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TOPIC: OMC Rebuild

OMC Rebuild 22 Jan 2020 17:45 #101556

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The trash can idea works but I found if I get anything over idle keeping it full enough is a challenge.
I ended up buying a 120 gallon cattle tank off craigslist. Problem solved.

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OMC Rebuild 22 Jan 2020 17:12 #101554

Thanks for the info!
I use a large plastic trash can and probably fill it higher than needed.
I get a little wet, but at least the pump is happy.

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OMC Rebuild 22 Jan 2020 15:20 #101553

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Muff is "earmuffs" - like headphones - that clamp on either side of the motor to cover the water intake. You connect a garden hose to them to pump water into the engine so you can start in your driveway, etc.

I thought I was doing OK starting my Suzuki in a barrel, but I had only filled the water in the barrel to a level that covered the water intake grates, and the motor didn't pee when I started it. I learned that I needed a taller bucket, and the water level needed to be high enough on the motor to submerge the water pump - which on my motor sits n inch or two above the cavitation plate. Unless the water head is sufficient to fill the pump, it won't get "primed" to suck water when you start the motor. While you're underway in the water, the motor does rise to a level where the pump is above the waterline, but by then the pump is full & pumping water.

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OMC Rebuild 22 Jan 2020 13:47 #101552

I love rebuild articles!
Coming into this one late and wondering what a MUFF is?

terry

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OMC Rebuild 22 Jan 2020 12:39 #101551

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I don't think the groove gets clogged, I have pulled several apart that have had the same problem, and there is a small hole in the wear plate on the pressure side of the pump that feeds water into the groove under pressure.
Where it melts is right at the hub of the impeller where there is a lot of rubber against the plate, I think starting it dry is like taking off with the brakes locked, all that friction just creates a lot of heat very quickly.
I do think OMC could have sourced a better type of plastic, I have seen the pump housing melted pretty badly on the 35 HP models made from the 70's forward just from exhaust heat.

As far as the muffs go, at least on the OMC lower units, I have tried a bunch of different types but have never found one that does not leak a ton of water under pressure. The pump is way above the water intake and there is a rather large cavity to fill completely before the pump picks up, I'm a barrel man myself :biggrin:

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Ray

"Every man takes the limits of his own field of vision for the limits of the world."
Arthur Schopenhauer

1956 Vagabond I - 50 HP Johnson
1950 Flyer - 50 HP Evinrude
1/2-195something Flash - KG7
1956 Golden Rocket, Sawzall Special
Last edit: by Locomotion.

OMC Rebuild 22 Jan 2020 00:08 #101545

Very interesting about no water tube and how it's casted in the midsection. That's a different impeller that I am used to seeing. Only three wings.

How did the center part of cover heat up and melt? Do you think the groove got clogged at one point?

Why do you not like using muffs? Doesn't water get forced up the tube from the garden hose making its way to the impeller?

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Mercury Marc, 1958 Hawk II. 1961 Merc 400

OMC Rebuild 21 Jan 2020 23:31 #101540

Great pics and info! I remember reading quite some time ago that OMC performed a test to determine how long it would take to destroy an impeller if it was run w/o water. If I recall, it took less than 15 seconds.
Fast forward to my being at various ramps and hearing/watching boaters start their motors and rev them before putting them in the water. Being the helpful kinda guy that I am, I've approached people and tactfully warned them about the damage they were doing to their impellers by running them dry. I stopped doing that after more than one boater told me to mind my own business. Fine. Rev the crap out of it for all I care. :)

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OMC Rebuild 21 Jan 2020 21:39 #101537

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Here is why I do not like to run one of these engines on muffs and I never dry start one even for a second, the black streaks you see here are melted rubber, you can feel it in the cup and it has started to deteriorate the impeller.





These are heavy duty impellers and I have never seen one come apart, but why take the chance?



The heat builds fast, the discoloration at the center of the plastic housing is melted plastic that has migrated into what was a groove that carried water to lubricate the center of the wear plate.



A good indicator of how fast the heat traveled, here you can see red grease that was not heated enough to melt but the plastic did.

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Ray

"Every man takes the limits of his own field of vision for the limits of the world."
Arthur Schopenhauer

1956 Vagabond I - 50 HP Johnson
1950 Flyer - 50 HP Evinrude
1/2-195something Flash - KG7
1956 Golden Rocket, Sawzall Special
Last edit: by Locomotion.

OMC Rebuild 21 Jan 2020 21:33 #101536

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Getting into the lower unit, the first thing I do is remove the water pump, the yellow plastic unit right on top.



Four bolts and it pulls right off. The rubber fittings on top of the pump fit into recesses in the midsection casting. The smaller one is the output from the pump it routes the water from the pump into the midsection casting which carries the water up to the powerhead, eliminating the water tube which, on some outboards, can be a pain to install and a point of failure if not installed correctly.




The inside of the pump.




Be sure and keep track of the drive key, here it is sitting on top of where it fits into the impeller.
You can also see where the impeller has heat damage near the center.

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Ray

"Every man takes the limits of his own field of vision for the limits of the world."
Arthur Schopenhauer

1956 Vagabond I - 50 HP Johnson
1950 Flyer - 50 HP Evinrude
1/2-195something Flash - KG7
1956 Golden Rocket, Sawzall Special

OMC Rebuild 15 Jan 2020 14:30 #101398

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HawkEyes wrote: Ray you do fantastic work! B) nice Job on the motor!! Cant wait to see the Boat resto next. :hmm:






It's pretty easy when you take near two months to build one this simple, I hope it doesn't take two more to rebuild the lower unit :hand:
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Ray

"Every man takes the limits of his own field of vision for the limits of the world."
Arthur Schopenhauer

1956 Vagabond I - 50 HP Johnson
1950 Flyer - 50 HP Evinrude
1/2-195something Flash - KG7
1956 Golden Rocket, Sawzall Special
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