Engine Rebuild Saga

Good evening folks, So I got to the engine part of the '74 cj5, it's a 258 1bbl. After the removal of the manifold(s) discovered where the exhaust leak was; the intake side where they mate together is very uneven and will need to be replaced. It doesn't seem to be available. Any suggestions on after market? Then removed the head.... found an old thermostat stud repair botched up, now in the market for a new head. Then ran the block to the machine shop, It needs to bored out at least 20 over, so new pistons and may as well do the cam and all the rest. So started looking for a complete engine rebuild set, There seems to be a couple different types of the 258(?) Which one? Are there different versions of the 258? What a morning. Now i know why some of these restored Jeeps go for what they do. Any suggestions and recommendations would be most appreciated. Dave

 

Is the manifold uneven or the cylinder head? Both can be surfaced by your local automotive machine shop, so they seal. Or is it the area where they bolt together? Exhaust or intake? Your description is not clear.

If you need a replacement intake manifold, I'd ussgest a junkyard or a parts car online. A 1V AMC 6 intake manifold is not very much in demand.

These days, a remanufactured engine will probably be cheaper than building the engine yourself. Good for you if you want to do it yourself, but the factories over the border can probably do it cheaper than you can.

I would suggest this is not complicated; instead you are a naif. Not a problem though - just keep learning and use what you learn.

There are some internal differences, but a complete 258 motor from '72-80 will be compatible with your Jeep. I can't list all the differences, but if you buy parts or a complete engine, the seller must work with you to make sure the parts or engine are correct. If you worry, get the '74-80 Jeep factory parts book and match what you buy using the factory part numbers. The book is available at RockAuto on CD-ROM for less than $25.

 

Hmmmm, interesting reply. Good day sir

 

A little more detail about the engine changes - to the best of my knowledge.

Considering a replacement engine, there are three main versions of the 258.

In 1970ish, AMC discontinued the older 199-232 engine and replaced it with the 232-258 inline sixes. Much of the older engine design was used for the new engines, but the '70 and older 232 is not the same as the newer '71-up 232, and the 199-232 has its own bell pattern. The newer 232-258 engine's bell pattern was unified with the AMC V8s from the same era (2nd and 3rd gen AMC V8s, 290-343-390 and 304-360-401 resp.)

The '71 258 has its own crank flange, and is not compatible with the other 258s.

In 1972, the crank flange was revised and remained unchanged through the life of the 258.

There were internal changes through 1980, but these '72-80 engines are all interchangeable if you remove the external parts and install them on the new engines. The rocker arms went from shaft mounted to pivot mounted sometime in '73-74. The head bolt diameter changed from 7/16" to 1/2" (or 1/2" to 7/16"?) some time around 1978 or 1979. The head bolt size matters if you want to put a newer head on an older engine, or vice-versa, but it's otherwise unimportant to the exchange or repair of these engines. The 232 was discontinued in 1978 or thereabouts.

For 1981, the 258 was updated with a lighter block and crankshaft and improved manifolds for more performance and lighter weight. The easiest way to tell these newer engines is by the aluminum intake manifold, or by the infamous plastic valve cover. These engines can still be exchanged for the '72-80 engines if all the external parts are used from the older engine. This engine was used in Jeeps through 1990.