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Stock engine RPMs

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RoMow:
Heymowers, 

   In the Driveline section, there is a post entitled "Getting speed out of Drive Shaft Mowers?" and one of the questions was about tweaking the governor to get more than 3600 RPM from the engine.  One of the Replies cautioned about going beyond 3800 RPM.  Allow me to share an incident from a factory service school:

   In February of 1999, I attended the Kohler Engine Level 2 Factory School in Kohler, Wisconsin, and on Thursday afternoon of the 5-day school, the class was given two Command 25hp V-twin engines to "do with whatever you'd like."  Since in our shops, we only see an engine needing repairs after it's been damaged, we decided we'd run one wide open and the other without oil.  For the wide-open engine, the instructor wired the governor open, set the engine stand outside (just in case), and started it up.  The tachometer read 5700 RPM -- for 45 minutes!  It never missed a beat, and would have run faster but the valve springs began floating, so 5700 was its maximum RPM-- well above the "recommended" governed 3600-3800 RPM.  Even with the factory muffler, the sound was impressive!

   Engine RPM limits are dependent on keeping with the design engineering of a maximum metal stress in a stock engine of 2,500 feet-per-minute (FPM) of travel, with allowable momentary speeds of 3,500 FPM.  An engine with a 3" stroke will travel 6" per revolution.  This engine turning 5000 RPM is at the 2,500 FPM industry-acceptable limit.  And with the precision manufacturing and materials of today's engines, these stresses are even more controlled.  An engine with a  2.75" (2-3/4") stroke can run over 5400 RPM to reach the 2500 FPM limit.  The stroke on the CH25 Kohler engines we maxed out is 2.64" which, at the 2500 FPM stress limit, is 5,681 RPM. 

   This applies not just to Kohler engines, but to all engines -- Tecumseh, Briggs & Stratton, Kawasaki, Honda, etc.

   Hope this helps. 

Respectfully, 
Rodney Rom 
Rom's Reworks 
Butler, MO
   

cycloneracer:
If racers want to keep their insurance they won?t spin engines faster than the recommended 3650 with a stock flywheel. 


This has been a long standing stance by heymow as well.

We don?t discuss or recommend dangerous practices.  This includes modifying a flywheel or running a stock flywheel faster than 3650.

RoMow:
Paul, 

   So, any engine run over 3650 RPM requires a billet flywheel?  What if the manufacturer's allowable maximum RPM is 3800-4000?  Some are --depends on the engine's Type or Spec Number. 

   I didn't post this to create issues -- my apologies if it did -- I was just noting that the engines can do this without self-destructing internally. 

Rodney

Knoot:
I think you saw my post, kudos for being able to give the guy better information than me, I don't know a bunch about those hydrostatic setups.

Thing is, you might be able to spin a honda engine that fast, but if you spin a B&S OHV at 5000 rpm, well lets say you're going to become very familiar with the internals very quickly. I've seen people blow up stock B&S engines in otherwise great shape even at 4000rpm. See https://www.youtube.com/watch?v=H3WUKBLJsF4

I wouldn't tell people to rev their briggs over 5000 rpm  :worried: at the very least they're going to have to buy a new engine, at the worst someone could get serious injuries when the rod decides to take a trip through the block and into their face.

cycloneracer:
According to the insurance companies 3650 is Max for stock flywheels.  Heymow agrees. 

I don?t make the rules

If I did they would look much different!!! And I?d probably still be racing.....

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