352 Compression exam ??
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From: Mddl A MexCans
352 Compression exam ??
Ok I hope this was done correctly. removed all spark plugs, disconnected coil lead to dizzy, installed compression gauge on C#1 had my bro stand on gas pedal and hit the starter, highest reading was 120-122, same one 2-4, started opposite side at 8 and got 120+ as well on 8-7, 6 however was just a liitle shy of homebase (nada) is thsi possible ?
I noticed that the plug was black in comparison to the others, and # 5 looks same however # 5 tested 120+ as well, so I re tested # 6 and it maxed at 30psi. OK now I get the idle issue..
So is this normal of compression failure ?
I'm wanting to define the cause of the issue... and assume it's valve related.
I noticed that the plug was black in comparison to the others, and # 5 looks same however # 5 tested 120+ as well, so I re tested # 6 and it maxed at 30psi. OK now I get the idle issue..
So is this normal of compression failure ?
I'm wanting to define the cause of the issue... and assume it's valve related.
Posting Guru
Joined: Jul 2003
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From: Colville, Washington
That is a sign of trouble
Did you try it with some oil added?? I really think you have a valve issue, the dark plug means that cylinder is not firing well(obviously) and the fuel builds up. It sounds like you will need to fix a cylinder head. You might try pulling the valve cover to see if anything is amiss with the valve on #6, but it really is academic, because the head will need to come off.
Did you try it with some oil added?? I really think you have a valve issue, the dark plug means that cylinder is not firing well(obviously) and the fuel builds up. It sounds like you will need to fix a cylinder head. You might try pulling the valve cover to see if anything is amiss with the valve on #6, but it really is academic, because the head will need to come off.
Fleet Owner
Joined: Sep 2005
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From: Lake Tahoe, Nevada
Get the dead cylinder at the top of it's compression stroke, then blow air in the spark plug hole. You will be able to hear the air escaping into the crankcase if the piston is bad, into the intake if it's an intake valve, or into the exhaust if it's an exhaust valve.
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From: Mddl A MexCans
I will try the air in the cylinder today and see what gives. Might pull the valve cover as well and look at the springs on # 6. With any luck maybe I'll find a broken spring..
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From: Mddl A MexCans
OK - update: the low cylinder is 7 not 6. I set the balancer to zero / dizzy on #1 and rotated crank with ratchet 540º until the dizzy was pointing at 7. Took the gauge of the tester line and removed the stem valve from the base fitting on test hose. Inserted the fitting into spark plug hole and connected compressor line. I heard air escaping and went to the tailpipe where it was coming out pretty freely. So before I decide to do something drastic..
1. How bad is it to just drive it until this can be remedied ?
2. Anything I should check before taking head/s off ?
TIA Redman
1. How bad is it to just drive it until this can be remedied ?
2. Anything I should check before taking head/s off ?
TIA Redman
Fleet Owner
Joined: Sep 2005
Posts: 28,609
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From: Lake Tahoe, Nevada
Smart way to do the test Redman.
When you have a bad exhaust valve, the flame leaking out is almost like a cutting torch. Over time it will erode the valve seat and if left long enough it will also damage the cylinder head.
When you have a bad exhaust valve, the flame leaking out is almost like a cutting torch. Over time it will erode the valve seat and if left long enough it will also damage the cylinder head.
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From: Colville, Washington
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Logistics Pro
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From: Mddl A MexCans
So if the spark was cut to that cylinder ? worse than the norm ? Considering the $$ to solve this stuff.. Maybe best to go with a 390 out of a F350 for $200.00 I found..but who knows as the history of it is unknown.. desizUnz!!
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From: Colville, Washington
You would be dragging a dead cylinder around, not good for wear, efficiency. That cylinder would still be receiving a fuel charge, so it would wash down the cylinder and contaminate the oil, as well as ruin that bore.
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