Heymow - Lawnmower Racing Forum

Engine Help => Briggs Flathead => Topic started by: joelwcassell on June 11, 2017, 02:15:51 pm

Title: Briggs 40CI to 42 CI
Post by: joelwcassell on June 11, 2017, 02:15:51 pm

Gentlemen, I am a newbie working on a Briggs Opposed Twin 40 CI engine.  I am putting it into a mower, and it will be stock from a RPM perspective but was wondering what I could do to improve low RPM torque.  The model number is 402437.

1.  My first thought was to increase the displacement.  I hear you can put a 42 CI crankshaft and rods in and they interchange?  I was looking at a crankshaft number 690639 (which fits a 422437).  It looks the same as my crank, but it does have an additional oil groove on the flywheel side that my crank didn't have, and it looks like it was cross drilled for oiling.  Are their any issues or other parts I should replace?
 Crankshaft can be seen here:  http://www.smallenginesuppliers.com/html/engine-specs/briggs/Briggs_421400_422400.pdf

2.  Any other ideas to improve torque?

Joel

Title: Re: Briggs 40CI to 42 CI
Post by: flatlanderfornow on June 22, 2017, 08:20:36 pm

sounds like a pressure lube crank, although a 422437 indicates splash lube. Should work fine to change the crank and rods.

Title: Re: Briggs 40CI to 42 CI
Post by: PJG56 on June 23, 2017, 08:04:05 am

2.  Any other ideas to improve torque?

Joel
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Keep it simple,advance cam 1 tooth and call it good