Compression Check

[klone]

My warranty is just about up, so I took the Lotus in to get checked out. I have not had any serious issues, but just wanted to make sure everything was in order. My question is regarding compression. Where should my numbers be? I do not have them in front of me, but cylinders 1, 3, and 4 ranged from 191 to 195, while cylinder 2 was at 180. Is this a concern? I am not familiar with compression numbers. The search that I did brought up some compression numbers, but no real information. They were either higher or much lower.

Thanks in advance

[JLSELISE]

The actual number is not too important since it can vary with cranking speed, gauge accuracy and other factors. Cylinder-to-cylinder variations are potentially important, though, and probably should be less than +/- 5% -- about 10 psi for a 200 psi base line. So the 180 reading might be suspect. The problem, if it exists, could be rings or valves, and that can only be determined by a leak down test, which requires some specialized equipment and a good mechanic.

[klone]

The printout said there was a 6.x% difference. The dealership was not too concerned, but I wanted other opinions from the forums as well. Thanks for the input. I can look into a leakdown test.

[glb]

cheap, temporary test w/compression:

If low reading in a cyl, squirt oil into it and try again. If compression jumps up, likely it's rings.

Leakdown is the way to go.

[tesprit]

The compression reading you have for cylinder 2 may or may not be a problem. Have your mechanic do a full leak down test on your cylinders and if #2 comes in low compared to the others, then it is time to worry.

[JLSELISE]

Kind of semantics here, but it is a high leakdown (expressed as a percentage) relative to other cylinders that points to a problem.
Check this out for more info:
Leak-down tester - Wikipedia, the free encyclopedia

[tesprit]

Originally Posted by JLSELISE

Kind of semantics here, but it is a high leakdown (expressed as a percentage) relative to other cylinders that points to a problem.
Check this out for more info:
Leak-down tester - Wikipedia, the free encyclopedia

Yes, finding a high amount of air leaking past the rings and/or valves (high leak down) with a constantly maintained air pressure is the problem. Using a leak down tester, this shows up as a too low air pressure reading (too much air leaking past the rings/valves gives a lower than optimal pressure) compared to the constant air pressure being applied to the cylinder via a compressed air source.

[klone]

I have seen others have low pressure readings on cylinder #2, is this a known issue?

[Demonized]

Originally Posted by klone

I have seen others have low pressure readings on cylinder #2, is this a known issue?

Sticking valve due to "known" camshaft problem, perhaps?

[charliex]

cylinder 2 gets the most abuse, so its the one to show problems first.

[ChrisH]

Originally Posted by charliex

cylinder 2 gets the most abuse, so its the one to show problems first.

How does one cylinder get more abuse than another? Uneven air flow form the intake manifold?

[davecarama]

I looked up leakdown testers and it appears they can be had for $40.

Is it that difficult to do a leakdown test? I was planning on etting the tool and doing one myself this weekend on my Meeyotter.

[fishguy]

Originally Posted by davecarama

I looked up leakdown testers and it appears they can be had for $40.

dave,
i have been looking into getting one also.
$40 is pretty cheap. the ones i have been looking at are all ~$100, and usually you get what you pay for, and with tools skimping is frequently not a bargain.
the one i see from longacre looks pretty good to me.

[JLSELISE]

Originally Posted by davecarama

I looked up leakdown testers and it appears they can be had for $40.

Is it that difficult to do a leakdown test? I was planning on etting the tool and doing one myself this weekend on my Meeyotter.

Looking through the Wikipedia link I posted above should give you a pretty good idea what's required. In addition to the tester, you'll need a source of regulated air pressure of course. To do the testing, it's best to rotate the motor by hand with the valve cover off so that you can see when you are exactly at TDC (Top Dead Center) or BDC (Bottom Dead Center) on each cylinder you want to pressurize to determine leak down precentage. If the leak down is excessive, check for hissing air in the crankcase for an indication of a ring problem, or at the exhaust/intake for an exhaust/intake valve problem, or check for bubbles in the coolant for a head gasket problem.