Took '55 7.5 HP Evinrude for a spin

[WATERTIMES]

Went on the lake the other day and she ran fantastic ! One thing I'm not sure of was when I had her at WOT she ran with a high rev but wasn't moving the boat any faster and when I turned the throttle down a bit she was movin the boat pretty good, thought it was the pitch so I tried every notch and she did the same thing when I had her at WOT, I'd look down,and she was clearing and trench , I started thinkin she wasn't gettin enough water?? Could that be because it's a short shaft?? Other than that I can't complain at all. I got alot of thumbs up by the old timers on the lake as well as well as alot of smiles from folks sitting lakeside on their docks.I couldn't
ask for a better runin motor she ran better than I expected her to.I ran the no wake zone which is a very long travel area, I ran her as slow as slow can get and she ran without a skip or beat, I was very, very impressed ! My buddy was out on the lake {the one who said sell it} and he said I got a steal on the motor, he was impressed. I guess he had to see it in use.
But what could be the reason for her reving at WOT and not moving the boat?
When I backed her off just a little she ran great. Prop size? Short shaft? ???

 

[tashasdaddy]

Re: Took '55 7.5 HP Evinrude for a spin

well if you are running short shaft motor on a long shaft boat that could be part of it. your motor should measure 17 inches from where it sits on the transom, to the plate just above the prop. your transom should measure 15 inches.

you also could have a spun prop, the prop is made of and inner metal hub, and an outer hub, with a rubber bushing between. you will not be able to see it. this rubber goes bad, and the inner hub, then slips, when under load, not spinning the blades as it should.


when was the impeller last changed. if you do not know, or remember change it before you burn it up.

 

[WATERTIMES]

Re: Took '55 7.5 HP Evinrude for a spin

Thank you tashasdaddy ! you are right, it all measures right, I will now replace the impeller. If I get the impeller kit ,does this come with the rubber bushing ? I think my parts guy gave me a price of $60 for this kit, does that sound right? Thanks again !

 

[tashasdaddy]

Re: Took '55 7.5 HP Evinrude for a spin

yes, for price, and the bushing should come if you bought a water pump kit.

 

[TN-25]

Re: Took '55 7.5 HP Evinrude for a spin

Man, you really did get a steal on a fine running motor by the sound of it. If your boat requires a long shaft and your 7.5 is short, I'd be terrified of sucking air instead of cooling water. It would be a tragedy to destroy it by something as simple as that. Also running a shaft that is too short will cause cavitation and over-revving, another motor killer.

Look after that motor properly and it should last a long time. Also be absolutely certain to run the proper mixture, never less than 24:1. Those bronze-bushed motors, when they get worn in the crank and bearings, can't be rebuilt (at least not in any practical or affordable way).

You posted pictures before. Maybe something while the motor is tooling along...

 

[wbeaton]

Re: Took '55 7.5 HP Evinrude for a spin

Its not a spun prop. That motor doesn't have a rubber bushing in the prop. It has a shock absorber in the lower unit. I would take a close look at your boat/motor setup before anything else.

I recently rebuilt a lower unit on a 1958 that did the same thing. The spring in the shock absorber didn't appear broken, but it would fail under heavy torque. However, it eventually failed completely on the same outting.