Flex plate & unbalanced 360 crank

[David Wiser]

On Fri. I received my B & M flex plate for my '79 360 rebuild with the unbalanced crank. There were no directions enclosed. Now, I know it only fits on the crank one way, but I was wondering how you balance it. I thought the unbalanced cranks were individually balanced. Since there were no directions or weights, the only thing I can assume is all the unbalanced cranks are unbalanced the same.
Is this true ??

[dave571]

What do you mean by unbalanced crankshaft?

All cranks are balanced, it's just by what means(internal or external). Even if you didn't have it rebalanced at time of rebuild, it was still balanced when it was built at the factory(although factory specs are really slack).

The weights are normally on the torque converter. On externally balanced engines(360,400, cast 440) the weights are on the converter... not the plate. The plate will only go on the crank one way, and will only go on the converter one way as well. I had to have a weight added to my torque converter on my 400. The converter was from a 383(internally balanced) Cost me $20 at a transmission supply shop.

You will only need a weighted flex plate, if you are using an non-weighted aftermarket converter.

[mtrv8n]

Confusing terms here..
The motor has a cast crank, and is not internally balanced. That means the flexplate has the balancing, and it should already be properly balanced if you bought the right one, one made for an externally balanced motor.

That's why it only goes on one way.

[dwc43]

If you have a flex plate that has a bite missing out of it the converter needs no weights to balance it. The missing bite dose that.
If it's solid round or a production type it needs weights on the converter to balance it.
Race converters don't have weights on them and that is what the flex plate with the missing bite is for.

[451Mopar]

The B&M flexplate for the 360 has the missing bite as dwc43 mentions and I belive the amount of weight the B&M ballance has is the same as what the factory used on the 360 torque converters so you can easely use the flexplate on a stock 360 and then use any normal ballance torque converter.
If you notice the B&m flexplare has three sets of holes in it, one set is for the large stock 11-3/4" torque converter that uses the 5/16" bolts, the second set of small 5/16" holes is for the 10-3/4" stock torque converter and many aftermarket converters that use the smaller torque converter bolts, and then there is the 7/16" set of bolt holes used with most race converters.

If you are rebuilding the engine it is best to have the engine re-ballanced anyhow as the stock ballance job usually is not too good, and your new pistons probbable are a different weight than stock, hopefully lighter weight

[David Wiser]

Thanks for all your responses. My questions were answered.

This forum continues to be such a great asset for amateurs like myself.

[dwc43]

Glad we coould help !