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L79 - Crankshaft?

brumbach

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Mar 6, 2004
Messages
330
Location
Middleboro, KY
Corvette
1965 convertible
I'm building (or having built) a correct L79 for my 65 vette. I've got the block, heads and intake manifold. Now for the internals. I've located a crankshaft with the following description. Will it work? What difficulties may I encounter if I use it?

"It has been index ground on the rods only. This is a process where the journals are all ground exactly 90 degrees from each other when blue printing an engine. It has sat around a significant time since grinding and will need to be ground on the mains for sure and maybe a regrind on the rods also. It is currently standard on the mains and .020 on the rods. It is part number 4577."
What's your thought on this one? " #2680 forged crank small journal, It mic's at 2.300 mains and 2.000 rods."
Thanks,

Bill
 

Tom Bryant

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7,333
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
I can't understand why a crank would need to be reground just because it has set around unless someone let it get rusty. I have an index ground 3" 283 crank that has been laying around here for 30 some years. I coated it with a cosmoline type of compound and I check it occasionally. It is as good as it was when I first bought it. If that crank is so rusty that it can't just be polished I'd doubt that it will turn down to a still usable demention. The journals are only surface hardened and the more you grind off the closer you get to softer metal.

Index grinding is a good thing to do for a race engine but not necessary on a street rebuild. It just assures that the journals are at exact 90 degrees from each other. That can become critical when using a very high lift racing cam that leaves little clearance between the open valve and the piston top. If a journal is off a few thousands then there is a possiblilty of parts meeting that weren't supposed to.

I would pass on this crank unless you can take it to your machine shop to have them check it out before you buy it.

Tom
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
That crank was originally "Tufftrided", which is a surface hardening treatment about .010" deep; unfortunately, the Tufftriding has now been ground away on the rod journals and will disappear from the mains when they're ground. I'd pass on it.

:beer
 

brumbach

Well-known member
Joined
Mar 6, 2004
Messages
330
Location
Middleboro, KY
Corvette
1965 convertible
There is no new replacement cranks for the L79, right? If there are none, should I be looking for a unmolested 4577 or 2680? Would it make any difference where it was a 4577 or 2680? What about 3884577?
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
A 4577 or 2680 will work fine, preferably not cut more than .010"/.010"; all small-journal 327 cranks are forged steel, so they're plenty stout. :)
 

brumbach

Well-known member
Joined
Mar 6, 2004
Messages
330
Location
Middleboro, KY
Corvette
1965 convertible
A 4577 or 2680 will work fine, preferably not cut more than .010"/.010"; all small-journal 327 cranks are forged steel, so they're plenty stout. :)

I found a 2680 on ebay that's been reconditioned with the following: Mains @ .020 and rods @ .010. Should I pass?

S
 

brumbach

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Joined
Mar 6, 2004
Messages
330
Location
Middleboro, KY
Corvette
1965 convertible
A 4577 or 2680 will work fine, preferably not cut more than .010"/.010"; all small-journal 327 cranks are forged steel, so they're plenty stout. :)

But if it is cut to .010/.010 wouldn't the hardening treatement (Tufftrided) be removed since it's only to that depth?
 
Joined
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Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
But if it is cut to .010/.010 wouldn't the hardening treatement (Tufftrided) be removed since it's only to that depth?

Yes, but it's still a good forged crank; the Tufftriding provides additional wear resistance on the journals, but the way we care for and use these cars, you'd never see the difference. I just don't like to see them cut more than .010"/.010".

:beer
 

brumbach

Well-known member
Joined
Mar 6, 2004
Messages
330
Location
Middleboro, KY
Corvette
1965 convertible
Yes, but it's still a good forged crank; the Tufftriding provides additional wear resistance on the journals, but the way we care for and use these cars, you'd never see the difference. I just don't like to see them cut more than .010"/.010".

:beer

Well I've bought and received a 4577 crank. I'll be taking it to a auto machine shop in the morning to have it magnafluxed. If it checks out, what do I tell them to do to recondition it? It is supposedly standard on the journals. So I guess I should tell them to grind the main and rod journals at .010 under, right? I'd like get it balanced too. What about polishing? Anything else?
 

Tom Bryant

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Joined
Nov 9, 2000
Messages
7,333
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Well I've bought and received a 4577 crank. I'll be taking it to a auto machine shop in the morning to have it magnafluxed. If it checks out, what do I tell them to do to recondition it? It is supposedly standard on the journals. So I guess I should tell them to grind the main and rod journals at .010 under, right? I'd like get it balanced too. What about polishing? Anything else?

No. Don't cut it undersize if it doesn't need it. That's just wasting a good standard crank. If the machine shop says it's ok and will polish up fine that's all it needs.

Tom
 

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