72DartSwingerV8
Well-Known Member
Are the cranks the same? I was under the impression that both have the same stroke but different bores. Is that true or is the stroke on a 340 different? Thanks
318 v 340 Crankshaft
- Thread starter 72DartSwingerV8
- Start date
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cudavert
DARTAHOLIC
Unless there is some difference in the weight of the counterweights, I would believe they're the same.....3.31 stroke and the mains/rod journals the same too....
The only difference is most 318's are cast cranks except the early ones and some of the trucks. Unlike the 360 cast crank though, the 318 cast cranks are internally balanced so they will work in the 340's if you don't mind running a cast crank.
They will both fit(318-340) but the balance is different so it would have to be balance.........this could be good or bad(Talking about the hard to find steel version)
If you want to put it into a stock 340, it will require Mallory metal, which is vary expensive
Now if you were looking to make a high winding 340 W/ light weight part,(aka Light Weight custom Piston and alu. Rods) the 318 crank could cost a lot less, to balance.
I have a 318 steel crank in a p.o.s. dodge motor home, that i had thoughts about............But have decided that a slow turning Stroker will be much more maintenance free, and longer life then a zinging 8000+ rpm 340 and cost less too!........But it still would be fun:cheers:
Very good point, same thing with the 273 crank, even less counterweight than a 318 crank. All three engines have same stroke/main journals.
72DartSwingerV8
Well-Known Member
So a forged 318 crank would be good? I'm not looking for a screaming 340 just a fun one.
Longgone
John/68 Barracuda & Dart
Unless you go with super-light components you`ll have to add weight to the crank which is expensive.
72DartSwingerV8
Well-Known Member
So I basically need to find a 340 crank because it is heavier. Are forged and cast about the same weight? How much weight needs to be added on?
Longgone
John/68 Barracuda & Dart
Yeah starting with a 340 crank would be easier. 68-71 used a forged crank, that would be your best bet but if all you can find is a cast crank, that would be fine for your application.
It doesn't matter what crank you use, you need to have everything rebalanced anytime you switch cranks, rods or pistons. Even if they are the same size engine. Your engine should be balanced withing 3 grams and those that don't know how much that is, a dollar bill is about gram.
It is correct that the 318 crank has less counter weight, but if you are running after market pistons, you will more than likely still have to remove some weight since most after market pistons are considerably lighter than stock, even stock replacement pistons are a lot lighter than stock.
It is correct that the 318 crank has less counter weight, but if you are running after market pistons, you will more than likely still have to remove some weight since most after market pistons are considerably lighter than stock, even stock replacement pistons are a lot lighter than stock.
Yes but what they are saying is it will be cheaper to remove a bit of weight then have to add weight. So there will be a bit of cost savings in using a 340 crank over a 318 crank in most cases. If you aren't going for a screamer then a cast crank will be fine.
I understand that, my point was that most aftermarket pistons are still lighter that stock 318 pistons so you probably wouldn't have to add weight. I would weight everything first if it is a concern.
72DartSwingerV8
Well-Known Member
Alright, so the most cost effective way to do this would be getting a forged 318 crank and have some metal removed, balanced, with aluminum pistons and all that stuff. It would be cool to get a 340 crank but I really don't like the idea of metal added and the cost of that will obviously be a lot more. AM I missing anything?
I don't know about that, the 318 crank is the lighter crank. I would have the 318 pistons weighed and then check around for aftermarket pistons, most manufactures have the weight advertised with the piston so you wouldn't need to buy any till you know for sure.
It would definitely be easier to find a good 318 cast crank than a good 340 crank but the forged 318 cranks aren't as easy to find as a cast 318 It would be cheaper as long as you get aftermarket pistons that are lighter than the stock 318 pistons. I personally would stay away from the cast 340 cranks.
With all things considered though, if all you have is a block, the cheapest may be to buy a stroker kit since any used crank will need machine work as well as the rods. some of the stroker kits come complete and balanced ready for use. The reason a lot of people use to use the 318 cranks in 340's is because there were really no options for aftermarket cranks 20+ years ago and it was the only option to build a 340 if all you had was the block or one with a bad crank.
The best advice would be to shop around and get the prices from machine shops on the machine work needed with an old crank and the prices from aftermarket companies on the parts you need to use the 318 crank, 340 crank or a stroker kit and make your decision based on what you find.
72DartSwingerV8
Well-Known Member
Hmm, aren't prices for a stroker kit really expensive? Do you only need a crank with the rest being stock stuff? I've never really worked on an V8, only inline sixes. The price i have right now is $500 for a 340 block, 318 forged crank, j heads, intake, with everything in between. I just have to rebuild it all. SHould I go with that? or look around some more? Are Eagle stroker kits any good?
AARCuda I probably won't be attending because I don't have a finished mopar, extra money for the trip, and I'm not old enough to enjoy Vegas to the full extent haha.
AARCuda I probably won't be attending because I don't have a finished mopar, extra money for the trip, and I'm not old enough to enjoy Vegas to the full extent haha.
Mad Dart
Nothing to see Here!
Take the block in for the Normal Machine work Sonic check etc and have your rotating assembly balanced with what you have when you buy your pistons. You can get KB pistons for around $200.00 rings, bearings etc about another $200.00. Put it together with what you have and go have some CHEAP FUN!!!
Well I mean Cheaper fun.......:cheers:
Well I mean Cheaper fun.......:cheers:
.........so this is a running eng that just need to be rebuilt? Or. just a bunch of spare parts some one has.
If it is just a bunch of spare part, then, it sounds like He found out just how much it was going to cost for machining and is selling them now!
If it's a running eng then you just need to put the same brand(aks weight) piston back in when rebuilding..........It was balanced before.
That's not a bad price if everything is usable, even if you had to ad some weight to the crank. Just make sure the bore and crank journals are in good shape and not past the point of machining.
72DartSwingerV8
Well-Known Member
The guy owns Sweetwater Wrecking and is a pretty honest person. It's a bunch of spare parts so I have to put it all together. Everything is in tolerance so no issues there. I'll have to talk to him and figure it out. Maybe I'll be able to find a 340 crank close to home.
mopar340dave
Well-Known Member
about two thirds of the way down it talks about the stock internals:
http://www.allpar.com/mopar/318.html
http://www.allpar.com/mopar/318.html
Longgone
John/68 Barracuda & Dart
There`s a guy on Ebay that sells early OE 340 cranks that are reground. They come with both rod and main bearing sets for around $375.00.
2 Darts
A-body Addicted
No, the cranks are different. Both the 340 and 318 have a 3.31 stroke and the same rod and main journal sizes, but that's where the commonality ends. You are correct, however, the stock 318 bore is 3.91", and the 340 is 4.04".
All 67 & > 318s in cars used cast cranks that were balanced for light duty rods.
All 68-72 340s used forged cranks that were balanced for heavy duty rods.
The 73 340 used a shot peened cast crank that was balanced for heavy duty rods.
Alternative sources for LA 318 forged cranks are all balanced for light duty rods and include some LA 318 trucks, 64-67 273 LA, and 57-66 318 poly V-8.
The confusion may arise from the 360 crank. This cast crank has a 3.48 stroke and is balanced for heavy duty rods. The rod journals are the same as the 318 & 340, but the mains are larger. For this reason, the 360 crank can not be used in the other LA blocks without turning the main journals and re-hardening them.
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