Saturday, April 12, 2014

Another Impeller!

In my last post I mentioned that I've been focusing my recent attention on my dinghy (a.k.a. family car).  While I work on the registration and debate the best way to fix the leaks in the Caribe RIB, I figured I would look over the motor and see if I can get it running.

The motor is a 15 hp, 2-stroke Yamaha engine.  Using a manual I found online (the previous owner didn't leave me the hard copy), I opened it up and went through all the basic checks to make sure the controls work and it had at least a reasonable potential to start.  While mounted on the storage mount, I hooked up the gas tank and a clamp-on adapter to provide fresh water for cooling.

It took a couple tries, but the motor did fire up.  Of course, the stream of cooling water failed to appear from the appropriate hole in the motor housing where it is supposed to be found.  Since running the engine without cooling water is very bad, I quickly shut down the engine.  With my recent impeller experience, I figure there is a very good chance that this is the problem.  Now, where do they hide the water pump on an outboard motor?

Looking through the manual, I found that the water pump is actually located in the lower end of the motor on the drive shaft.  I guess it makes sense, but it certainly isn't a convenient location for checking the impeller. Guess I will need to disassemble the engine just to check and see if my suspicions are correct.  As I've learned to do, I consult Google and YouTube for additional information on the process and I found this video that demonstrates the general process.

A little more complicated than replacing the impellers on the inboard engines, but it doesn't seem too bad. I locate the impeller (actually a kit, more on that below) at a local store and begin the process of checking and changing the impeller.

Motor on the cockpit table...where else would you work on it?

I remove the lower unit containing the transmission and the water pump housing just like it shows in the video (except I disconnected the transmission linkage before I removed the other bolts).  I disassemble the water pump and viola, the culprit of my lack of cooling water is found.  Another destroyed impeller.  As I've learned, it is very important to locate all the pieces of the impeller and I dig through the passages and am able to find enough rubber bits to account for the entire thing.

Disassembled pump, another destroyed impeller found.

Yamaha did something kind of clever with the pump.  Instead of just providing the impeller, they provide a kit that contains not only the impeller, but also replacement walls for the housing and a few other bits so you can rebuild the water pump and all of the working surfaces are new.  They do this with simple stamped metal parts so the entire kit costs about the same amount as a single impeller for my Westerbeke engines.

New shiny pump walls.

With a refurbished pump, I reassembled the motor.  I did check the lower unit (transmission) oil before reassembly.  With everything back together, I put the motor on the storage mount, hooked everything back up and gave it a try.  As soon as the motor fired, a good stream of water came shooting out of the motor housing just like it was supposed to. Another impeller problem solved.

Of course the engine only ran for a minute or so and then sputtered to a stop.  I probably need to get some fresh gasoline, but at least now I know the motor does run and seems to be in better condition than I suspected might be the case.


  1. Great job Mike! I've got my outboard at a friend's house right now and we're rebuilding it. Hopefully it'll be back up and running soon!


    1. Good luck Mike! I still have some other work to do on my outboard as well. Always something to work on on a boat.