Is This Bad?

[BamBamGTI 0]

so can i interchange pistons? I have some pistons off another 1.9 with slightly different rings. They are in good nick, so should I change all of them or just the knackered one?

[welshpug 1,622]

that liner is knackered!

[BamBamGTI 0]

Yea, took another good one from the other engine... Hey maybe this could be a good thread for all the fubar stuff from all the members...

[ALEX 98 1 Cars]

those marks are from very heavy detonation. What is controlling your fuel and ignition? is it a standard ECU?

 

I wouldn't say detonation, looks like swarf has dropped in one of the bores to me.

It doesn't look too bad though, You wont benefit much from changing the pistons.

I'd just fit new rings and and have the liners re-honed (or buy a honing tool and do it yourself).

 

Edit:- This is what detonation looks like.

detonation pic

 

Now that IS kna***rd

Edited July 7, 2009 by ALEX

[welshpug 1,622]

you'll never hone marks like that out

[ALEX 98 1 Cars]

Probably not, but they're no deeper than the existing honing marks, so not really a problem.

The scratches do go vertical though, so there could be a slight loss of pressure, but how much? 1 PSI?

Hardly worth forking out for a new piston and liner!

 

Edit:- if you can get hold of a better secondhand piston and liner then change it.

If not it's not worth changing unless your planning on Spending loads on it anyway.

Edited July 7, 2009 by ALEX

[BamBamGTI 0]

Ill have to correct you there, they are much deeper than the honing marks!!! maybe 1/4mm!! Yeah I agree though, something fell in there and caused this. Luckily I have a spare engine in bits anyway so Ill use a piston and liner from that

[ALEX 98 1 Cars]

Fair do's

 

I've started to do a compression test before I strip down an engine now.

It will help on deciding what to do in cases like this.

[sub205 5]

look at the photos, at least at the lower part of the liner the scratches are really deep.

 

i would never build an engine with such a liner, remember: the piston rings rotate am bit, you'll ruin them!

 

and engine with this liner/piston will run for maybe 10-20tkm and then die with locked piston rings and no compression.

 

change them! trust me! ;-)

[ALEX 98 1 Cars]

engine with this liner/piston will run for maybe 10-20tkm and then die with locked piston rings and no compression.

 

 

How would that happen then??

[sub205 5]

How would that happen then??

because the rings get marks from the scratches of the liner and rotate, so other parts get damaged. also the rills in the piston where the rings sit can get deformed at the places of the liner-rills and so the ring can eventually not get out and press at the liners surface anymore.

 

i had one piston like this several years ago. why use badly worn parts when its no great problem to change it while refurbishing the engine? i dont understand why it is questionable at all to change this liner/piston? anything except changing both is just botched work!

Edited July 8, 2009 by sub205

[ALEX 98 1 Cars]

because the rings get marks from the scratches of the liner and rotate, so other parts get damaged. also the rills in the piston where the rings sit can get deformed at the places of the liner-rills and so the ring can eventually not get out and press at the liners surface anymore.

 

That sounds theoretical to me!

 

Chances are those bits of swarf have been bouncing around in there for a while, got embedded in the head and some escaped though the exhaust valve.

The damage had already been done probably way before it was taken apart and the resulting damage wouldn't cause any further premature wear.

 

 

i don't understand why it is questionable at all to change this liner/piston? anything except changing both is just botched work!

 

It's not now he said he has a spare, which I said to use if he had one.

The reason is the cost! AFIK you can't buy them new separate and a full set costs over £300!

 

If it was me and I was pressed for time and couldn't get a cheap replacement, it'd be going back in (honed with new rings obviously).

Edited July 8, 2009 by ALEX

[sub205 5]

That sounds theoretical to me!

 

Chances are those bits of swarf have been bouncing around in there for a while, got embedded in the head and some escaped though the exhaust valve.

The damage had already been done probably way before it was taken apart and the resulting damage wouldn't cause any further premature wear.

 

 

 

 

It's not now he said he has a spare, which I said to use if he had one.

The reason is the cost! AFIK you can't buy them new separate and a full set costs over £300!

 

If it was me and I was pressed for time and couldn't get a cheap replacement, it'd be going back in (honed with new rings obviously).

ok, when he has no chance of getting replacement, except buying new ones, then its probably ok.

 

but i think here in the forum are enough people that can give him a liner with piston. if not, i can send him one from germany ;-)

everything is better than using damaged stuff. (and driving around everytime thinking about theres something damaged in the engine that could possibly destroy all the good work!)

 

i had main bearing faults several years ago and even today i am very suspicious when i hear noises from the engine.

 

theres a saying: a child which burnt the fingers on the oven does not touch it a second time

Edited July 8, 2009 by sub205

[BamBamGTI 0]

Not to worry guys, I got a liner and piston in pretty good nick to replace the damaged ones. Problem is, they are slightly different pistons with different markings on (see pic) and also different bottom rings. So I think ill change all four pistons and get new rings for them.

 

Piston from damaged engine with stamps on right

 

 

Replacement with different markings

[sub205 5]

Not to worry guys, I got a liner and piston in pretty good nick to replace the damaged ones. Problem is, they are slightly different pistons with different markings on (see pic) and also different bottom rings. So I think ill change all four pistons and get new rings for them.

C and B are the markings for the size, depending on the fluctuation of production ;-)

there are afaik 4 groups. 83mm, 83.001mm, 83.002mm, 83.003mm or something like that.

 

anyway, good that you got some new, its a better feeling inside when you know that every part is ok and are pushing the engine hard :-)

[sideways danny 0]

I wouldn't say detonation, looks like swarf has dropped in one of the bores to me.

It doesn't look too bad though, You wont benefit much from changing the pistons.

I'd just fit new rings and and have the liners re-honed (or buy a honing tool and do it yourself).

 

Edit:- This is what detonation looks like.

detonation pic

 

Now that IS kna***rd

 

 

NO

 

I'm not speculating. the original picture IS detonation damage, that would have been audible and quite nasty

 

 

The picture you've put up is a little different. I'd guess that came out of a bosted engine?

[Tom Fenton 1,525]

I'd agree with you, those marks are detonation on a NA engine, detonation on a boosted engine does hole pistons.

[ALEX 98 1 Cars]

Not to worry guys, I got a liner and piston in pretty good nick to replace the damaged ones. Problem is, they are slightly different pistons with different markings on (see pic) and also different bottom rings. So I think ill change all four pistons and get new rings for them.

 

 

C and B are the markings for the size, depending on the fluctuation of production ;-)

there are afaik 4 groups. 83mm, 83.001mm, 83.002mm, 83.003mm or something like that.

 

anyway, good that you got some new, its a better feeling inside when you know that every part is ok and are pushing the engine hard :-)

 

I guess you could mix and match different sized pistons as difference off 0.003mm isn't going to make any difference as long as you use the corrosponding piston with it's liner.

Just use a set of four with the least wear, feel for the lip at the top inside of the liner where the piston rings stop.

 

 

I'd agree with you, those marks are detonation on a NA engine, detonation on a boosted engine does hole pistons.

 

I'd bet my bottom Dolla it's swarf

[Tom Fenton 1,525]

I'm sorry but you are simply wrong, if you can't accept that, fine.

[ALEX 98 1 Cars]

Ok..Ok Lets not argue!

 

At most were both making an assumption at best, even if you are a professional engine builder unlike me, it doesn't mean you can't be wrong too.

Edited July 9, 2009 by ALEX

[sideways danny 0]

Ok..Ok Lets not argue!

 

At most were both making an assumption at best, even if you are a professional engine builder unlike me, it doesn't mean you can't be wrong too.

 

 

I'm making no assumptions. I've seen it many many many times. Marks that look like someone's taken a pin punch to the piston are generally from excess ignition timing. The melting that you posted up would on a boosted engine be down to a combination of too much boost, very high EGT and chamber temps, possibly lean fueling and probably too high compression for what's being asked of the engine. I had a box full of 4AGE pistons like that from the supercharger kit development engines we pushed to and past their limits

[ALEX 98 1 Cars]

What would a piston look like if swarf had dropped down the bore?

 

 

What your saying it's not even a possibility that some foreign material entered the chamber then?

 

Remember it's only on one cylinder as well.

And as for you keep banging on about that pic I put up, that was on an extreme case, so its bound to be on a boosted engine!

If you want to see some examples of detonation, type it yourself in Google.

 

 

Edit: "Marks that look like someone's taken a pin punch to the piston"

Yeah I agree, his piston doesn't look like that. The markings are all shaped, like flakes of metal.

Edited July 10, 2009 by ALEX