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John Hamilton
John Hamilton
Navarre, FL
(23 posts)

Registered:
10/28/2009 11:18PM

Main British Car:
1965 MGB 1840 cc MGB

4.0 crank grinding
Posted by: John Hamilton
Date: December 12, 2020 07:27PM

Just wondering if I can turn down a 4.0 crank from 2.185" down to 2.1" so I can use Chevy rods? Will this compromise strength in a 7000 RPM race motor?


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(6469 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: 4.0 crank grinding
Posted by: BlownMGB-V8
Date: December 13, 2020 01:57AM

Shouldn't


MGBV8
Carl Floyd
Kingsport, TN
(4512 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB Buick 215

authors avatar
Re: 4.0 crank grinding
Posted by: MGBV8
Date: December 13, 2020 09:48AM

How do the 3.9 cranks hold up with their 2.0" rod journals?
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mgb260
Jim Nichols
Sequim,WA
(2463 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: 4.0 crank grinding
Posted by: mgb260
Date: December 13, 2020 11:28AM

If you use the 2.1 rods, make sure you use the ones with 3/8" bolts. The 7/16" ones are too wide.


minorv8
Jukka Harkola

(269 posts)

Registered:
04/08/2009 06:50AM

Main British Car:
Morris Minor Rover V8

Re: 4.0 crank grinding
Posted by: minorv8
Date: December 13, 2020 02:08PM

I am not 100 % sure but I believe than you need to machine the rods narrower anyway.


mgb260
Jim Nichols
Sequim,WA
(2463 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: 4.0 crank grinding
Posted by: mgb260
Date: December 13, 2020 02:34PM

Yep, .050, both sides and both ends.


minorv8
Jukka Harkola

(269 posts)

Registered:
04/08/2009 06:50AM

Main British Car:
Morris Minor Rover V8

Re: 4.0 crank grinding
Posted by: minorv8
Date: December 14, 2020 06:50AM

My stroker crank has TVR sized rod journals (narrow) and the rod big end width is 19,4 mm ( just over 3/4"). They needed a bit more machining. Also the bearings had to be machined narrower.



roverman
Art Gertz
Winchester, CA.
(3188 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: 4.0 crank grinding
Posted by: roverman
Date: December 22, 2020 11:55AM

Hi John, First off, you have verified all manner of components to get you max power at 7k rpm. ? If so, by all means, 2.100 journals. Don't assume taking .050" off each side of big end of rod will put end, in center of bore . Use bigger fillet on journals, if possible. If 3/8" bolts, use AP 2000.
What is your hp. level ? Don't expect your cast iron crank to live many happy racing miles, at hi hp. and rpm.
Good luck, Art.


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