Transmission problems after spun prop (1974 Merc 20 HP)

[kkatarn327]

Hello all,

Being in my third month of boat ownership, I have already found this forum to be incredibly helpful and wanted to become part of the community. I hope that with experience I will be able to contribute beyond merely asking questions like the one I have for you folks today.

A few months ago, my father-in-law gave me his boat (a 16' Sanpon Catapon manufactured in Fresno, CA circa mid-1970s, if anyone is interested and/or has heard of these boats) which has a 1974 Mercury 200 20HP motor. I have operated this boat and motor several times each summer for the last few years so I am not unfamiliar with it. However, now that it's parked in my driveway, we've been putting it to very good use this season. When I got the boat, the only issue was that the water pump impeller on the motor was deteriorated and thus not circulating water. We replaced it at the beginning of summer and it has run fine (nearly every weekend) until last week.

We were up at Lake Edison here in the Sierras (I'm never taking a boat on that road ever again!) when the prop ate a mudbank hard enough to kill the engine. After this episode, the motor had the telltale symptoms of what I later learned to be a spun propeller, and I took it out of the water immediately. After bringing it home and spending a week drenching the prop nut and shaft with penetrating oil, I was finally able to remove the prop and saw that indeed the rubber hub had sheared completely off the shaft insert and was more or less in a pulverized state. Being that the prop was about as old as the motor and a two-blade, I ordered a new Black Max prop to replace it which should be here in about a week.

Now even with the prop and shredded hub removed, I am still experiencing some abnormal behavior which I'm hoping is not, but likely is, an issue with the transmission. I will do my best to describe as follows.

Turning the prop shaft by hand:
-F: turns clockwise normally (with "click" every half turn or so), doesn't turn counterclockwise.
-N: turns freely in either direction (also normal)
-R: shaft locks in both directions, doesn't turn at all (abnormal)

Pulling the starter cord just slowly enough to rotate the flywheel and driveshaft:
-F: turns clockwise (normal)
-N: turns counterclockwise (not normal)
-R: turns counterclockwise (normal)

Additionally, shifting to reverse is difficult and requires some "wiggling" of the prop shaft and/or starter cord, which was not the case prior to the incident (I also confirmed that there is no obstruction to the shift cams in the power head). When we replaced the impeller a few months ago, we (involuntarily) gained much experience attaching and removing the lower unit, and I can confirm that at that time, this behavior was not present.

My question (finally, I know) is, based on these observations, are there any issues with the transmission or crankcase? If so, how can I best approach them? If I do need to remove the lower unit to address the issue(s), I'd like to do it prior to installing the new prop and changing the gear oil.

Any and all advice is welcome. Please let me know if any additional information would be helpful. Thank you!

 

[GA_Boater]

Welcome to iBOATS.

Turning the prop shaft by hand:
-F: turns clockwise normally (with "click" every half turn or so), doesn't turn counterclockwise. NORMAL
-N: turns freely in either direction (also normal) NORMAL
-R: shaft locks in both directions, doesn't turn at all (abnormal) NORMAL

These are perfectly fine and the way it works. The forward clicking is the dog clutch and the locking in the opposite direction, you are trying to turn the crankshaft, which if hard to do without forcing. The locked reverse is also normal because reverse has no dog clutch and you are trying to turn the crankshaft.

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Additionally, shifting to reverse is difficult and requires some "wiggling" of the prop shaft and/or starter cord, NORMAL

The lack of a reverse dog clutch makes it hard to shift into reverse when the motor is not running. The stars and planets and gears were in alignment if you were able to shift into reverse without the motor turning. That's why wiggling or turning the motor allowed reverse when the motor wasn't running. It is not recommended shifting into reverse with a stopped motor unless the prop or crank is turned while shifting.

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Pulling the starter cord just slowly enough to rotate the flywheel and driveshaft:
-N: turns counterclockwise (not normal) NORMAL

The viscosity of the lube in the lower unit causes the prop to lazily turn in neutral. Hold the prop and it will stop. Try pulling the rope while holding the prop. Start the motor on muffs and watch the prop turn in neutral.

Caution - When you are pulling on the rope and fiddling with the prop make sure the motor can't start.

Change the lower unit lube and install the new prop with grease on the splines and go boating. Watch out for the shallows.

 

[kkatarn327]

GA_Boater,

Thank you for your quick and detailed response! I'm glad to hear that what I thought was abnormal is indeed normal. I was basing my observations on what I could remember when trying to align the shifter rod while reinstalling the lower unit all those times a few months ago. Of course I'll trust your experience over my memory any day.

Thanks again!