mopar crank

David Lee · 04-29-2008, 12:18 AM

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

Chris DeGidio · 04-29-2008, 08:54 PM

Yes.

George Mirza · 04-29-2008, 09:20 PM

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.

Myron Piatek · 04-30-2008, 11:38 AM

Quote:

Originally Posted by George Mirza

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.

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.

George Mirza · 04-30-2008, 07:42 PM

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

340Cuda · 04-30-2008, 09:38 PM

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

Myron Piatek · 04-30-2008, 10:03 PM

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.

Bub Whitaker · 04-30-2008, 10:28 PM

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.....

04-29-2008, 12:18 AM	#1
David Lee VIP Member Join Date: Oct 2007 Posts: 1,097 Likes: 404 Liked 250 Times in 101 Posts	mopar crank Can an 318 crank be legally used in a 340? They both have the same stroke and bearing sizes

04-29-2008, 08:54 PM	#2
Chris DeGidio Member Join Date: Jun 2007 Posts: 364 Likes: 8 Liked 2 Times in 2 Posts	Re: mopar crank Yes. __________________ Nautilus Racing

04-29-2008, 09:20 PM	#3
George Mirza Senior Member Join Date: Jan 2002 Location: North Attleborough Ma. Posts: 522 Likes: 0 Liked 0 Times in 0 Posts	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.

04-30-2008, 07:42 PM	#5
George Mirza Senior Member Join Date: Jan 2002 Location: North Attleborough Ma. Posts: 522 Likes: 0 Liked 0 Times in 0 Posts	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

04-30-2008, 09:38 PM	#6
340Cuda VIP Member Join Date: Apr 2003 Location: Tulsa, Oklahoma Posts: 1,570 Likes: 3,193 Liked 677 Times in 290 Posts	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

04-30-2008, 10:03 PM	#7
Myron Piatek VIP Member Join Date: Nov 2001 Location: Florida Posts: 1,538 Likes: 34 Liked 132 Times in 48 Posts	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. __________________ LOCOMOTION Racing

04-30-2008, 10:28 PM	#8
Bub Whitaker Member Join Date: Feb 2005 Location: Dayton, MD Posts: 222 Likes: 0 Liked 1 Time in 1 Post	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..... Last edited by Bub Whitaker; 05-02-2008 at 09:32 PM.