MAXIMUM CRANK UNDERSIZE

[CFD244]

What say ye all!

How far undersize can you practically take a forged internally balanced 340 crank. Referring to both rods and mains.

Thanks

 

[RustyRatRod]

People routinely have the 440 cranks ground down to 400 size on the mains to fit the 440 crank in the 400 for a 451. That's a .125" cut.

 

[rumblefish360]

Depends on how thick you can find the replacement bearing. I’ve seen .030. Don’t know if you can still find them, good luck with the search.

 

[ch1ll]

Go far enough and you grind out the hardened bearing surface.

 

[33IMP]

Depends on how thick you can find the replacement bearing. I’ve seen .030. Don’t know if you can still find them, good luck with the search.

Thats it. You can cut as far down as you can find bearings for.

 

[PROSTOCKTOM]

In todays supply issues .030" under on the mains and .030" undear on the rods will probably be all that you'll find. 30-years ago you could have found .060" under for either journal. Worrying about the balance will be no issue. What you take off the crank you add back with the thicker bearing shell. If your still concerned just remember a 500" NHRA engine uses a 2.5" main journals/ 1.88" rod journals and turn almost 11,000 rpms. To many people get freaked out on under sized bearings. If you need more than .030" under to correct your problems I would try posting an wanted ad for whatever size you need to make it right, weld the crank back to standard, or get a different crank.

Tom

 

[33IMP]

You can always cut it down to a small chevy size on the rod bearings, run long small chevy rods and custom pistons. A lot of work and expense to save a crank.....

 

[RustyRatRod]

Generally speaking, induction hardening goes down about 3mm or so dealing with the diameters we're talkin about. Nitriding even further. I've talked to Ken Heard at Oregon Cam Grinders and he says on Chrysler camshafts and crankshafts alike, they are hardened much deeper than a lot of other makes stating that the camshafts are hardened almost clear to the center of the core and crankshafts he's had experience with are hardened to the tune of around 3/8". That's pretty dang deep. I'll also add I've never in my life heard of anyone having a problem with a 440 crank in a 400 because of the hardening being ground away, so there must be something to it. The Chevy boys used to do it by the truckload putting the 3.75" stroke small block 400 cranks in the 350. Never seen a mass problem there, either and all those cranks were cast. This was long before all the stroke stuff was available over the counter.

 

[ch1ll]

One does wonder how deep the hardening actually is, testing is destructive.

 

[oldkimmer]

I have used .060 bearings and had the crank Offset ground. Kim

 

[CFD244]

I've got a line on a .020/.020 crank. Unfortunately there is a enough scoring to feel with a fingernail. Not sure if another .010 will do it.

 

[needsaresto]

Generally speaking, induction hardening goes down about 3mm or so dealing with the diameters we're talkin about. Nitriding even further. I've talked to Ken Heard at Oregon Cam Grinders and he says on Chrysler camshafts and crankshafts alike, they are hardened much deeper than a lot of other makes stating that the camshafts are hardened almost clear to the center of the core and crankshafts he's had experience with are hardened to the tune of around 3/8". That's pretty dang deep. I'll also add I've never in my life heard of anyone having a problem with a 440 crank in a 400 because of the hardening being ground away, so there must be something to it. The Chevy boys used to do it by the truckload putting the 3.75" stroke small block 400 cranks in the 350. Never seen a mass problem there, either and all those cranks were cast. This was long before all the stroke stuff was available over the counter.

I'd call this a definitive answer, there's expertise being quoted.Don't worry about it is the answer. Mopar boys been dropping 440 cranks in 400 blocks long before there was anything aftermarket.