Melted Piston

[grayg40]

Erm... If the pistons are all 75.5mm and the same make why would they be out of balance 

you will never get 2 pistons the same unless you buy a matching set. when i got a new piston it was heavier than my others so i had to buff away a part to get them the same,
your other pistons will have wear on them and making them lighter than the new one.

[PeteG40]

if yr buying a new vag piston at best part of £200 i'd be tempted to save £600 for a proper rebore

[Andy]

My old G guy (that I won't be using again) didn't put the Lambda sensor in properly, Matt was able to unscrew it with his fingers, should it be like that? Could that have caused the melt from wrong readings? The sensor itself is fine though and not damaged!

You can't assess the health of a lambda probe just by looking at it - post-piston meltage I replaced mine as a precaution, they don't take kindly to oil fouling.

I very much doubt a faulty lambda has anything to do with the piston meltage. At full throttle/high load (i.e. when conditions are harsh enough for melty melty piston) the ECU ignores the lambda anyway.

Flow test and clean the injectors, check out the engine block waterways/cooling jacket for blockages, check your fuel pressure (replace the pumps if they've never been done - and deffo the filters!).

As Yoof said, what spark plugs were you using? Do you have a picture of them?

[Dirrt]

you will never get 2 pistons the same unless you buy a matching set. when i got a new piston it was heavier than my others so i had to buff away a part to get them the same,
your other pistons will have wear on them and making them lighter than the new one.

Is this true?

if yr buying a new vag piston at best part of £200 i'd be tempted to save £600 for a proper rebore

Urgh, my head hurts thinking about it all. What needs fixing now including the piston for parts alone is over £500
I don't know what I should do for the best, I just wanted it running again ASAP but I do totally see your knowledge in a rebore

You can't assess the health of a lambda probe just by looking at it - post-piston meltage I replaced mine as a precaution, they don't take kindly to oil fouling.
I very much doubt a faulty lambda has anything to do with the piston meltage. At full throttle/high load (i.e. when conditions are harsh enough for melty melty piston) the ECU ignores the lambda anyway.
Flow test and clean the injectors, check out the engine block waterways/cooling jacket for blockages, check your fuel pressure (replace the pumps if they've never been done - and deffo the filters!).
As Yoof said, what spark plugs were you using? Do you have a picture of them?

Melty melty  Does it? I learn something new every day
I can get pictures!

[lance]

iridium spark plugs?

[Yoof]

Cheaper to buy a healthy rebuild engine 

[Tommo]

Yoofs right, the chances are buying another engine is easyer/cheaper and then you have a spare as well.

I would be wanting to see the spark plugs you took out before fitting the new ones. Any det damage or sign of running lean?

I wouldnt worry about piston weights too much, as long as its the same brand as the rest. These things dont rev very high anyway.

Did it make a sound like a machine gun before it died? If not then its probably been gradually dieing of det for a while, rather than a sudden change in mixture/timing.

Do all the cylinders have major det marks? If so then its a timing/chip fault. If its just a select few then its down to injectors I suppose. Obviously the cylinders that run hottest will be prone to det first (the middle two) although I wouldnt be surprised if the ECU retarded the timing slightly on the middle two cylinders to compensate anyway.

Was it overheating at all at the time of the damage?

[Yoof]

ECU can't retard individual cylinders, it's base retard. Also Cyl 1 runs the hottest on the Polo engines, especially on the G40 motors mostly due to the exhaust manifold design.

[Dirrt]

Cheaper to buy a healthy rebuild engine 

Keep selling it baby  haha I am tempted, but no...

Yoofs right, the chances are buying another engine is easyer/cheaper and then you have a spare as well.
I would be wanting to see the spark plugs you took out before fitting the new ones. Any det damage or sign of running lean?
I wouldnt worry about piston weights too much, as long as its the same brand as the rest. These things dont rev very high anyway.
Did it make a sound like a machine gun before it died? If not then its probably been gradually dieing of det for a while, rather than a sudden change in mixture/timing.
Do all the cylinders have major det marks? If so then its a timing/chip fault. If its just a select few then its down to injectors I suppose. Obviously the cylinders that run hottest will be prone to det first (the middle two) although I wouldnt be surprised if the ECU retarded the timing slightly on the middle two cylinders to compensate anyway.
Was it overheating at all at the time of the damage?

I don't want or need a spare haha. As much as I am a petrol head and I'm one for power coming before looks and all that jazz I just want my G running sweet as fook, I'm happy with the power and don't want to spend any more on performance. If I do more I'll spend a lot off the time paying someone to sort it out for me. Most off you bois enjoy spending your weekends under the hood fixing it, tweaking it, playing with it and then driving it. I wish I had that gift but I dont and certainly wont for a while, when my G's running I do 300 miles easy in it on weekend. I am saying this in a nice way btw because sometimes i can get ready as blunt and mardy 
I just want it as it is running perfect, so I can enjoy it, keep it and then move onto the Jap metal dream

I changed back to standard Bosch ones before melted piston and it was deffo running lean!
We weren't worrying about weight too much tbh
That's a good word for it, my comparison was a scooby... but deffo a machine gun, yes!
I'm not sure but I can get that checked... Right OK, more knowledge, what I like to read, learn and take in  No not at all, it did run to about 90 whilst i was sat, but that was about 45 mins before this happened on motor way and it had cooled right down after i moved from sat location after 10 mins and was normal at time of this taking place

[Nick_S]

Good news
I got some good luck for once but I'm not holding my breathe, I always expect the worse with me and this car There are no marking on the bores so replacing the piston for now is gonna do the job
I don't have the money to do anything else yet, so boring it out will have to wait until after Christmas where I shall be starting a new G fund and putting money by for lots of things. It's a long process but if the G's running whilst I'm saving, I'm happy  

My old G guy (that I won't be using again) didn't put the Lambda sensor in properly, Matt was able to unscrew it with his fingers, should it be like that? Could that have caused the melt from wrong readings? The sensor itself is fine though and not damaged!

Everything else is being checked...

Right, where's the best place for me to source a 75.5mm standard piston (.5 oversize and not forged as it wont match the rest!) and how much should I be paying for one?

I think VW main dealer does slight overbore size pistons. Probably have to buy a full set though.

[Dirrt]

Thanks Nick

[hayesey]

I didn't think VW sold oversize pistons for a g40 engine?  I know you can get them from engine builders but you'd need to do the full set.

Quote from: Yoof on Yesterday at 07:32:34 pm
Cheaper to buy a healthy rebuild engine  Wink
Keep selling it baby  Cheesy haha I am tempted, but no...

that's going to be your cheapest option that will guarantee a healthy engine at the end of it all.

[Dirrt]

I don't get how me replacing whats wrong, is then leaving my engine "unhealthy"  It's old like everyone elses but everyone is not replacing theirs?
Sorry if my questions are tedious and you're probably all rolling your eyes at me but I ask so I understand. It's actually really hard when I don't know myself and i don't know what is best, so I have to seek guidance and advice. I am being told different things and every man and thinks he knows best and his way is best and that they know what they are talking about when reality is probably only about 3 off the 15 that give meadvice do. A new engine would make any car the healthiest it could be, but in reality it's not always needed.

I have it in mind to replace the piston, the rings, clean injectors and the head has gone so that needs doing and probably change the pump aswell. Why would this not be OK?
The plan is to fix this, get it running and driveable and then start my Jap fund and even put by for Yoofs engine if I can tbh as a fall back.

[Phil]

I changed back to standard Bosch ones before melted piston and it was deffo running lean!

Did you swap the map as well?

[hayesey]

I don't get how me replacing whats wrong, is then leaving my engine "unhealthy"

how do you know what's "unhealthy" without replacing practically everything?  You could be flogging a dead horse or fighting a lost battle etc... 

I'm not trying to make you buy yoofs engine, it's just you might be better off using a healthy engine than trying to fix up one that's suffered a lean out (which could have damaged all sorts, the block could even have warped...).  Yes when I bore-washed my old block I just replaced it with another one that I rebuilt and knew was good.