mopar crank
 

Can an 318 crank be legally used in a 340? They both have the same stroke and bearing sizes

Re: mopar crank
 

Yes.

Re: mopar crank
 

It will fit, but it may not balance properly. 340 cranks have a hole through the rod journal to offset the piston/rod weight. Also most 340 cranks are steel and most 318 cranks are cast and externally balanced. Find a steel 340 crank and do it right, you'll be better off in the long run.

Re: mopar crank
 

George,

All 318 cranks, cast and steel, are internally balanced, as are 340 steel cranks. (All have neutral balancers/dampers & converters.) Only the 340 cast crank is externally balanced (and 360's).
But balance will need to be checked anytime you start swapping parts around. 340 pistons are obviously heavier than 318 parts.
I use to hear that the steel 318 truck crank was a good, strong piece because it didn't have the journal holes.

Re: mopar crank
 

Thanks Myron,

I didn't kow that.

I always thought all the LA cast crank motors had external balance.

I have also heard the 318 steel truck crank was a good piece. What was the last year for that?

George

Re: mopar crank
 

Its a chore but you can drill the holes in the journal just like the 340 cranks, we have done it several times.
Bill Lamb

Re: mopar crank
 

George,

Sorry, I don't know the last year for the truck cranks. I may still have one with a damaged thrust surface.
Cast is also lighter than steel, so that may have something to do with the need for external balance on the cast 340's and 360's. Not sure what they did with the 318's, unless the pistons got lighter.

Re: mopar crank
 

Use the 318/340 cast cranks, they internal balance just fine especially with the new combined weight specs. Also take advantage of the fact that you can use 2.100" large journal chevy rods the proper length on these engines. This spec is .024 under chrysler spec and opens a new world of bearing selection that isn't offered for 340's. Also it gets rid of the rolled factory fillets that cause rod journals to crack, thats if your crank guy knows how to put nice radiuses on the sides. Also it pays to have the crank hardened / nitrided as you won't belive how much happier the bearings look after the abuse you guys subject them to! Also select your oil pans wisely.....