Corrosion of Yamaha Casing

[Pacific Offshore]

Hi, My father and I have a 9.9 Yamaha engine "kicker" working alongside a Yamy 90 HP main engine mounted on an 18 foot welded aluminum boat The kicker sees limited use, and is only used when fishing and *****ing for salmon. What I have noticed is the anode on the leg of the engine is still like new, and the casing of the leg is starting to develope quite deep cancer mainly limited to one particular area of the leg. It is quite ugly to look at. This damage is quite clearly electrolysis to my eye (Professional Marine Engineer). The main engine is in good condition and the anodes on it require regular replacement particularly the one on the bracket where the 90hp attaches to the transom. These engines are mounted on a welded aluminum boat (Silver Streak) and are also isolated from the battery with an isolation switch. This kicker is a pull start and complete runs on its own (no battery, charger, manual control, etc..) The anode on the leg of the kicker is factory, and has been there since the engine was purchased in 92-93. Has anyone else experienced this problem, and what did they or Yamaha do as a result. I suspect the contact of the anode is not good?! Any ideas from this forum would be appreciated. It has been this way since new, and only in the last couple of years has developed this hole in the casing in way of the leg. I am concerned that I will need to clean it out and fill with expoxy product of some kind. The engine is excellent and runs forever on a gallon of gas and we quite like it, however this may certainly shorten its useful life compared to others.
Help

[Ken]

John,
I would make sure that the anode on the kicker is making good electrical contact with the lower unit. Take it off and clean the contact surfaces both on the anode and the aluminum housing. Does the kicker have a secondary anode also? If so, clean it also.
If the "cancer" is deep enough, you might want to get the hole welded - if not, then sanding, primer and paint should do the job.
The "leg" should be in two pieces. The lower casing is the gearcase - it is attached to the upper casing. If the electrolysis is in the lower casing and you want to get it welded, then I would recommend that you pull the lower casing, drain the oil and take it to a welder. You need to install a water pump kit anyway if you have never done one on the kicker.
Good luck,
Ken K

[vicman2]

Check the potential voltage between the boat and batteries,and the kicker and the batteries. Also check with the kicker running and the main engine ignition switch open but engine not running. It wouldn't take much difference to cause electroloyis. As Ken says if the anode is not grounded propery it won't do its job. Check the voltage the same way you would check the potential of your downriggers. If your moored in a marina for any length of time these places are full of stray electrical currents

[Pacific Offshore]

Thanks all,

The corrosion is in the upper casing on the back (not the lower gearcase)?. It is in way of a particularly thick piece of the casting.
I have tried cleaning the anode and the mount for it, and we have put it in for some saltwater fishing, and the corrosion continues to get worse. we do have a battery isolation switch within the boat, but I will try and measure the potential between the different components. Otherwise I am lost....

[Pacific Offshore]

Thanks all,

The corrosion is in the upper casing on the back (not the lower gearcase)?. It is in way of a particularly thick piece of the casting.
I have tried cleaning the anode and the mount for it, and we have put it in for some saltwater fishing, and the corrosion continues to get worse. we do have a battery isolation switch within the boat, but I will try and measure the potential between the different components. Otherwise I am lost....

[Ken]

John,
Try measuring voltage between the kicker and the alum hull while running with the kicker. Find a good solid ground on the kicker and bare alum on the hull. If there is any voltage at all (measure with a digital voltmeter), say even in the tens of millivolts, then I would connect a grounding wire between the kicker and the hull.
Good luck,
Ken K

[Pacific Offshore]

Hey all,

Turns out our/the manufacturer had a bad run of lower casing designs or gaskets at that the time of manufacture. The casing was blowing out from the salt and corrosion caught within a small passage internal to the lower casing itself!!? It had nothing to do with electrolysis or the boat at all, it was all within the motor, and the build up of salt and corrosion. In fact the authorized dealer had another of the same type with exactly the same design failure!! No amount of flushing with freshwater would alleviate it. I wasted considerable time chasing around electroylsis (thanks to you all for your advise) as one would assume that it was something else. Authorized dealer charged over $900 (Can) to repair the manufacturer defect, and that amounted to no more than replacing the lower casing (with the same) in order to do the job, and get me back into business!?. Claimed there was nothing forthcoming from the manufacturer?! Design defect from the early 90's and we all get stuck with it. Fortunately my memory is not short and having been responsible for the purchase of hundreds of outboards my personal experience here is bad.

Tight lines all.

JC