I need to do a compression test on my 67 200ci before I take it out to clean up the engine compartment. Can anyone tell me what kind of numbers I should be looking for? Sorry if this is a repost question but I've seen numbers ranging from 115 to 175. Also what kind of variance between cylinders is OK? Thanks for any response.
Compression Test
- Thread starter 67ride
- Start date
Your main concern is that the cylinders are all about the same. Lower compression motors have lower pressure in the cylinder that's why you see variances all across the board (115-175) I consider myself lucky when they come in through the 120-140 range. And you want the variance between cylinders to be no more then 10% So if your highest cylinder is 130 you don't want any lower then 117.
hope that helps.
-ron
hope that helps.
-ron
from 115 to 127 they are pretty darn close to 10% difference (126.5 is really 10%) close enough for me. Tell me about the conditions under which this compression test was run?
1. Was the engine cold?
2. Did you do it 'wet' or 'dry'?
3. How many times did you cycle the motor for each reading?
The numbers could be low for many reasons. Like
1. Low compression motor
2. Worn Rings
3. Valves not seating fully any longer
I usually have number 1 as my primary problem :roll:
-ron
1. Was the engine cold?
2. Did you do it 'wet' or 'dry'?
3. How many times did you cycle the motor for each reading?
The numbers could be low for many reasons. Like
1. Low compression motor
2. Worn Rings
3. Valves not seating fully any longer
I usually have number 1 as my primary problem :roll:
-ron
The engine hasn't been started in quite some time but has been well maintained. I wanted to get the test done before I pulled the engine to clean up the engine compartment. I let the engine cycle until the pressure gauge stopped increasing (at least four or five times, I don't really remember). Each cycle it would jump 20 to 30 psi until it peaked around 120. I'm not sure what you mean by wet or dry, but yes, the engine was cold when I did the test. Is that a bad thing?
Those numbers seem good to me, especially hearing the details. Is this motor new to you? Or did you drive it/ hear it run? If you know it was a 'good' motor I would figure its all good and not mess with anything except maybe some seals and gaskets if there were any sign of leaks. I would not pull the head but out of the car is the easiest time to do things like oil pan and rear main.
I have had this car since 1993, it was my first car. I drove it as my daily driver for over four years. I drove it periodically up until five years ago when I started doing some major suspension work. It has been garage kept since the day I got it. The engine ran strong and never had any problems with it at all. The engine has got some muck on it but no oil leaks and it didn't burn oil. I used to want to convert it to a V8 but then I saw the error of my ways and decided to stay with the six and put a t-5 behind it.
A "proper" compression test is done with the engine at operating temp, with all the plugs out and the throttle held wide open. The battery should be on a charger to maintain a full charge so the engine cranks at the same speed every time.
Run the test dry first and then add a tablespoon of oil to each cylinder and run the test again. Crank each cylinder the same number of times for the best results. I use 6 compression pulses, others use 5.
The compression test is, at best, an indicator of the comparable pressures developed at cranking speeds. A leak-down test performed at normal operating temp will give you much more information on the condition of the engine.
Tests run with a cold engine are a poor indicator of anything.
Run the test dry first and then add a tablespoon of oil to each cylinder and run the test again. Crank each cylinder the same number of times for the best results. I use 6 compression pulses, others use 5.
The compression test is, at best, an indicator of the comparable pressures developed at cranking speeds. A leak-down test performed at normal operating temp will give you much more information on the condition of the engine.
Tests run with a cold engine are a poor indicator of anything.
What PaulS said!! Motor should have been hot, take all the plugs out and OPEN the throttle plate. I personally disconnect the fuel pump inlet (no need to dead head the gas in the fuel lines and also disconnect the electric to the dizzy.
I one time did the "wet" test using WD-40, because I could spray it into the cylinder easily...WRONG! The oil was too light, it didn't give me a correct reading. If you do decide to try the test "wet" use good ol' motor oil. And like PaulS said, use about a teaspoon. The oil will burn off fairly quickly after the engine is started. It will produce white-blueish smoke for a few minutes.
The "wet" test is done to tell if the piston rings are leaking. In my expeience the pressure will jump a little when you add the oil regardless. If it jumps about 5 psi that's normal. If the increase in pressure is higher, then what the oil is doing is sealing around the rings resulting in better compression. Taht mean the rings are leaking
I one time did the "wet" test using WD-40, because I could spray it into the cylinder easily...WRONG! The oil was too light, it didn't give me a correct reading. If you do decide to try the test "wet" use good ol' motor oil. And like PaulS said, use about a teaspoon. The oil will burn off fairly quickly after the engine is started. It will produce white-blueish smoke for a few minutes.
The "wet" test is done to tell if the piston rings are leaking. In my expeience the pressure will jump a little when you add the oil regardless. If it jumps about 5 psi that's normal. If the increase in pressure is higher, then what the oil is doing is sealing around the rings resulting in better compression. Taht mean the rings are leaking
