340 crank questions

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gliderider06

gliderider06

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So, I have a cast crank 340 that needs a re-build. I was wondering if I could use an internal balanced 318 crank in the 340 instead? I was also contemplating on using a 360 crank, grind the mains down to the 340 journals and hanging .060 360 pistons on the rods, bore the block .020, and go that route as well. Will any of my ideas work?
 
..........U can use a 318 crank but will need to have everything balanced because the 318 crank is lighter....just do a 360 the.................kim...................
 
Anytime you start swapping parts around, you need to rebalance the rotating assembly. Even OEM balance jobs weren't that accurate, but were "acceptable". Most 318 cranks were cast also. But even the forged ones were also internally balanced for the lighter 318 components.

It's all been done. The 360 crank is a good way to get extra inches, but personally I wouldn't get too carried away building a higher HP and RPM combo around it. It's the larger mains that overlap the rod journals that help the strength on a cast 360 crank.
 
Summit racing has a 373 kit to drop in. Sell the 340 crank and such to off set the cost of the old tyme stroker kit.
 
You can use the lighter crank but if you are using the stock 340 rods and stock 340 weight pistons, you will have to add weight to the 318 crank and that will be costly.

That will all change if you use lighter pistons and/or lighter rods. We have a 273 crank in a 340 and with KB hyper pistons and SCAT rods, considerable weight was taken off of the 273 crank for balance.

What pistons and rods are you planning? It is not hard to take those numbers and compute the bobweight of the new combination and compare it to the standard 318 bobweight.
 
Compare the price of having the 360 crank ground down VS buying one. I built this combo about 16 years ago when the cranks weren't available. It cost me over $300 to get the crank ground down and my machinist cursed me out because he had to spend so much time on it. Its a good combo though. If I did it today I would buy one.
 
I was just thinking of ideas. I think the cast crank340 is good only needing a polish. I have the other 2 cranks/rod combo's sitting around and thought about making a mini stroker out of the 340. I have a 73 Duster I was thinking about putting the 340 in instead of the already built, Eddy headed 5.2 magnum I have on the stand. I think the resale value will be greater with a 340 in it versus a 5.2. I could use the Eddy LA top end assembled on the magnum, on the 340 and use the 5.2 elsewhere.
 
340 cast crank were used in 318s. Pistons are heavier which's why the 340 had to be balanced externally with the same crank. IIRC my '84 302-head 318 truck's crank and '73 340 had the same cast #.

gliderider06 said:
I was just thinking of ideas. I think the cast crank340 is good only needing a polish. I have the other 2 cranks/rod combo's sitting around and thought about making a mini stroker out of the 340. I have a 73 Duster I was thinking about putting the 340 in instead of the already built, Eddy headed 5.2 magnum I have on the stand. I think the resale value will be greater with a 340 in it versus a 5.2. I could use the Eddy LA top end assembled on the magnum, on the 340 and use the 5.2 elsewhere.
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That is the best way to sell a 340, with a car wrapped around it. And 'course the 360 stroker thing'd work. Actually not a bad plan since you can start with a 360 crank too worn to be usable in a 360 main application. Still will cost 'bout 3 bills most cases but you prolly won't pay for the core crank.
 
More kyoobs is always better. I like the 360 crank idea.
 
Though I have not done it myself, (and is like to try it.) the 360 crank in a 340 is a nice combo is like to try. Old tyme stroker when there were no other options for bigger.
 
I think I will talk to my machinists Friday and see how much it will cost to cut it down to the 340 mains.
I did search ebay today and found a 372 stroker kit for under 1, 100 I will have to see what shop costs will be plus parts if the kit will be the less expensive route to go.
 
I have a 340 balanced steel crank rotating assembly, rods and .030 over pistons. Though I don't recall what pistons they are right now. I'd sell it if interested
 
I got a 360 crank turned down to 340 mains. With stock low comp 318 pistons, i figure they are out only about .015 out of the hole. Enough to bolt some heads and Felpro gaskets on. Its not balanced and has a chipped crank flange between 2 bolt holes. FedEx dropped it in transit when I sold it. I refunded the dude and FedEx picked it back up, deliver it back to me AND paid $250 that I had it insured for....not the best way to sell a crank but I got my money...and the crank back. Ill use it for a mock up on a 273 I'm toying with. 318 crank will need to be lightened big time to handle the heavier 340 rods, thats where the 340 holes come from. Youll spend more in machine and mallory metal to balance that 360 than it would cost to buy an Eagle cast 3.58 or 4.00 stroke crank. Yeah, Eagle doesnt have the greatest name, but if you dont overwork them, they are ok.
 
Not exactly. The hardness is only super thin but the crank can be machines down to fit the smaller mains. Rehardening the crank is another issue and not mandatory to do but advisable to do.

The outer hardness doesn't limit the abilty to machine the crank.
 
pishta said:
I got a 360 crank turned down to 340 mains. With stock low comp 318 pistons, i figure they are out only about .015 out of the hole. Enough to bolt some heads and Felpro gaskets on. Its not balanced and has a chipped crank flange between 2 bolt holes. FedEx dropped it in transit when I sold it. I refunded the dude and FedEx picked it back up, deliver it back to me AND paid $250 that I had it insured for....not the best way to sell a crank but I got my money...and the crank back. Ill use it for a mock up on a 273 I'm toying with. 318 crank will need to be lightened big time to handle the heavier 340 rods, thats where the 340 holes come from. Youll spend more in machine and mallory metal to balance that 360 than it would cost to buy an Eagle cast 3.58 or 4.00 stroke crank. Yeah, Eagle doesnt have the greatest name, but if you dont overwork them, they are ok.
Click to expand...
For that matter,a Scat 9000 series crank,isnt much more...
 
rumblefish360 said:
Not exactly. The hardness is only super thin but the crank can be machines down to fit the smaller mains. Rehardening the crank is another issue and not mandatory to do but advisable to do.

The outer hardness doesn't limit the abilty to machine the crank.
Click to expand...
The


Can you Tufftride,a cast crank?....
 
gliderider06 said:
I think I will talk to my machinists Friday and see how much it will cost to cut it down to the 340 mains.
I did search ebay today and found a 372 stroker kit for under 1, 100 I will have to see what shop costs will be plus parts if the kit will be the less expensive route to go.
Click to expand...
The 372,is a sweet combo done right. Seen one,run elevens,in a 71 'Cuda(hydraulic flat tappet,ported x castings....
 
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