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I performed a cylinder pressure check the other day on my 240Z. I'm concerned about the results. The first two cylinders were 140 psi. Three and four ranged about 125 to 135 psi. The last two ranged about 130 to 135 psi. What is the normal cylinder pressure for the L24's with twin SU's? The car runs fine but starts to smoke when idoling for a long period. Could the valve seals be leaking????
 

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on the L28 the book says from 164 to 178 psi. I think the compression ratios are close between these engines (stock anyway). You can check if it is rings or valve seals/seats by adding a small quanity of oil to the cylinder and checking compression again...if the pressure stays low, it is a valve issue, if the pressure gets higher...its the rings. Hope this helps.
 

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<b>On a 73 240Z....</b>

Last time I tested mine, they came in at 160 to 168. Your numbers sound low to me. How many miles are on the engine? it might be getting to be that time....

Good Luck,
Dennis
 

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Kevin are you running the stock cam??

If you are running a peformance cam and have not increased your compression ,your cranking psi will be lower than stock.
 

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<b>Thoughts on Valve Stem Seals</b>

Kevin,

The valve stem seals are not likely the cause of low compression. They seal oil from leaking into the combustion chamber via the valve stem. They have nothing to do with compression. The valve "seats" are where the angled portion of the valve seals against the head. This is where you can lose pressure.

The other advice (above) is all true and should help you determine the exact cause. I suspect it is your rings due to the relatively even levels across the cylinders. A bad valve would tend to show up in isolated cylinders. This is not definitive, but just "most likely", based on my experience.

By the way, your readings are almost exactly the same as mine on a '77 280. I knew this when I bought it and figured at the time I would be rebuilding it soon.

Good luck!
 

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<b>RE: WHAT IS THE NORMAL CYLINDER PRESSURE FOR L2

Kevin,
I think the group's right, your motor's in a bad way. Compression's supposed to be highest in the L24, and Gary Gent said his L28 books in at 164-178. That means yours SHOULD be in the 175-185 range. That's quite a bit, but try the techniques the guys gave you anyway. Good luck...
 
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