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0psi Compression?!

gt-ahhh!

By gt-ahhh!,
in Engines & Forced Induction

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gt-ahhh! Proficient

gt-ahhh!

Posted
Posted (edited)

howdy folks,

story goes that i lost my turbo and possibly my engine. havent had the engine checked out yet, but my mate has a compression tester so we thought we'd have a go and see if we could learn anything.

EDIT: r33 rb25det, stock turbo, 87000km, 10000km on motor, 3" turbo back, pod, not much else.

unfortunately it started raining so we only got through the first 3 cylinders (front to back). cylinder 2 and 3 got 140psi dry, which sounds fine to my limited knowledge, but cyl 1 apparently has 0psi compression!

the needle on the tester doesnt budge at all!

admittedly i am unknowledgable in this department, but im thinking that could be because the piston is smashed, theres no rings at all, or the valves are jammed open. thoughts?

just by shining a torch in im pretty sure the piston is moving, and it doesnt have a hole that i can see. we also took off the valve cover on the inlet side (thinking maybe the turbo bits had smashed the valves) but everything seemed fine there.

im quite sure it will need to be rebuild, but as i bought the damn thing freshly rebuilt 6 months ago, and now this has happened inside 10000kms, i am rather annoyed and want to know what happened.

any help greatly appreciated!

Edited by gt-ahhh!
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45ULT Rising Star

45ULT

Posted
Posted

did the car have a dead miss when running? like was it running on 5 cylinders all through the rev range and not just at idle? its nearly impossible to get 0 psi reading if your piston is in one piece. as even with no rings on there is still some sort of compression. what sort of guage are you using? screw in or push in? also whats the next number after 0 on your guage?

R34GTFOUR Mentor

R34GTFOUR

Posted
Posted

i doubt the valve would be jammed open cause the rb25 isnt a free running motor, which means if the valve stays open the piston will smash into it which isnt a good thing haha.

i mate of mine had a sr20det that pulled 0psi on one piston, but that had severe detenation and the piston had a massive hole in it so its possible. Finish off the rest of the test and see what comes up

gt-ahhh! Proficient

gt-ahhh!

Posted
  • Author
Posted
did the car have a dead miss when running? like was it running on 5 cylinders all through the rev range and not just at idle? its nearly impossible to get 0 psi reading if your piston is in one piece. as even with no rings on there is still some sort of compression. what sort of guage are you using? screw in or push in? also whats the next number after 0 on your guage?

it runs like a bag of ass, and someone told me it was missing but im not sure.

its a screw in gauge, and its analog with a needle so there are many numbers in between 0 and 300 or so. with the other cylinders it quickly went up and sat on 140. cyl 1 it didnt budge!

it blows a bit of smoke out of the pcv? if that means anything.

gt-ahhh! Proficient

gt-ahhh!

Posted
  • Author
Posted
i'd say you have a severly melted piston, or missing a nice chunk of it. But you would have a lot of piston blowby, and it would blow alot of smoke

as in clouds of smoke out the exhaust? its got that when you rev it even slightly...

gt-ahhh! Proficient

gt-ahhh!

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Try doing the test again properly when its not raining, I mean if it was raining, was the test on that cyl completed properly? or rushed?

nah, we tried it at least 5 times. same everytime. it was only after we decided to pull the valve covers off, had a look, and then went to test cyl 4,5,6 that it started raining.

gt-ahhh! Proficient

gt-ahhh!

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Story goes you lost your turbo, how much boost were you running? Sounds like piston damage, leaned out and bad detonation. Start pulling it out....

stock boost. all its got is a pod and a 3" turbo back. i think it may also have a dump pipe because it was 180rwkw which seems a pretty good return from such minimal mods.

i think the engine went first and possibly caused the turbo failure from lack of oil or debris. i hoping this is the case, because it was 10000kms out of a fresh rebuild and they can fix the damn thing if its as bad as it sounds. the turbo only went when the car was switched off a couple of minutes after noticing smoke coming out of the bonnet and pulling over.

does that seem likely? it was still developing boost until i shut it down, but then when i started it next, no turbo!

SECURITY Grand Master

SECURITY

Posted
Posted

worn (really f**ked up) valve guides will give you the same kind of symptoms.

if you want to check if its the head of pistons, try this:

hook up a hose with the same size fitting as the spark plug hole to it on one end, and a fitting for a compressor to the other.

connect it up and run the compressor and see where the air comes out of.

you'll need the piston to be at BDC all valves are closed (i think theyre closed at BDC, check your cam lobes as you spin the motor).

then sit and listen to where the air is coming out of.

if its your pistons it will probably blow out the dipstick, if its the head you will probably hear air hissing out of the head somewhere.

if you cant find one, i have that same size fitting for the spark plug hole somewhere from when i was doing my valve stem seals. let me know if you need to borrow it and we'll organise something.

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