Water pump design question....

Mark42

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I was told that Johnson/Evinrude motors are designed in such a way that if the impeller failed, just the movement of the lower unit through the water will force cooling water through the motor.<br /><br />Is that a true statement? Will sufficient forward speed cool the motor even if the impeller failed?<br /><br />I have not heard this before. <br /><br />Thanks,<br /><br />Mark.
 

Mark42

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Re: Water pump design question....

Thanks! It sounded a little fishy to me.
 

Dhadley

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Re: Water pump design question....

I've heard people say that for years and have never figured out where or how that got started.
 

marinemech

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Re: Water pump design question....

yes it is true but, there is always a but! the impeller a. won't pump at slow speed<br />b. the piece of impeller that broke off will restrict cooling flow<br />if in an emergency situation you can remove old impeller (and pieces) reinstall impeller housing and run motor at a planning speed and it will cool properly
 

ob

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Re: Water pump design question....

I'm wondering what sort of emergency would afford enough tools and expertise to remove the impeller and broken fragments.I'm trying to visualize dropping the lower unit on my engine at sea or washed up on a spoil island.I think that's when I begin constructing a make-shift sail from a T-top.
 

OBJ

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Re: Water pump design question....

ob...That's why I carry a lotta' long necks.....for just such and emergency...... :D
 

rodbolt

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Re: Water pump design question....

years ago most little engines used the pressure of the water to aid in cooling. we built some race motors with a billet head that had no water pumps. had hand built gear cases as well. but they did not work well at medium speeds and not at all at idle. todays modern engines would not develop enough water pressure with just the gearcase and no impeller.
 

Mark42

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Re: Water pump design question....

if in an emergency situation you can remove old impeller (and pieces) reinstall impeller housing and run motor at a planning speed and it will cool properly
If you're going to all that trouble, might as well cary a spare pump kit and install it.<br /><br />I think I better start carrying more tools....<br /><br /> :p
 

ob

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Re: Water pump design question....

In all fairness to marinemech,perhaps he was refering to such an earlier design as mentioned by rodbolt.I know I learned something new. :)
 

rodbolt

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Re: Water pump design question....

ob<br /> in years past some motors took the cooling water from the prop wash and/or a snout on or near the skeg. as long as the prop turned they would stay cool. as port timing got better and clearences tighter and hose power higher it became nessasary to use a higher pressure. now most all outboards have a pressure relief to compensate for pressure fluctuations as the t-stat opens and closes.<br /> one day I will try to get Ron over at Rons marine to let me take some photos of the last 3cyl 75 jonny rude he and the late Tom Hardin built. home built gear case, hand built prop, home made hot head, single ring TRW pistons. custom homemade sleeves with finger ports. a 3 amplifier 3 point set triggered ign system running 3 coils. home made flywheel homade dry exhaust with movable tuner pipe. it was and is a wild looking beast.the hull was sold after his last wreck, that one almost killed him but he did set an altitude record that day with an estimated 85 ft in the air. he also got to find out how come everytime he got tossed he would end upback in the hull. he had justben clocked at 118 MPH. then got a tad of air and took some flying lessons. laid him out for almost a year and he got some bacterial infection from the water and lost a section of his calf muscle, almost lost a leg. <br /> he does stillhave the motor :) <br /> I am trying to talk him into reassembling it one more time as a showpiece.but thats to much for on of them hydros made out of paneling and furring strips with 2 coats of varnish for strength :) :)
 

ob

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Re: Water pump design question....

Wow.Interesting read rodbolt.Like to see a pic of the whole rig if he still had one around.Some years back,I watched a guy runnning a 25 hp John/Rude firecracker on the back of a maybe 9ft. race style hull at the L-head jetties in downtown Corpus.Quite amazing the speeds this thing was producing.He had foot pedal rigged throttle control and a large set of oysters. :)
 

seahorse5

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Re: Water pump design question....

Rodbolt,<br /><br />Would that be Ron Hill who raced OMC's back in the '60s?<br /><br />I remember the 3 banger racing engines with the Hubbel 1:1 gearcases with just a hole in the leading edge for water pickup. Of course the "no water pump" gearcases were straight geared, no neutral or shifting capabilities.
 

rodbolt

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Re: Water pump design question....

seahorse<br /> Ron Pierce and Tom Hardin. both had machine shops and both were very talented. Ron is no longer racing and Tom is deceased. Tom used to build entire 1 and 2 cyl race two strokes . he manufactured every thing but the cranks. he also built working minuature Lathrops for christmas gifts. Ill try to get Ron to let me scan some of his photos. yep straight geared and rope start no timing advance. bring her up on a compression stroke and be braced. if it kicked back you may go swimming:) happened to more than 1:). those motors would run backwards as fast as forwards
 
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