Compression test, your thoughts?

[vling]

Went to go see an early 71 240z today, did a compression test and got

1 179

2 168

3 163

4 170

5 167 Exhaust(?) valve was stuck open for the first couple tries (0 pressure). Took off the valve cover and popped the spring back on right and got the 167 reading

6 200 why so high??

The engine is a L28 N42 block and early E88 head with SU carbs, been sitting for 2 years and I had to test it cold because the car doesn't run (no fuel)

ps. What can I do to solve the valve stickiness?

[Carl Beck]

Get the car running. Drive it for a few hundred miles... then repeat the test. If it hasn't ran in two years and wasn't near normal operating temp.'s a compression test will actually tell you nothing..

FWIW,

Carl B.

[esprist]

Went to go see an early 71 240z today, did a compression test and got

1 179

2 168

3 163

4 170

5 167

6 200 why so high??

As Mr. Beck said, proper procedure should be taken.

Here is the basic procedure:

1. Engine at normaly operation temp.

2. Wide open throttle(Max air & no fuel from carbs)

(*Disable fuel pump if equipped)

3. Battery fully charged.

4. All the plugs out.

5. Now do compression test (Dry)

6. Sqirt little oil into the cylinder, and do compression test (Wet)

Now here is the deal that many people misunderstand about compression test.

The most important thing about compression test is variations. All the cyclinders should be within 15% in variation.

High compression means there might be carbon built up as well.

If compression jump up more than, lets say, more than 20% in wet test, you have leaky rings. If there is about 15% in difference in wet test, it is normal.

If you have low compression, and does not make any diffeence after dry and wet test, I urge you to run Cylinder leak test and diagnose it farther for:

-Intake or Exhaust valve leak

-Head gasket leak either into water jacket, or between cylinder (This case

to cylinder side by side should have same low comp)

Now getting back to your case here, go over alll the procedure above, especially dry and wet result.

Your cylinder #1-5 look totally fine in numbers and variation until you see#6.

There might be a possibility that #6 being in good shape while the rest being weak. If compression of #1-5 go up to 200 in wet test, while #6 goes up by15% or so, you have leaky rings. Considering its age, 200 is normal due to carbon built up.

Esprist

[vling]

Thank you,

Carl - will do

Esprist - I will do the wet test next time I see it.