340 Cast crankshaft and Balance Question

[SGlez10]

Hi guys,

I have a couple cast cranks for my 340 here are the casting numbers:

3462387
2658393

I’m in the process of buying bellhousing, flywheel, and clutch.

There’s a lot of info out there and some say that there’s no difference between a 318 and a 340 cast crank but some say there is.

I will attach a picture of the balancer and pictures of the casting numbers of these cranks. Depending on which crank I use do I need to balance the engine with the flywheel and all?

All recommendations and help is welcome. Thanks is advance.

 

[Keith Mopar]

Just checked my part no book and the first crank no.3462387 can be 74-86 318 cast or 73 340 cast.
2nd crank no.2658393 shows it can be for 67-86 318 cast or 68,69 273 this crank does not show for a 340.

Well in my records anyway!

 

[RustyRatRod]

Ok, lets clear this up right quick like. I THOUGHT I had. I guess not. The 318 was NEVER externally balanced. NEVER. NOHOW. NO TIME. EVER. So, that right there proves the two cranks are different. That's why I told you "whichever" to BE SURE to have everything balanced. The only reason ANY BOOK shows a 318 and 340 crank the same is because they had the same stroke and it's a simple misprint......even with the forged crank motors,because even they were not balanced the same. No matter how many times you ask the question, you're still gonna have to have the balance checked. If somebody gives you the answer you wanna hear and you slap it together without balancing, you're gonna regret it.

 

[RustyRatRod]

Just checked my part no book and the first crank no.3462387 can be 74-86 318 cast or 73 340 cast.
2nd crank no.2658393 shows it can be for 67-86 318 cast or 68,69 273 this crank does not show for a 340.

Well in my records anyway!

Well the book is WRONG. NO 318 ever took an externally balanced crank. EVER. PERIOD.

 

[RustyRatRod]

And I'm not usin caps to yell, I'm just tryin to hammer the point.

 

[SGlez10]

And I'm not usin caps to yell, I'm just tryin to hammer the point.

Thanks RRR. For the record I’m going with the 318 crank only because the 340 crank needs grinding and then I’d have buy bearings, which is going to take a while, plus more $... Regardless I will balance the assembly so it’s all done right.

 

[RustyRatRod]

Thanks RRR. For the record I’m going with the 318 crank only because the 340 crank needs grinding and then I’d have buy bearings, which is going to take a while, plus more $... Regardless I will balance the assembly so it’s all done right.

Just make sure you do, because that 318 crank is dedicated internally balanced. Now......here's a twist. Take them a 318 balancer. Let them check it with that. It might be that it will cost a lot less that way, since the 318 crank was internally balanced. With the 318 internal balancer, it should take less Mallory metal and be much cheaper to balance. I would also recommend a quality balancer too. Having it balanced with the 340 external balancer would get costly, since the crank is internally balanced and would likely require a lot more Mallory metal. Dat chit ain't cheap.

 

[SGlez10]

Just make sure you do, because that 318 crank is dedicated internally balanced. Now......here's a twist. Take them a 318 balancer. Let them check it with that. It might be that it will cost a lot less that way, since the 318 crank was internally balanced. With the 318 internal balancer, it should take less Mallory metal and be much cheaper to balance. I would also recommend a quality balancer too. Having it balanced with the 340 external balancer would get costly, since the crank is internally balanced and would likely require a lot more Mallory metal. Dat chit ain't cheap.

Yes I purchased a 318 damper so that’s what will be on when they balance it.

 

[RustyRatRod]

Yes I purchased a 318 damper so that’s what will be on when they balance it.

It may end up needing very little work, then. That was smart.