Cylinder leakdown test and compression test results
#611937
02/12/10 10:25 PM
02/12/10 10:25 PM
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Joined: Oct 2004
Posts: 480
Kentucky, USA
derekeh
OP
mopar
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OP
mopar
Joined: Oct 2004
Posts: 480
Kentucky, USA
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As some of you know ive been having trouble getting my 340 to run right for a while now. Again my 340 is a stock standard bore 1970 340 that has been reringed. The cam is a Hughes Engines whiplash cam. Anyways I done a cylinder leakdown test and compression test on all the cylinders today. Engine was first warmed up. I done the leakdown test at 100 PSI and with the rocker arms off. So anyways the results from back to front of engine to front are...
Passengers side:
-155 psi, 6% leakage
-150 psi, 18% leakage
-152 psi, 6% leakage
-160 psi, 8% leakage
Drivers side
-70 psi, 87% leakage
-176 psi, 7% leakage
-169 psi, 7% leakage
-160 psi, 8% leakage
I am wondering why two cylinders have considerably higher compression than the rest but it could be due to a cheap compression tester that I cant tighten down too well to the spark plug hole so it could be leaking. The cylinder with 87% leakage is an exhaust valve issue as I can feel the air coming out the tail pipe. Im more concerned with the cylinder that has 18% leakage. Is this too bad? And is their anyway I can tell why it is leaking? I wasnt able to tell by sound or feel if it was an intake or exhaust valve.
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Re: Cylinder leakdown test and compression test results
[Re: derekeh]
#611939
02/12/10 11:34 PM
02/12/10 11:34 PM
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Joined: Oct 2003
Posts: 2,309
South, FL
cudaized
top fuel
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top fuel
Joined: Oct 2003
Posts: 2,309
South, FL
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Do the heads have hardened exhaust valve seats?
Since the heads are coming off again, take the valves out and check the seats. Maybe you have to clean the seats and combusion chambers with a good wire wheel. Also wire wheel the valve stem and faces. Not to agressive, but to clean them up. See if they have damage.
I suspect either a burnt exhaust valve or fuel\oil\carbon deposits on the valve seat not allowing #1 to fully close.
There could be carbon deposits in the two higher compression cylinders. Causing erroneous readings.
Last edited by cudaized; 02/12/10 11:57 PM.
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Re: Cylinder leakdown test and compression test results
[Re: derekeh]
#611940
02/12/10 11:50 PM
02/12/10 11:50 PM
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Joined: Dec 2003
Posts: 5,314
Carstairs, Alberta, Canada
dave571
master
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master
Joined: Dec 2003
Posts: 5,314
Carstairs, Alberta, Canada
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Quote:
As some of you know ive been having trouble getting my 340 to run right for a while now. Again my 340 is a stock standard bore 1970 340 that has been reringed. The cam is a Hughes Engines whiplash cam. Anyways I done a cylinder leakdown test and compression test on all the cylinders today. Engine was first warmed up. I done the leakdown test at 100 PSI and with the rocker arms off. So anyways the results from back to front of engine to front are...
Passengers side:
-155 psi, 6% leakage
-150 psi, 18% leakage
-152 psi, 6% leakage
-160 psi, 8% leakage
Drivers side
-70 psi, 87% leakage
-176 psi, 7% leakage
-169 psi, 7% leakage
-160 psi, 8% leakage
I am wondering why two cylinders have considerably higher compression than the rest but it could be due to a cheap compression tester that I cant tighten down too well to the spark plug hole so it could be leaking. The cylinder with 87% leakage is an exhaust valve issue as I can feel the air coming out the tail pipe. Im more concerned with the cylinder that has 18% leakage. Is this too bad? And is their anyway I can tell why it is leaking? I wasnt able to tell by sound or feel if it was an intake or exhaust valve.
You have one obvious bad hole.
Keep it simple. The problem is obvious. 
I suppose, since you have to pull one head for sure, pull them both, and get the second checked out at the very least. If there is a problem with one valve, there could easily be problems with more. I'd be surprised if you still have a problem after you do some head work. Just make sure you look closely at some of the valve train stuff when you put it backtogether(lifter preload etc..)
As for the general numbers you are getting (around 150) that is absolutely fine. NOTHING wrong there. The relationship between cranking compression and compression ratio is not a concrete one. I have comp tested strong running actual(not advertised) 10:1 motor's with number's as low as 135 psi.
I have comp tested 10:! advertised motors, as low as 115 psi.
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