Yamaha half grounded

[olyron]

Hi. This is my first post on iboats. I have a 2005 Yamaha T8pxhd (high thrust with Pwr T&T and electric start). I have signs of corrosion on the lower unit and pitting on the aluminum hull adjacent to the lower unit when operating. I have Continuity between the engine mounting bracket and Hull. However I DO NOT have Continuity between the power head/drive and the mounting bracket. I also have 3V between the hull/mounting bracket and Powerhead/drive when attached solo to a battery. Thus the electrolysis. I can't figure out why the power head/lower unit is electrically isolated from the mounting bracket/hull.
Help......

 

[yamatech43]

Re: Yamaha half grounded

Just buy a piece of stainless wire and use crimps to make two loops. Drill and screw a place on bracket and one on upper drive and bingo boingo you have a ground....you didn't say where you boat....so don't know if you require an aluminum(NOT saltwater), zinc(NOT freshwater), or magnesium anode on motor, but make sure it's in good shape. If you don't have one install one.

 

[olyron]

Re: Yamaha half grounded

Thanks Yamatech. I actually did this today but not with SS wire and it worked. After looking at the prints on Yamahaoutboards.com it looks like the design of the connection between the mounting bracket and the power head/pwr t&t/steering modules does not allow for electrical connectivity.

That is the only connection is the hinge bolt for the pwer t&T, however the bolt is electrically isolated by plastic bushings. If this is so the dealer who installed my motor 7 years ago did not properly ground the engine to the hull and I didn't notice it until visible corrosion appeared late last season.

Thanks again.

 

[olyron]

Re: Yamaha half grounded

Just to complete this thread and to help anybody with a similar problem. The 'jumper' groundwire suggested by Yamatech actually didn't work (thanks for the effort). In fact the jumper allow the low voltage to flow thru the hull and eventually was able to power my trim and tilt on the main engin even though the engine was not connected to a battery. Confusing huh? Well evidently somewhere an accessory is grounded to the hull under the dash. Thus a very low voltage was able to pass from the 8hp thru the hull to the accessory ground and power the 100hp trim and tilt.

Here's the problem and the solution.
My Hewescraft boat has two batteries. One is a cranking and the other is a deep cycle. The 100hp and the dash board accessories are connected to the Cranking Battery. The 8hp, auxilary bilge and wash down pump are connected to the Deep Cycle. both batterys are wired to a Selector Switch via the positive poles of the Batteries. originally the Negative Poles were wired together with a battery cable also. this settup made for a complete grounded circuit. Like an idiot I removed the Negative connecting cable a few years ago...thinking it was putting my batteries in Parallel. When I removed this cable my electrical system was not grounded and allowed stray voltage to find the easiest path to the hull....thus the electrolysis from the 8hp lower unit over to the hull. As soon as we hooked up the negative cable everything perfect.

Hopes this helps somebody.