Scale/Oxidation in lower unit

[fdmsiv]

I have just dropped the lower unit on a 1975 85 HP for the first time(my first time). The seller assured me that the motor was only run in fresh water. There is a build up of powdery white stuff that is on just about every surface. I am assuming that it is just built up aluminum "rust" (I don't know the term for oxidized aluminum). Could it be a mineral build up like calcium?

Should I try to remove as much as possible or not worry about it? My only worry is that some may get pushed through the cooling system, but it is small particles and no large chunks.

Should I worry about a similar build up in the power unit?

 

[ezeke]

Re: Scale/Oxidation in lower unit

One of the problems of the 1970's V4 motors was that there were no anodes on the motor. The build-up is from corrosion which is accelerated in instances where the motor is anchored near other boats or in acid water, as well as in salt water.

You can bolt anodes to the top of the anti-ventilation plate and they will work quite well. Use stainless bolts and try to avoid the trim tab. Check for continuity with an ohmmeter.

You can use T-20 teardrops or the standard OMC/BRP pre-tapped anodes PN 123009.
http://www.boatus.com/boattech/casey/23.htm