashing the bearing out of shape. Under the piston, if there is a lot of brown coloration, this can indicate detonation heating the piston and cooking the oil underneath the crown... or just plain simple excessively high Exhaust Gas Temperatures(EGT) overheating the exhaust valve... leading to fatigue failure. The shape of the hole looks pretty irregular, like a chunk has just cracked out. It will be interesting to see if the other valves have distorted faces ?

 

Was this engine running any form of anti-lag or "pops and bangs" tune ? I've seen similar in Rally motors. The washing of the piston... almost looks a bit normal. I've seen similar on a lot of motors...

[silvertop]

Benzo4gt
No increase in fuel consumption I have always got aprox 480 km to a tank and also the oil didn't blacken what I would consider "overly quick". I did however lose a fair bit of power about 15 min prior.

Blackvr
The engine is almost completely standard with a few breathing mods. These were the 3 pics that the mechanic sent me so I'm unable to see the underside of the pistons. I have actually not even seen it personally yet.

Thanks for the quick replies and help.

[jack be nimble]

Reckon its just a valve that has been leaky that finally gave up the ghost.
Shows the importance of routine compression tests. These would over time show a worsening condition as the valves leaked more and more.

Relap all the valves, poke in a few new valves as required, remove carbon from the centres of pistons leaving a bit around the edge, then bang the head back on. Beautiful.

Edited by jack of all, 29 June 2014 - 09:50 AM.

[jack be nimble]

Plastigage and inspect big ends as blackvr said too.

Edited by jack of all, 29 June 2014 - 09:51 AM.

[MDK87]

What's the idea behind leaving the perimeter of the piston dirty Jack?

[jack be nimble]

The carbon protects the top compression ring on a half worn out engine.
I think. Unless someone has a better thought.

Youve challenged me now, I dont recall why ive always left the edge. Have to ring my old school uncle

[MDK87]

Haha oaww shieet.. and the gloves come off..
Nah I was just curious..

[evo-gsr]

Would have asked the same question......interesting theory.