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post #1 of (permalink) Old 12-09-2000, 08:48 AM
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Compression test results?

I just did a compression test on my 87 258. Spark plugs were 'dusty black'; running too rich?
Dry compression is: #1-161psi, #2-164, #3-133, #4-139, #5-141, #6-150
Getting some oil out of the valve cover at the PCV grommet. PCV is new.
I need some advice. Is #3 too low? What now?

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post #2 of (permalink) Old 12-09-2000, 10:16 AM
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Re: Compression test results?

If memory serves me correct , there should be only 10 % difference between the highest and the lowest cylinder reading . I`d be concerned about 3 & 4.


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post #3 of (permalink) Old 12-09-2000, 11:08 AM
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Re: Compression test results?

Thanks, Jeff. Yeah, 3 & 4 concern me, but it seems 1 & 2 are very high also. I do seem to have blowby oil in the ait cleaner and the rear seal has started to leak.
Maybe its time to look for another 258.

Butch

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post #4 of (permalink) Old 12-09-2000, 12:03 PM
 
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Re: Compression test results?

take the hose off of the compression guage, and hook it to your shop air at about 40 psi to start.
CHOCK THE TIRES, PUT IT IN NUETRAL

bring each cylinder to firing position, ( both valves closed) and screw the guage into that plug hole and pressurize, then listen for the leak, increase pressure if you need to, Id do this on each cylinder, you might have a bad head gasket or head sealing problem between 3 and 4.

youll hear the air hiss thru the exhaust, or carb, or bubble in teh radiator.



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post #5 of (permalink) Old 12-10-2000, 06:57 AM
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Re: Compression test results?

Thanks, Matt. Maybe a bad headgasket would also explain the blowby (high pressure in bottom of engine). I also get a little squirt of coolant if you rev the engine up to about 3500 rpm. The coolant comes from the intake gasket (new) area near #3 & #4 cyl.
I don't have a compressor, guess I'll have to take it to a mechanic.
Thanks for your good advice!
Butch

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post #6 of (permalink) Old 12-10-2000, 09:46 AM
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Re: Compression test results?

i'm rebuilding my buddy's engine right now and his cylinders were rated at 170 psi.his cylinders were running at about 105psi. we took the head off and every cylinder had oil blowing right by his rings, you turn the engine over by hand and as the pistons hit the bottom stroke, you could see the oil run back down the cylinder walls like running paint. the blow by was pretty bad.a rebuild book on your engine will tell you what your compression is suppose to be at and then it's not suppose to drop below 10% of that.don't forget that if your valve seats are bad your compression is going to be bad too. i hope this helps you some Gary

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post #7 of (permalink) Old 12-10-2000, 09:52 AM
 
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Re: Compression test results?

most that ive seen with some actual miles on them will have a littel blowby, the coolant at 3500 RPM is probably a headgasket.

Id guess you have some ring wear coupled with a bad head/headgasket sealing problem.

the ring wear may/may not warrent a rebuild.

good luck!


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post #8 of (permalink) Old 12-10-2000, 04:46 PM
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Re: Compression test results?

Well, I know what I have to do now. Wet compression test, leakdown test and new head gasket.
Thanks guys, I appreciate your williness to help!
Butch

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