5.9 Magnum flywheel - DIY with bolt-on weight??

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Idaho

Idaho

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This is an issue for those wanting to use a 5.9 Magnum in an A-body with manual tranny. The truck size flywheel apparently will not fit. The external balancing of the Magnum differs from the LA 360 so these are not an option.

I found posts describing a Magnum flywheel being machined down and the ring gear from an LA flywheel being pressed on. Apparently the balance is not disturbed by this. I don't know what this would cost but this does not strike me as a simple attractive solution. Perhaps this was done before aftermarket suitable flywheels were available. The problem with these is cost. It would be nice to find a less expensive solution.

http://www.mopartsracing.com/parts/trans.html
$286.95 + shipping for the mopar performance unit.

http://www.mopartsracing.com/parts/trans.html
$319.95 + shipping for the Mcleod unit.

An LA 318 flywheel (neutral balance I think? - someone verify please) goes for not much over $100 and of course the junkyards would have them cheap for resurfacing. Yes I know, cast vs billet but I'm not sure that's so important unless you're going for 500 hp (other opinions on this - how much hp/rpm is a cast unit good for?)

A point of confusion came up looking at cast flywheels. LA 360 flywheels for cars are listed as 143 tooth units. This is the same as truck size (I think?) Are we certain we need smaller 130 tooth units? (Maybe the Rock Auto catalogue is wrong).

Look at the Mcleod site. It looks like the same flywheel (likely with neutal balance to start - important point that I'm not certain of) is sold for different applications, for the Magnum with a bolt-on weight.

The factory LA flywheels use drilling to provide external balance. This page shows how a neutral 318 flywheel can be converted.
http://www.moparaction.com/Tech/quest/internally.html

I suspect it would not be a big thing to add Mcleod's weight to a 318 neutral balanced flywheel. Just position it right I'm thinking, using the Mcleod unit for reference.

It's not huge dollars but hey it all adds up and a lot of folks could benefit. It is after all as much as many are paying for their entire junkyard engine! Anyway its always good to find ways to get it done for less.

I'm hoping those who know a lot more than me will give an opinion on the unkowns I listed, and the feasability of this.

link to bolt-on weights: http://mcleodracing.com/products/Counterbalance+Weight.+Steel+Flywheel.mcl
 
Sorry, not sure what you're asking - engine? I'm buying a used 5.9 Magnum.
Putting it in a 73 Duster to Demon clone soon to go on the rotisserie.
 
I think there's a diagram with the weight removal (drilling) of a neutral balance flywheel. You would probably need a machine shop to do it for you. I went with the MP flywheel for my 360 magnum with a viper T56 tranny. My clutch is a 10.5 mcleod unit for a camaro and works perfectly.
 
A diagram would be nice. Can't be that hard?
 
The thing I see there at the McLeod site concerning weights IS "THEIR" FLYWHEELS

I would think that the weight of the flywheel would make a difference. You are contemplating using them?? on a factory 318 cast wheel?
 
As lucrative as the low buck method may seem, just buy the right flywheel. Trust me on this one.
 
67Dart273 said:
The thing I see there at the McLeod site concerning weights IS "THEIR" FLYWHEELS

I would think that the weight of the flywheel would make a difference. You are contemplating using them?? on a factory 318 cast wheel?
Click to expand...

Just contemplating, that's all. I'm fairly sure there's enough expertise on this board to rule it out if it's not the right thing.
 
Revhendo said:
As lucrative as the low buck method may seem, just buy the right flywheel. Trust me on this one.
Click to expand...

There's a few questions asked.
I appreciate input but specifics are nice to have. :-k
 
Idaho said:
There's a few questions asked.
I appreciate input but specifics are nice to have. :-k
Click to expand...

Okay. Specifically. The appropriate specs for the flywheel, (size, balance, et al) are in the Mopar Performance engine manual. Follow the recommendations there and you should do fine.

Short of that.
Cutting down a flywheel and installing a ring gear is sketchy unless you find a good machinest with experience in this operation. (Not many left).

143 tooth flywheels are big. They require bigger bellhousings and it also moves the starter out which will get entertaining when you go for headers/exhaust. I don't recall if many A bodies came with the bigger set up, if they did, they weren't common. So finding a bell would become a treasure hunt.

You could try and modify your 318 cast flywheel for the McLeod bolt on weight. But remember that it is bolting on to the engine side so there may be some block interference issues. The McLeod flywheel is the same for all Mopar engines, (respective to size and bolt count), it's the weighting that is different. McLeod's flywheels have a recess that the weights bolt into. Notice that the prefix on the part numbers are the same and the suffix is different. The suffix number, 15A, 12C, 44Z, whatever is the weight and the location on the flywheel where it bolts.

You could take your 318 cast flywheel to your local machinist and have them counter drill it to balance it as outlined in the Mopar Performance manual. If they have experience in it, you should be fine. I don't know what the costs would be in your neck of the woods, but you would be shocked at what I was quoted by a "friend". Hopefully they follow the instructions correctly or you're gonna have this weird off idle vibration that will come back in a bit further up range. Or they do it really wrong and you get a flywheel that cracks and sends pieces out at speed.

Or you can spend a few extra bucks and get the correct quality piece for your car that you can have confidence in.

The whole billet, aluminum, cast or whatever flywheel thing has to do with intended use of the vehicle, type of vehicle and inertia.
 
Thanks, very helpful.

I actually don't mind buying the part if I know I need to but there is a process in arriving there, and there is learning in getting there.

Some of this might seem stupid to the old hands but if so you have forgotten where you started out.

There's still some questions.

Is there a factory 130 tooth 360 flywheel or did the 360 cars use the truck flywheel with a truck bellhousing?

How do cast flywheels hold up to hp/rpm?

Is the 318 flywheel neutral balanced? Interesting that the Mcleod unit has a recess. I wonder if that means its not neutral without weight. Maybe there's a "neutral weight" that just takes up the space?

Again, a lot of this for me is curiosity and learning (fun). I posted with a title that should make it easy to find for others who run into this issue. I've learned a TON with the search button.
 
For those researching this issue I'll throw in this info from crackedback. It's the solution for using an engine from an auto application. This bushing fits the recess in the crank for the converter.

BCA #FC69907, or Mopar # (53009180AB).

There is a bronze bushing one as well, IIRC, PB287 comes to mind. Old mopar number is 4338876

(from this thread http://www.forabodiesonly.com/mopar/showthread.php?t=177902)

The moparts link was dead. This one has it.
http://www.forabodiesonly.com/mopar/editpost.php?do=updatepost&postid=1737495
 

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DartFred said:
I think there's a diagram with the weight removal (drilling) of a neutral balance flywheel. You would probably need a machine shop to do it for you. I went with the MP flywheel for my 360 magnum with a viper T56 tranny. My clutch is a 10.5 mcleod unit for a camaro and works perfectly.
Click to expand...

This option still seems a possibility to me. Others have apparently done this on other applications.
http://www.moparaction.com/Tech/quest/internally.html
No weight to get in the way.

I noticed too the mopar performance flywheel is cast so there's no real advantage other than the right balance.

I'm not confident enough to just buy the book and do it (not good if you get it wrong) but I am curious to hear opinions from anyone who's done this kind of thing.
 
Idaho said:
This option still seems a possibility to me. Others have apparently done this on other applications.
http://www.moparaction.com/Tech/quest/internally.html
No weight to get in the way.

I noticed too the mopar performance flywheel is cast so there's no real advantage other than the right balance.

I'm not confident enough to just buy the book and do it (not good if you get it wrong) but I am curious to hear opinions from anyone who's done this kind of thing.
Click to expand...

As far as I know, the LA 318s are neutral.
There is one advantage to the McLeod flywheel. You can use the flywheel with different engines by changing the weight (or removing it for neutral engines).
 
340duster1
06-03-2003, 04:35 PM
To clear all of this up:
1) the 360 magnum is externally balanced
2) it is different from the "old style" 360
3) the 318 magnum is internally balanced
4) Mopar performance has a flywheel available, last time I priced it out it was $499Canadian.
5) The magnum engine book does not tell you how to rebalance a standard flywheel to work on the magnum engine. So don't waste your money on this book, I already wasted mine. I bought the book for that reason!
6) If you have a copy of the mopar chassis manual, it explains how to put the proper imbalance into a flywheel for a number of engines (but not the 360 magnum). The location or angle for the holes is shown in the book (use the regular 360) but the weight removed will be different. You will need to remove 2.28 oz of metal at a radius of 5.625".

I successfully rebalanced the flywheel for to work on the 360 magnum in my stock car. It sees lots of 6000rpm jaunts (twice per lap) and no vibrations.

If you need more details I can probably email or fax you a drawing.
Click to expand...

http://www.moparchat.com/forums/archive/index.php?t-71263.html

Just an FYI, someone successfully did this.
 
The Moparchat thread has been updated with how to balance a neutral flywheel for the magnum.

There's a pic there of a Magnum flywheel (factory I think), drilled in the same locations but with a different amount of weight removed. Per the diagram, the weight removed for an LA is 19.79 inch oz which equates to 5.1 oz at 3.88 inches from center (weight removed varies inversely with distance from center).

340duster has provided the weight for the Magnum: 12.825 in oz (my thanks to him).
He used a radius of 5.625" and removed 2.28 oz. This info is available on the moparchat link given, along with his source. One more needed factor is the weight of cast iron at .265 lb/ cubic inch.

I see no reason not to do the mod. I may have a friend with a milling machine do it with a square bottom bit to make the calculation easier, or do a drill and weigh experiment with a regular bit and some cast iron scrap.
 
I purchased a 5.9 flywheel and decided to measure the balancing holes. Here's the math I've done with the result.

Weight of cast iron is 0.265 lb/cubic inch x 16 = 4.24 oz per cubic inch.

1 cubic inch = 16.387 cc

The balance hole volume is 18 cc / 16.387 = 1.098 cubic inches

1.098 x 4.24 = 4.65 oz. at 3.9"

Center of flywheel to center of holes measured using a caliper = 3.90" I suspect the intended measurement is 3.88", the same as the LA 360 but I will use my measurement.

4.65 oz x 3.9" = 18.13 inch oz.

This is much closer to the LA flywheel which has a known balance of 5.1 oz at 3.88" = 19.79 inch oz.

There is a shallow drill spot closer to the outside with a volume of about 0.2 cc. I suspect this is a final balance adjustment. There is an angled hole through the thinner center portion that has a volume of about 0.3 cc.

I doubt these are significant. In my view the 3 large holes are what make up the balance specification. I'll post some pics tomorrow.

A couple more bits of data: the holes measure 1.043" diameter and 0.660 depth. I added a pic showing the drill bit angle (I get 30 degrees).
 
Pics.
 

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Wow, I'm late to this party.

Looks like you bought the MP specific flywheel for your swap, correct? If so, that was the best path to take.

Just to clarify some, the only issue I am aware of when swapping a Magnum into an early car with a manual is if you want to keep the EFI. The 143T flywheel was turned down and a 130T ring gear pressed on because there is no available flywheel with the right ring gear and the notches for the crank sensor. So, if you want to keep your A833 but run the factory EFI, you have to find some Frankenstein setup to put it together.

If you are going with a carb, buy the MP piece and bolt it on. Done deal.
 
DionR said:
If you are going with a carb, buy the MP piece and bolt it on. Done deal.
Click to expand...
This.

What I think Idaho might be missing is that there's far more to it than just drilling holes.

The 5.9 wheel has the holes clocked the same as a 360, and I think they're the same radius from the crank center, they're just smaller holes.

To be fair, it's way simper just to build a crank trigger and run it off the front of the motor. 8 slots, evenly spaced, is 8 slots evenly spaced, no matter where they are.
 
Going with the carb. If I had the info I posted I would have drilled a neutral flywheel. Not difficult.
 
I have this posted at Mochat. A member there says the flywheel is cast steel not cast iron. If true the weight goes up by 5%.

I could not verify that it is cast steel. Mopar Performance just lists it as "cast" and sells steel flywheels under a different part number. Summit advertises it as steel, does not even say it is cast. JEGS does not use the word steel.

Anyone know?
 
hello everyone I just put a 360 magnum in my Dakota and am having some balancing issues...

I'm running a 318 magnum flywheel with at the moment 1oz bolted on at 4.9" from center (I found holes drilled around the outer edge on opposite side of the flywheel, which to my math equaled .67 CI) I was aiming for 12.8" per oz.

I have tried a few different weights with not much change, 3.5oz @ 4.9'', 2,8oz @ 4.9'', 2.6oz @ 4.9''. they were all bolted on the same spot on the flywheel and im able to change the weights without pulling the motor!

when I bought the 360 mag it came with a flex plate that had a 3.5-3.7oz weight on it, I drilled the weight off and lined the flex plate up with the flywheel then bolted it on in the exact same location.

the worst vibration is when I take the weight completely off and I would say its best with the 1 oz weight, you cant feel any vibration above 1500rpm but at idle you can hear it and slightly feel it. motor has the correct harmonic balancer on it.

I'm really lost right now as I am not a rocket scientist lol I'm hoping someone can help me with finding the actual degrees from TDC where the weight needs to be and exactly how much weight I need!
 
You'll need to clarify. Sounds initially like you have a 318 flywheel with balancing holes.

Next you are talking about bolting weights onto the flywheel. Factory flywheels don't have mounting holes for weights.

Then you are talking about removing weights from a flex plate.

Explain what you're trying to do.
 
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