In the early months of the year, ‘cabin fever’ often
strikes the Stationary Engine Mailing List on the Internet. Subject
matter goes wildly off topic and tempers have been known to fray.
This year, however, we have enjoyed some of the best discussions
seen for a long time, including discussions on the correct way to
lift an engine, pouring babbitt bearings and making hopper
gaskets.
While ‘talking’ via e-mail about what people like to see
at shows, the subject moved from displays and the engines
themselves to how they should be run. Before long there was so much
information flying back and forth around cyberspace that even by
keeping to the most relevant and informative mails I found myself
with an article too long for a single issue of GEM. So, here is
Part 1 on the governing of stationary engines. Enjoy!
One thing to keep in mind when belting your show engine up is
whether you have a constant or variable load on the engine. If you
have a constant load, your hit-and-miss engine is going to be
hitting all the time, same as a throttle-governed engine. In other
words, your hit-and-miss engine that usually coasts for long
periods between firing will not be coasting anymore.
It’s my understanding that if a hit-and-miss engine hits all
the time it will damage the engine. If it hits all the time you
need a bigger engine.
I do know that a larger hit-and-miss engine will latch up on the
governor even if it is under a constant load. My 5 HP Economy would
hit all the time when we belted it up to several implements. My 9
HP Galloway would not. Perhaps someone with some old literature can
shed some light on this discussion.
That is not to say that hit-and-miss engines would not do the
work they were rated for or that running them at their rated speed
and work load would cause damage. It is simply and correctly saying
that any hit-and-miss engine pulling a load that does not allow the
Governor to function is an engine that is being asked to work above
and beyond it’s designed rating, and it will soon suffer from
such use.
I have heard this before, and have never seen any documentation
to tell me why. In other words, it takes a larger hit-and-miss
engine to perform the same work as a throttle-governed one? I
haven’t run my Alamo under load for more than an hour or so at
a time, but it hasn’t seemed to hurt anything.
It’s not good for lots of throttle-governed engines to run
at full power continuously, either. I notice the Wisconsin manuals
advise not loading them at over 80 percent of rated horsepower.
Even with the optional stellite-faced exhaust valves, seat inserts
and valve rotators. A hit-and-miss always ‘hits’ at full
power, so if it’s hitting continuously it’s wide open.
The first thing to suffer in an overloaded engine is likely to
be the exhaust valve. Different materials for valve heads and
seats, different designs of valve stems and guides, the cooling
around them, exhaust gas temperatures, free oxygen in the exhaust
gas, dwell time of the valve off the seat, exhaust backpressure,
contact of the valve face with the seat when closed, perhaps the
barometric pressure and phase of the moon, can all influence how
long a valve can last.
Exhaust valves in gasoline engines running hard can glow cherry
red and draw their heads out into a tulip shape as they bump into
the seat on closing. That’s where the idea to make some exhaust
valves in that shape came from. Our engines don’t run at the
high power densities of things like supercharged aircraft engines,
but I’ll bet something like my 3 HP IHC M with its uncooled
‘hot’ head can get the valve temperature right up there
under full power. Or a similar hit-and-miss hitting all the
time.
It would seem to me that for a hit-and-miss engine to fire every
second revolution would be much the same as running a
throttle-governed engine with the throttle wide open. In both
situations I am assuming the load will keep the rpm at the governed
limit. Not many engines like being run flat out for long.
I doubt that any manufacturer of these old engines intended them
to be loaded that heavily, but expected they could put out their
rated horsepower with less than full throttle or not hitting at
every opportunity. To run an engine at full output means that if
the load increases a little, the engine will be reduced in speed,
which will probably reduce output – and it may even die under load.
The effects of excessive heat on the exhaust valve may also, as has
been mentioned, lead to premature wear.
why do they put a rated speed on a hit-and-miss engine if it can
harm it to run that speed?
The rated speed is the number of revolutions per minute. It
doesn’t harm it to run at that speed. But, if the load is
increased to the point the engine is firing at every opportunity in
order to maintain the rated speed, you are getting maximum output
from the engine, and the increased heat load may bring about early
failure.
You are forgetting that the governed limit can be reduced by
quite a bit, at least on the three engines I have. I can set my
Alamo, which is rated at 360 rpm, to latch out at probably half
that speed. Of course, it isn’t producing 7 HP at that speed,
either. I am not going to run this engine wide open, but I
don’t think I have harmed it by running my cane mill or the
grist mill, both of which I run under full load much of the
time.
The only reference to favoring a throttle-governed engine over a
hit-and-miss in my old books is in applications that require a
constant speed. There is no mention of avoiding running a
hit-and-miss engine under a constant load.
These are books published in 1910 and 1912. Dyke also mentions
the same reasons in his short treatise in my 14th edition of
Dyke’s Motor Manual (1925). The reproduction ‘directions
for setting up and operating’ the IHC engines booklets I have
all say basically the same thing, and none of them mention anything
about operating speeds.
I’ve seen discussions of this in some of my early engine
books, but can’t seem to find them when I want to quote
them.
The thinking is that a hit-and-miss engine that is under too
much load not to miss never reaches its rated operating speed and
is constantly lugging. With a throttle-governed engine you would
almost need a tachometer to see if it is running at rated speed, or
watch to see if the throttle ever fluctuates. It wouldn’t kill
the engine in short order, but it would be overworked.
I have seen this also. However, if the hit-and-miss engine is
hitting every time, would it not be running at a constant
speed?
Faulty logic. The failure of the governor to latch up under a
heavy load is an indication that the load is so great the engine is
unable to overcome it and attain the set speed point. The speed
will not likely be constant.
As the demand for power increases the speed of the engine will
drop, and the pressures inside the cylinder will increase until the
amount of pressure required to force the piston down the bore is
greater than the amount of pressure created by combustion, at which
point the engine stalls.
The bearings and cylinder will heat up unless the lubricators
are opened up to increase flow to carry away the extra heat
generated.
Perhaps so, but perhaps not. The question was concerning a
hit-and-miss engine hitting all the time. I’ve done a little
reading (dangerous?) and a little thinking (always dangerous), but
try this out.
When a hit-and-miss engine ‘hits’ it fires with a full
charge in the combustion chamber. If it is firing with a full
charge all the time (and constantly) it is running at maximum all
the time. A throttle-governed engine hitting all the time is not
necessarily firing with a full charge in the combustion chamber.
There would be a full charge each time it fires only if the
governor were set to it’s maximum position. Usually this is not
the case, and I believe that constant firing in the maximum
position would likely damage the engine. I’d have to do some
more research, but I believe throttle-governed engine instructions
would indicate as much.
If I am correct here, running a hit-and-miss engine in such a
way as to not allow it to lock up on the governor, or to run a
throttle-governed engine with the governor set wide open for any
extended period of time, would have the same results. Either engine
can be expected to produce a BANG of the type we would prefer not
to hear!
We’ll continue this great conversation next month. See you
then.
‘It’s my understanding that if a hit-and-miss engine
hits all the time it will damage the engine.’
Why do they put a rated speed on a hit-and-miss engine if it can
harm it to run that speed?
Engine enthusiast Helen French lives in Leicester, England.
Contact her via e-mail at: Helen@insulate.co.uk You can join the
Stationary Engine List on the Internet at: www.atis.net
