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Discussion Starter #21 (Edited)
Oh ghod, my aching brain... A bullhead fish larva jumped two inches and entered the thru-hull for my head sink and died, blocking it nicely. Maybe they have a thing for beer-urine?

Anyhow, I disconnected the keel-engine bond and interposed my DVM last night with the positive lead on the motor and the negative lead on the keel. Previously it (the bond) had been connected (to the motor) for a couple of days, and recall that the zinc was installed on Saturday as I was doing the anti-fouling paint -- one coat after scraping off the freeloaders. So the keel is painted, with the exception of the bit of iron behind the zinc. I did not paint the zinc.

With that arrangement, I measured +100mV. As the evening progressed, the DVM reading slowly climbed to +160MV. I should note that (a) my temporary LED strip cabin light draws 240mV, and I tend not to use the remaining incandescent fixtures. The fresh-water pump is used sparingly. (FW system needs a small expansion tank. TODO.) So I knock off for the night and shut off the DVM. Today I was busy starting the top-down back-to-front Cleaning Job so did not ogle the DVM until a few minutes ago. So I turn-on the DVM and it show -90mV, which has slowly climbed/fallen to -95mV in the last half-hour. Clearly there is something slightly fishy going on.

Clearly my prior hypothesises is/are somewhat in error and more investigation is needed. Time flies like a banana, et al.
 

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mA?
 

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Discussion Starter #24 (Edited)
There don't seem to be any A detectable. The DVM set on microamps shows a big fat zero between the keel and battery - terminal. Since my last post I have left the keel-motor bond disconnected and it has stabilized at a potential of -170mA, which signifies that the keel is charged to a potential of 170mV above battery -. I briefly thought that there might have been a capacitance effect operating here, however the lack of current draw while measuring amps indicates that the effect may be electro-chemical like a battery but with negligible capacity.

I am reluctant to draw any firm conclusions as it seems I have been taken in relation to the boat purchase. The boat's electrical system appears to have been sabotaged instead of merely neglected, which is something that has only become apparent as I have been working my way through its systems. For instance, there is a two-relay "charge controller" integrated with the simple instrument panel. This charge controller was disconnected from battery "ground" in such a way that the house electrics had a ground path that traveled through the instrument panel and thence to the starter-generator. This was only discovered after I removed the starter-generator to inspect the brushes, etc. This resulted in electrical fun-and games which included non-functioning house electrics (but not the 240mA LED temporary lighting installed in the cabin) and the temperature meter pegging hard-right. Fortunately the meter was not destroyed.

I renewed the cooling system temperature valve on the heat exchanger, which resolved the intermittent over-temperature condition which was merely another factor in the operation of this engine. I have photos of this procedure which I will add to an existing MD6A thread on this site. Unless the temperature valve is utterly destroyed there should be no real need to replace it most of the time; its design is simple enough that its absolute destruction seems unlikely. Running the engine subsequently to test it after this renewal resulted in intermittent lighting of the oil pressure idiot light, which was unexpected since I ran the motor for several hours before and after replacing the oil filter and oil without incident. Further investigation has revealed salt-water corrosion in the top of the motor, primarily on the underside of the rocker arm and on or near three of the valve springs, etc.. Loose corrosion product appears to have impinged on the sump strainer or filled the new oil filter, resulting in intermittent lighting of the oil pressure alarm. I am currently debriding the corrosion product in the top of the engine and will do what I can to clean things out as much as possible short of pulling the engine and removing the sump and strainer. Any suggestions in relation to this procedure would be welcome.

This correlates with the observed oil condition prior to the oil change I performed. It looks a bit like a small amount of salt water was introduced through the oil-fill cap and the engine run for some unknown number of hours over a period of a year or so. Alternately, a sulfuric acid spritz to the affected area would produce the observed corrosion. There is at this time absolutely zero evidence of a cooling system leak. Furthermore, the engine-hour meter is non-functional in the cabin, so despite the good seal on the piston rings, there is no reliable indicator of its absolute age. This and several "minor" additional factors pretty much indicate fraud and misrepresentation on the part of the seller, however given the state of the courts and law-enforcement community in Canada, actually fighting the seller is probably a losing proposition. I paid 5K for the boat, which is not entirely unreasonable minus the deliberate neglect/sabotage. There are also externalities which are likely aggravating factors.

So far, the damage to the motor does not seem so bad that it is not fixable at moderate expense, my apparently entirely valueless man-hours notwithstanding. This expense is moderate only because I am extremely good at field-expedient fabrication in my amateur class of tinkering. The electrical system is another matter, and as I have not had enough time to properly asses the deliberate and retarded ****ery associated with its current state, I cannot as yet properly assess its influence on the keel-motor voltage potential issue which is the proper subject of this thread.

Stay tuned, though. I will almost certainly have salacious updates in the near future.

Free advice: Please do not purchase vehicles from Murder, Inc. Identification of Murder, Inc. representatives is of course left as an exercise to the student.
 
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