OEM 360 balance question

What flex plate did the oem LA 360 use as delivered?

Im supposed to drop parts to get my rotating assembly balanced today, so what flex plate do I take them?

Thanks.

any OE flexplate is fine (pretty sure the 904's and 727's used a different one so grab the one for your choice of transmission). You would be using the OE externally balanced torque converter with the weights on the front flat face side of it. For a performance app I would have everything internally balanced & you can even have that done with keeping the offset external balanced harmonic dampener in the front then you can use any performance (or OE) internally balanced converter & not have to be concerned with balance issues as aftermarket ones are all internally balanced. for the nth degree lightest bobweight I'd get a neutral (318) harmonic dampener/regular neutral plate/your choice of internally balanced converter OR if external balance is the plan just get the B&M plate (10239 for a 904) & keep the OE dampener up front & externally balance it then you can use any performance/OE (no front face weights) neutral converter you want.

Wow, I got lost in that.

360s had quite a bit of factory imbalance and used a neutral balanced flexplate with an imbalanced torque converter. So the torque converter needs to spin with the crank. This isn't too attractive to someone who isn't used to it, and I wonder if it's safe at all. Maybe someone else will tell us it's done every day.

There are flexplates with the factory imbalance built in. Then you can use any neutral balanced converter. I think doing this would make most sense because the crank would be balanced to factory spec. Torque converter selection becomes so much easier.

Another approach would be to use an LA360 flywheel for balancing.

Blazin' Bob always suggests neutral balancing the 360 but that will involve using Mallory Metal (tungsten) to achieve neutral balance with stock bobweight. I think you're looking at close to $300 extra to neutral balance the 360 crank with a stock bobweight.

Something else for those who haven't already bought pistons, is to use aftermarket rods and pistons which can save 200grams per cylinder, and then I wouldn't be surprised if that 360 crank would neutral balance without costly Mallory.

One more thing: There are at least four different amounts of factory imbalance and they are not the same at all.
Cast Crank 400/440
Cast Crank 340
LA360 (all had cast cranks)
5.9 Magnum (all had cast cranks)

I hope you find your way through this mess.

R.

This is what I did. I've got a B&M flexplate on my 360 and can use any neutral balance convertor I want. Still using the stock weighted damper in front.

Ive got several of the B@M plates, the 10236 for the 360/727 and no weights on the vert.

Ive also the B@M 10230 net. plate I use on my strokers.

What I need to know here is what do I need to use that will mimic the 360 plate as if it were a production line 360. BEFORE adding or using a aftermerket flexplate to change things.

Ive got to sort this out myself because the shop does good work but needs the specifics from me.

Ive got a 360 mag crank, the light scat I beams and I need to get a piston weight. But im lighter then a la piston/rod, maybe lighter then a mag piston and rod.

I did this long ago with a mag crank, mag rods, and the h116cp hypers and the crank needed just a bit of weight, so I think im not going to need any weight.

Just mainly need to know what flexplate to get the OEM factory balance before I start swapping flexplates and verter weights.

And Yes, if I had to do it again id just net. balance the things and still might since im already out for a new balancer and flexplate I can go either way.

Thanks for the help.

I think I will make a parts list with pics and then maybe I can get more specific input.


I just weighed some parts, the approx 200 grams I saved on the rods im giving back on the piston and pin weight. So my rod and piston weight combined is within 20 grams of la specs.

Looks like im just stuck on what they want it takes weight wise att his point.

either a regular 727 or 904 OE production plate (which is internal) along with the OE (external) 727 or 904 converter with the weights on the front face, this is the 360 LA factory externally balanced combo.

That makes sense to me Robert, I wasnt factoring in the vert itself.

So if I take the B@M 10236 it will take the place of the vert/oem flexplate...correct?


Here are the specs on the la weights and the mag. below.

Ive the magnum crank, my piston is 626 grams, my pin is 180 grams.

The scat rod is 562 grams, so what I save on the lighter rod, I give back on the piston and pin.

Engine 1971-92 360 LA vs 1993-03 Magnum 5.9L

Piston 584 grams vs 470 grams
Piston Pin 154.6 grams vs 134 grams
Connecting rod small end 239 grams vs 225 grams
Connecting rod big end 519 grams vs 519 grams
Ring Set 56.6 grams vs 40 grams
Rod Bearing 47.6 grams vs 47.6 grams


Reciprocating Weight 1,034.2 grams vs 869 grams
Rotating Weight 566.6 grams vs 566.6 grams
Weight per Cylinder 1,600.8 grams vs 1,435.6 grams
Total Bob Weight 2,167.4 grams vs 2,002.2 grams

(1) my buddy Dog is helping me K.I.S.S. (he's gotta alot of work ahead of him). (2) I'm assuming the B&M 10236 is the external plate for the LA/727, yes on a stock externally balanced LA 360 (I ain't up on mags) with that B&M plate you then run any internally balanced 727 converter (OE or aftermarket). (it just moves the imbalance (that the OE eng needs) from the converter to the plate) so that you can run good aftermarket converters (which are internal) if you choose (& the eng doesn't care if the imbalance is in the plate or the converter) & you keep the offset 360 LA dampener up front. As we know OE balance is not the best for anything other than a DD grocery getter.

It more then not will not take a bit of weight, but at this point I dont care, just want it done.

Alot of good reasons to go int. balance but this is not a high end build but rather super low budget.

The last one like this I did with flat tops made 430hp and was ext. balanced and was ok.

that'd make a believer out of me.

I just dropped my LA 360 rotating assembly at the machine shop. In order to balance it, I gave him the crank, rods, pistons, balancer, B+M flexplate, rings, bearings and balancer bolt.

That should work.

It's funny, we gripe about the 18 lb-inches of imbalance while most Ford V8s from the last 30 years have 50 lb-inch.

R.

I dropped it all at the machine shop... machine works in this case and he said I can even get it back yet this week.

I showed the weighted flex plate and he knew exactly what it was and said he also had "lock outs" to bolt to the crank that do the same thing but he would use my plate since I brought it.

THANKS! Rapid Robert and the others....for all the help on this.

Got all back today and things look and so far measure perfect.

Even converting a few things from oz to gram I was 11 grams off on my predicted bobweight.

I had 1922, turns out it was 1911.7.

LA is 2167

Mag is 2002

So im 91 grams lighter then a mag, although things have moved around alot with a 805gram piston/pin weight.

Cost of balance job $189

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