340 Steel Crank Questions

[KP]

I recently sold a like new 20 plus year old still in the original box 340 Steel Crank on eBay (Item # 330181279119).

The buyer is telling me this crank has no centering ring to mount the flex wheel and the flange holes are not threaded. He also told me a machine shop in his area said this is a “Boat Crank”.

Can anyone tell me if this could be accurate and if there is such a thing as a boat crank and can it be machined for uses in and car engine?

 

[djwhog]

I recently sold a like new 20 plus year old still in the original box 340 Steel Crank on eBay (Item # 330181279119).

The buyer is telling me this crank has no centering ring to mount the flex wheel and the flange holes are not threaded. He also told me a machine shop in his area said this is a “Boat Crank”.

Can anyone tell me if this could be accurate and if there is such a thing as a boat crank and can it be machined for uses in and car engine?

I have heard of a:
cast crank
forged crank
8 bolt flange race crank in various strokes from Mopar
Of course current after markets
And there was a 318-3 forged HD truck unit too.

but I dont think so??? To my knowledge.

 

[robertnb64]

YES there is a boat crank or called a marine crank. they are backwards as I understand it. marine engines run the other direction than an auto engine. Sorry I don't know how to tell the differences between them.

 

[grumpuscreature]

In the late '60's, early '70's, Chrysler had a marine division that made outboards and stern drives. I know for a fact that the 150 HP stern drive was a /6 and the 250 HP was a 318. So yeah, there was a 3.31" "boat crank" per se. Can't tell much from the pics you posted in the sale listing, but the D1 78 stamping is interesting. What were the circumstances of your acquisition of the crank? If this crank was produced in 1978 it could be a marine replacement or a heavy duty truck crank. Yes it can be machined to accept a flywheel and the flange holes tapped, but it would be cheaper to buy another crank. On the other hand, are you sure the buyer is telling you the truth?

Not all marine engines are reverse rotation. The difference is the cam and water pump. Everything else is the same.

 

[street demon]

Marine or not the crank still has to attach to something. Never messed with boat motors but I still think the back for the crank should be machined....marine or not.

 

[bobscuda67]

Marine or not the crank still has to attach to something. Never messed with boat motors but I still think the back for the crank should be machined....marine or not.

Yea that's right. You still have to bolt on a flywheel with a starter ring on it. I have messed around with jet boats and they all had flywheels.
I don't see why they can't machine it to fit.

 

[ACME A12]

I have also heard before that due to the designed reverse rotation you cannot adapt a marine crank to an automotive application. The serrations on the crank mating surface for the rear main seal are machined in the wrong direction and will force oil out rather than away from the seal if run clockwise. I've never tried to use one so I don't know definitively but thought that I'd share what I've been told.

Ray

 

[robertnb64]

I have also heard before that due to the designed reverse rotation you cannot adapt a marine crank to an automotive application. The serrations on the crank mating surface for the rear main seal are machined in the wrong direction and will force oil out rather than away from the seal if run clockwise. I've never tried to use one so I don't know definitively but thought that I'd share what I've been told.

Ray

That is TRUE. It happened to a friend of mine. That's how we NOW know about marine cranks!

 

[340mopar]

I wish there was a pic of the flange because that sounds interesting. It may be a 3.31 stock crank but I don't think it is/was a 340 crank because of the rod throws are not drilled. It could be an old DC crank that came semi-finished so the crank pins would not have been drilled and the flange would not have been machined yet. If the "78" is a production year it would be the right year for a DC part.


Chuck