360 balance issue

To make a short story long, I am helping a friend who has a 360 with a balance issue. It shakes severely. I had the pan down and it has a stock 360 crankshaft. No sign of internal balancing (Mallory metal). It has the correct B&M flex plate, no weights on the convertor, and a 360 dampener. But I noticed there are three 360 dampeners out there. One with the big weight, one with a scallop machined in the front of the dampener, and one with scallops machined front and back of the dampener. The engine a 1-7-71 casting.

The engine was rebuilt with no miles, but the builder did not install the plate that holds the cam in. Thus no oil pressure. I corrected that and the only damage was scuffing of the rod bearings which I replaced. It carries 75 PSI of oil pressure.

Thanks,
Don

All external balanced 340 and 360 need the matching converters and flywheels, they are externally balanced on both ends of the crankshafts, not just the balancers

My '74 360 had a big weight on the converter.
Like Cab says, external balance is accomplished at both ends of the crank.

I never noticed 360 balancers with "scallops" front and back, just the front. But when they changed from the original counterweight cast into the front to the scallop in the front, it was on the opposite side of the face. Basically the offset weight remained the same but they saved the amount of metal used. Are the internal parts OEM rods & pistons or different parts with possibly different weights? 360/5.9 Magnum are externally counterweighted but a lesser amount than a LA 360 and more than a cast crank 340.

Yes, I am well aware of the balancing of a 360. Once again, it has the 10236 B&M flex plate which eliminates the balance weights on the convertor. The rear balance is correct.

Until you take it apart and have it spun for balance, it's all just guessing and hoping. S/F.....Ken M

Engine was rebuilt.
New pistons?
New pistons with weights very similar to OE pistons?

I can add that, 30 years ago I built a 360 with trw forged replacement pistons. Weights very close to stock.
I used the B&M flex plate, and balanced it myself.

It needed more weight on the rear than what the flex plate provided.
I ended up adding three fairly large holes to the flexplate to increase the amount of imbalance to get the crank to balance out.

The front, which had the factory balancer, was fine.

Knowing for sure is way better than hoping and guessing

here are several different designs of 360 LA balancers but the external weight is the same for all.

As noted above, the problem is probably incorrect weight replacement pistons.

Problem solved. The crankshaft is a cast aftermarket piece. It is internally balanced. It is a 3.58" stroke. I put on a neutral balancer and flex plate and now all is good. Apparently the previous owner purchased a rotating mass assembly which is internally balanced. But since he died some years ago, we were on our own.

Nice find!!

glad to see it was a relatively simple and cheap fix.