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post #1 of (permalink) Old 06-03-2001, 11:41 AM
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Compression Spec.s on a 258?

Anyone happen to know what psi compression I should be getting out of each cylinder on my inline 6 258? It's in my '80 CJ7. Just wanting to know how good of shape it's in before I take it to Moab in 4 weeks!
Thanks

Jed
80 CJ7 258w/TR,Holley carb,5" lift,33x12.5's.
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post #2 of (permalink) Old 06-03-2001, 12:15 PM
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Re: Compression Spec.s on a 258?

If your compression on all cylinders is within 5% or so of each other and none is lower than about 125, you are still OK.

Brad
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post #3 of (permalink) Old 06-03-2001, 12:24 PM
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Re: Compression Spec.s on a 258?

yeah i agree brad-
my 87 has 150-160 in all cyl's
never could find the compression spec in my chiltons but it does list the 2.5 and the 4.0 at 120-150 PSI.

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post #4 of (permalink) Old 06-03-2001, 02:27 PM
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Re: Compression Spec.s on a 258?

I'm thinking of replacing my 258 in my 90YJ she is in bad shape the highest is 125 and the lowest is 95 so I'm thinking a nother 258 but I'm willing to consider others.

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post #5 of (permalink) Old 06-03-2001, 03:48 PM
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Re: Compression Spec.s on a 258?

For any of those that are interested, the recommended compression pressure for a 258 6-cyl. engine is 150 psi at each cylinder. Should provide a refrence to base your actual results upon at least.

--Digger--


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post #6 of (permalink) Old 06-03-2001, 04:17 PM
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Re: Compression Spec.s on a 258?

The real key here is the difference between cyls. Any more than around 5% is unacceptable.

Brad
ORC Land Use Section Editor
http://www.off-road.com/land
Vice-Pres. Rock Garden 4 Wheelers, Farmington, NM
http://rockgarden.rockcrawler.com
post #7 of (permalink) Old 06-03-2001, 05:11 PM
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Re: Compression Spec.s on a 258?

Great, that means I'm good to go, then. The cylinders are all 120 on the first revolution of the engine, and bump up to 150+ psi on the second crank. I replaced the timing gears and chain, fixed the air/fuel mixture screws, and it runs like a dream now!
The only problem left is the lifters (I think) are clacking rather loudly at times. . . I don't think there is anything I can do about this short of a rebuild, though, and I don't have the resources for that now. Anyone have a suggestion on other stuff to check before the big trip?
Thanks,

Jed
80 CJ7 258w/TR,Holley carb,5" lift,33x12.5's.
post #8 of (permalink) Old 06-03-2001, 06:21 PM
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Re: Compression Spec.s on a 258?

Motor mounts, all your fluids of course, belts and hoses, heck just go over the whole darn thing end to end. Also, get on a creeper and go under the Jeep, lay there for about 10 minutes just staring at stuff, grabbing and pulling on things, I do that about once a month, amazing what will suddenly jump out at you.

Brad
ORC Land Use Section Editor
http://www.off-road.com/land
Vice-Pres. Rock Garden 4 Wheelers, Farmington, NM
http://rockgarden.rockcrawler.com
post #9 of (permalink) Old 06-03-2001, 10:03 PM
 
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Re: Compression Spec.s on a 258?

I'll second that comment on laying under it and putting your hands on things. 3 weeks after being under mine, I took another look at it today. Turns out the 'core' of the starter was loose on the end that has the drive gear/bendix. Less than 5 minutes later and everthing was tight.

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