compression test

[astate]

Hi all, looking for some advice, I purchased '66 1200 estate just before xmas. MOT'd and a driver, but low on power, usual oil splatter from oil breather cap. Done a compression test with engine warm, accelerator pedal held fully down.
Dry readings: 1 = 100, 2=145, 3=100, 4=140
then with 2.5ml of oil in pots 1=110, 2=110, 3=110, 4=110
Does this indicate that new piston rings are required.
Engine is GA209899HE, with I believe hardened valve seats for unleaded, as there is a bill for that work in the paper file.
No.1 PLUG was a bit sooted up, compared to the rest.
Thanks
JH

[Pete Lewis]

Were all the plugs out for the test ?
Check valve clearances are 0.010" cold
pete

[herald948]

Two numbers went up and the other two went DOWN? Hmmm.... Regardless, I don't see that as indicating a problem with rings, as you'd expect numbers to go up considerably (or at least significantly) after adding the oil.

Was the car in regular use before you bought it, or had it been sitting for some time?

Can you beg, borrow or steal a different compression gauge and rerun the test?

[astate]

Thanks for thoughts.
All plugs were out, I was told it was in regular short journey use, but can't be sure.
I might try test again, it's a new Sealey gauge so should be ok, maybe it was the way I was using it, never done compression test before.
I thought the readings would go up when oil added.
I think there is some blow by, hence the oil splatter.
I want to keep it as a rolling resto, so wanted engine running as best as I can whilst sorting doors out etc.
Thank you
Jh

[RobPearce]

I'm also suspicious of the compression readings going down, and of the "with oil" ones being exactly the same for all four.

A little bit of blow-by is normal, hence the crank case breather. The oil splatter is also very common.

If it was in regular short-journey use, it may just be a bit coked up. Sometimes a good blatt will recover some of the missing power.

[warphi1970]

are you cranking the engine the same amount of turns for each test i have always used 3, it is really un-usual to get a reduction when adding oil.

i may be telling my granny to suck eggs but here goes.

Technically, You should do this when the engine is hot, But you can do it when the engine is cold. A hot engine would probably read a few pounds more, but a cold reading will tell you what you need to know.
Run the test on each cylinder one by one.
All the cylinders on an engine should be within ten pounds of each other.
In other words, a four cylinder engine reading 150 PSI, 149 PSI, 147 PSI, and 152 PSI would be considered good. If it had 135 PSI, 149 PSI 150 PSI, 150 PSI, it would not be considered good. Something is starting to go wrong with that first cylinder. OK, you have a cylinder that reads low. Is it valves, head gasket or rings, leaking that compression ?

The following are the steps to take to get correct readings
1. Make sure the battery is fully charged. A battery with a low charge will give low compression readings because of reduced cranking speeds. Youshould maintain 380-420 rpm for a good cranking rpms.
2. Warm the engine slightly for 10-15 seconds to produce metal expansion and to reduce oil drag. A cold engine will give slightly lower readings. But if you take cold readings everytime, it will give you the same baseline.
3. After the engine is warm shut it off and remove all the spark plug wires.
4. Remove one spark plug.
5. Block the throttle open.
6. In turn, carefully insert/thread the compression gauge in each cylinder and with the starter, turn the engine over for five seconds roughly or until the compression gauge has reached its desired target PSI reading.
7. Reinstall spark plug and Repeat these steps for each cylinder.
8. Make a note of the readings from each cylinder. What was the pattern? Does the gauge pump up fast? Is the max reading obtained after five seconds? (Very important)
9. Check the spark plugs from the cylinders with abnormally low or high readings. look for carbon buildup or oil deposits.
10. Replace the spark plugs after each individual reading and torque them to the recommended specs.

Once you've got the readings, it's time to evaluate them to determine just what the future of your engine is going to be.

If the gauge pumps up slowly, such as 30, 50, 70, 90, etc. to an almost normal reading, you probably have ring problems. A general rule is that a maximum reading should occur after two-three seconds. If oil is added to a low reading and the pressure improves, this will confirm worn rings. A persistent low reading generally indicates head gasket sealing, worns rings, scored cylinders or valve problems.

Oil lost through worn valve guides will not be determined through compression testing. Low readings can also be caused by a warped head and occasionally, two cylinders will have very low compression which can be the result of a blown head gasket.

It is important to remember that the addition of oil to the combustion chamber will not improve the compression readings if your engine has burned, warped or stuck valves. High compression readings can be the result of carbon buildup or head surfacing.

Generally, if the variation between the cylinders is 5 to 10 lbs., this is acceptable, but always check the specs in the manual. It would seem that equal pressure is necessary to have smooth running engine, but it's been found that with only 70% of normal pressure is enough for running smoothly. Also, manufacturers specs usually list a bottom line acceptable pressure and a good engine will usually read 20 to 30 psi over the acceptable readings.[/size]