Spark Plug and Compression Test Talk and Evaluations

[HotRodPC]

http://www.jegs.com/i/GM-Performance/809/12568758/10002/-1?parentProductId=753961

Jegs Crate GM TBI Motor. $1799 + $159 truck freight. $1958

 

[89Suburban]

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.

I had all the plugs out except for that stuck #6 plug. The battery f'd me, I knew it was on it's way out, when you cold start it it drops down between 8-10 volts, but I got a new and bigger and better battery this morning so that issue is covered. I'll try again this weekend to do the comp tests and see what all the cylinders read. Anybody know how I should tackle this frozen spark plug? Maybe I should just leave it in there. Just like I should have left that phukin frozen thermostat housing bolt alone.

 

[89Suburban]

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.

Yes, it does not show any sign of antireeze on them, I don;t get it, unless it's the olug I can't get out.

 

[89Suburban]

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

Sumbitch.

 

[Old77]

Just think...you LOVE wrenching!!!

 

[89Suburban]

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.

You know what else, my ****** ass Haynes manual says to squirt some oil in all the cylinders before you do the test, which I didn't do, so maybe I should do that too...

 

[89Suburban]

Just think...you LOVE wrenching!!!

I was ready to kill last night when I saw that 65 psi reading, and the battery going dead, and , and the spark plug, it's stuck and wont come out, and, and it's cold. That's too much bad stuff all at once.

 

[RetroC10Sport]

You know what else, my ****** ass Haynes manual says to squirt some oil in all the cylinders before you do the test, which I didn't do, so maybe I should do that too...

That's why it's a ****** haynes manual, no you don't do that.

put oil in a low cylinder, if the reading is the same it's the valves, if it's higher it's the rings.

squirt some PB Blaster in plug no. 6 with it out as far as it will come then run it in and out a couple of times. after it's out, chase the threads with a tap.

 

[HotRodPC]

You know what else, my ****** ass Haynes manual says to squirt some oil in all the cylinders before you do the test, which I didn't do, so maybe I should do that too...

NO, DO NOT Squirt the oil in just yet. So you first take your readings just as you did, with all plugs out.
Then, if you don't like the readings, you squirt a shot or 2 of oil in the cylinder and test it again. If that raises your reading, then you know your rings are tired since the oil is taking up space for your rings. If it does NOT raise you reading, then you compression loss is due to valves, valve seat or valve guide issues. But, it is likely your compression will be a tad higher than the normal dry test since you do have oil in your crankscase. So the manual is trying to give you real operating compression, but its not a good idea for purpose of diagnostics, if that makes sense at all.

 

[89Suburban]

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.

I totally agree. I aint dumping money into this motor, and I aint tearing into the heads. I am just gonna run it and try and save some money for another motor I guess.

 

[HotRodPC]

That's why it's a ****** haynes manual, no you don't do that.

put oil in a low cylinder, if the reading is the same it's the valves, if it's higher it's the rings.

squirt some PB Blaster in plug no. 6 with it out as far as it will come then run it in and out a couple of times. after it's out, chase the threads with a tap.

Dammit, you muthafucka !!! You beat me by 2 minutes.

 

[89Suburban]

That's why it's a ****** haynes manual, no you don't do that.

put oil in a low cylinder, if the reading is the same it's the valves, if it's higher it's the rings.

squirt some PB Blaster in plug no. 6 with it out as far as it will come then run it in and out a couple of times. after it's out, chase the threads with a tap.

 

[89Suburban]

Dammit, you muthafucka !!! You beat me by 2 minutes.

Hahahahaha!!!!!!

AGood **** guys, it really helps to have pals to help me through this **** and point me in the right direction.

 

[Old77]

 

[HotRodPC]

Yep, I'd also do the PB Blaster as suggested in the hole. Its not going to get down in there right away, but it will seep in as you slowly remove it. Just work it in and out as mentioned slowly, and bring it out a hair more each time til you feel it give way if it ever does. Also, it probably would not hurt to do with while the motor is fairly warm The heat might help a bit.