Since the boat is out near the front of the shed this year, we get a nice morning and mid-day sun (at least for a while) that warms the cabin. We began by checking out the wiring at the lower helm. The starboard engine engine gauges (especially the voltmeter) have always read low and while that engine has always been reliable, we thought it useful to check things out by making a few voltage readings.
Silverton's wiring plan is to run all of the engine wiring directly to the lower helm and there, split it off and run all of that wiring in a bundle up to the bridge. We have a schematic drawing of the engine wiring so we had an idea of the color codes used on individual circuits. In most cases that schematic was correct but in some places the wiring colors didn't quite match.
The wiring at the lower helm may have been neat when Silverton built the boat but after 30 years of the two previous owners adding things such as trim tabs, an AM-FM radio, etc., it isn't what we'd call "neat" right now. Someone added a small terminal strip as a common point for DC grounds and that isn't what we'd call very well done, although it works. Silverton's grounding method was simply a very long bolt with nine or ten ground wires attached together. It would be impossible to add another ground wire and we suspect that's why someone added the terminal strip.
There is also a very sloppy connection for a number of +12 VDC connections and this could have been done much more effectively if someone had thought about it while the helm wiring was being done at the factory. Maybe Silverton didn't do this but if they didn't, some amateur did over the years. Here's what it looks like.
The upper right shows the grounding terminal strip we mentioned earlier. Just below and to the left is a mega-connection of seven +12 VDC wires all bolted together. They are +12 VDC from the port engine bolted to a wire that feeds +12 VDC to the bridge; +12 VDC feed to the starboard fuse bank; +12 VDC feed to the port fuse bank; +12 VDC to the trim tab switch; +12 VDC feed to the stereo and lower station VHF radio; and the +12VDC feed to the head. Notice how close this thing is to the top of the aluminum steering helm?
We're going to remove all this crap wiring and replace it with a terminal strip that we had in stock. That will mean lengthening and rerouting all of those wires. That's not going to fix the problem with our starboard engine but it will let us sleep better.
We also found something funky going on with the port gauges. The voltmeter is sluggish and reads way below the true battery bank voltage of about +13 volts. When we measure the voltage at the ignition switch "BATT" terminal, we get a little over 13 volts, which is what we would expect. When we measure at the ignition switch IGN terminal (key on), we get only about 11 volts.
If we do the same measurement at the starboard ignition switch, we get +13 volts at both terminals.
Are we losing 2 volts in that crusty old ignition switch? Maybe, but rather than guess, we are going to simply replace it. We previously replaced the other three so we might as well do this one too.
The picture of the rear of the switch doesn't show much but we took it for reference.
Those two yellow wires connect to the START terminal and the red one above it (with an extra wire that someone added over the years) is the IGN terminal.
Again, none of these repairs will do anything to fix the problems with the starboard engine but since we're poking around at the lower helm, we might as well correct these things.
Before we left on Sunday, we removed the ballast resistor from the starboard engine. This is a Mallory part that came with the new solid state Mallory distributor. It is a variable resistor between the battery and the coil and is there to limit the current to the coil. Our thinking was that if the resistor was somehow faulty, it could be the cause of our consistent coil failures. (That's not really logical thinking since when these ballast resistors fail, they open, not short, but at this point we need all the info we can get.)
This particular ballast resistor should show 0.75 ohms when cold and 1.5 ohms when hot, the idea being to provide a little hotter spark when the engine is cold and a little less spark when the engine is warm. Our digital voltmeter won't read resistances that low so we took the resistor home and set up a little experiment that would be right at home in an 8th grade science class.
We used a 12 VDC power supply and connected the output to a 12 volt car tail light bulb. The no load voltage of this power supply is 13.8 VDC. We inserted the ballast resistor in the positive side of that circuit and measured the voltage at the bulb. It was 11.92 VDC. Then we used a heat gun to simulate a hot engine and as we heated the resistor, the voltage dropped steadily to 11.25 VDC. It wouldn't go any lower.
All we managed to learn is that the ballast resistor does, in fact, increase in resistance as it is heated. We don't know the amount of current drawn by the coil in the boat and we suspect that it is a lot more than that drawn by the tail light bulb. If that's true, the voltage drop would be higher on the boat.
If you're still reading this far, you may wonder why we didn't measure these voltages on the boat. Well, we did, just before the boat came out of the water. Here's what we found:
Starboard (problem) engine.Ignition on, engine off: +12.4 VDC at the input side of the resistor and 7.0 VDC at the coil side. Engine on at 1400 RPM: 14.2 VDC at the input side of the resistor and 11.2 VDC at the coil side.
Port (reliable) engine
Ignition on, engine off: +10.5 VDC at the input side of the resistor and 6.4 VDC at the coil side. Engine on at 1400 RPM: 11.6 VDC at the input side of the resistor and 8.5 VDC at the coil side.
Since we were tied to the dock when we took these readings, the engines weren't really hot but simply warm.
The readings we took at home on the starboard coil are really pretty much in line with what we found when we measured on the boat. What we don't know is, is 11.2 VDC to high a voltage and is that why we keep getting coil failures after about two hours at cruising speed?
The starboard engine never fails no matter how hard we push it but the voltage at the coil on that engine is only about 8.5 volts or maybe a little less when the engine is at operating temperature.
The ignition parts (ballast resistors, coils and distributors) are identical on both engines and both alternators have recently been rebuild by a very reliable shop.
This blog post is getting too long but it's good for us to put all of this data down in one place even if just for our own reference. If you know anything about coil voltages, please share. We need all the intelligence we can get.