sb crank numbers?

[ray79rt]

Hi, I hope someone will enlighten me alittle. I am restoring a 72 340 duster with the numbers matching motor. when I got the motor apart, I found it was a late 72 that had a cast external balance crank. The balancer stated 340 cast crank only on it. The crank number was 3462387. The torque converter had no weights on it. I know the 360s have weights on the converter and the balancer. Should the cast 340s have that also? I was thinking of putting a steel crank in the motor so I pulled the pan on another 340 with a build date of 5-68 to check it (with the thought of using it). It is not steel either, casting number 3751841. Is that one a 318 crank? Are any 318s external balanced? Does a 360 converter work with a cast 340? Maybe I should just use the original crank as it is in good shape. I just thought a steel crank motor might be more desireable since I may sell the car in a year or two. Thanks, Ray

 

[340mopar]

The 340 external convertor is special just like the balancer. 3751841 would be a 318 crank and all 318 LA's are internal balanced. The 318 crank is a direct bolt in as far as size but it needs to be rebalanced to match the weight of the 340 piston and rod. I put a '65 poly 318 crank in my '73 340 because all poly cranks are forged.


Chuck

 

[bobs340dartsport]

If you are building a numbers matching engine for the car then I wiould think you would want the original cast crank , if it is in good shape.

If you have the original cast 340 balancer then all you would need is the correct 340 external balance converter. Or an aftermarket flexplate that is for a 340 external balance engine or you might be able obtain the external balance weight kit from Mopar that can be used to convert an internal balance converter to external balance.

If you were building a highly modified race engine then I would want a steel crank, but for the typical restoration street performance car I think a stock 340 cast crank would work just fine.

just my $.02,

Bob

 

[ray79rt]

Thanks guys, I think I will go with the cast crank since I do have the correct balancer. I need to buy a converter anyway so I'll get one for the cast 340, thanks, Ray