205 turbo crank pressure problems

[stevieturbo]

Ive seen cracked/broken forged pistons before.

No piston is indestructible, especially when improper tuning is involved.
Power rarely breaks pistons, detonation will kill any almost any piston.

[Evoluzione]

What breaks ringlands though?

[stevieturbo]

Evoluzione said:

What breaks ringlands though?

detonation would be the main cause.

[ninjacost]

not had any det problems but i have missed a gear a couple of times at high revs too so maybe thats whats destroyed it when i strip down i'll post findings thanks to all for the replies

[Evoluzione]

stevieturbo said:

Evoluzione said:

What breaks ringlands though?

detonation would be the main cause.

Just wondering how, but I'm guessing shock waves...

[PaulKemp]

Detonation is like hitting the piston (and ring lands) with a big hammer at the wrong time in the stroke i.e. as the piston comes up the burn happens spontainiously earlier than it should

[Mr2Mike]

PaulKemp said:

Detonation is like hitting the piston (and ring lands) with a big hammer at the wrong time in the stroke i.e. as the piston comes up the burn happens spontainiously earlier than it should

You are maybe confusing pre-ignition with detonation. Detonation can be caused by pre-ignition, or it can happen when the spark plug is fired.

[ninjacost]

Hi guys removed liners checked rings on piston with low compression and it all looks ok no damage to pistons at all any ideas ?

[Evoluzione]

Head gasket leaking between combustion chamber and oil way?

[ninjacost]

on initial inspection of gasket it looked ok maybe i need to take another look will post some pics once i have engine apart

[jimbob82]

could it be detonation has bent a rod? i've seen it happen before...other than that, if the piston and rings are fine it could be valves not seating, burnt seat or a bent valve ?

[Evoluzione]

How would that pressurise the crankcase?

[jimbob82]

Evoluzione said:

How would that pressurise the crankcase?

Lol. I forgot about that small detail

[PaulKemp]

Pre ignition, detonation, pinking all the same to me
If you mean ignition to far advanced then max cylinder pressure will hit befor the piston has reached TDC
Crank pressure will be blow by past rings due to broken something.
Compression test, leak down test will show the weak bore
Gasket leak can often be found with test fluid in the header tank

[ninjacost]

ok guys pulled engine out this morning on close inspection of liners there are vertical score marks 3/4 of the way up the liner most are very feint but i can get my finger nail into a couple of them would you say this is enough to cause my problem ?

[jimbob82]

the scores would have to be much much worse than that to lose compression. Have you checked the ring gaps and clearances?

any chance of some pics of the piston skirts and crowns?

[Mr2Mike]

PaulKemp said:

Pre ignition, detonation, pinking all the same to me

Then with all due respect you don't know what you are talking about.

jimbob82 said:

the scores would have to be much much worse than that to lose compression.

Vertical scores big enough to feel with your nail will caused increased blowby. There should be absolutely no scoring like this.

[jimbob82]

Mr2Mike said:

jimbob82 said:

the scores would have to be much much worse than that to lose compression.

Vertical scores big enough to feel with your nail will caused increased blowby. There should be absolutely no scoring like this.

I should have elucidated my post a bit more...

I know and agree it would increase blowby but I was referring to the 50psi compression he has, the scores aren't bad enough to lose THAT much compression.

[stevieturbo]

ninjacost said:

ok guys pulled engine out this morning on close inspection of liners there are vertical score marks 3/4 of the way up the liner most are very feint but i can get my finger nail into a couple of them would you say this is enough to cause my problem ?

That is absolutely not your problem.

Either a piston is broken or the rings are damaged. It's about the only thing that can cause that sort of loss of compression ( other than an obviously blown head gasket )

[jimbob82]

i'm wondering if it's a case that the rings are weak allowing excess blowby, coupled maybe with a bad valve/seat causing compression loss?

it doesn't HAVE to be only 1 thing it can be a couple of things adding up to give the symptoms. Though I do suspect it's piston still, need to see pics as I requested above...