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[omega2018]

Assuming correct test procedures, that's still a very wide range across both banks, which would strongly suggest bad cam-timing. Considering how well mine ran with all four cams a tooth out, I wonder if each pair is incorrectly timed to each other.

i'm struggling to get my head round how a cam being out would not equally affect all cylinders in that bank but open to explanations

[LC0112G]

Wikipedia (yes I knoiw) says X30XE compression ratio is 10.0 to 10.8. Atmospheric pressure is 14.7psi. Therefore, at low RPM (such as when cranking), the maximum cylinder pressure should be between 147 psi and 158.76 psi. X32XE is listed as 10:1, so 147psi.

Given the accuracy of most cylinder pressure gauges (my Gunson one is carp) anything from 140-160 psi would seem 'normal'. Of your readings, only Cyl#1 looks Ok to me. The fact you've got some above normal, and some below normal suggests to me it isn't valve timing. 190 psi in Cyl#6 makes no sense to me.

One thing you can do is buy a cheap borescope/endoscope off eBay. Shove it down the spark plug hole and take a look at the piston crowns and if possible valve faces. If one or more pistons are cleaner than the rest, then this is a sure sign of water in the bores steam cleaning them. They'll probably be black (covered in carbon), but if they're coked up good and proper then you're getting oil in the bores which is either piston rings or valve stem seals

Chucking loads of oil in can change the compression ratio if any ands up sitting in recesses in the piston crown. This will raise the compression ratio. The purpose of the oil is to help seal the piston rings on a dry/cold engine and as such you only need enough to get down the sides of the pistons in the bores to wet things. If you're doing it on a warm engine, then oil shouldn't be required because the bores and rings will still be wet (hopefully!) from normal running.

 

[Ulap31]

Right every one James v6cdx( think that's right) is coming over to help get to the bottom off the mystery hopefully
I appreciate every ones input and once she's running I can then start to do the minor restoration bits that need doing.
One thing that keeps me persevering is my insurance company has valued it at
Wait for it.............£1800
Double checked & they say they couldn't replace it so they feel as these are quite rare & hard to find that would get something of the same spec etc.

[tigers_gonads]

Right every one James v6cdx( think that's right) is coming over to help get to the bottom off the mystery hopefully
I appreciate every ones input and once she's running I can then start to do the minor restoration bits that need doing.
One thing that keeps me persevering is my insurance company has valued it at
Wait for it.............£1800
Double checked & they say they couldn't replace it so they feel as these are quite rare & hard to find that would get something of the same spec etc.

Best have a look at this thread mate 
http://www.omegaowners.com/forum/index.php?topic=135836.msg1742488;boardseen#new

[05omegav6]

Don't mean to be the bearer of bad news, but you might not read the other sections...

http://www.omegaowners.com/forum/index.php?topic=135836.0;all

[Ulap31]

Wow that really has sent a shiver down me and I didn't meet James yet.
I hope to god he will be ok & there's no long term problems
He'd e- mailed and text a couple of times to arrange to pop over next week to try help me resolve the problems with my car.
I'm thinking sod the car as life is precious and you never know what's round the corner
I wish him a speedy recovery and my thoughts are with him

[Kevin Wood]

Wikipedia (yes I knoiw) says X30XE compression ratio is 10.0 to 10.8. Atmospheric pressure is 14.7psi. Therefore, at low RPM (such as when cranking), the maximum cylinder pressure should be between 147 psi and 158.76 psi. X32XE is listed as 10:1, so 147psi.

Given the accuracy of most cylinder pressure gauges (my Gunson one is carp) anything from 140-160 psi would seem 'normal'. Of your readings, only Cyl#1 looks Ok to me. The fact you've got some above normal, and some below normal suggests to me it isn't valve timing. 190 psi in Cyl#6 makes no sense to me.

One thing you can do is buy a cheap borescope/endoscope off eBay. Shove it down the spark plug hole and take a look at the piston crowns and if possible valve faces. If one or more pistons are cleaner than the rest, then this is a sure sign of water in the bores steam cleaning them. They'll probably be black (covered in carbon), but if they're coked up good and proper then you're getting oil in the bores which is either piston rings or valve stem seals

Chucking loads of oil in can change the compression ratio if any ands up sitting in recesses in the piston crown. This will raise the compression ratio. The purpose of the oil is to help seal the piston rings on a dry/cold engine and as such you only need enough to get down the sides of the pistons in the bores to wet things. If you're doing it on a warm engine, then oil shouldn't be required because the bores and rings will still be wet (hopefully!) from normal running.

Your predicted pressure would be correct but for 2 factors:

As the air in the cylinder is compressed, heat is generated. This further increases the compression pressure. It won't be completely adiabatic due to heat loss to the cylinder walls, and it will depend greatly on engine temperature and cranking speed.

Valve timing is offset relative to TDC/BDC, so for some of the compression stroke, the intake valve is still open. at cranking speed, this is enough to effectively reduce the length of the stroke.

It matters not. The variation between cylinders is what is significant, and I think this engine is not in the best of health.

Given the lowish mileage, I'd guess it might have had a cam belt failure and be suffering from bent valves, or piston rings having been crimped into their grooves by impact with the valves.

I too suspect that compression would be low across the board (or at least on one bank) if the cams were timed incorrectly.

[LC0112G]

Your predicted pressure would be correct but for 2 factors:

As the air in the cylinder is compressed, heat is generated. This further increases the compression pressure. It won't be completely adiabatic due to heat loss to the cylinder walls, and it will depend greatly on engine temperature and cranking speed.

Valve timing is offset relative to TDC/BDC, so for some of the compression stroke, the intake valve is still open. at cranking speed, this is enough to effectively reduce the length of the stroke.

Fair enough. I was only trying to give a finger in the air, first order guestimate of what to expect. Heating will increase the pressure and intake valve overlap vs BDC will decrease it. Difficult to guestimate how these two things affect the results 

I still think 190psi smells wrong though. We know compression ratio should be 10:1 ish. Ignoring temperature effects that should result in a roughly 10:1 pressure increase, hence 147 psi. 190 psi implies almost 13:1 "compression". If 190psi is correct then this increase can only be due to the heating effects. At ambient (20C /293K) that would require the cylinder gas to reach 378K /105C. Not sure I believe that.

However, if 190psi is correct, then then other 5 cylinders are well and truly 'dangle berries'ed (I think that's the correct technical term).

Any way up, something is seriously awry though.

[Ulap31]

Ok I'm in luck brother in law has inspection camera that he's kindly lent me so plan to look inside engine on Sunday weather permitting
I know that things aren't right but it still goes fast as f*ck
Took on board what everyone has said & can see a strip down coming on
Now need to put my mind at rest and feel knowing what's wrong will it would benefit people on the forum & stop others wasting money.
I.e changing bits that certain garages say are not working when there's clearly nothing wrong with the old parts.

[omega2018]

here for what it's worth are the haynes manual figures for the 2.5v6

Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 to 15 bar (174 to 218 psi)
Maximum difference between any two cylinders . . . . . . . . . . . . . . . . . . 1 bar (15 psi)

the 2.5 compression ratio is 10.8:1.  the 2.6 compression ratio is 10.0:1 so you can take approx 8% off  the haynes figures (but not the difference between cylinders of course).

[Ulap31]

Problem found at last
After months of frustration, bad backs money changing this part and that part this is what I've found?
Camera into cylinders 1&3 there's rust markings all around including the bottoms of the valves
Cylinder 5 is as you'd expect of a healthy engine
Not bothering with 2,4,6 as I'm going to strip it down
I believe that who I bought it from maybe put some K SEAL in it to disguise the problem as I recall there was no eml bulb in the car when I bought it
If engines gone then I'll strip it for parts unless someone has a better idea

[omega2018]

thanks for updating the thread, so often we never hear the final outcome. 

a sad blow for the theory that head gaskets never go on the v6 i think . 

[Rods2]

When both head gaskets went on my 3.0 mfl, both rear cylinders gave unexpected high readings. My conclusion was that this was due  to water being drawn into the cylinder on the compression stroke and therefore reducing the combustion volume on the compression stroke it raised peak compression. This gave the opposite result of what I was expecting as gas leaking past the gasket would give a lower reading, but a compression tester has a non-return valve so you are only recording peak pressure.

This is a practical real world reading where both rear cylinder fire rings were corroded and breached, where it was badly treated as a Vx fleet car before I bought it with the first service at 18k miles!

[terry paget]

Fascinating thread, congratulations to Ulap for perserverance and diagnosis and this forum for its infinive wisdom.
So rust in 1 & 3 cylinders but not in 5. Has it been parked for a while with water in 1 & 3? Is the other bank similarly afflicted? Engine is beyond econmic repair, but I wonder what happened to it.

[05omegav6]

Could have previously been driven through a puddle, thrown the belt and left standing for a period of time pending repair... more than one way to get water into the bores...