ailing 258 - how bad is it???? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 06-06-2001, 03:42 PM Thread Starter
 
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ailing 258 - how bad is it????

I have an '85 CJ-7 with a 258. unk mileage.
did the Nutter Bypass a couple weeks back (big improvement) and am still tweaking on ign timing and fuel mixture.
At about 700 rpm with the vacuum advance disconnected and plugged, the timing mark jumps between about 8deg BTDC to about 14deg BTDC. the jumping is rhythmic, not random. bump the idle up to about 1500 rpm and the timing mark jumps between about 8deg BTDC to about 10deg BTDC (still rhythmic).
I've never seen this happen before. Seems to me that it would mean something but I don't really know what. My first thought would be worn timing set. Anyone know about this?

maybe it is ready for rebuild and not worth nursing... ???
at cold startup, it always gets about 5-6 good whacks in before the lifters inflate and oil pres goes to about 45psi but drops as temp rises. at full temp, indicated oil pres is about 10psi at idle and about 25psi when cruising 55mph. sometimes at idle the lifters clatter like a room full of old clocks. sometimes quiet. sometimes the clatter fades in and out at random. the rear main seal leaks. the rear breather tube (that connects to the air cleaner) doesn't blow oil but it does lightly puff a white steamy smoke, more at higher rpm. goes through just over 3qts oil in 2k miles. mostly leaked out, I think, because it only makes tiny oil smoke from the exhaust. the drain oil at changes (2k mi) is black, thick and dirty but does not smell like gas. have not performed a compression check. I will, just haven't been able to yet. it always starts and always runs. power seems ok, but I don't know what it should be. ???

I'd be-a-thinkin this engine is showing some age and heavy wear. Are these symptoms death moans from a 258? I could give it new oil pump, timing set and gaskets/seals... should help a bunch. probably $200 in parts. Maybe I'd be better off using that money toward a rebuild or conversion. ???
what are some opinions about the AMC 258 when it gets to this point?

the engine is not my only concern, the Jeep needs other help too. the engine wasn't a priority, maybe it should be...

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post #2 of (permalink) Old 06-06-2001, 03:54 PM
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Re: ailing 258 - how bad is it????

Boy, that 2nd paragraph describes mine to a 'T'. I was just told (unsolicited) that I should start thinking on a new powerplant. Not right away but somewhere on the horizon. He said a new oil pump won't help much, the problem is that there is too much room for the oil to go (between bearings and such).

post #3 of (permalink) Old 06-06-2001, 04:29 PM
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Re: ailing 258 - how bad is it????

I think it is a common opinion that a 258 wil run for a long long time if it's got oil in it. [img]/wwwthreads_images/icons/smile.gif[/img] I had 195,000+ on mine before I replaced it, and it still ran ok.

If the jeep needs other important improvements, fix the leaks and keep running it. New valve cover gaskets, oil pan gasket, rear main, etc., aren't that much $. Of course, if the compression test says it's not good (like one cylinder really weak compared to the others), then I'd reconsider that. If all the cylinders read about the same, even if they are kinda low, and if the motor is solid, just tired, it'll run for a long time, in my opinion. Mine used to push so much oil out the breather that I rigged up a quart oil bottle catch mechanism to catch it all. I even had the timing chain get so loose that when I went to start it, it would turn a bit then stop solid (!) because it was trying to jump a tooth. She'll run a long time before things go bad.

Personally, I did the nutter bypass on my old motor, and wasn't impressed. I prefer the GM HEI much better.

Just my opinion.
Good luck
Pete

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post #4 of (permalink) Old 06-06-2001, 05:19 PM
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Re: ailing 258 - how bad is it????

The timing jumping around is probably due to a stretched timing chain. The low
oil pressure is probably just old worn bearings. My motor had these symtoms so
I put in a reman. long block with a high volume oil pump. It's the only real
cure. You can nurse it along, but sooner or later you'll need a new motor.

Gary
post #5 of (permalink) Old 06-07-2001, 08:30 AM Thread Starter
 
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Re: ailing 258 - how bad is it????

> Personally, I did the nutter bypass on my old motor,
> and wasn't impressed. I prefer the GM HEI much better.


I agree that better solutions exist for the BBD enigma.

But... the nutter completed in under an hour, did offer improvement and most important to my current wallet - it was free. No improvement in power or fuel economy. It will idle now, major blessing at startup/warmup. Much much less spark knock. Fuel mixture is closer to right.

Thanks for the info about my engine. It runs kinda OK now.
I'll replace some seals & gaskets than will be spending my time and limited dollars on more urgent needs, like the body tub which is held on by just slightly more than the fuel filler and gravity.

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post #6 of (permalink) Old 06-07-2001, 10:27 AM
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Re: ailing 258 - how bad is it????

My 258 is exhibiting some of these characteristics, but not as bad as what you describe. I am a relative newbie to this engine - what is this Nutter Bypass everyone is talking about?

post #7 of (permalink) Old 06-07-2001, 10:46 AM
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Re: ailing 258 - how bad is it????

Kerns;
Check out
[url]http://www.off-road.com/jeep/jnutter1.htm[url]
for an explanation of the "Nutter bypass"


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