4.0 crank grinding

John Hamilton · December 12, 2020, 07:27:32 PM

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?

John Hamilton · December 13, 2020, 01:37:50 AM

-- moved topic --

BlownMGB-V8 · December 13, 2020, 01:57:02 AM

Shouldn't

MGBV8 · December 13, 2020, 09:48:14 AM

How do the 3.9 cranks hold up with their 2.0" rod journals?

mgb260 · December 13, 2020, 11:28:06 AM

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 · December 13, 2020, 02:08:11 PM

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

mgb260 · December 13, 2020, 02:34:43 PM

Yep, .050, both sides and both ends.

minorv8 · December 14, 2020, 06:50:37 AM

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 · December 22, 2020, 11:55:50 AM

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.