Cylinder compression test

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Marcelo Dart BR

Marcelo Dart BR

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We tested the compression of the cylinder #3 on my 318 and it showed 70 psi. The motor is fresh, it has about 350 miles yet, has a relatively big solid cam and the valve lash is not perfectly adjusted.

Is it normal?
 
Marcelo Dart BR said:
We tested the compression of the cylinder #3 on my 318 and it showed 70 psi. The motor is fresh, it has about 350 miles yet, has a relatively big solid cam and the valve lash is not perfectly adjusted.

Is it normal?
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I would say 70 psi is way to low.
Bad gauge or you need to get a leak Down tester and find out if its valves or rings.

If its idles good, and runs good, i would guess its the gauge!
 
How much pressure would be acceptable?

I'm worried now, the engine idles and runs fine. Could the cam duration or valve lash cause that? The cam is 241 @ 0.050.
 
You must have a bad gauge. @70 psi you would have a miss at idle at the least. What do the other cylinders read? Try another gauge.
 
SGBARRACUDA said:
You must have a bad gauge. @70 psi you would have a miss at idle at the least. What do the other cylinders read? Try another gauge.
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x2
if it only had 70 psi it wouldn't be fine at a idle.

A compression gauge is really only for comparison between cylinders. so if you don't get to hung up on the numbers, you could test all the rest and compare.

How are you using the compression gauge? if your only letting it hit compression once, 70 is probably all you would get!

I always make it hit 4 time before i read it! some will say to go more and some with say less, but as long as you count the same each time and compare with the rest of the cylinders..........You will find if you have a bad hole or one cyl that has much lower pressure.
 
All spark plugs should be out, throttle should be held wide open and the engine cranked until the needle on the gauge stops moving (about 6-10 seconds).
 
OK, the spark plugs were on, the throttle was closed and I just cranked for 6 seconds.

I think I find my problem... but I want to try the right way.

Thank you guys for the help!
 
1)First and foremost use a quality gauge.
2)Remove all the plugs
3)remove coil wire
4) block the throttle wide open
5) check each cylinder for 4 compression strokes
6)record the results and post them here.
One other thing, a cylinder should attain 80% of its value on the first compression stroke, this is a good indicator of the condition of your engine.( rings,valve seal,cylinder walls). In other words if your reading after 4 stokes is 150, it should read 120 in the first compression stroke.
 
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