Being of this first type, some mysterious but undeniable voice in my mind recently said: "Hey, it's been a few months since you last checked your exhaust riser for rust, don't you think it's about time to check it again before you head to Barkley Sound?" So not being one who likes to ignore those voices and then have the double guilt of it failing and knowing you could have prevented it, I set about to check the little devil.
Well when I checked it, I noticed quite a bit of rust and the unmistakable surface buckling of rust having gotten under the surface of the metal and gone deep. As I started to chip away at the rust, I went deeper and deeper, until I began to worry I was going to break through to the inside. Although this never happened, I did go might deep before reaching something solid. Something odd though, is that some of the material I removed had the chalky feel and grey appearance of graphite, even though it was by all accounts just rusted metal. Anyway, I knew right away that I had to replace this riser as I couldn't trust it any longer with that much metal removed. Sure enough, when I started the motor, a very small amount of water seeped out of the spot where I had dug out metal.
So I've ordered the replacement part from Gallery Marine here in Seattle. It is a 1.25 inch Universal exhaust riser with a 2 inch exhaust hose end. When I get the new one installed, I'll add a picture and tell the story of whether it was straightforward, or not.
1 comment:
The graphite like stuff you found actually was graphite, cast iron contains lots of carbon flakes (2-3% by weight for gray cast iron, as opposed to <.3% for mild steel, and lower still for low carbon alloys), they give it its desirable thermal properties (especially shrinkage for castings) at the expense of total strength. Silicon is added to prevent the carbon from forming iron carbides that would reduce the amount of graphite in the iron.
As the metal corrodes the iron forms iron oxide but since graphite is really noble it just sits in the middle of the oxide mush without changing form.
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