Engine Overhaul.

Hi all, I’ve dropped my engine off at my trusted mechanic for a rebuild. The condition of the motor is much worse than I had expected and it needs pretty much everything redone.

I’m not sure if the engine is original to the Jeep or not. Engine code dates it as a 70, Jeep was built in April of 71. The rebuilder said it had previously been rebuilt, but poorly. Two of the cylinders have pitting. The pistons are 30 over.

I’m leaning towards doing the full rebuild but wanted opinions on rebuild vs. remanufactured Long Blocks vs newer model engines that would bolt in with minimal modifications.

I really like the 225 and long term I would like to try fuel injection, electronics ignition etc.

I always appreciate the thoughts this group contributes.

 

What do you call minimal? A 225 from a Buick car will drop in, as will the later 231 in odd-fire or even-fire form. 231 pistons are 50-over from 225 and supposedly can be used in a 225 rebuild. 60-over should also be easy to obtain, and ok in a conventional gray iron block like this.

I get the impression that used 231s aren't that plentiful today. The 4.3L V6 from a Chevy is a popular swap to these Jeeps now, but most would not consider the changes from a 225 minimal.

The only difference between rebuild and reman is the factory setting. A reman takes used parts from possibly different engines and builds a refurbished engine. Rebuilt typically means using your block and refurbishing it.

What does your mechanic want to do? Usually installing a reman is a pretty good job for them.

 

Thanks very much for the reply. The Mechanic is great and will do whichever I prefer, finish the reman long block or machine and rebuild my engine. It sounds like the advantage to rebuilding my engine would be new parts. They would try to go 40 over on all cylinders to get the bad spots out of the two cylinders. He mentioned a reman engine to save me some money.

So a 231 odd or even fire would bolt up to the frame, transmission without any modifications? Would the a new engine like the 4.3 V6 with fuel injection need different frame mounts and a Chevy bell housing? I have the T14/D18 that whichever engine I choose need to match up with.

 

Just to add, the mechanic also said they may need to go 60 over to clean up the cylinders. The cost of the rebuild with parts and machining could approach $4K.

 

A reman or a rebuild would be equivalent in terms of new parts. The pistons are the most expensive item in the parts list. Any engine that's been in service for a while gets bore taper when the rings erode the cylinder walls. New oversize pistons are needed to straighten the cylinder bores and provide like-new longevity for the refurbished engine.

If you hone the bores and keep the old pistons, that's often called an overhaul rather than a rebuild. If you reuse the pistons without straightening the cylinders, the refreshed engine won't have the same longevity as an actual rebuild. Again, an engine rebuilt in a factory ("remanufactured") will be made from used blocks and cranks and rods and heads in the factory stock. The reman and your mechanic's rebuild will get the same bunch of new parts - pistons, rings, bearings, lifters, cam, timing set, oil pump, gaskets ... likely other stuff I'm overlooking.

The 231 has been covered a lot in old posts - you should search, read, and do your research if you are interested in this. I'm not the right guy to comment on this, since I have no personal experience with the Buick V6s other than my dealership days.

If you have a '70 or older 225, the Chevy can use the same transmission adapter with a Chevy bellhousing. That's all the compatibility AFAIK - everything else will have to be new - mounts. plumbing, electrical, etc. Again, better that someone with personal experience here should comment, and you can do your own research by reading old threads. Lots of threads to read.

 

Thanks so much for the reply. The remanufactured engine is going to end up being considerably less expensive than the machining, new parts and whatever of my existing motor.

My heart is leaning towards having my engine Remanufactured by the local machine shop and builder, but my wallet is considering the remanufactured option. Although I don’t know that my engine is original to my Jeep since it’s. 70 and the Jeep is a 71. Anyway, it’s original to me since it came with the Jeep I Bought 16 years ago.

I appreciate all the input. I’m going to sleep on it, toss a coin and see what my mechanic thinks. I prefer to stick with the 225 since that’s what the thing came with. I’ve just got to give more thought to redoing mine vs going the reman route. Boils down to money like most things in life.

 

This isn't necessarily true. If you buy a budget reman, you're likely to get used valves that have been machined down a bit thin, valve seats that may be machined deeper into the head than ideal, knurled rather than replaced guides, possibly worn rocker arms .,..etc. The heads are more effected by cutting corners than the block. Some remanufacturers replace all this stuff and do very quality work but you need to do your research.

One advantage to have a trusted mechanic do the rebuild is knowing exactly what was done.

As for a 231, yes it's a direct bolt-in to the transmission and motor mounts. There are few differences that may or may not cause issues:

• The 70's V6s use the larger bore 2GC carburetor. They typically have electric chokes, your old air cleaner will not fit without an adapter, and the fuel inlet is in a different location. They have a different bolt pattern on the intake manifold, so you need to swap on a 225 intake if you want to use the original carb.
• All 231s come with EGR built into the intake manifold. This can be disabled by making a plate to block it off.
• All the 231s come with HEI ignition which is nice.
• The 231 water pump is a about an inch longer (with a deeper pulley so the belts still line up). Depending on your radiator, this may cause the fan to be too close. The 225 water pump and pulley can be used to solve this,
• The angle of the oil filter is slightly different and can cause clearance issues with the lower radiator hose. Using the 225 oil pump cover if you can find a good one solves this.
• You can use your heavy Jeep 225 flywheel on the odd-fire 231s, but you can not on the even fire 231s. They have different balance.
• Starting in 1977 (I think), they changed the head casting and the valve cover mounting surfaces are at a steeper angle more like a small block Chevy. They are closer to Horizontal on the older V6s so depending on the 231, it will be visually different.
• The heads are not interchangeable between a 231 and a 225. The oiling system for the rocker arms is completely different.
• Stock, the 231s typically make less power than a 225 due to a compression ratio of 8:1 vs 9:1. This can be changed during a rebuild.

Here's a picture of the '77 odd-fire 231 in my '69 CJ5. It was there when I got it:


When I switched to a thicker Champion Aluminum radiator, I needed to use the shorter 225 water pump/pulley with a 1/2 spacer:


My oil filter rubs on the lower radiator hose, so I've got another chunk of hose zip-tied between them as a rubbing block:

 

I see two advantages to the local rebuild - 1) you get to pick and choose the brand and quality of the new parts. The factory-built engine will come as a package, though some builders like Jasper (?) give you some choice there. 2) You assign the measurement and assembly to someone you trust.

For your mechanic, depending on how much he can do in his shop and how much he has to send out, the factory-built engine has some advantages. The R&R process should be something he can do quickly and economically. He still get the profit from all the might-as-wells that go along with this. I'd expect the main advantage - he off-loads any liability for the rebuild quality on the factory. If there's a problem, the factory will cover his time to fix it (he is a certified mechanic, so no issues there), and any warranty comes from the factory, not him. Like I said, I'd think this is a pretty good job for him. The customer is happy too, because the factory engine costs less than the local rebuild.

 

Regarding the budget rebuild, you could have the heads done locally and buy a factory short block.

In my experience, it's really hard to get cost savings from your local shop doing the heads. Again IME, up-charges on heads are the norm. I know that every set of heads that I sent in came back with "advise knurl and surface." I measured my personal heads for flatness, and they were fine, but the shop advised surfacing (which I declined). New exhaust valves were often recommended. This is money in the shop owner's pocket. They will be happy to spend your money.

There is a spec for this stuff, if the shop takes the time to measure.

 

Agree that buying a reman short block and doing the heads locally can be a decent compromise. The heads are where most corners are cut on a reman.

 

Between 3-4 k is about right. My OF231 runs extremely smooth, spend the money to have the rotating assembly balanced. Personally I would avoid the 75-77 of 231 it's getting a little more difficult to source cams and heads these last few years support is dwindling. The first year even fire ( late 77,78) has a couple quirks. Even fire 231 79 and up generally has wide compatibility up through the engines run. Good take outs can still be found ( 3-4 here on FB marketplace at the moment)The only downside is the manual transmission flywheel is a little spendy for the even fire.
Solid advice by Fireball and Timgr.

 

Thanks, great information! I love the help and support of this site!

 

Regarding an engine rebuild, what's the fun in having someone do it for you? I'd do the machining myself if I could afford the equipment and the time needed to learn!

Tom Monroe's book is a good primer if you want to learn more. https://www.amazon.com/Engine-Builders-Handbook-Tom-Monroe/dp/1557882452 Except for the unusual firing syncopation, the 225 is a good ol' USA iron block engine like all yer Chevies and Fords. Nothing unusual there.

 

Update, I’ve decided to move forward and have the rebuilder rebuild it. I would really love to try it myself, but haven’t ever done a complete rebuild myself. I’ve got another Jeep project coming up and I plan to have that block machined and I’ll give the rebuild a try.

The rebuilder is truly an expert at what he does and I feel really good about putting this in his hands.