Compression numbers

[RipRocK]

My Pilot just had its 72,000KM/45,000miles service done. I haven't quite racked up that many miles on it yet, but I'm on a 5,000KM/3,000mile service schedule, instead of the 6,000KM/3,750miles interval.

Anyway, I noticed on the work list sheet, one of the things they performed was the Compression Test. I think this has something to do with cylinders? The numbers which were written down for it was all 180, save for the #3 and #5 cylinders, which were 175.

Anybody know what these numbers indicate and if they're normal? The service advisor told me that it's OK, but just wanted to confirm and learn a bit more about it.
Is having a few cylinders with different numbers something to be concerned about?
Any explanation for the differences? Is there anything that can be done to bring all the numbers the same or is that not necessary? Thanks for your time and courtesy.

[desertpilot]

Quoting from the '03-'04 Pilot Service Manual under Engine 6-6, Cylinder Head, Engine Compression Inspection


Compression Pressure:

Above 990 kPa (10.1 kgf/ cm2, 145 psi) - 200 rpm


Maximum Variation:

Within 200 kPa (2.0 kgf/ cm2, 28 psi)

(Note: cm2 = square centimeter)


It seems that your numbers are in psi, maybe you could confirm this with your technician. If it is psi, then the max variation allowed is 28 psi, your difference of 5 is well within the allowable tolerance.

[RipRocK]

desertpilot, thanks for your quick reply and looking up the info for me. Really appreciate it. It's good that the differences in the numbers are well within the variation spec. Thanks again.

[desertpilot]

You're welcome RipRocK, I just happen to have my service manual handy near the computer. I just got it about a week ago, lots of interesting info in there.

I wish I have the same results as you when the time comes to get my compression test.

My truck is developing a clunk from the rear brakes, I'll have to show the service dept. TSB 04-019 by my next service schedule.

[pjb3]

There is nothing to be concerned about. The variations are due to slight differences in the sealing of the piston rings and the valves. Variations between cylinders of 10% or less is considered normal.
With all cylinders between 175 and 180 psi your engine is excellent.

In case you are interested, compression tests can be performed two ways, wet and dry. If there is a significant difference between cylinders dry ( such as 100 psi VS 180 psi ) then a wet test is performed. A wet test involves squirting about a tablespoon of oil in each cylinder and running the test again. If the cylinder that had a low value is now in the same range as the others it means that the cylinder has a bad piston ring and the oil is creating a seal. If the bad cylinder still has a low reading wet then the problem is not the piston rings but most likely the valves or a head gasket.

[RipRocK]

desertpilot, I had those brake shim installed a while ago and the noise is pretty much gone. It does creep back once in a while, but overall, I'm glad how it's worked out so far.

pjb3, thanks for the detailed explanation. Had I known that a compression test was going to be performed on my car, I would've went into the work area to take a look. Sounds pretty interesting.

Do you know if any of the scheduled services require the manifold gasket to be taken off to expose the innards of the engine? I'd sure like to see that. I might even take my camera with me for that

[sblvro]

Originally posted by pjb3
There is nothing to be concerned about. The variations are due to slight differences in the sealing of the piston rings and the valves. Variations between cylinders of 10% or less is considered normal.
With all cylinders between 175 and 180 psi your engine is excellent.

In case you are interested, compression tests can be performed two ways, wet and dry. If there is a significant difference between cylinders dry ( such as 100 psi VS 180 psi ) then a wet test is performed. A wet test involves squirting about a tablespoon of oil in each cylinder and running the test again. If the cylinder that had a low value is now in the same range as the others it means that the cylinder has a bad piston ring and the oil is creating a seal. If the bad cylinder still has a low reading wet then the problem is not the piston rings but most likely the valves or a head gasket.

very well said