Re: Governors on 345/392 engines...

[jlandry@domain.elided (John A. Landry)]

While making mud pies in the back yard, jmbrodsky@domain.elided giggled:

>        I posted about this some weeks back but never heard a reply.  
>     The questions is:  How does the governor work to limit the revs at 
>     3900 for the 345 and 3600 for the 392?  Is it electrical, and if 
>     so, can I use it to power a tach drive?  If it's mechanical 
>     how-d-hell do they do it?  It seems to really drop off quick in 
>     power when I get around 3500rpm, but it doesn't sound like it's 
>     cutting the ignition.

What type of IH vehicle is this on Joel?

I know I'll be immediately corrected if I'm wrong, but I don't think you're
going to find a governor on the stock engines in the Scout II series.  I
can't say about the earlier Scouts.  I'm sure they were most used on heavy
IH vehicles.

I have seen references and repair instructions for IH distributor mounted
governors in the IH shop manual.  While I don't know for sure, I suppose
the IH distributor mounted governor retards the timing by varying degrees
to limit power beyond a certain rpm.

If you do in fact have a stock IH engine (not one swapped in from a bigger
vehicle like a dump truck or bus) and you *think* you have a governor, then
something else is possibly wrong.  You could have weak valve springs or a
problem with fuel delivery or a problem with the carburetor.

That being said, certain aspects of the mechanical design of the engine
will naturally limit the maximum rpm it can achieve.  Typically the valves
begin "float" instead of being able to properly open and close at higher
rpms.  Also, the capacity of the ignition system to effectively and
accurately fire each cylinder in the neighborhood of 40 - 50 times per
second (at 5000 - 6000 rpm) can also be a limiting factor.  If some design
characteristic or capacity doesn't naturally limit the rpm first, then
mechanical failure of a part will... like a connecting rod flying out of
the oil pan!

Repeatedly exposing an engine to high rpms (for which it was not designed)
can damage parts even if there isn't some catastrophic failure.  Valve
springs are one of the more common items to be weakened, although
(depending on the design of the engine) bent valves and damaged pistons can
also occur.
     
>        Any ideas?  I'm just curious, and I'm not planning on going up 
>     to 5000 rpm soon, like any Ch@^y owner out there.

Smart move!  For the long life and health of your engine, I sure wouldn't
exceed the redline (or even come close to it) unless I beefed the engine up
substantially.

As an aside, I have a Honda V65 Magna motorcycle and it redlines at 13,000
rpm!!!  That's scary... I can't begin to imagine the g-forces some of the
internal engine components are subjected to at those high rpms.  And think
about this... at 13,000 rpm, the air / fuel mixture has to be ignited in
each cylinder approx. 108 times *per second*!  And if that isn't enough, in
the case of the V65 Magna with it's solid state ignition, each spark plug
is fired for each revolution of the engine crankshaft (verses every second
revolution on a normal four-stroke engine).  The spark plug is fired at the
beginning of the power stroke and the exhaust stroke.  So at 13,000 rpm,
each spark plug is fired approx. 216 times each second.  It's a wonder it
even works!

And this concludes another exciting episode of "Those Amazing Machines."

Regards,

John
------------------------------------------------------------------------
jlandry@domain.elided             |
Conservative Libertarian        |  Scout(R) the America others pass by
Life Member of the NRA          | in the Scout Traveler escape-machine.
WA Arms Collectors              |
Commercial Helicopter - Inst.   |    1976 Scout II Traveler "Patriot"
http://www.halcyon.com/jlandry/ |