Engine compression

[Tex_Mx]

I have started to strip down the 6. As I have a few bits to do and it just isn't feasible to drive and mod at the same time.

So first I thoughtI would do a compression check on the the cylinders to see if there might be any problems lurking as there has been a bit of smoke recently.Which I have been putting down to the valve stem seals.Also by the state of the plugs there has been a bit of overfueling.

So anyone know the compression rate for the ze? And what varyation should be considered unexceptable between cylinders? I did one check dry and one with a bit of oil down the cylinder.

On #5 cyl I couldnt see if the oil went in the hole so I might of put a extra squirt down the hole.So when there was such a difference I spun the engine with the tester out and rechecked but still got 250 psi.

________Dry_____with oil
#1 cyl. 209 psi____230psi
#2 cyl. 230 psi____245psi
#3 cyl. 220 psi____238psi
#4 cyl. 230 psi____245psi
#5 cyl. 220 psi____250psi
#6 cyl. 212 psi____228psi

Any and all input welcome.And will probably have a lot more questions yet.As I want to sort it all out as I go along.I am planning on pulling the whole engine and give it all a good clean.Strip off the heads for a bit of work as well.So any tips or suggestions send them my way.lol.

Thanks in advance....
Roy

[Oddball]

Roy... All can offer is the STD compression on the 9.2-1 DE for comparisson .. thats 203 .. max difference between cylinders is 28 ...
If you are thinking of strippng the motor for a good clean out, then a new set of rings and bearing shells are a must. Just check the cylinder widths for any out of round, if none a simple hone and new rings should bring her back to top compression for the ZE.

Paul.

[Tex_Mx]

Thanks Paul.
I was thinking if the rings look ok that I would leave the bottom end for the minute.But the testing leads me to believe that it will pay to do it now with a 21psi difference.Even though some of that could be the valves.

This is do or dont time for the s/c.I will strip off the intake and m/c first and do a mock up before I pull the engine.

Also Paul have you recieved the headers yet? I was wondering if the resonator will bolt up.

Roy

[Postal Dude]

General rule of thumb is no more than 20% difference between cylinders and not even knowing what the compression figures should be it's obvious yours are very healthy being in the 200's. Plus look at the figures and think about it. The oil seals the rings on all pots and of course the compression readings rise accordingly! but they have all risen roughly the same proportion to each other. Obviously any leakage is the valve seating as the oil doesn't seal the valves. You just need to bed the valves in if you have the head off at anytime, definately not worth taking it off to try and equal those out though.

Gerry

[Tex_Mx]

Originally Posted by Postal Dude

The oil seals the rings on all pots and of course the compression readings rise accordingly! but they have all risen roughly the same proportion to each other. Obviously any leakage is the valve seating as the oil doesn't seal the valves.
Gerry

...Wouldnt that mean that the leakage is coming from the rings and not the valves?As the oil sealed the rings causing an increase in compression.

Also I am going to retest.As I forgot to block open the throttle.So will double check just to make sure.

[Oddball]

Originally Posted by Tex_Mx

Thanks Paul.
I was thinking if the rings look ok that I would leave the bottom end for the minute.But the testing leads me to believe that it will pay to do it now with a 21psi difference.Even though some of that could be the valves.

This is do or dont time for the s/c.I will strip off the intake and m/c first and do a mock up before I pull the engine.

Also Paul have you recieved the headers yet? I was wondering if the resonator will bolt up.

Roy

If you are definately going to pull the engine and are thinking of putting the SC on, then i persoanlly would get the whole motor sorted whilst it is out of the car. The fact your compression figures went up after adding oil shows its your rings leaking and the valves seem to be seating ok. But again, if your going to pull the enigne, then as you say, why not strip it and re-con it, just means more cost in gasket kits etc, but at least all that extra air being forced in will be staying in the cylinder.
The headers will be with me at the weekend m8, i could not make it up to Justin's in time, before he left for home, so i asked my mum to pop over as she only live about 20mins away from him. and i 'hope' my good lady wife has no grand idea's of what i could be doing to the house on my next set of days off, and i can fit them, along with the de-cat. I'll let you know when they arrive and i will do a mock up and see what meets where.

Paul.

[Postal Dude]

The test shows your rings are fine. There is no set of piston rings on this planet that can give a 100% seal. The fact that your readings only rose by a small amount shows that they are in good condition. The only time you should do the oil test is if you have a large drop in pressure eg 200 in 5 cylinder and 120 in another. If after adding a teespoonful of oil the readings don't change then it is a valve or similar. if it goes up then the oil has sealed the rings.

Gerry

[Tex_Mx]

Originally Posted by Oddball

and i 'hope' my good lady wife has no grand idea's of what i could be doing to the house on my next set of days off,

I'm sure we could talk her into wanting a few shelves putting up,and a bit of painting always sounds like a good idea.... Or maybe just take her to a few dozen differnt shops to look at shoes.lol

Anyway I did a retest.This time with the throttle jammed open.The results are.

#1 220psi
#2 235psi
#3 220psi
#4 232psi
#5 220psi
#6 239psi

No or little change on #2 #3 #4 #5. But on #1 it went up 11psi and #6 27psi. That seems to be a heck of a difference ..I double checked and still got the same.Thats more than it went up with the oil.Any ideas on that one..lol