Jeep Strokers

My question is, is the head from the 4.0 interchangeable with the head on the 258?

billy_bob wrote:My question is, is the head from the 4.0 interchangeable with the head on the 258?

Start reading in this section, you will learn a lot.

http://www.jeepstrokers.com/forum/viewforum.php?f=6

It will work but its not as simple as swapping heads

By the way Welcome aboard

ist it really necessaary to fill the holes in the head? their are no holes on the block and the gasket should seal it.

i always wondered that too...

Hesco sells its head for both applications

Back in 1989 I installed a 87-90 4.0 head on my 1973 258 and only used a 4.0 head gasket/ No leaks what so ever. Was I lucky, maybe so. But before I was going to do all the plugging that is now comonly done I was determined to at least try it first and waste a head gasket if need be. Broke the crank in that motor and made my first stroker mid july 1990.

Note that two different sizes of cylinder head screw were used in the 258ci - one was threaded 7/16"-14, and the other 1/2"-13. The 242ci head accepts a 1/2"-13 screw.

If you're putting a 242ci head on an earlier 258ci block (should be 7/16" screw,) you'll need to use 7/16" screws and have sleeves made to positively locate the cylinder head when you bolt it down. However, the later 258ci tended to use the 1/2" screws, meaning you can drop the head right on.

Apart from that - and the coolant passages - all of the AMC six heads will swap readily, provided the rocker arm mounts are the same (the shaft-mounted rockers tend to oil through the shaft, while the pedestal-mounted rockers tend to oil through the pushrods. Oiling shaft-oiled pushrods through the pushrods is going to cause you some significant trouble...)

5-90 wrote:Note that two different sizes of cylinder head screw were used in the 258ci - one was threaded 7/16"-14, and the other 1/2"-13. The 242ci head accepts a 1/2"-13 screw.

If you're putting a 242ci head on an earlier 258ci block (should be 7/16" screw,) you'll need to use 7/16" screws and have sleeves made to positively locate the cylinder head when you bolt it down. However, the later 258ci tended to use the 1/2" screws, meaning you can drop the head right on.

Only a couple of years of 258 in the early eighty's used the 7/16 head bolts, of all the AMC sixes I've ever messed with only one of them has the 7/16 bolts.

i was wondering how a 258 head works on the 4.6 stroker?

do you maintain good speed turning 90 degrees? haha anyway, the ports on the 4.0 HO heads and newer have a more gradual bend into the chamber as compared to the 90 degree bend on the 4.2 head.

SIXPAK wrote:Back in 1989 I installed a 87-90 4.0 head on my 1973 258 and only used a 4.0 head gasket/ No leaks what so ever. Was I lucky, maybe so. But before I was going to do all the plugging that is now comonly done I was determined to at least try it first and waste a head gasket if need be. Broke the crank in that motor and made my first stroker mid july 1990.

The early 258/232 have the block shape straight under the water jackets, just like the 4.0L block and not like the newer 258.


Newer 258 block

4.0L (rradford9 pic)

IH 392 wrote:

5-90 wrote:Note that two different sizes of cylinder head screw were used in the 258ci - one was threaded 7/16"-14, and the other 1/2"-13. The 242ci head accepts a 1/2"-13 screw.

If you're putting a 242ci head on an earlier 258ci block (should be 7/16" screw,) you'll need to use 7/16" screws and have sleeves made to positively locate the cylinder head when you bolt it down. However, the later 258ci tended to use the 1/2" screws, meaning you can drop the head right on.

Only a couple of years of 258 in the early eighty's used the 7/16 head bolts, of all the AMC sixes I've ever messed with only one of them has the 7/16 bolts.

Do you happen to recall which ones, so I can update my notes?