Re: 258 for AMC Spirit

[farna@xxxxxxx]

As Matt posted, only a 1971 258 (or any pre 72 AMC six) would be a problem. All others, including the 4.0L, have the same mounting points whether in a Jeep or car. There are four bolt bosses on each side of the block in a trapeziod pattern. Cars use the forward three, jeep the rear three. Just save the metal plates that bolt to the side of the block.

Since you're building an engine, you might want to get a 4.0L block. It's a bigger bore than the 258, and a 258 crank can be used in it. With a 0.030" overbore and 258 crank it makes a 280 cubic inch six. You can use a 258 or 4.0L head, but the 4.0L head is the better one. When you stroke a 4.0L like this, you end up with about 9.7:1 compression using stock replacement 4.0L pistons. That's not a problem with a carburetor, but the EFI system doesn't like it much. If you plan on converting to EFI the easy way is to choose a high overlap cam that bleeds off some pressure. You can use the carb intake from a 1981 or later 258, but will need the 4.0L exhaust manifold. The older ones crack easy, but are stainless and easily welded. Keep it from cracking again by installing a muffler hange near the manifold -- the tubular manifold doesn't support the weight of the system as well as a cast iron manifold. 

The only special thing needed is that the front of the 258 crank needs to be trimmed 0.30" or a thick spacer (washer) made to go between the balancer bolt and balancer to push it back further. You will also have to run an electric fuel pump since the 4.0L block has no provision for a mechanical pump. With a carb you can run almost any cam you want. 

4.0L rebuilders are pretty plentiful now, and cost no more than a 258. If you don't want to use a 4.0L block, consider the head anyway. It flows much better than a 258 and is a popular Jeep upgrade. Manifold caveats listed above would apply, and there are some holes that need to be filled, but that's easy. 



--
Frank Swygert
Publisher, "American Independent 
Magazine" (AIM)
For all AMC enthusiasts
http://farna.home.att.net/AIM.html
(free download available!)

original message--------------------------------------------
>My son is taking high school auto tech, and is wanting to rebuild his first
>engine.  He's thinking of doing a 258, and then installing it in our 83
>Spirit.  I'm thinking of picking up another 258 for the rebuild, then
>swapping them out when he's done.
>
>Will any 258 fit in the Spirit?  Are the mounting points different for a Jeep
>or an Eagle?
>
>Thanks,
>
>Todd