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Engine rebuild or buy used engine?


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So I'm buying a Comanche with a 4.0 that currently doesn't run. A local mechanic had it and it didn't have compression in a cylinder or 2 and he put a new head on it ( brand new or new to the vehicle I don't know). Still didn't fix it. I also found out it went through the flood we had here in Oregon back in December of 07.

 

Now my main question is whether it would be worth a rebuild or not. Assuming the heads in good shape would a new bottom end be good enough? Maybe a whole used engine? The cost difference isn't huge, but the labor time is a bit.

 

I haven't gotten the truck yet so maybe when I get it and I pull the head it will be so crappy that a different engine will be my only option. I feel that a rebuilt engine would be a more worthwhile investment, but I want some outside opinions.

 

And would maybe boring out the cylinders some be a worthwhile investment? Would I even notice the difference?

 

Thanks.

 

-TyeT.

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I'm going to offer you just one meager opinion, starting with a question:

What are your plans for the truck? If all you intend is for casual road

use, I suggest you seek out a tight, used motor, with under 100k miles

if possible, and just transplant. That will likely be your "least cost" option.

Now then, if you're interested in rebuilding yourself, and have the time, the

tools, the talent, and the budget, you may prefer that option. BUT, fair

warning, you mentioned increasing the bore, and you could be on the

cusp of the very slippery slope of a modified engine. You could spend

many thousands of dollars, and then discover that more power requires

modifying any number of other parts of the truck. Be careful!! This is

highly addictive! Your wife, children, and possibly even your dog, could

abandon you due to your total focus on your truck alone. You will wind

up poor, family-less, and have only an awesome truck to show for it. Not

a bad trade - right? You have been warned. AND, welcome to the group.

 

You didn't mention what year and configuration truck you're buying, besides

4.0. Details please. Also, if the truck was in a flood, I have more concerns

than just the motor, and suggest you may be better off to keep shopping,

unless that truck is really, really cheap -like almost free.

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My opinion is that you will save a ton of money going used. Rebuilts are 1500+. Even if you do it yourself, machining costs are high. Tons of used JEEP motors around. Even if you go HO, which requires some mods you'll save. It's been done, thats the route I will go when the time comes.

 

Good advice above :agree:

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I plan on making it a street legal wheeler for the time being, but I want to eventually make it into a 100% off road machine. I'm lookin at either 33's with 4.10 gearing or 35's with 4.88 gearing. I also am getting a Chrysler 8.25 if the guy doesn't sell it before I get some money together.

 

I don't currently know what year it is and I don't know if anything is messed up other than the engine so far. I'm only paying $200 for it and besides the engine it's only missing the front clip.

 

And yes I do have to resources and enough help to rebuild it on my own. Half my family is mechanics. I think I'm gonna stay away from boring it after that statement too lol. I'm really just trying to get this truck together in time for some snow wheeling and of course mud.

 

I posted a little more info over in the build section too.

 

Just talked to the guy it's an 89.

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I'm getting ready to do a n HO conversion with a motor that I'm building from scratch (my 1st one) money, time, parts, more money,and more time, I could have easily bought a reman engine for all I've got into this one.

My suggestion is to find a cheap complete wrecked XJ for all the parts you'll ever need. So far I've bought 2, an 89 (paid $175 complete and runs like a top) whose motor went into the Chief last month, and a 95 XJ with AX-15 for $200. Both of these vehicles paid for themselves over and over again. Nice thing about XJs, they feed my MJs all the parts they'll ever need. Cheap too.

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So if all goes according to plan I'm gonna have $2,000 to $2,500 to spend on everything. I can get tires on a payment plan if needed so I don't have to factor them into the total for now.

 

I have seen master rebuild kits going for $500 on ebay and economy kits for $300. How much would machining be if I just needed to clean up the cylinders a little bit?

 

I'm trying to make this project into something I can say I built as much as possible. I have bought lifted rigs in the past and I want to instead be able to say I built this thing.

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Back in 03 I bought my TJ, which was hydrolocked. Had two rods snapped in half and had punched holes in the oil pan. The other four rods had nice arcs is them. It required a 0.020 overbore to clean up the cylinder walls. I simply rebuilt the motor and went on with life. This Jeep has no more power than any other stock 4.0. I now have 80k miles on the rebuild. The rebuild did cost me more than the temporary WJ 4.0 I had in there while I was rebuilding the motor.

 

If you have the skill and most importantly, the time, to rebuild I say go for it. It may be more spendy, but you will know what's going on inside the motor vs praying a used unit wasn't trashed.

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My opinion is that you will save a ton of money going used. Rebuilts are 1500+. Even if you do it yourself, machining costs are high. Tons of used JEEP motors around. Even if you go HO, which requires some mods you'll save. It's been done, thats the route I will go when the time comes.

 

Good advice above :agree:

 

That number seems a bit high. I got my rebuilt H.O. done at Blaine's. They will either rebuild yours, or give you a rebuilt off the shelf in exchange for a core. It cost about $850. Granted it helps that they are local and deal in very high volume, I'm sure.

 

And even with a knock, there is a high probability that your core is still good for rebuilding.

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