the dreaded corrosion on an '88 merc 115

[ianmoore]

I bought this motor a couple of years ago. I have taken meticulous care of it since; flushing after every trip, and trying my best to control the corrosion that i got when i bought it, but there are some issues that I am running into.
A couple of days ago i noticed that the right side ground strap was broken. Merc has two that connect the engine to the frame. The other one is fine. I would like to replace the broken one, but the cylinder screw is so rusty that I'm pretty sure it would break off.

I have read enough to know the impending problems with older saltwater motors, but this is what i can currently afford. So far I am holding well, and as i said, i have the motor pretty clean since i got it. What is the best route to go if i do need to remove cylinder bolts? It seems like a pandoras box to try to drilll out a rusty bolt.

Thanks
Ian

 

[jimmbo]

Get a longer strap or wire and utilize a bolt on the block that isn't all corroded, bolts that hold the crankcase halves together are off limits.

 

[Chris1956]

You can run a ground wire from the main ground on the casing to the bolt that holds the starter to the block. Neither is usually corroded.

Also, look for some water leaks on the cylinder head water jacket. That is likely where the corrosion originates. You can buy a spray on anti-corrosion substance. That works very well.

 

[ianmoore]

Thanks for the tips on the ground strap. Chris1956 are you talking about one of the 2 bolts on the casing that originally had the ground straps on them?
I have a number of anti-corrosives that i use pretty religously. I haven't seen any obvious leaks coming from the water jacket. Next time I run it on the muffs i will look around again

 

[merc850]

Why no use the one above it seems to be cleaner, if those bolts are thru ones with nuts undo them and replace them, I use Merc's anti-corrosion grease on bolts and fittings.

 

[Chris1956]

No, I was referring to the main ground bolt. Trace the engine wiring harness large ground wire from the quick disconnect to the lower cowling, and use that as one end of the ground. Use one of the lower starter mounting bolts as the other end of the ground wire. I would use a #10 copper wire and crimp and solder some ring terminals on it's ends. That should take the place of both OEM ground straps.

 

[ianmoore]

No Title

Chris1956 Thanks! I attached a ground wire here before I heard back from you. It seems like a pretty solid connection.

Now looking to some of the other(non cylinder) bolts that have some serious corrosion.
One of the worst is the bolt(#27 on the diagram) I have been trying to loosen the bolt, but it is so corroded, that I don't think I can get it out. It looks like I could probably cut it out if i can't get it off and replace with a new bolt. Seems like it might be worth taking care of sooner than later. What do you think?

 

[Chris1956]

I would doublecheck that ground with an ohmmeter. Check from the main ground to the lower cowling to the block. say the carb body. The reason is that the waterjacket cover has a gasket, and the bolts are rusty. The ground is likely good, but I would recommend you check it. Remember, the spark plugs touch the block, not the water jacket cover...

As for replacing the bolts...They will likely break, if you try to remove them. If the cover doesn't leak much or at all, why break the bolts now, when you can break them later, when you have a real need (and leak). JMO.