Flywheel balancing

[cstout]

I've read a few threads here regarding the external balancing for cast cranks. I have a '78 440 with a cast crank and a 4-speed tranny that I'm about to drop into my Dodge pickup. The flywheel does not appear to be weighted and based on what I've read here in this forum, it needs to be.

The question is does the flywheel need to be balanced with the engine or can I simply take the flywheel alone to a machine shop to have them balance it? If I have to haul the entire engine down to a machine shop to have it balanced, it would be too expensive.

It seems illogical to me that the crank itself is not balanced internally so if someone could explain the concept of external balancing, that would be appreciated too.

Thanks!

Chris

[pishta]

Only if the engine is neutral balanced. If it is "detroit" balanced, it was balanced as a unit, and probably had added weights to the convertor or flywheel.

[Blaine Peterson]

As I understand it Mopar externally balanced the cast cranks (cast iron is lighter than steel) because internally balancing them would have required heavy metal such as mallory be added to the crank in its counter weights. That was too costly. So they hung weight on the outside via the vibration damper and convertor or flywheel to even things out.

A few years ago I rebuilt a '78 400 (cast crank) and wanted to fire it up before it went into the car. I needed the proper flywheel to do this but didn't have it. So I took a flywheel for a steel crank 440 and had the machine shop remove some weight from it by drilling some very SHALLOW holes in it as per the instructions in the Mopar Performance Chassis Book. This created the right amount of counter balance I needed. It worked!

You didn't mention it but are you sure the four speed trans is going to work with your crank? Have you considered what pilot bearing you're going to use? Is the end of the crank drilled deep enough to accept the input shaft of the trans?

[cstout]

I bought the engine with the 4-speed already attached so it does have the proper pilot bearing. However, someone told me that the flywheel was not weighted so I'm trying to figure that out. Sounds like I need to get my hands on the Mopar Performance Chassis book. Thanks.

Originally posted by Blaine Peterson:
As I understand it Mopar externally balanced the cast cranks (cast iron is lighter than steel) because internally balancing them would have required heavy metal such as mallory be added to the crank in its counter weights. That was too costly. So they hung weight on the outside via the vibration damper and convertor or flywheel to even things out.

A few years ago I rebuilt a '78 400 (cast crank) and wanted to fire it up before it went into the car. I needed the proper flywheel to do this but didn't have it. So I took a flywheel for a steel crank 440 and had the machine shop remove some weight from it by drilling some very SHALLOW holes in it as per the instructions in the Mopar Performance Chassis Book. This created the right amount of counter balance I needed. It worked!

You didn't mention it but are you sure the four speed trans is going to work with your crank? Have you considered what pilot bearing you're going to use? Is the end of the crank drilled deep enough to accept the input shaft of the trans?

[Blaine Peterson]

cstout, I wanted to double check on the reference info I gave you yesterday, and when I did, I couldn't find it in MP Chassis book. I checked my file and found a copy of it. I had forgotten it came from an earlier MP book. Not sure why MP didn't include the info in the later book. Maybe it weakened the flywheel, I really don't know.
For what its worth the page I have, has "162 MOPAR PERFORANCE" on it. There is a diagram on the page that shows where and how much to remove by drilling with a 31/32" bit.

If I could scan it I would but don't have that capability right now. If you want to get a PO Box # to me somehow, I'll be happy to drop a copy in the mail for you.

[cstout]

Please give me an e-mail address and I'll give you my home address. I would VERY much appreciate a copy of that! I ordered the Chassis book but they said it could be over a week before I get it.

I talked to someone else who said that I can only use a flywheel for a cast crank. I'm trying to figure out if I can use the flywheel I already have or not.

Originally posted by Blaine Peterson:
cstout, I wanted to double check on the reference info I gave you yesterday, and when I did, I couldn't find it in MP Chassis book. I checked my file and found a copy of it. I had forgotten it came from an earlier MP book. Not sure why MP didn't include the info in the later book. Maybe it weakened the flywheel, I really don't know.
For what its worth the page I have, has "162 MOPAR PERFORANCE" on it. There is a diagram on the page that shows where and how much to remove by drilling with a 31/32" bit.

If I could scan it I would but don't have that capability right now. If you want to get a PO Box # to me somehow, I'll be happy to drop a copy in the mail for you.

[Hemichuck]

You can use the flywheel that you have now it just has to be balanced to work with your motor.Mopar performance sells a package with instructions on how to do this.Fortunatly I have a local machine shop(owned by mopar nuts) that does this for me(about $75)

[cstout]

I've checked with machine shops in my area and none of them had any idea what I was talking about. The only guy who said he would do it told me I'd have to completely disasemble the engine, take all the parts to him, and he would completely balance the engine. This was a tad more than I was hoping to do.

Mopar Performance cannot get me the kit, they claim it's nonexistent nowadays. I'll keep searching for an answer.

[Blaine Peterson]

cstout, the diagram is in the mail. You should get it in a few days.

[GTXMONTE]

I used to work in a race shop and I did the balancing, heres the scoop....cast cranks are lighter in the counterweights than a forged crank, so to offset the weight of the piston and rod assy, weight has to be added to the counterweight, since you can't do that, you make the counterweight "think" it's heavier by adding a weighted balancer and flywheel. If you look at a cast crank motor, the weight on the balancer lines up with the counterweights.
The "only" way to properly balance an externally balanced engine is to take the rotating assy to a machine shop and have it done. After the bobweights are set, the crank(with balancer and flywheel installed) will be set in the balancing machine and "spun".
Of course if it's a factory engine the "balance" will be close enough to run. In your case, if you find a factory cast crank flywheel and bolt it on, you will be fine. If there is not a "pad" or some similar source of weight on the wheel you have, it is not a cast crank wheel.

Ok, for you technical guys, I said above that you "can't" add weight to a cast counterweight, I was speaking of a factory type setup and not referring to a race application, where "mallory metal" could be added. Did'nt want one of you to come back and try to hang me out..LOL!!

Hope this info helps you cstout

Monte Smith

[cstout]

Blaine Peterson was kind enough to mail me the specs for balancing my existing flywheel. My crank is definitely cast and the flywheel I have, I'm told, is from a steel crank because it has 143 teeth. However, my flywheel has obviously been machined (I can see the machine marks on it) and it has two wide, shallow holes drilled in it for balance. I'm not sure if these holes were to zero balance or offset balance. My damper is obviously correct for the cast crank. The internals of the engine all appear to be factory. That's about all I know. When the specs that Blaine sent me arrive, I'll find a machine shop who can take a look.

By the way, this engine is not going to be raced or run hard in any way. It's simply going in my pickup for regular street driving. Therefore, I don't forsee any high revs or excessive workloads. Given that, a "close enough" balance should suffice. I don't think perfection is important here.

Thanks to all!