258 rebuild thoughts

[Zorm]

Ok, I have been hearing a low knock in the engine for a little bit now. So my thought is to try and find an older 258 short block (maybe pre 80s) and rebuild.
Next question is, since I will be doing this over a little time, should I get, even if not needed, bigger pistons, get the block bored out anyway for maybe more umph? is there anything else I can do? I was also thinking about a different camshaft, any thoughts on what type?
I will be keeping the HEI dizzy, the 4.0 head and will be putting a Holley pro-jection on, so if there are any thoughts of how to beef up the lower end please let me know, and no, I will not put a 360 in.

thanks

[Blue & Gray]

As far as the bottom ends go you have some options. You could run the earlier heavy crank (12 counterweights) for a bit more beef. It doesn't rev high but it moves with some authority. The later cranks are all 6 counterweight and feel about the same, naturally they spin up alot easier but because of that I think they lack the longevity of early 258's. There's a lot of steel lost in the crankshaft in the later years.



I would get my block/crank work done first. Then you know what you need an you only buy once.


Comp Cams has quite a few grinds for the 232/258 family. There's a few more who sell bumpsticks. I think anything is better than stock, which is gutless really.

[Fitzworld]

Seems that the early models had 7/16" head bolts and then they went to the 1/2", so I not sure that the early heads would work on the latter block without mods.

[tgreese]

The large and small bolt hole heads are interchangeable with either some machining (enlarge the holes to 1/2") or with spacers (7/16" bolts in a 1/2" head).

You may or may not need pistons. The best way to decide is by measuring the bores at the top and bottom for taper. I forget how much taper is allowed, but I'd guess it's between 0.005" and 0.010" ... I'd use cast iron rings on old pistons, to minimize additional wear of the bore and for easy break-in.

How much you do really depends on how close to factory-fresh you want the engine to be. The only way to eliminate bore taper is to rebore, and then you'll need pistons. Pistons are the single most expensive item of a rebuild, so not replacing them may be fine for a hobby car that won't accumulate a lot of miles.

Boring the cylinders won't make any difference in "oomph." The change in displacemnt is trivial. It only matters to longevity of the rings.

[bushwood44]

What about a 401?:)

[Zorm]

don't tempt me bushwood44, then again I would need to change out the tranny and xfr case too

[mdill]

4.6, 4.0 Cores are cheap enough, MPI would be great, but it is not looking real cheap/easy to get my 2005 4.0 setup in the 79 Cherokee.
But no reason a Carb and your HEI would not be happy on top of 4.6L
What I am finding is so far Pre 1995 EFI/MPI Jeep setup is the most supported, but even then no one has hacked the Jeep CPU that I have found yet.

Mike D.

[Al Johnson]

You could always build a stroker with your crank and a 4.0 block and head. Or just put on a 4.0 HO head for way better performance at minimal cost.

[69 Gladiator]

If you are needing more umph , larger displacement is the easiest way to get it. I like what Al Johnson suggested if you go that way, stroker.
If you like your engine just check the codes and replace the bearings if the crank mics out good and your bores aren't excessively worn. Your low knock could be piston slap.

[Zorm]

Ok, here is another thought, I already have the 4.0 HO head on the 258, is there something I can do the the 258 kinda like the 4.0 stroker thing? Like V-8 pistons or something?

[tgreese]

Ok, here is another thought, I already have the 4.0 HO head on the 258, is there something I can do the the 258 kinda like the 4.0 stroker thing? Like V-8 pistons or something?
To make a stroker, you need a different block. A stroker is a 258 (4.2L) crank in a 4.0L block. Combining these parts makes a 4.5L (ca 274 cid) engine. If the 4.0L block weren't available, you might think about punching out the 258 block and running custom pistons, but that would be way more money than changing to a 4.0L block.

There's a whole forum now about stroker engines: www.jeepstrokers.com (http://www.jeepstrokers.com) You might also want to convert to the 4.0L MPI; that would provide a big power boost over most carburetors.

[mdill]

There is not enough meat in the 258 block to punch it out for a 4.6, way cheaper to go with the 258 crank, 4.0 block/pistons and make 4.6, you will have to go to a electric fuel pump though as the 4.0 block does not have provisions for a mechanical pump.

Mike D.