Got 50 Psi In Cylinder No. 5

[GTS733]

Hi guys,

I am a newbie so here goes, I have an R33 GTST with an RB25DET in it. Now here is the tricky part, had it rebuilt 30, 000kms ago (spent shitloads mind you) and now it runs like a hairy goat.

Modifications are as follows:

Front Mount Intercooler

3.5" Turbo Back Exhaust

Did compression tests and now no. 5 cylinder has 50 PSI and the rest have 150 PSI on an average. Now in the rebuild, apparently i got a pretty good one due to the fact it cost me around 10 big ones so as you could imagine i am pretty pissed of this is only happend as the garuntee has run out and also when i try to ring the workshop the number is disconnected. this workshop was recommended by the warranty company but i have come to the decission that i will do it myself this time round.

I have mechanical experience, but not when it comes to things like this so i was just wondering if any of you guys out there have come across something similar and if so what was the problem and then the solution.

Obviously every car is different but i just want to know what a may be looking at before i go pulling it all out.

Thanks in advance

Martin

[Swiper the Fox]

Hi guys,

I am a newbie so here goes, I have an R33 GTST with an RB25DET in it. Now here is the tricky part, had it rebuilt 30, 000kms ago (spent shitloads mind you) and now it runs like a hairy goat.

Modifications are as follows:

Front Mount Intercooler

3.5" Turbo Back Exhaust

Did compression tests and now no. 5 cylinder has 50 PSI and the rest have 150 PSI on an average. Now in the rebuild, apparently i got a pretty good one due to the fact it cost me around 10 big ones so as you could imagine i am pretty pissed of this is only happend as the garuntee has run out and also when i try to ring the workshop the number is disconnected. this workshop was recommended by the warranty company but i have come to the decission that i will do it myself this time round.

I have mechanical experience, but not when it comes to things like this so i was just wondering if any of you guys out there have come across something similar and if so what was the problem and then the solution.

Obviously every car is different but i just want to know what a may be looking at before i go pulling it all out.

Thanks in advance

Martin

broken piston ring...or if only cast pistons were used in the rebuild id say a broken ring land.

welcome to the forums....not a good way to start...bugger eh

Edited July 22, 2008 by DiRTgarage

[FineLine]

More than likely what DG said. There's an off chance it could be valve related but 99 of 100 rb25 engines with these symptons end up as above.

[Bumblebee]

rings. for sure

i dont think the rings r broken then.. coz then it wouldnt have any compression.. but the rings r definately f**ked

[blind_elk]

Have you done a "wet" compression test? Or a leakdown test?

It's most likely going to be in the rings area - a cracked ring can still give some compression. Less likely is a valve, either bent, or maybe carbonned up so it doesn't close properly.

[Swiper the Fox]

rings. for sure

i dont think the rings r broken then.. coz then it wouldnt have any compression.. but the rings r definately f**ked

a broken ring will still give compression.

[INVRTD]

ay mate i have 80psi in number one atm and very interested in this, looking at a rebuild, what did you put in the engine???

[Bumblebee]

depends how broken it is DG lol and also if its just the one ring thats broken..

u didnt reply to my GB question

[Swiper the Fox]

depends how broken it is DG lol and also if its just the one ring thats broken..

u didnt reply to my GB question

yeah a break closer to the ring end gap will have more compression than a break opposite it as the ring will have no tension on the bore.

what was the question?

[TiTAN]

also depends if its stuffed the bore. more machining costs and a new set of pistons.

[VB-]

wet compression test to confirm its piston related, then start looking to what has caused it

[D_Stirls]

^^^ +1

and if the wet test doesn't yield any answers then a leak down test would be the next test to do, or just pressurise the cylinder and listen to where it is leaking and don't worry about the leak down values.

[GTS733]

Rightio guys thanks for the help i might have a crack at it in the next few months as i have a 07 VE SSV Ute i can drive around in till then so yeah it sucks having two cars hey

once again thaks for the advice this has sort of helped me make up my mind about keeping it cause it was just about off to the glue factory if it were a horse

[Zensoku]

What type of head gasket was used? I'm trying to think outside of the square and it could be as simple a blown head gasket giving a terrible seal...

What are the engine temps like?