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LA 360 Balancing

Aussie Challenger

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I am rebuilding a LA 360 using different weight pistons and rods so will need to get everything re-balanced.

Question.. How much extra is it to have the crank internally balanced, that is is it major re-balancing?

I am not looking for costs so don't quote me prices as I am in Australia, just the effort involved and is it worth the expense.

I know about the harmonic balancer and flywheel weight differences.

Thanking you all in advance

Aussie Challenger
 
Is there any way you can adjust the weight of the new pistons to match the originals? OEM oversize pistons are physically larger but have the same weights, meaning some part of them must be thinner or smaller. If the new pistons are heavier, you might be able to shave off a little metal from the wrist pin bosses without causing any problem. Don't forget that polishing the surface of a metal object can reduce the possibility of fatigue cracks forming, meaning you might be able to remove some metal that way without sacrificing any strength even though the thickness may then be less.

If your new pistons are lighter, I wonder if a person could fill the wrist pins with molten lead and then carefully drill out the excess until you get the correct total weight? If for some reason the lead ever decided to let go and move laterally inside the wrist pin, lead is soft enough that it wouldn't damage the cylinderwall like a wrist pin does when it contacts the cylinderwall.

What I suggest probably isn't what you first envisioned, but when I work with livestock producers, I tell them that whenever possible, sidestep a problem rather than meet it head on. Good luck.
 
Is there any way you can adjust the weight of the new pistons to match the originals? OEM oversize pistons are physically larger but have the same weights, meaning some part of them must be thinner or smaller. If the new pistons are heavier, you might be able to shave off a little metal from the wrist pin bosses without causing any problem. Don't forget that polishing the surface of a metal object can reduce the possibility of fatigue cracks forming, meaning you might be able to remove some metal that way without sacrificing any strength even though the thickness may then be less.

If your new pistons are lighter, I wonder if a person could fill the wrist pins with molten lead and then carefully drill out the excess until you get the correct total weight? If for some reason the lead ever decided to let go and move laterally inside the wrist pin, lead is soft enough that it wouldn't damage the cylinderwall like a wrist pin does when it contacts the cylinderwall.

What I suggest probably isn't what you first envisioned, but when I work with livestock producers, I tell them that whenever possible, sidestep a problem rather than meet it head on. Good luck.
Why would you ever want to make your pistons heavier ?
 
I am rebuilding a LA 360 using different weight pistons and rods so will need to get everything re-balanced.

Question.. How much extra is it to have the crank internally balanced, that is is it major re-balancing?

I am not looking for costs so don't quote me prices as I am in Australia, just the effort involved and is it worth the expense.

I know about the harmonic balancer and flywheel weight differences.

Thanking you all in advance

Aussie Challenger
It really depends on what your plans are for the motor . Are you building an all out , high reving race truck , are you building a driver , or what ? It's always best to have everything balanced together but I've taken aftermarket pistons and rods and mated them with a stock crank and have never had issues . I hope that helped with your question .
 
Thanks Bear this engine is to only be strong cruiser with the little bit extra from it if needed. I will be having the rotating items balanced and wondered if having lighter Pistons and Rods whether it was worth having the assembly internally balanced.
I will be speaking with the guy who does my balancing and see what the results could be from his recommendations. I have been told that having lighter pistons and rods it might be beneficial to have it internally balanced. I know about Mallory Metal may be used so if it is a reasonably priced option I will go that way.
 
Yeah , They'll either take a little away or add a little depending on what it needs . I'm glad I could be of some help . Just curious , Is this the motor for your lil Red ?
 
Yes, I am finally able to do something, I have been rather busy lately, I am hoping to have all the machining done before Christmas so I can assemble it between working.
This engine is actually not the original but one I was going to build up for my '70 Challenger. Once I have built and installed this 'extra' engine I will be rebuilding the original LRE engine for installing later in the year.
 
Cool ! Glad to hear it ! :D
 
quote "Why would you ever want to make your pistons heavier ?"

If the new pistons are lighter than the originals and you wanted to eliminate the need to spend big bucks balancing the entire rotating assembly, you would add enough weight to the new pistons to make them equal the weight of the original pistons. That's why you would add weight. If the new pistons are heavier than the originals, you lighten them to acheive the same weight. Simple.

According to a paper an old Chrysler engineer wrote, the reason the 340-360 engines are externally balanced is because they use the same connecting rods at the internally balanced 270-318 engines. I don't know if the rods were very expensive to manufacture, machine, design new ones or what the reason was, but supposedly that's why they had to externally balance the flywheel/torque converter and harmonic balancer on the big LAs.

It could be the same reason the '58 Chevy was a one year only model as opposed to the more customary practice at that time of having at least two model years using the same body stampings. Ends up the front doors were the most expensive body part for GM to manufacture on any of their cars. Starting in 1959, the same door stamping was used on the Buicks, Chevy, Olds, Pontiac and I believe the Caddy as well. When you have a part that requires multiple, complex stampings and assembly, you're better off making a bunch of the same one rather than fewer ones that are all different. And in actuality, the actual stamping or forming of the metal part wasn't overly expensive, it was the time consuming, very expensive process of creating the dies used to make the stampings. Beginning in '59, all GM divisions had to design their bodies around the same door.

Studebaker wasn't exactly flush with money and anyone familiar with the Studies knows that the bodies and front doors of the passenger cars were identical from about '57 through '64. There were minor differences in the roof line, hood shape, creases in the fenders and so on, but it doesn't take much to make a new stamping die for something with large, simple contours like a roof, hood or trunk. Or even the outer door skin. Take a good look at your average older car door and you will see that the inner portion has much more complex bends, curves, contours and holes-openings than the skin on the outside. All of those surface changes requries the die be machined to make that change.

So maybe that's why Chrysler used the same connecting rod on two similiar but different engines that had basically no other major internal parts that were the same or interchangable. In manufacturing, similiarity translates to less cost, which is why these days, all GM cars of every brand use the same, "GM" engine. Up until the very early 70's, each GM division designed and manufactured their own engine. Buick had unique Buick designed and built engines, Cadillac had theirs unique engines and so on. Today a Buick has a GM engine just like a Caddy has a GM engine and you can swap parts between the two all day long.
 
To spell it out I deliberately bought lighter Pistons and Rods knowing I would have to have the rotating assembly re-balanced. I would have bought factory rods and pistons if I wasn't going to balance the rotating assembly.
From memory the 273 &340 rods have fully floating pins, the 318 & 360 don't. My rods are different, having lighter but stronger Rods and Pistons is a plus when building a performance engine.
All 340's were internally balanced except for the last year of manufacture and were an embarrassment to the legend of the 340.
My engine falls between a high performance and standard (LRE) engine but I want the best of both worlds and will have it with what I am building.
Fraud's have had a lot of trouble over the years with their externally balanced engines, one of the many reasons I would never entertain having a Fraud.
 
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