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Old 15 January 2009, 14:10   #1
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Running Prop in Air

I've seen this a couple of times at boat yards and engine dealers. They are running up an outdrive or outboard on flush muffs and have the forward gear engauged with prop spinning round.

Obviously this IMHO is a very dangerous practice, but is it damaging to the bearings and gears in the gearbox. With no water, there is no forward thrust or load applied. So guess it's not going to be too good.

What do you think?
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Old 15 January 2009, 14:56   #2
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OK I'm a newbie - but what is a 'flush muff'? I have a flush hose in my Mer Optimax which I use to flush the engine after a run is that what it is? Is is safe to run an engine with water running through it on the flush hose?

Duh!!
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Old 15 January 2009, 14:58   #3
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Quote:
Originally Posted by Hightower View Post
I've seen this a couple of times at boat yards and engine dealers. They are running up an outdrive or outboard on flush muffs and have the forward gear engauged with prop spinning round.

Obviously this IMHO is a very dangerous practice, but is it damaging to the bearings and gears in the gearbox. With no water, there is no forward thrust or load applied. So guess it's not going to be too good.

What do you think?
Depends how hard they are revving it. It's unlikely to damage the gearbox but if they are revving it hard it's not very good for the powerhead.
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Old 15 January 2009, 15:26   #4
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as NOS 4 just said i dont think any harm will come to the gearbox but the power head bearings could rattle a bit ,think some people think there motorbikes its a bit dangerous all the same , putting it backwards and forwards alot at speed i suppose could put things at risk if the props still spinning ,but the gears will get more stick than that in normal useage when going from ahead to astern and the boats still moving through the water.i once had to repair a johnson engine where the flywheel woodruff key had sheared because the owner kept revving it up on the hose ,he dident know till the next time he launched and the engine wouldent start as the timing had slipped slightly so yes i suppose you could do harm if you wind the throttle a lot .
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Old 15 January 2009, 15:34   #5
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OK I'm a newbie - but what is a 'flush muff'? I have a flush hose in my Mer Optimax which I use to flush the engine after a run is that what it is? Is is safe to run an engine with water running through it on the flush hose?
Duh!!
Most manufacturers state that the engine should not be run while flushing through the hose connector. Suzuki is, as far as I am aware, the only exception (they used to have a link to a video on their site that showed an outboard running with the hose connection supplying cooling water.)

Flush muffs are a couple of suction-cup-looking thingies mounted on a wire frame that cover the water intakes on either side of the lower unit. One or both of the cups have a connector for a garden hose. You put the muffs on, connect the hose, turn on the water, and run the motor at idle. The impeller circulates water through the motor and flushes out salt and stuff.

Later motors have a dedicated port that you hook a hose up to. Same thing, without having to run the motor (though many will argue about effectiveness, for some reason or another.)

jky

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Old 18 January 2009, 07:26   #6
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Thanks for the info jyasaki.
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Old 26 January 2009, 12:23   #7
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Originally Posted by Hightower View Post
I've seen this a couple of times at boat yards and engine dealers. They are running up an outdrive or outboard on flush muffs and have the forward gear engauged with prop spinning round.

Obviously this IMHO is a very dangerous practice, but is it damaging to the bearings and gears in the gearbox. With no water, there is no forward thrust or load applied. So guess it's not going to be too good.

What do you think?
I agree with NOS. Given that the bearings and gears are designed to run with the load on them (and varying substantially if you consider they're designed for people like Rogan who spend quite a bit of time airborne), I can't see any harm to those parts from running without the load.

Human extremities are, of course, another matter.


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Old 27 January 2009, 07:37   #8
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..i once had to repair a johnson engine where the flywheel woodruff key had sheared ...
Yep - I've had to change a couple of these too. Quite a common problem on old 70s/80s Jonnyroods, it would appear.
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Old 27 January 2009, 08:35   #9
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Why dont you just stick the leg of the outboard in a barrel full of water. As long as its running at tickover, it shouldnt throw all of the water out
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