Spark Plug and Compression Test Talk and Evaluations

[89Suburban]

Ok, here's a shot of my plugs. They are in order just like facing the motor. Right side is 1,3,5,7 and left plugs are 2,4 & 8. #6 refused to come out easily.

You must be registered for see images

Here is 2 close ups of the 2,4 & 8 going left to right in the pic. Note the broken insulater tip on the #2 plug.

You must be registered for see images

You must be registered for see images

Here is a close up of the right bank plugs 1,3,5 & 7 going right to left in the pic.

You must be registered for see images

 

[Old77]

 

[89Suburban]

Here is compression on # 1 cylinder.

You must be registered for see images

Here is # 3 cylinder. I had to stop there because my battery apparently took a ****, I picked up a new one this morning, and a new spark plug.

You must be registered for see images

 

[Old77]

What is the PSI supposed to be?? Is there a range of pressures or is it supposed to be right around 90?

 

[89Suburban]

The damn #6 plug comes out about a 1/4 turn or so then starts jamming up. I tried running it back and forth like 10 times and got about 3/4 to 1 turn out of it but still won't come out. Maybe it's corroded on the inside??? I don;t know, and I am afaid to strip the threads forcing it.

 

[89Suburban]

What is the PSI supposed to be?? Is there a range of pressures or is it supposed to be right around 90?

I looked in my ****** ass Haynes manual and I couldn't find the spec. Anybody here know?

 

[davbell22602]

350 carb engine for psi? I'll look in my HP chevy SB book.

 

[HotRodPC]

I'm thinking 90PSI is going to be good on a low compression 8.0- 8.5:1 motor. More importantly is if all cylinders are within 20% of each other. 65 is obviously a little low, but that could also be cuz the motor wasn't cranking good enough. The proper way to do a compression test is to pull all the plugs, then test each cylinder.

 

[HotRodPC]

Those plugs really aren't looking that bad either. Good color, the electrodes don't look severly worn or rounded off, no sign of overheating or detonation, no sign of oil or gas fouling.

 

[davbell22602]

Here's what the HP Small Block book says

105-120 8/1, 120-135 9/1, 140 or so for 10/1 for all CR engines. Pressure readings more than 30-35 below the these readings means rings or valves or both maybe tired or sick

 

[Old77]

^^^this won't be good news for 89Sub I don't think but maybe like HRPC said the low PSI was due to the bad battery and not getting good crank....

 

[HotRodPC]

No doubt its a tired motor, but a few things can cuase low compression. Tired motors can still go a long way, just lack some of the original power they once had. His guage could also be inaccurate. But still, even if the guage is inaccurate, he can still measure how uniform each cylinder is to each other. I still think its a good idea to do these tests though. If he finds its to tired, I wouldn't waste money on getting the head gaskets changed. As long as the plugs aren't fouling, just keep an eye on the coolant level, a good on the temp guauge and be saving funds for a motor. Believe it or not, saving the $200 in labor and $80 in parts, since 89S can probably do a long block motor swap himself. Personally, I'd rather do a motor swap than take those heads off.

 

[HotRodPC]

http://www.newgmengines.com/12520270.html

The LO5 Crate motor !!!

 

[Old77]

I agree with that and refer back to one of my other posts on a different thread stating to find a good, used but cheap 350 on CL and slowly build that up as funds allow while babying the current motor along. Then when the other motor is ready swap them out some weekend and you will be good as new you should be able to find a good core 350 for fairly cheap!!

 

[davbell22602]

http://www.newgmengines.com/12520270.html

The LO5 Crate motor !!!

My 88 C1500 has one of those target crate motors.