1958 Fastwin - New Clutch Dog?

[RSchendel]

I have a 1958 Evinrude 18hp Fastwin. Model 15024. In forward, it runs OK at slow speed. As soon as I start to speed up, the engine revs quickly up and the forward speed actually slows down. I have previously marked the prop hub and prop with a sharpie and the hub is not slipping. Is this symptomatic of needing a new clutch dog? Any thoughts on a good place to do the work in the Minneapolis area? I have done a lot of work on this motor myself, but I do not feel comfortable digging into the lower unit. i have done carb rebuilds, water pump and retro-fitted an electric start.

 

[kbait]

Clutch dog failure would be a clunk, like hitting a log, as the dog jumps out of the forward gear, then quickly jumps back in. Your prop and hub must have just lined up to the same marks when it stopped slipping.. sure sounds like a spun prop hub to me.

 

[AlTn]

is the drive pin for the prop in good shape?

 

[boobie]

Kbait has a good point, check your prop hub again.

 

[RSchendel]

Yes, the pin is fine. The marks line up perfect. Since I marked both ends of the pin slot, that means that there is 180 degrees of possible positions. Figuring, a 2-3 degree variance due to the fact that a sharpie is not a precision instrument, that still means the odds are between 1 in 45 and 1 in 90 that the marks would line up if the hub slipped. I should also add that this prop was re-hubbed about 2 years ago. There is no clunk when this occurs, more like a quick slip.

 

[racerone]

There is nothing difficult about working on one of those lower units.

 

[kbait]

When you decrease throttle after it over-revs, is the shifter still in forward? And prop 'grabs' at lower throttle setting? Spun prop hub. Probably more 'sticky' at that part of the revolution, that's likely why marks still line up after slip event.

 

[RSchendel]

Yes, the shift lever stays in the forward gear. When I slow the throttle, the over-rev stops until I increase the throttle again. Interesting thought that the hub may catch at the alignment marks. I do have an older spare prop that I should try.

 

[F_R]

Any thought about it may be cavitation or ventilation (air pocket around the prop)? Is the motor too high on the transom? Are there weeds in the lake that may be snagging on the lower unit? Anything on the bottom of the boat that may be making stream of bubbles ahead of the motor? If it isn't the prop or actually physically coming out of gear or clunking or banging, it must be one of these.

 

[boobie]

Good point F_R. I forgot about that.