Flywheel Differences

[amcinstaller]

it wont. either the depth or tooth count is different. pretty sure its the depth though.

[SIXPAK]

INstaller is right, Ring gear on flywheel(flexplate) will not line up with the starter. IF you could locate a 4.0 starter this would be your best bet. They draw much less amperage and have more power. They do fail MUCH less often BUT do cost more to replace. I went with the 4.0 starter on my jeep just to get rid of the old MOTORCRAFT (or MOTOR-CRAP) starter! Hated them, hated them, hated them!

[amcinstaller]

and ill second sixpak. as well, i cant justify this with fact, but the 4.0 starter is smaller, MUCH nicer, and im putting up a dollar that its lighter too. havent really had both around while i had a scale and thinking about it though. besides, newer parts are easier to replace.

[Jeep-Power]

I just swapped an OBD1 flywheel onto my 4.2.

I am using the AA nv-4500 belhousing, which allows me to run the 4.0 EFI's CPS.

As stated above, the 4.0 flywheels's ring gear is about 1/2" closer to the block than the ring-gear on the OEM 4.2's flywheel. This means that the aftermarket Powermaster starter that I was using on the 258 will not work, as the starter teeth are always engaged in the 4.0 flywheel teeth.

has anyone fabbed up an adapter/spacer to allow them to keep/use a 4.2 starter on a 4.0 flywheel?

[Landon]

Hello, I do have some experience with the 258 flywheels.

Stock on my '79 J10 with the heavy crankshaft, is 29.2 pounds. When I got it, the teeth were trashed, I was lucky to get home. The PO provided a replacement in the bed. Unfortunately, it only weighted 26.5 lbs. I weighed these on our digital bathroom scale. Wife was not happy. The rings did match up, as far as I could tell.
Are they otherwise interchangeable ? NO. Given the same bellhousing. The ring gear spacing from the crankshaft is off by 3/8", so your starter won't line up. I believe the stock 79 is 3/8 further spaced from the crankshaft.
Hmm, must swap ring. But not change composition of steel ring by overheat and local cooling. Hmm. Ok, it can be done with a kitchen oven and some patience, and a hammer, and a 2x4 and a flat garage floor and some cardboard.
I can't tell you with confidence exactly what the lighter flywheel came from, but it does make a difference.

[amcinstaller]

if it had notches in the surface on the outside ring, it would be from a renix or newer 4.0. im not sure if there was a difference in the 199/232/258 flywheels in early years

[Landon]

so is it ok to run the lighter flywheel on the 258 crank in a stroker? to get the notches for the fuel injection, and match up to a 4.0 starter? Does the 4.0 starter bolt onto the old bellhousing ok ? In my case it's the aluminum housing in front of the T18.

- Landon

[amcinstaller]

should be fine, i plan to do the same in my spirit. old bell, new flywheel, new starter.

[IH 392]

You will need to modify the T-18 bellhousing for the TPS or move it to the front with a modified dampener.

[Jeep-Power]

I'm very sure the 4.0 starter will bolt up to the 4.2 bellhousing-- atleast I hope it will, as I plan on doing so with mine.

[flash443]

This is an older thread but as of 2017 Centerforce offers a steel flywheel that weighs 40.1 pounds. The stock 4.0L flywheel weights about 23.5 pounds. Finally an inertial flywheel for the I6.

I have been in search for more flywheel weight for a long time. My buddies with the old Dauntless V6 could lug down to such a low speed it was a joke. They could maximize their tire traction and go where I and my 232 couldn't. The old v6 had a massive flywheel for a 231 cu engine.

I found every AMC flywheel would bolt up to any AMC engine in the pre 80's. The stock clutch for a 232 was 10.5". A J10 was 11" with a heavier pressure plate. It would bolt onto any AMC flywheel.

I also found that the V8 flywheel off a 304 was 10 pounds heavier than my 232 flywheel. Then I learned the difference between internally balanced engines and externally balanced engines. The V8 is externally balanced. The straight 6 is internally ballanced. I didn't leave the 304 flywheel on my 233 long. A flywheel which is about 1 pound out of balance is most dramatic. But so is the extra weight.

[IH 392]

I learned the difference between internally balanced engines and externally balanced engines. The V8 is externally balanced. The straight 6 is internally ballanced. I didn't leave the 304 flywheel on my 233 long. A flywheel which is about 1 pound out of balance is most dramatic. But so is the extra weight.

We had a CJ5 in the shop last fall that had a 304 in it, it had a 258 flywheel on it, it would just about BUZZ your teeth out!, we couldn't find a 304 flywheel to save our lives!??, the owner ended up buying a NEW Centerforce flywheel for a 360, I was able to match the weight to a 304 flexplate that I have, smooth as a baby's bottom when I got it put back together!