Power slippage

[dwat4350]

Hi, I have a 1973 Chrysler 55. I was running at almost full throttle when the engine seem to come out of gear but it was not.
At idle, the boat would move but when power was applied it would slip.
Can this be a prop slip or does this boat have a shear pin?
Any suggestions?

 

[Maclin]

Re: Power slippage

Those are the classic symptoms of a spun prop hub.

 

[Frank Acampora]

Re: Power slippage

That engine has a splined prop shaft with a thrust pin in the hub. (always a sore point with me and early Chryslers) Remove the cotter pin from the white tail cone/nut, unscrew the tailcone, slide the pin out of the hub, and slide the prop off the shaft. You have three options:
1. Buy a new or used prop.
2. Send your prop out to a prop shop for re-hubbing--about 35 bucks. Your local marina will send it out.
3. Drill and pin the back side of the hub to the prop casting. -- Do-able but not a good option. You lose the impact protection the rubber hub affords the gearcase.

Actually, if you have a press, a fourth temporary option depending on the condition of the rubber hub could be to press out the hub, coat liberally with a good quality silicone RTV and press it back in. The RTV will glue it and it may last for a couple of more runs.

No matter what you do, buy an inexpensive spare prop as an emergency replacement. Props for that engine frequently come up for auction on e bay. 10 3/8 diameter, 11,12, or 13 pitch depending on load. If you can find a real cheap older 40 hp Evinrude prop, the prop is the same It just needs to be re-hubbed for the splined Chrysler shaft.

 

[Kenny1970]

Re: Power slippage

I have a 120 that only does it at higher Rpms but when I let off the gas a little it grabs and starts to pull again.
It is only when I do 5500 rpm or more,But I can do 5300rpm all day with no problems at all.Does that mean I have a spun prop or one that is about to spin?

 

[Frank Acampora]

Re: Power slippage

Difficult to tell, Kenny. Typically, a spun hub will get worse over time and the slipping will happen at a lower power setting. However, some of them just let go and will not grab at anything over an idle.

Remove your prop and mark the hub, and prop, where the hub fits in it. Then replace and run the boat. Remove the prop. If the marks have moved relative to each other, the hub is going bad. If they have not moved, you are probably experiencing prop slippage, or cavitation, or ventilation. Cure for this condition is to cup the prop, or lower the engine slightly on the transom, or back off on the trim adjustment.

 

[Kenny1970]

Re: Power slippage

Thanks Frank.
I will try that.
I sure hope that it is not the prop because I have been looking for a new one and can not find one any where.

 

[dwat4350]

Re: Power slippage

Thanks everyone,
I marked the prop to the outer nut as I had read in earlier postings. It was prop slip.
I am going to send this prop out to be fixed as a spare today but I bought a new prop Saturday.
Had to take the wife fishing! Yea!

Thanks again

 

[eedwards]

Re: Power slippage

That engine has a splined prop shaft with a thrust pin in the hub. (always a sore point with me and early Chryslers)

Why a sore point?
I love that i can change the prop in the water in less than five minutes.