340 crank..junk or saveable?

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cosgig

cosgig

MoBro Inc.
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Howdy all, I know a nice young man who is building a 340 for his 64 Cuda, and he is in need of a crank for his build. I have a crank for him, but upon miking all of the journals, I’ve found the mains to be 2.480 (.020 under) and the rod journals to be 2.110 (.015 under) The crank has been mag’d and the journals would need to be cleaned up and polished. Is this thing mill able, or is it junk? I’m offering it to him for the shipping, so in case it can be used he can spend his loot of cleaning it up. What do y’all think? It’s a Michigan to Washington ship and I don’t want to send him junk.

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Mr. Sinister said:
318 crank
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273/early318 cranks have a lot less rotating mass- they balance up nicely with a lighter weight reciprocating assembly for a sweet-revving 340. He can probably score one locally and have it prepped for less than the cost of shipping yours (which by the way, I wouldn't call junk!).
 
The problem with grinding cranks way undersize is two fold. Crank journals are induction hardened. It only goes so deep like case hardening. You can get bearings up to.06 under but those past.03 are Chinese and you may not be able to trust the quality. The other problem is the corner radius or the under cut on a mopar crank. You could also have the rods ground for chevy size rods, that is another option. Most machine shops that service big trucks and construction equipment are well versed in crank repair unlike most run of the mill automotive machine shops.
 
ch1ll said:
The problem with grinding cranks way undersize is two fold. Crank journals are induction hardened. It only goes so deep like case hardening. You can get bearings up to.06 under but those past.03 are Chinese and you may not be able to trust the quality. The other problem is the corner radius or the under cut on a mopar crank. You could also have the rods ground for chevy size rods, that is another option. Most machine shops that service big trucks and construction equipment are well versed in crank repair unlike most run of the mill automotive machine shops.
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that’s what I’m afraid of, and have been told that cleaning it up would likely compromise the hardening. I’m leaning towards not sending it
 
cosgig, re-measure your throws, from where I'm sitting I don't see any abnormal wear that would indicate a .015 under as opposed to a possible .010 under grind that was done on that crank!
Now if it is a 318 crank like Mr. Sinister has illustrated between the two variations , the 318 choice is a much more desirable selection when building a 340 WITH modern day light weight pistons and rods.
 
ch1ll said:
The problem with grinding cranks way undersize is two fold. Crank journals are induction hardened. It only goes so deep like case hardening. You can get bearings up to.06 under but those past.03 are Chinese and you may not be able to trust the quality. The other problem is the corner radius or the under cut on a mopar crank. You could also have the rods ground for chevy size rods, that is another option. Most machine shops that service big trucks and construction equipment are well versed in crank repair unlike most run of the mill automotive machine shops.
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I grind cranks down from the big, retarded Chrysler Rod throws to BBC (2.375 to 2.200) and small block Chrysler stuff down to SBC SJ (2.125 to 2.000) and never ever found an issue with hardness.
 
cosgig said:
that’s what I’m afraid of, and have been told that cleaning it up would likely compromise the hardening. I’m leaning towards not sending it
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that is why I suggested finding a big truck machinist. they repair cranks all the time. it costs too much to replace them. how would you like to pay for a new crank for a cat D10 bulldozer? I had a rod journal welded and reground on a chebby V6 that spun by a shop that specialized in that sort of thing, cant tell you how if faired however cause I sold the truck shortly after that.
 
yellow rose said:
I grind cranks down from the big, retarded Chrysler Rod throws to BBC (2.375 to 2.200) and small block Chrysler stuff down to SBC SJ (2.125 to 2.000) and never ever found an issue with hardness.
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and didnt the folks that do that work for you specialize in that sort of thing? did you ever ask them if they re-hardened it? if they have the means and experience its not that hard to do.
 
yellow rose said:
I grind cranks down from the big, retarded Chrysler Rod throws to BBC (2.375 to 2.200) and small block Chrysler stuff down to SBC SJ (2.125 to 2.000) and never ever found an issue with hardness.
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Ken from Oregon Cams said it's all bullshit about grinding hardness off on Chrysler cams and cranks. He told me Chrysler hardened their cams and cranks almost to the core.
 
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ch1ll said:
and didnt the folks that do that work for you specialize in that sort of thing? did you ever ask them if they re-hardened it? if they have the means and experience its not that hard to do.
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Anyone that’s a decent machinist and has a crank grinder can do it. Nothing trick involved in it.
 
RustyRatRod said:
As long as youhave good oiling, is the hardening thing really "ALL THAT" important? I've never thought so......
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It’s not. Unless you are really beating on them. I turned most of my cranks to SBC LJ and a few to SBC SJ because bearings were much easier to get. Of course you have to use chevy rods, but it’s worth it when you need to find bearings in a pinch.
 
I've run .030 crankshafts with no problems over the years, & as stated grinding beyond the hardened portion is a MYTH.
 
Times 3 on thats bullshit. Just think of all those 451s that are blowing up everywhere from being cut up B size mains...
 
cosgig said:
Howdy all, I know a nice young man who is building a 340 for his 64 Cuda, and he is in need of a crank for his build. I have a crank for him, but upon miking all of the journals, I’ve found the mains to be 2.480 (.020 under) and the rod journals to be 2.110 (.015 under) The crank has been mag’d and the journals would need to be cleaned up and polished. Is this thing mill able, or is it junk? I’m offering it to him for the shipping, so in case it can be used he can spend his loot of cleaning it up. What do y’all think? It’s a Michigan to Washington ship and I don’t want to send him junk.

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I don't like the look of that throw with the chunk missing out of it in the last photo.
 
toolmanmike said:
I don't like the look of that throw with the chunk missing out of it in the last photo.
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that’s not a chunk missing, it’s the rough edge of the weight. You can see on the one next to it that it is sort of ramped to a ledge, the one next to it going the other way. I suppose it could be cleaned up, but may change the balance if you did.
 
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