Replace a 258 in a 1980 j10 or what? - JeepForum.com
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post #1 of 11 Old 10-15-2021, 10:26 AM Thread Starter
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Replace a 258 in a 1980 j10 or what?

Can I replace a 1980 J10 cuin 258 with a 1994 4.0?

my 258 just bent 5 push rods. I am thinking that the timing chain jumped a tooth or two. I have not got the head off yet to see what damage is inside, but i am figureing that a piston or two smacked a valve so not only is the push rods bent but the valves are bent to.

I know a place that has a 4.0 that has been recently completely rebuilt that I can get for $500. so the question is What will work on a 4.0 such as intake/exhaust and motor mounts and bell housing?.

Then again if I am going that far with engine swap should I just put in a 304 or some other engine. I suppose I could look at a chev 350 but I am not a fan of the 10 MPG and also the additional cost of carb, exhaust, and the adapter to transmission.

So many dicission to make,

Suggestions would be helpful.

Thanks


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post #2 of 11 Old 10-15-2021, 11:03 AM
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As I said in your other thread about this, bent pushrods are not a reason to rebuilt or replace an engine.
It's highly unlikely your timing chain jumped any teeth...258s generally just don't do that, especially at only 75k miles. And even if it did jump teeth, the 258 is a non-interference engine, meaning the pistons can not hit the valves even if the chain fully breaks.
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post #3 of 11 Old 10-16-2021, 10:48 AM Thread Starter
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So why would 5 cylinders out of 6 has bent push rods. this is something I have not seen.

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post #4 of 11 Old 10-16-2021, 12:57 PM
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I gave a list of possible causes in your other thread in the FSJ section.
Multiple bent pushrods is probably from either extreme over-revving or the engine backfiring badly.
Or, you said in your other thread that the Jeep sat for 15 years. How did you go about starting it? If you just threw a battery in and cranked it right up without any sort of prep, some of the lifters may have been collapsed or the valves might have been stuck which could bend the pushrods...
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post #5 of 11 Old 10-16-2021, 05:01 PM Thread Starter
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Not sure how it was started but it was running when we bought it. dorve it home with out any problems about 60 miles except a leak from teh rear main seal. ran good. then we had a problem with bad old gas. and she would not run. then it would not start again.

I just pull the head and it looks good, cylinders look ok. the PO must have changed the timing gears and chain, they look new.

Right now I am stumped on what to do next. I do need to replace the rear main seal. so I can drop the oil pan and see where that leads me.

Engine has 87K miles original miles on it.

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post #6 of 11 Old 10-16-2021, 05:20 PM
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It's not very likely they replaced the timing gears/chain. At that mileage, they are like new. Those timing sets are famous for outlasting the rest of engine and usually don't need replaced until the engine is rebuilt. They are well sealed in their housing, so they always look clean no matter how many miles are on them.

And "bad old gas" is well known to cause backfiring (much like a bad tune). Backfiring is one of the potential causes for bent pushrods I outlined right from the start. Sounds like the head didn't need to come off. You probably just needed to slap some new pushrods in and flush the fuel system.

Some dude in your other thread kinda hinted at this....
Quote:
...At this point, even pulling the head may be overkill if it was just something like a mis-tuned engine was simply back-firing.
Figure out what caused it, you may not need to do anything more than replace the pushrods and tune it up.

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post #7 of 11 Old 10-17-2021, 11:23 AM Thread Starter
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Got some input from the PO. He did change the timing gears and chain as well as the cam and lifters.

So I am agreeing with you it must have been the bad gas and a back fire.

I re-looked at the push rods and only 3 were bent and 2 were just off the rocker arms. I was pissed and did not look that hard at them.

I still have the head off and going to pull the oil pan to replace the rear main seal. and I will then replace all the gaskets and seal in the engine and we should be good to go. I hope.

I am thinking thinking the ole jeep has been outside for 20 years setting in a field that now she is in a dry garage. she don't want to go outside again for a while. I have had 3 flat tires on it while it has been in the shop. lol

Can you think of anything else I should look at while I have her this far tore down?

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post #8 of 11 Old 10-18-2021, 02:09 PM
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I would check the cam spec. Sounds like you either have a bunch of collapsed lifters or flat cam lobes if you kicked out that many pushrods/bent pushrods when the lash went away. Depending on what cam was used, if it was a higher lift cam on a smaller base circle, that would require new longer pushrods as the 258 has a non adjustable valvetrain and could not be adjusted correctly for the new cam and would leave the pushrods loose to jump out/bend.
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post #9 of 11 Old 10-19-2021, 07:23 AM Thread Starter
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that does sound like an idea. I have it all apart, might as well check it it be on the safe side. 5 out 6 cylinders either bent or jumped out of place. there has to be something going on.

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post #10 of 11 Old 10-19-2021, 08:03 AM Thread Starter
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Quote:
Originally Posted by Fourtrail View Post
I would check the cam spec. Sounds like you either have a bunch of collapsed lifters or flat cam lobes if you kicked out that many pushrods/bent pushrods when the lash went away. Depending on what cam was used, if it was a higher lift cam on a smaller base circle, that would require new longer pushrods as the 258 has a non adjustable valvetrain and could not be adjusted correctly for the new cam and would leave the pushrods loose to jump out/bend.
I wonder if he got the wrong cam or the wrong lifters from the parts house? Sounds like a trip to Tacoma.

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post #11 of 11 Old 10-19-2021, 11:59 PM Thread Starter
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found the valves were stuck or sticking. head is off to the machinist to be cleaned up and repaired. Now get all the parts and pieces together.

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