205 turbo crank pressure problems

[stevieturbo]

More often than not, a valve related problem will have a much greater loss in compression.

[ninjacost]

will get pics of rings and pistons guys really appreciate input could the boost magnify the problem? ie blow by increase due to boost pressure which is 1.2 bar

[jimbob82]

Yes boost can magnify it. Have u checked ring gaps and clearances as per my previous post?

[ninjacost]

going to do it tomorrow hopefully have more pics etc by the evening

[ninjacost]

ok guys found problem was a hair line crack in casting between rings so had a bit of a fiddle with it and this is the result !

[ninjacost]

and another view

[ninjacost]

i was lead to believe these pistons were forged ?i think they are cast but im no expert

[jimbob82]

whether forged or cast, it's certainly borked

the grain makes me think cast though...could be wrong.

[ninjacost]

just found out they are cast so i'll be going forged for rebuild !

[anonymous-user]

Max_Torque said:

Anyone else betting the 2nd Land is cracked??

How do i claim my winnings?? ;-)

[ninjacost]

that was a very good shout !unfortunatley due to rebuild costs there are no winnings ! lol

[jimbob82]

Max_Torque said:

How do i claim my winnings?? ;-)

You'll get a cookie mailed to you later

[anonymous-user]

It had better have chocolate chips in it, or i'm going to flounce off in a huff........

[jimbob82]

Max_Torque said:

It had better have chocolate chips in it, or i'm going to flounce off in a huff........

[stevieturbo]

ninjacost said:

just found out they are cast so i'll be going forged for rebuild !

And dont forget to have the engine checked and tuned correctly so you dont destroy the forged pistons.

[jimbob82]

Max_Torque said:

It had better have chocolate chips in it, or i'm going to flounce off in a huff........

your cookie is enroute

stevieturbo said:

And dont forget to have the engine checked and tuned correctly so you dont destroy the forged pistons.

+1 I'd advise going for H-beam rods too, those you have currently loko like the original cast ones

[stevieturbo]

There is little need fitting forged rods if they are not needed. Even pistons....it was detonation that broke those, not any specific weakness in the piston.
A forged piston may survive longer, but if there is a problem, it's going to fail eventually.

[Evoluzione]

stevieturbo said:

There is little need fitting forged rods if they are not needed. Even pistons....it was detonation that broke those, not any specific weakness in the piston.
A forged piston may survive longer, but if there is a problem, it's going to fail eventually.

Hmmm, I disagree, when you find out you need them it's too late.
Build it right and strong first time, forged pistons and 4340 rods aren't too expensive (compared to stock items) these days. This is an N/A engine that's been turbo'd and putting out twice as much power as it was originally designed for.

[Evoluzione]

jimbob82 said:

+1 I'd advise going for H-beam rods too, those you have currently loko like the original cast ones

Cast rods?

[anonymous-user]

stevieturbo said:

There is little need fitting forged rods if they are not needed. Even pistons....it was detonation that broke those, not any specific weakness in the piston.
A forged piston may survive longer, but if there is a problem, it's going to fail eventually.

I don't think there is any evidence to support a particular failure theory. Certainly i'd want to have a very good look / measure up of the remaining parts to identify any detonation or ring land pounding tell tales etc.

Even without detonation phenomina, a piston can fail either as a direct result of overload (thermal/mechanical load combination) and Fatigue failure (cycles accrude at a load resulting in work hardening, grain disruption leading to eventual crack initiation and hence failure)


Generally speaking, detonation leading to immediate and gross 2nd land failure would leave a telltail footprint on the crown/topland real estate etc.

It will be well worth measuring the ring gaps on the non damaged pistons to look for deformation, chances are, all pistons would have failed eventually.

Of course, the engine calibration can be adjusted to limit Pmax although at the expense of a higher thermal load on the exhaust line etc.