Re: How far have you run a turned down crank
[Re: scottb]
#2608954
01/19/19 01:23 PM
01/19/19 01:23 PM
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Joined: Jan 2003
Posts: 1,237 North Central, Indiana
Roughbird72
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,237
North Central, Indiana
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Many stock 440 cranks have had .125 taken off the mains to install in 400 blocks and taken a beating. I'm not sure another .010-.020 would make that big of a difference from where you're at now.
72 Plymouth Roadrunner 11.08@123.25
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Re: How far have you run a turned down crank
[Re: scottb]
#2608968
01/19/19 01:49 PM
01/19/19 01:49 PM
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Joined: Jan 2005
Posts: 2,540 Milwaukee WI
TRENDZ
master
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master
Joined: Jan 2005
Posts: 2,540
Milwaukee WI
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Turn it down to whatever you can get bearings for.
"use it 'till it breaks, replace as needed"
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Re: How far have you run a turned down crank
[Re: TRENDZ]
#2609047
01/19/19 05:17 PM
01/19/19 05:17 PM
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Joined: Feb 2007
Posts: 2,578 sweden
1Fast340
master
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master
Joined: Feb 2007
Posts: 2,578
sweden
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Turn it down to whatever you can get bearings for. This!
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Re: How far have you run a turned down crank
[Re: Roughbird72]
#2609051
01/19/19 05:26 PM
01/19/19 05:26 PM
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Joined: Dec 2003
Posts: 22,696 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Many stock 440 cranks have had .125 taken off the mains to install in 400 blocks and taken a beating. I'm not sure another .010-.020 would make that big of a difference from where you're at now. That makes sense to me. Wonder why for decades a .010-.030 turned crank was so frowned on.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: How far have you run a turned down crank
[Re: jcc]
#2609057
01/19/19 05:36 PM
01/19/19 05:36 PM
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Joined: Sep 2014
Posts: 4,457 Washington
madscientist
master
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master
Joined: Sep 2014
Posts: 4,457
Washington
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Many stock 440 cranks have had .125 taken off the mains to install in 400 blocks and taken a beating. I'm not sure another .010-.020 would make that big of a difference from where you're at now. That makes sense to me. Wonder why for decades a .010-.030 turned crank was so frowned on. Because back in the day, like before my time most likely the mid 70's at the latest undersized bearings all had the same shell thickness and the overlay was made thicker to get the next undersize. As the overlay became thicker (I've heard it was anything more than .020 under) it would start to migrate and then flake off. It became worse as the undersize was more and the HP/RPM went up. Now, they all use different shell thicknesses and they use the same thin overlay. Grind it down to small block Chevy large journal if you want. Makes bearing choice much easier. I did that on every Chrysler crank I did. The customer would [censored] like crazy until rebuild time came. No one wanted to grind a new crank, but I did it anyway.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: How far have you run a turned down crank
[Re: scottb]
#2609073
01/19/19 06:24 PM
01/19/19 06:24 PM
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Joined: Dec 2005
Posts: 11,566 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,566
Fulton County, PA
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I cut a 360 iron crank to 340 size to get some cheap cubic inches. Worked fine. Broke the motor, but it wasn't the cranks fault. Offset grinding to get a smaller pin + more stroke is common. My level of comfort would depend on the material.
If the results don't match the theory, change the theory.
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Re: How far have you run a turned down crank
[Re: scottb]
#2609076
01/19/19 06:28 PM
01/19/19 06:28 PM
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Joined: Feb 2005
Posts: 1,557 New Smyrna Beach FL
scottb
OP
pro stock
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OP
pro stock
Joined: Feb 2005
Posts: 1,557
New Smyrna Beach FL
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It’s a 4340 crank it’s a molnar 3.79
Last edited by scottb; 01/19/19 06:37 PM.
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Re: How far have you run a turned down crank
[Re: scottb]
#2609159
01/19/19 11:10 PM
01/19/19 11:10 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
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New York
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No data w/r/t MoPar cranks, but factors on regrinding other makes: 1. the drilled oil transfer hole is slanted in the journal, and is uncovered with a big undersize - lost OP 2. the grinding didn't use the correct cheek radius, too large (not enough metal removed) will bind the shell 3. crank stiffness is reduced by both the extra stroke and smaller journal, typically small enough not to matter. Read more in my article: http://victorylibrary.com/mopar/journal-c.htmI wrote an .xls spreadsheet to compare the actual (intersecting lenses) overlap area vs. nominal (diameters compared) area, e-mail for a free copy.
Boffin Emeritus
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Re: How far have you run a turned down crank
[Re: Dragula]
#2609284
01/20/19 01:03 PM
01/20/19 01:03 PM
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Joined: Jan 2003
Posts: 1,237 North Central, Indiana
Roughbird72
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,237
North Central, Indiana
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If you can get bearings for it, fine...Never seen -.03 though. I believe King makes a .030 under main bearing.
72 Plymouth Roadrunner 11.08@123.25
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Re: How far have you run a turned down crank
[Re: 500ciDuster]
#2609364
01/20/19 03:48 PM
01/20/19 03:48 PM
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Joined: Aug 2003
Posts: 43,176 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,176
Bend,OR USA
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Was thinking years ago they made .060 under for rods & mains Maybe for some other brands and industrial applications I can't remember the name of a company in SO CA that specializes in old car parts but I seem to remember them offering under size bearings for some old motors in .040 and maybe smaller I have seen .040 listed years ago for early Poly 318 motors and the same for the 273,318 and 340 LA motors
Last edited by Cab_Burge; 01/20/19 03:49 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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