A potential nightmare averted:
This story is all about paying attention to details. It's also about cleaning up someone else's mess. Once you notice a non-obvious problem, you own a piece of the responsibility. If you can do the job properly and it won't take too long, you fix it. If not, you let the owner know in writing he has a problem that needs attention. One way or another, you've done your duty.*
I was doing a routine inverter install on a 32 foot sailboat. The inverter manufacturer recommends grounding the case of the inverter as a safety precaution. I took a look at the engine block, which is the mother of all grounds on a boat. The battery cable was connected to a fairly accessible bolt on the engine block, so I figured I'd put my inverter safety ground in the same place. Removing the bolt, I noticed something odd. The bolt threads were coated with crankcase oil. Looking closer, I noticed the washer under the head of the bolt was copper colored. The washer was also indented where the bolt head tightened against it. You can see all this in the photo at the left. The bolt that was holding the battery cable to the engine block was was originally just sealing an unused engine oil pressure test port. With a little too much vibration working against the battery cable, the bolt could loosen up. It doesn't take too much imagination to envision a scenario where the engine pumps its lubricating oil into the bilge while the boat is cruising along. In the photo on the right, you can see the engine oil dipstick just above the center the picture. The oil pressure test point is just above and the left of the dipstick. The battery cable lug, with a telltale black oil stain on the inside, is between and below them. The rusty hole to the left of the battery cable lug at the left edge of the picture is an unused blind, tapped hole in the engine block. That's probably where the cable should have been terminated.
When the boat was repowered from gas to diesel some years ago, whoever did it picked an unfortunate place to attach the battery cable to the engine block. Years have gone by and there hasn't been a problem. But they're very well could be a problem, particularly if I terminated one more cable under the same bolt. Probably nothing bad would happen. But I don't want to ever have to explain why I made a second ground connection at an engine oil pressure test point.
So I've identified a good place were both cable should be connected. Over the years, however, the threads in the 10 mm hole have become coated with enough rust you have to look closely to even see that the hole was tapped. The rust has to come out if a new bolt is ever going to go in. Fortunately, this electrician carries a set of metric taps. The lower left photo was taken during the process of chasing the original threads with a tap to clean them out.
The lower right photo shows the happy ending. Both the battery negative and the inverter grounding cable are securely fastened to the engine block with a new 10 mm bolt. The oil pressure test port plug is back in place. Strictly speaking, copper gasket washers shouldn't be reused because they work harden the first time they're put in and don't necessarily seal as well when they are reused. If this were the fuel system, I probably would have gone out and hunted down a new washer. But this washer still had some "squish" remaining when I tightened it down again, so I think it will do for the engine oil system. I'm not an absolute perfectionist.
I did scrape the paint off the engine block where the cable lugs were going to seat. I didn't really have to because the bolt made perfectly good contact with the engine block. With this small an engine, there's not enough starting current to heat up a bolt if it's tightened down properly. But I have had it happen, so I scrape the paint off anyway. But that's another story.
This is one example of the totally unexpected things that can arise in a seemingly unrelated job. And it's why I charge by the hour.
* Having written all this, there are limits to the duty to disclose or remedy shortcomings on a boat. I don't feel obligated to test every bilge pump I see. If the terminals in back of the dash are corroded I have to assume the owner knows he has an old boat. If there are taped, barely supported connections visible inside the lazarette it's reasonable to assume the owner knows this too. Boating is an inherently dangerous undertaking. There are no guard rails on docks, nor should there be.
January 18, 2007