48 replies to this topic

[james4563]

Just been diagnosed with low compression on all 4 pistons and 'amber' leakage during leakdown test on all 4 pistons. Engines supposedly only done 20k since it had whole new bottom end... Not really sure what to do with the car now. Advice?

[vocky]

I see you have a stage 4 tubby, so possibly the valves leaking or a leaking head gasket ?

[james4563]

They seem quite confident its leaking past the rings and coming back up out of the oil cap, you can hear it apparently. 😔

[gaffer1986]

Can go out the oil cap via the gasket. Is it normal for all 4 rings to go together? Maybe stage 4 is too much for the engine, do you have standard internals?

Edited by gaffer1986, 11 May 2018 - 11:49 AM.

[james4563]

Well I'd assume its not too much as Courtney quite happily tune to stage 4 without saying you need forged internals. It's not part of the stage 4 requirements. I don't think all 4 is normal but they are suggesting they're worn at equal rate causing them all to be low which make sense but given the low milage it's a bit strange.

[PaulCP]

Diagnosed by someone you have confidence in?

[gaffer1986]

I don't know the power of a stage 4 but I would guess increasing the power by 50% is going to have an affect on a standard engine unless it is very over engineered. Trouble is so many people only do a handful of miles how would we know? Anyone on here who has a stage 4 with standard internals who has done 100k+ miles without it wearing out? Either way it sounds like you need to rebuild it. Maybe send Vocky a message, he has a lot of experience with these things.

[Nev]

What were the actual compression readings for each cylinder? Find out if they had the throttle open or closed, and whether it was done with a hot or cold engine, was the battery in good order and ask what make/quality of compression tool they used (low quality ones can be very hit and miss).   You need to start being as precise and accurate as possible mate, as you've had these problems for a while now and an accurate diagnosis will depend on good info.   It's common for rebuilt engines to have seemingly low compression/leakage for various reasons (both good and bad) and not necessarily a terminal thing. I have low compression in my engine (deliberately so) and yours may be the same if it's been rebuilt. Even if it is unexpectedly low, there are ways to mitigate the problem.   Other pertinent questions are:   i) does it burn oil, and how much per 1000 miles? ii) is the crank case pressure causing the cold side seal of your turbo to leak oil? (ie is there oil on the first few inches of the inlet of the compressor housing)?

Edited by Nev, 11 May 2018 - 12:38 PM.

[Arno]

Just been diagnosed with low compression on all 4 pistons and 'amber' leakage during leakdown test on all 4 pistons. Engines supposedly only done 20k since it had whole new bottom end...

Looking at the low mileage I'd expect either the bores were glazed by improper running-in (motorway munching at constant RPM and too low loads so no bedding in of the rings happened) or way too rich mixture bore-washing the oil off, or the assembly of the engine was done incorrectly and too large piston to cylinder wall clearances were used allowing the pistons to rock/rattle in the bores too much and prematurely wearing/grinding down the piston rings and grooves.

 

Not too much else, apart from a seriously 'open' intake without an air filter letting in debris, would cause a newly built engine to develop leaky rings in such a short mileage.  

Not really sure what to do with the car now. Advice?

Post-mortem first.. Pull engine, dis-assemble and examine the parts. If assembly/build problem: stern talking to engine builder If bore wash/running-in problem: ditto for the tuner/RR-operator. Bye, Arno.

[james4563]

For info the engine was a short block direct from vauxhall, which was fitted by back on track. Then it was run in for 5k by the previous owner before going to Courtney for stage 4 map and mods. I don't think it's burning any oil. I'll have to monitor it more closely.

[siztenboots]

leaking past rings and escaping the dip stick?

 

have you checked cam timing?

[NOSBandit]

Try putting a bit of oil (enough to seal around the piston) in one of the cylinders and redo compression test on that cylinder, if it improves it's definitely rings. Sent from my SM-G935F using Tapatalk

[james4563]

leaking past rings and escaping the dip stick?   have you checked cam timing?

That's what they told me yes. They showed me the tester while it was still hooked up it was leaking and in the amber zone on their gauge. I couldn't hear it leaking myself at the time the oil cap was on but I don't know about dip stick. Would cam timing really cause that? Wouldn't it run like rubbish if the timing was even one tooth out?

[NOSBandit]

If it is cam timing causing low compression it wouldn't be coming out of the dipstick, it would be coming out of the intake or exhaust valves. Does it have aftermarket cams? Sent from my SM-G935F using Tapatalk

[james4563]

No standard cams as far as I know. 

 

I am going to compression test myself later I think to double check what I had compared to them.

 

From memory of what the mechanic had written down the compression was ~125, ~130, ~125, ~130. All were in the region of 125-130. Unfortunately without taking it to another garage I cannot run a leak down test myself.

 

[NOSBandit]

At least they are all very similar, sometimes static compression can measure quite low on turbo engines depending on cams. My compression is very similar but it is caused by the 272 cams I have fitted, the most important thing is dynamic compression. If you aren't burning any oil I wouldn't worry, it might just be the way the car is setup. I assume they did the tests with then engine close to running temperature? If it was done cold or cool it will let air past the rings. Sent from my SM-G935F using Tapatalk

[gaffer1986]

Is it just me or does 125 sound reasonable for a turbo? Equivalent to 8.5:1 compression ratio?

[Nev]

Is it just me or does 125 sound reasonable for a turbo? Equivalent to 8.5:1 compression ratio?

Yep, it's a little low (compared to OEM) but nothing to worry about, in fact for a stage 4 is probably better to be a bit low seeing as it will regularly see 20 PSI of boost and you could add extra ignition at higher RPM as a result. My own engine is around 125 to 130 PSI too and it seems to work fine.

Edited by Nev, 12 May 2018 - 09:27 PM.

[Strugs]

Does it run ok?

[gaffer1986]

125 psi is 8.5:1 compression ratio 130 psi is 8.96:1 compression ratio Standard a Z20LET engine has 8.8:1 compression ratio so I would guess that's fine. I have a suspicion from what I've heard that old Vauxhall engines don't perform all that well in leak down tests even when they're good and have a tenancy to use a little oil. Of course if I'm wrong about any of this please feel free to correct me. As the previous post, do you have any problems?