Accidental overspeed of Kicker

colbysmith

colbysmith

Active member
Ok, I'm sure someone else has done this also, but wondering if any professional mechanics here can give me their opinion. Today I had put my 6hp Tohatsu kicker in the down position while docked at a friends. Later, when we left, I forgot to raise it. I also had it left in reverse gear. (I do this while trailering, so the prop doesn't spin, and unless I'm using the kicker, when I'm boating, I tilt it back up but leave it in reverse, or sometimes forward, but usually in gear since that's where it is for trailering...) Anyway, I was up on plane for no more than maybe 15 minutes, and didn't really notice anything, until at one point I really trimmed the boat out for some speed (like about 26mph). At that point, all of a sudden I heard a vibration from the back and turned around to see the red low oil pressure light flashing on the kicker. I immediately stopped and realized what happened. (The prop on the kicker was turning in reverse gear.) Later I used the kicker for about 40 or more minutes total time, and everything seemed to work fine. After getting home and remembering my little tach/hour meter on the kicker would give me max RPM, I checked it and it showed 6100. (Outboard specs call for 5000-6000 wot). So, what if any damage could have been done that I really wouldn't know about but will have shortened the life span of this engine? Colby
 
I'm impressed: 6100 rpm backwards, from the water flow? And it still runs?

I'd have a beer and enjoy having dodged another one. But I guarantee you that's a non-expert opinion.

Boris
 
I would question the fact that you got 6100 ripms from water flow through the prop alone. But since the motor was in reverse and you were going forward there might be internal wear or damage as the engine was not turning in the proper direction and the oil pump would not be picking up any oil.
 
Also non professional opinion--I agree with Chuck above. Not sure if the oil pump would have been running-but if the engine was turning, then it should have been. I also question that the engine would have gotten up to 6100 RPM when dragging it thru the water on a plane...

I suspect that your engine would be fine--In any case, you are not going to have it torn down--just run it and watch out for any signs of damage.
 
No plans to tear it down, and it seemed to run just fine. I don't know if the tachometer was accurate, but it seems to be when running the engine, and I've never had it run past 5300 in WOT. Turning the prop by hand, in either direction when in gear is hard to do with the compression. I did try spinning the prop in forward, with it in reverse gear, and I doubt the water turned it at first. I didn't hear the noise and vibration (the noise was probably the exhaust) until I really trimmed the boat up and hauled butt. I normally run with the boats trim tabs down to keep it from running so bow high, which would also spoil the water coming at the kicker prop. However, when I decided to "trim the boat out" I raised the trim tabs fully, which would have dumped a lot more water on the kicker. I suspect the water pressure at that point over came the motor compression and spun the prop, turning the engine. If this is the case, it did not happen for more than 15-30 seconds max. I also checked the oil, which seemed fine. I'm keeping my fingers crossed....as I said, it ran fine afterwards as I used it through a long no wake zone, both going and coming. Just hope no unseen internal damage. Hopefully I won't do that again. That and I wonder if it would be wiser to leave it in FWD gear from now on. (That doesn't lock the engine down, but then I haven't had any problems with it bouncing up on the trailer anyway...)
 
I would not worry about it at all. Even though it was turning, there wasn't any force on the crank from the pistons and little heat. Plus you had just been running it and it was fully lubed up. Again, I wouldn't put much though into it.
 
Those little tachs run by vibration--and it is very possible that there were some harmonics set up by dragging the motor thru the water, which caused the tach to spin up.

We have a lot of experience with sail boat props, which are 24 " in diameter. The transmissions are hydraulic, so we don't want to let them spin--and use a lock on them. But even free wheeling a prop it is not easy to get them to spin fast. Some folks put alternators on them to get "free" power--not easy to do--but can be done.
 
Back
Top