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Posted by on Aug 29, 2012 in Boat Maintenance, Engines, Powerboating, Sailing, UK, US |

Boat Engine Rust: Warning of Bad Times to Come

What's the big deal about a patch of rust here and there on an engine? Think of it as a breach in the fortress wall. Turn your back and a whole army of badness can slip through.

We recently ran a blog by Ed Sherman called Stuffing Box installation: The Wrong Way, in which Ed delivered the bad news to the hapless boat owner in question: the only way to change the shaft packing was to unbolt the whole engine and move it forward. Ouch.

bad stuffing box

A double problem: Not only is the stuffing box too close to the transmission for the packing to be changed, but the set screw holding the shaft looks like it will disintegrate if turned by a wrench.

In the accompanying photo you can see that the bolt head on the set screw holding the shaft in the transmission coupling is so badly rusted that, even if the stuffing box issue could be solved by pulling the shaft, the owner would be staring down the barrel of yet another problem: That bolt head will fall apart the second a wrench gets near it – which means it’ll have to be drilled out and the hole retapped, probably. Ouch again.

In a damp, salty environment, rust is a constant, ardent enemy. Anything that can be oxidized will be oxidized if it’s not protected.

I winced when I read Ed’s blog, because I let my guard down and had a pretty big ouch myself this past season. A year ago, after my boat was hauled and when I put the winter cover on, I saw (OK, I was reminded) that the exhaust elbow bolted to the aft end of the expansion tank above the exhaust manifold was getting rusty, and was weeping rust where it was attached. The gasket between it and the tank looked bad. I decided to unbolt it in the spring and change the gasket.

rusted exhaust elbow

Too far gone, those bolts heads disintegrated before they would turn, but the shafts couldn’t be extracted, either. The whole exhaust manifold and expansion tank had to be removed and the elbow hacksawed off.

Five months later spring came, and when I opened the engine box, it was immediately apparent that all the demons in the Underworld of Rust had congregated for revels around that elbow interface. The conditions (a little antifreeze-laced bilge water for dampness, salt air, intermittent heat and cold under the dark tarpaulin, and the weepy salt exhaust water already on the rusty elbow) had created ideal party conditions for the demons. In those five months the elbow had gone from the near edge of purgatory to the depths of hell.

exhaust elbow repaired

The exhaust elbow and expansion tank were refaced and fastened with studs, not bolts, with the new gasket in between.

So the boat owner in Ed’s blog and I had something in common: Failure-To-Heed-Warning-Itis. Look at the picture. There was no way in the world I was going to get those bolts out of the elbow and expansion tank. I broke my extractor trying. So, I had to take off the tank, which is a big, ungainly one-piece partner with the exhaust manifold. To wrestle that whole thing out, I had to first take off the heat exchanger. And the exhaust line. And the muffler pot. And a bunch of other stuff. Then I had to hacksaw the elbow off the tank, find studs (not bolts!) to make the repair, and take everything to a talented machinist to extract the remainders of the bolts and reface the elbow and tank.

By the time I had the whole show back together again with a new gasket (the one I’d found months before, thinking it was all I’d need) the bilge was full of blood, sweat, and tears.

The only good news in this story was that with all those parts out of the way, it was easy to change the belts and the water pump impeller, and clean the heat exchanger. Also, it will never, ever, happen again – I’ll make sure of that.

- Doug Logan