258 head

[billy_bob]

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

[Flash]

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

[Plechtan]

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

[amcinstaller]

i always wondered that too...

[Plechtan]

Hesco sells its head for both applications

[SIXPAK]

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.

[5-90]

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...)

[IH 392]

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.

[billy_bob]

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

[amcinstaller]

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.

[coas]

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)

[5-90]

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?