AMC 304 Swap- Help!

[CamoCrazy]

Hey guys, its been quite a while since ive been on here but I'm ready to step up the motor in my 91 Comanche with an AMC 304 and was wondering if i can get any pointers and tips? I have an AMC 304 from a 76 CJ 7. I plan on using an AW4 behind it and an NP231. As far as room in the engine bay, i know it should fit. Ive seen a few people talk about flex plate problems as well as starter problems. Does anybody have any advice on what to do or what these problems may be? I also heard motor mounts are an issue but could be fixed.

 

Let me know of any tips or a link to a write up from someone in the same boat as i am, thanks in advance, Gavin

[Jeepman]

Being the 304 uses the Basic Jeep Bell housing bolt pattern, there shouldn't be any problems you just use the 4.0L XJ Flex plate and bolt up the AW4 and away you go using the 4.0L starter...

 

Wiring the AW4 to shift properly is another story depending on how your planning the swap...

[Incommando]

You would have to assure that the balancing was correct. Even the 304 & 360 take different flywheel weights, for example. There is more to consider than corresponding bolt patterns.

[dybamx]

you'll  need to have the flexplate match balanced to the one from the 304. your local machine shop should be able to do it, or know where to send it

[Jeepman]

Sorry Boys but the 304 uses the exact same flex plate/flywheel as the 4.2... Therefore no additional balancing required...

 

Flex plate (Auto uses a flex plate manual uses a flywheel)

304 Part number J323 2138

258 4.2L Part Number J323 2138

 

I have done Numerous 304 V8 Swaps into Jeeps and Always used the 4.2L flexplate or Flywheel and all has worked out perfectly...

[Incommando]

Novak disagrees but even the experts get it wrong sometimes.

 

"Flywheels and flexplates do not interchange between the I6 and the 304, 360 & 401 engines due to balance issues"

 

http://www.novak-adapt.com/knowledge/amc_i6.htm

 

But I do know a guy that swore his 304 flywheel on his swapped-in 360 was just fine until the bearings were shot at 10K.

[dybamx]

yep, it'll bolt up, vibration and lack of longevity are the side effects

[Jeepman]

Well All I can say is Mopar used the same parts for each item so I would go by that over Novak however Novak may have modified their product to but slightly Different...

[jpnjim]

Things we know;

 

AMC externally balanced their V8's

They did this two ways,

first, they had specific flexplate/flywheels and harmonic dampners for each sized engine

and second,

they dynamically balanced every assembled engine with an electric motor after they were assembled, and drilled holes in the flywheel/dampers to fine tune that balance.

 

Because of this ^

you have some crossover of parts,

I know 70-71 360-390&401's all start with the same flywheel,

but once its done being dynamically balanced (drilled),

the 360 flywheel looks a lot different from the 390/401 flywheel.

Even though they have the same part number.

 

What I don't know,

I *believe* the 6 cylinder AMC's were internally balanced,

that means they would have a neutral balanced flywheel/flexplate/harmonic damper.

I never build one of them, so I'm not really sure.

I do know that the 6 cylinders were dynamically balanced with the whole big electric engine rig & individually drilled just like the V8's 

so just like the V8's each flywheel/flexplate& damper is tailored to each individual engine.

Swapping one for another, even of the same exact engine is going to change the factory set balancing.

By how much is anyone's guess,

but even buying a brand new, correct part isn't going to match your engine as well as the original did,

unless you have a machine shop match balance it to the original. 

[jpnjim]

Because of the above,

whenever I pull apart an AMC engine,

the flywheel/flexplate/damper always get marked to which engine they came off of.

 

It was good, and bad that AMC drilled the weights individually to each engine.

It was good, because they ended up with a more well balanced engine than the manufacturers that didn't do it.

It was bad, because it threw standardization right out the window.

 

It's not like a small block chevy where every flex plate/flywheel or damper is the same as the next. 

[jpnjim]

 

 

But I do know a guy that swore his 304 flywheel on his swapped-in 360 was just fine until the bearings were shot at 10K.

It's funny,

because just like some of the flywheels,

 

AMC 304 & 360 crankshafts both start out with the same part number (both are 3.44" stroke). 

But the 304 crank looks like swiss cheese by they were done drilling the bob weight counter weights for the lightweight 304 pistons.

If you bought a rebuilt (formerly from a 304) crank to put in a 360,

you would be using the correct part number,

but the balance would be way way off.