Grumman-581 wrote:

Well, I've got some new information on my testing of my engine... Perhaps
this will make sense to someone...

I brought the boat home the other day so that I could do some testing on
it... As expected, it was rather difficult to start... The battery being
somewhat low didn't help matters much, but with a little starting fluid
sprayed into it beforehand, it fired... After a couple of times of this, it
ran long enough for me to get to the engine compartment so that I could give
it a burst of starting fluid every few seconds to keep it running... After a
minute of this, it was able to run on it's own with me just advancing the
throttle a little bit.. I looked at the engine installation, but I could not
find any sort of check valves in there... I don't doubt that they are there,
but the engine compartment is somewhat crammed and I probably don't really
know what I'm looking for...

I checked the cover on the oil reservoir over the engine and it was tight...
I checked the caps on the external oil reservoir and they were tight also...
I noticed a placard that said that if the caps were loose, it could result
in insufficient oil going to the engine... This got me to thinking, so I
loosened the cap on the reservoir and noticed air pressure was being kept in
there so I suspect that one of the hoses that runs to it is to pressurize
the reservoir to use that to pump the oil into the main reservoir over the
engine... After I shut down the engine, I noticed that there was still
pressure in the reservoir... Is this normal?

Yes they harvest crankcase pulse pressure into the tank to be the "pump" to
get it to flow, first up to the engine tank & then as you found into the engine
metering/pump system.

If this reservoir is under
pressure even when the engine is off, could it perhaps cause it to flood the
engine with oil?

Not normally because when the engine stops turning so too does the metering
system & the pressure soon seeps away, which means the oil "shouldn't" keep
going, but age & wear???

I tried to start up the engine soon after having shut it
down and it did not have a problem... I then again released the pressure in
the external oil reservoir... I came back to it today and attempted to start
it again without using starting fluid... Normally a wait of a day would
result in me having to use starting fluid to start it and there being a lot
of smoke being produced as the engine burnt off the excess oil that was in
the cylinders... That was definitely not the case this time... So, I have a
way around the problem, but I don't know exactly what the problem is really
caused by... Anyone have any ideas?

As originally said it's designed to try & fail safe,

(i) i.e. you run out of oil in the bottom tank?? no "immediate" danger
because you still have oil in the engine tank.

(ii) The engine tank is level alarmed (the cap??) so if it gets low on oil
as say the bottom tank is empty, but this is getting scary bananas close to a
serious problem because it can last a little while just on the engine tank (1/2
hr max) however once the last of that is gone........

(iii) The oil is pressure & gravity fed (as you've noticed) to the engine's
metering/pump system which is crankshaft driven & linked to the throttle
position. The metering/pump should turn whenever the engine does & give more or
less oil per turn depending on the throttle position. If this pump fails (the
drive uses plastic gears!!! & they break) some oil (In a clean system with nice
new filters etc etc maybe enough, in an old boat just out of winter??? maybe
not) still gets though just under the tank pressure & gravity, so it sorta
"fails half safe" :-)

(iv) As the metering/pump gets older it lets more & more oil through so you
see more smoke & if you tamper with the link adjustment to the throttles you
run the risk of under oiling at high speed (not to be done)

Like Yamaha the system is not too bad when newish & working as intended but
as moisture builds up each winter in the oil holding tank(s) & the bits &
pieces wear it gets less & less reliable till one day ??? Don't feel too bad;
the OMC system is such a bad design it should have been disconnected at the
factory, no gravity feeds nothing & an alarm that can only detect the obvious,
beit too late.

Again the safe thing is to do away with it & mix tcw3 in the tank @ 50 to
1. The dealers of course deny any of this but they have a vested interest & if
you choose to have the system properly serviced by one, you'll see exactly what
that is.

K