AMC V8 flywheel differences

Okay, I've searched on this and from what I've found everyone is of the opinion that the 304, 360, and 401 flywheels are different from each other in the way that they are balanced.

I have two flywheels, one taken off of a 360 and another taken off of a 304...I personally removed both. They both have an identical part number cast into the back. Clearly, the holes drilled for weight balancing are different, but I'd expect that in any metal object since none are identical.

So my question is, how sure are we that the flywheels are different from one another, especially the 304 and 360 types?

 

100%

They are balanced completely different. If you look on the back side there is a weight cast in in different locations around the flywheel. This is in a different location or missing depending on what application the flywheel is. If the ones you have are the same then it's most likely someone swapped one of the flywheels out at one time with the wrong part.

 

I expect you are looking at the casting number, not the part number. Same casting, machined differently.

 

The two wheels have the same weight location, its a small block in the cast that is approximately 1".

The biggest difference is the location of the drilled holes. That being said, is there any way to tell if its a 304 or a 360 flywheel? I've read that the 304 does not have balancing weights, but I'm not sure if that's for the MT flywheel or the AT flywheel, or both.

I'd like to NOT trash my newly rebuilt engine...and I'd also like to not spend $120 on a new flywheel.

 

All the AMC V8s are externally balanced so each one needs its own flywheel and its own crank pulley (harmonic balancer). The 360 and 304 aren't hugely different from each other, since they both use the same crank, but they are different (different rods? different pistons!). This applies to the automatic or manual transmission versions. The automatic flex plates have balance weights, just like the flywheels.

Since the differences between the 304 and 360 should be minor (just by my reasoning from what I know about them, not by any expert opinion or factory literature or whatever) it's possible that they use the same flywheel casting. I expect the rotating assembly is balanced at the factory, so they would machine the flywheel for each engine. An off-the-shelf flywheel will be a best-guess at what the balance requirements will be.

You should be able to take your parts and both of those flywheels to your machine shop and they can determine which is balanced for you, or they can change the balance to match your parts. I'm not sure what all is required for this, but I know it can be done.

Oh, and BTW - engines can be either internally balanced aka neutral balance, or externally balanced aka Detroit balanced. This is not an opinion thing - it's one or the other, part of the design of the engine.

 

I intend on having the machine shop that built my engine refinish the flywheel. I can't take the other parts with it because they're already assembled. I wish they would have mentioned this to me when the built the motor.

I do intend on purchasing a new harmonic balancer...I imagine that will help a little.

Thanks for all the input.

 

Norm, do you know which flywheel came off of which engine, or are they mixed up? Without more info, I think you have to just use the 360 flywheel on the 360.

Maybe Nick knows better, but I've read about this problem before. You aren't the first to notice that these flywheels can't be easily matched to the engines they came from. As I wrote above, I don't think it's a problem that the two flywheels mostly look alike, considering how similar the 304 and 360 are.

 

Actually, that's what got me thinking about this. I know exactly which one came off which engine...and they looked so similar, with markings and all, that I thought that they were the same part.

The other reason I asked is because the 360 flywheel is significantly more degraded than the one off the 304.

I think I'll take both to the shop and see what they think which one is best for refinishing and I'll do that one.

 

Mmm. I wouldn't use the 304 flywheel - but ask the shop. I didn't mean to imply that they are equivalent - they are not - but instead to say that it makes sense that they might look similar.

 

A simple web search turned up this site with flywheel info.

http://www.planethoustonamx.com/main/amc_production_figures_decodes.htm

There were more sites as well.
I looked under AMC flywheel identification

 

Yes. that is where I got the information that I do have...and based on that information (which is duplicated all over the Internet), it *seems* as though both flywheels are 360 even though I pulled one of them off of a 304.

 

Just an FYI, when I shoved the 360 in my jeep to replace the 304 I used the 304 flywheel. The 360 was an auto and I wasn't about to blow a couple hundred for a new flywheel. Haven't had any trouble and runs perfectly.

 

Based upon the only information found on the Internet (from various web pages), version 3 from the description below is the flywheel that I took off a 304. The flywheel fits the description exactly. My other flywheel from a 360 fits version 1, except without the "C" on the part number...go figure. I'm using the one off the 304 since I believe that someone put it on there from a 360:

THREE distinctly different versions of the flywheel with part #3197219. If you ...want to follow along with the
description that follows, place your flywheel flat on the bench with the
casting number facing up and at 12:00. (like you're reading a clock)

Version #1: #3197219-C
Crankshaft flange recess measurement: 4.500"
Counterweight position: at 7:30
Known to be out of a dead stock 1970 390 4-speed car.

Version #2: #3197219-C
Crankshaft flange recess measurement: 4.500"
Counterweight position: at 4:30
Known to be out of a dead stock 1970 360 4-speed car.

Version #3: #3197219 Does not have the "-C" after the casting
number, but does have "E-25" (or other letter/number combo) cast in
just above the counterweight.
Crankshaft flange recess measurement: 4.650 (approx. 5/32" larger
than the above two versions)
Counterweight position: 9:30
Exact application: unknown. Believed to be out of a 72/up 360 or 401
(304's do not have a counterweight)

All cast-in counterweights are one square inch, with the exception of
version #3 which is 1/4" shorter. (length 1", width 1", depth 3/4")​