Corrosion problem in Merc 4 hp 4 stroke

[Brian E. Evans]

I have a 2003 Mercury 4 hp 4 stroke that got very hard to turn over and finally got to the point where it refused to start.
I took it to my local dealer who removed the lower unit, in doing this, the drive shaft stuck up in the power head, destroying the pump housing as he pulled the unit off.
At this point he gave the engine back to me and told me it would cost more to fix than it was worth.
Out of curiosity I went ahead and pulled the power head ,and found that the the drive shaft was stuck in the housing that holds the oil seals. I removed this from the engine and found that the engine turned over easily.
The oil seal housing felt like it was welded to the shaft.
I tried placing the oil seal housing in a vice and drifting the drive shaft out, the housing promptly broke in half.
I then discovered a layer of corrosion had built up inside the housing until it was gripping the shaft like glue, the corrosion was also so hard you could barely scratch it with a screwdriver.
Has anybody heard of this problem before with these motors, or the other brands that are the same motor? I have four more of these motors on other boats, they are all flushed with fresh water after each use.
Would it be worth pulling the power heads to check this on each motor?
Brian Evans.

 

[Brian E. Evans]

Re: Corrosion problem in Merc 4 hp 4 stroke

I spoke to the owner of the Mercury dealership where I purchased these motors today and explained the problem.
He has asked me for the pieces of the oil seal assembly so he can show it to the mercury reps.
He said he personally had never, heard of this problem before, and suggested I bring the other motors in for inspection.
The suspicion here is that the problem may be building up in the other motors.
Anther piece of information, these motors are auxiliary motors on sailboats, and are used to power in and out of a harbor area in salt water.
They are flushed with fresh water after each use as the boat is put away.

 

[Brian E. Evans]

Re: Corrosion problem in Merc 4 hp 4 stroke

The pieces of the oil seal housing have now been sent to Mercury for their analysis.
My dealer says he has never seen corrosion in this position before.

He said " Corrosion in the drive shaft housing is quite common in motors of this type, run in salt water, but not in the oil-seal housing."
Has anybody else had this problem or am I the first of many to come?

Brian Evans.

 

[TOHATSU GURU]

Re: Corrosion problem in Merc 4 hp 4 stroke

You are the only person in the world to have this problem...And it is due to your application and circumstances. Your getting an abnormal electric discharge where the boats are moored. Your going to have to add extra zincs and try to find out where the stary current is coming from.

 

[Brian E. Evans]

Re: Corrosion problem in Merc 4 hp 4 stroke

I am familiar with stray current corrosion and do not have any evidence of it occuring. No bright spots on keels or fast eroding zincs.
These motors are mounted on 4 Pearson Ensign sailboats and are flushed ,then lifted clear of the water when not in use. The only time stray current corrosion could occur, is from the time the motor is lowered and started and the boat leaving the dock.
These boats have Nav lights only, run off a 12volt battery that is dis connected and removed from the boat for charging when not in use.
The zincs on the motors and the keels are in good condition and are replaced once a year whether they need it or not.
Brian Evans.,