External Balanced 360 With new parts still Balanced??

[72DMag]

Still repairing my buddies 360 magnum. If you replace a stock connecting rod with another stock connecting rod from another 5.9 magnum will that through off the external balance? In other words since the magnums are externally balanced at the damper and flywheel wouldn't all of the rods, pistons, and cranks weigh the same? So if you had 2 motors you could mix and match parts and with external balance it would still balance out correct?? As you can tell by the questions, I'm still figuring out how sensitive or accurate the external magnum balance is. Thanks

 

[67Dart273]

Factory motors are not "individually" balanced. But if you install aftermarket/ oversize pistons, etc, that can change things..............

 

[Wyrmrider]

so weigh the big ends nd the small ends and match if heavy
if light and not too light run it
factory installed with matched sets of rods and pistons
but sets could be different weights

 

[72DMag]

Okay that's what I was thinking. If I stay with factory replacement parts. So say a reconditioned factory connecting rod from rock auto. It shouldn't affect external balance.

 

[72DMag]

Like you said aftermarket parts if not same weight will cause external balance weights to be off.

 

[Dartfreak75]

I had this concern about building my 360 so what I did was done a bunch of research until I found a piston that weighed pretty much the same as my factory ones. I found that a speed pro h116cp. 03 over was within a couple grams of my factory pistons. @nm9stheham helped me out with it he did some research and testing of his own with the weight in the pins to get the piston the desired weight (factory weight) that way the balance doesnt change. Afterwards I talked to my machinist and he said for a street car thats not gonna be turning a consistent high rpm a few grams wouldnt hurt. I cant remember which way it was over or under but the factory balance was not perfectly balanced anyway and going over in weight would get you closer to a true balance. Going under weight like a kb107 pistons (they are considerably lighter) is where you start running into balance issues. I have no experience other than what I have read and talked to people so I cant say for certain that is true. I have talked to both types of guys one says rebalancing is mandatory in every build and others say they have never rebalanced one. I was talking to a mopar guy I work with that swears he built a 360 with kb107s and was spraying it with the factory rods and crank no rebalancing and it was running 10s in a 68 barracuda. Once again idk how much truth is behind that. My block is in the machine shop now i am not having the crank balanced I will let you know if I have any trouble with it.

 

[72DMag]

@dartfreak75 Thanks! Ive heard that swapping pistons with same weight you can get buy with. Hot rod magazine did it with their build. But after googling I haven't found anything regarding the connecting rods. I'm asking if you put in factory reconditioned rods and use factory damper and weighted flex plate. Would that work without a rebalance? In my mind yeah cause I doubt factory is perfect and they used the same damper and flex0late for every engine. but i couldn't find anything about the rod swap.

 

[oldkimmer]

I know years ago my buddy would swap in any crank that was handy at the time into any 273/318/340 and didn’t seem to have a balance/vibration problem. I took a 340 to the machine shop along with a 318 crank and it was way out, not even close. Would of needed at least 2 sticks of Mallory metal to balance it. Kim

 

[70aarcuda]

i have a 360 with seal power h116hcp pistons...stock weight.....Chinese h beams rods....stock weight.....got weighted balancer and flexplate on it......

go up and the track with no vibrations....

 

[Dartfreak75]

@dartfreak75 Thanks! Ive heard that swapping pistons with same weight you can get buy with. Hot rod magazine did it with their build. But after googling I haven't found anything regarding the connecting rods. I'm asking if you put in factory reconditioned rods and use factory damper and weighted flex plate. Would that work without a rebalance? In my mind yeah cause I doubt factory is perfect and they used the same damper and flex0late for every engine. but i couldn't find anything about the rod swap.

As long as you use the factory cast number rods for that crank you should be fine. 318 and 360s share the same 645 rods

 

[Dartfreak75]

i have a 360 with seal power h116hcp pistons...stock weight.....Chinese h beams rods....stock weight.....got weighted balancer and flexplate on it......

go up and the track with no vibrations....

What kind of times you run with that combo? I have a weighted or counterweighted flexplate for when I can change converters. I got it on here for a song so I had to pick it up. It a couple years when all the big money stuff is done and its running and driving and I want a little more I plan on upgrading the stock converter

 

[oldkimmer]

My rods were 732 to 752 grams. Same number rod. Not a chance in hell of using both of those in the same motor. Another 1 the big end was way to heavy. Needed to change that 1 also. There was a discussion b4 about u may have to have multiple sets of rods so u can find 8 the same. Kim

 

[Dartfreak75]

My rods were 732 to 752 grams. Same number rod. Not a chance in hell of using both of those in the same motor. Another 1 the big end was way to heavy. Needed to change that 1 also. There was a discussion b4 about u may have to have multiple sets of rods so u can find 8 the same. Kim

Was all 8 of those rods that weighed that different out of the same engine?

 

[oldkimmer]

Yes, that’s what I was told when I got it. But I was also told it was a 340 crank and it was a 318 crank. The rod that the big end was too heavy on was the same weight as most others for total weight. So we couldn’t take lots off the big end. It would of been way to light. Kim

 

[Dartfreak75]

Yes, that’s what I was told when I got it. But I was also told it was a 340 crank and it was a 318 crank. The rod that the big end was too heavy on was the same weight as most others for total weight. So we couldn’t take lots off the big end. It would of been way to light. Kim

Idk but I'm bought willing to bet they came out of different engines lol

 

[Dartfreak75]

Yes, that’s what I was told when I got it. But I was also told it was a 340 crank and it was a 318 crank. The rod that the big end was too heavy on was the same weight as most others for total weight. So we couldn’t take lots off the big end. It would of been way to light. Kim

Just for curiosity I have a complete set of 645s I know came out of the same engine I will weight them when I get home. Just remind me.

 

[72DMag]

So to conclude its pretty much what I thought. I can take any 360 magnum crank. Pistons, pins, and rods that are of equal weight or pretty darn close to it and put the factory harmonic balancer and flexplate on it and it should be fine.

Not sure how aftermarket harmonic balancers would work but if they are meant for the magnum 360 those would be acceptable too I'd imagine. Thanks everyone!!

Might do some more research to see if there are rods and pistons I can use that are full floating and the same weight as the stock pressed pins,pistons,and rods. I'm not a huge fan of the pressed pins.

 

[MOPAROFFICIAL]

My rods were 732 to 752 grams. Same number rod. Not a chance in hell of using both of those in the same motor. Another 1 the big end was way to heavy. Needed to change that 1 also. There was a discussion b4 about u may have to have multiple sets of rods so u can find 8 the same. Kim

That is why after balance to see the rods , some have the stub ground off the small end and other not so much, some square at the butt of the big end and others edged off to an angle.

Weight match, some really are too heavy or too light to match the others... and you end up getting another rod thats close enough to grind the weight down to desired spec and use it.

 

[Dartfreak75]

So to conclude its pretty much what I thought. I can take any 360 magnum crank. Pistons, pins, and rods that are of equal weight or pretty darn close to it and put the factory harmonic balancer and flexplate on it and it should be fine.

Not sure how aftermarket harmonic balancers would work but if they are meant for the magnum 360 those would be acceptable too I'd imagine. Thanks everyone!!

Might do some more research to see if there are rods and pistons I can use that are full floating and the same weight as the stock pressed pins,pistons,and rods. I'm not a huge fan of the pressed pins.

As long as it's a 360 harmonic balancer your fine. Just be aware there are different styles of 360 balancers make sure you match the one that came on your crank

 

[72DMag]

@dartfreak75 The only 2 magnum balancers that I know of are the neutral balanced and the balanced. Are you referring to something else? Or do you mean make sure to match magnum to magnum and la to la? Thanks!!

 

[Dartfreak75]

@dartfreak75 The only 2 magnum balancers that I know of are the neutral balanced and the balanced. Are you referring to something else? Or do you mean make sure to match magnum to magnum and la to la? Thanks!!

Yes I'm talking la to mag and vice versa also on Las there are two different types one early it was like it had like an eccentric built into it and the later had a long groove cut into it.

 

[70aarcuda]

What kind of times you run with that combo? I have a weighted or counterweighted flexplate for when I can change converters. I got it on here for a song so I had to pick it up. It a couple years when all the big money stuff is done and its running and driving and I want a little more I plan on upgrading the stock converter

75 Duster...3000 lbs with driver....has run 11.19 @ 118.56 in Las Vegas...

 

[Bobzilla]

If you are talking about swapping factory parts and running near factory RPM range, then swapping a factory piston and rod assembly does not require a re-balance. This is how the dealership does warranty repairs; block and crank stay in the vehicle, piston and rod assembly gets swapped out. This is, of course, provided there is no block or crank damage.
As for harmonic balancer, the same applies. If you need a new balancer anyways, BluePrint engines is offering one now too.

New BluePrint Engines Mopar Small Block Harmonic Balancer | 273 | 318 | 340 | 360 | 408 |

 

[nm9stheham]

My rods were 732 to 752 grams. Same number rod. Not a chance in hell of using both of those in the same motor. Another 1 the big end was way to heavy. Needed to change that 1 also. There was a discussion b4 about u may have to have multiple sets of rods so u can find 8 the same. Kim

Well now, hold the phone on this info... those rods of Kim's had the beams ground down on them quite a bit....so they are hardly 'factory rods', and can't be used for comparison to actual unmolested factory rods, which is the subject of this discussion.

I've weighed a few full sets of stock rods and they all fall within a tolerance of 5-9 grams and wiht the big and small ends measured, the effect on bobweight from their big and small end variations is in the range of under 15 grams max to min. I am sure that there are some sets out there with larger variations.

The OP should be fine in putting in another unmolested factory rod.

Might do some more research to see if there are rods and pistons I can use that are full floating and the same weight as the stock pressed pins,pistons,and rods. I'm not a huge fan of the pressed pins.

The number I have for Magnum rods is 744 grams, total weight each rod. SCAT and Eagle I beams are around 600 grams + or -, total weight each rod. So it looks like you will have to have the rods bushed if you want them floating.... or just honed out and floated directly in the small ends.

 

[Dartfreak75]

75 Duster...3000 lbs with driver....has run 11.19 @ 118.56 in Las Vegas...

That is impressive!