Crank question

[LinceCuda]

Ok so George calls me from the machine shop and says your 340 block is in great shape and all tests were negative for issue's. So he put new cam bearings, freeze plugs, and bored it another .010 giving it a total of .040. Then he said your crank has been turned .030 on both the main and rod journals. The rod journals are in good shape but if I want to make them perfect he could go to .040. The mains need to go to .040 and would be fine for cruising around but if I'm going to the drag strip or serious street racing I need a new crank, I'm just going to use it for street driving. The problem he has is all his info shows 318 - 340 main bearings are the same until you get to .040 over the part number changes for the center crush bearing. He can't find any maker for that center bearing but you can get a full set of .040 for a 318. So is this a issue because I have a factory steel crank and it is different from the cast crank, Oh and my engine is a 71 340 with it's original crank. Anyone run into this before? Thanks

[Chryco Psycho]

I have never taken a crank past 30 under so no I have nt run into this issue , The 318 set should be fine , it makes no difference with Cast or Steel crank
But at this point why not stroke the engine & go to 412 CI but keep the bore @ .040 with crank rods & pistons , the cost has to be similar ?

[Shane Kelley]

As CP said the 318 bearings will work just fine. But I never have cut a crank past 30 either. If everything is balance and machined correctly it shouldn't give you any problems. The other solution would be to find another crank.

[71GranCoupe]

Years ago at a major engine re-builder located in Spokane Wa told me the 318 forged crank is the same thing as a 340 crank. All the specs are the same. Lots of 318's with forged cranks and many have never been turned. So with that in mind, find a 318. I just hauled one off for scrap. 

[RUNCHARGER]

As long as you can get bearings I wouldn't worry about cutting it. As soon as a crank needs $$$ put into it though it is stroker time for me, unless you've already bought pistons.

[Chryco Psycho]

Years ago at a major engine re-builder located in Spokane Wa told me the 318 forged crank is the same thing as a 340 crank. All the specs are the same. Lots of 318's with forged cranks and many have never been turned. So with that in mind, find a 318. I just hauled one off for scrap. 

Not quite true , physically the cranks are the same but the balance is different so you would have to spend $$ on balancing which is not a bad thing , but the 318 froged crank is not a true drop in  .

[71GranCoupe]

Years ago at a major engine re-builder located in Spokane Wa told me the 318 forged crank is the same thing as a 340 crank. All the specs are the same. Lots of 318's with forged cranks and many have never been turned. So with that in mind, find a 318. I just hauled one off for scrap. 

Not quite true , physically the cranks are the same but the balance is different so you would have to spend $$ on balancing which is not a bad thing , but the 318 froged crank is not a true drop in  .

Ya, you are probably right on the balance part, never got into the details. I believe the company is still around today and they have a full blown machine shop so if a crank needed balanced, it was an easy task for them. They shipped short/long block assemblies all over the states.

[LinceCuda]

Yes the way I heard it was a 318 you have to add weight which cost more bucks as opposed to a 340 where you usually remove weight. The other issue is 68-71 340 cranks differ from 72-73 on the external internal balance issue. I have located a 71 340 crank  from a friend machined and ready to go $325 he also has a 73  340 ready to go $225. I don't think I could go wrong with his 71 so I plan to grab it tomorrow. Just want to say thanks for all the input much appreciated.

[Chryco Psycho]

[I would use a forged 318 crank over a 73 cast 340 crank
I would also remove weight by polishing the beams & removing the weight on the cap & running lighter pistons in the 340 to reduce rotating mass so you may not have to add weight to a 318 crank to make it work but you will have to pay for the balancing

[LinceCuda]

[I would use a forged 318 crank over a 73 cast 340 crank
I would also remove weight by polishing the beams & removing the weight on the cap & running lighter pistons in the 340 to reduce rotating mass so you may not have to add weight to a 318 crank to make it work but you will have to pay for the balancing

I agree CP that's why for the price of his 71 340 crank I don't think I can go wrong. I plan to get it tomorrow and take it to George to looking over. My friend says it's ready to go but he is going to let me pay for it after it checks out..

[Chryco Psycho]

Cool , I hope it is good