[changzuki]

One reason the overdrive wasn't engaging is because the incoming voltage to the solenoid was low. The reason: discovery of a 1991 Service Bulletin outlining a catastrophic failure... So, I was running off the battery with no alternator on that maiden voyage... Read on...

The original Centurion's Kubota D750 was equipped with a dynamo to charge its battery. Small, light and quite simple it would keep the battery up but running accessories might prove challenging and unless one is willing to go fully led (save the headlights) you probably won't do much night driving.
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Also, if you are using one of these dynamos - dump it - I did! The bottom line is they will produce too much drag for something like a Green Grand Prix competition. These dynamos operate on the same principle as most motorcycles do: and it's not a very efficient way to charge a battery... For example, when the battery reaches maybe 14.1 volts or so, the voltage produced by the dynamo beyond that setting will be shorted to ground by the external regulator. That's right - shorted to ground - and regulating by dissipating the excess as heat! So in essence, the dynamo's 25 amp output (and drag from it) is continuous from the moment the engine is spinning it, until you shut it off. Not very Green Grand Prix record setting friendly if that's your goal.
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Also, the dynamo below (next to the Delco 10si) is of the "permanent magnet" design and when you spin it by hand, you'll feel the cogging of those magnets making it tough to turn. Night and day in this respect to the standard alternator.
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This is the one time I would trade off light weight (of the dynamo) for the heavier electro magnet (field type) alternator. While this standard type of alternator does use energy just to create a field, its ability to taper off voltage to a fully charged battery (by not producing any extra) makes for a free'er spinning unit. In the case of Centurion, you don't need electricity once the engine is running, so it makes sense to have a charging system that will taper output down to a trickle, and not continuously short the excess to ground..
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It's also easier IMO to incorporate an alternator cut switch on a standard type alternator than a permanent magnet generator.
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In an earlier post I mentioned Centurion used a "stock mid-eighties Delco 10-SI with a 12-SI fan, and is a single wire-to-battery circuit". This is a robust alternator that is inexpensive, easy to rebuild if necessary, and very common.
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After a long-term assessment of it, the time has come to ask if this selection is still a good one.
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The answer is no - at least not for the D750/D850/D950. The reason for this is I've recently stumbled over a 1991 Service Bulletin from Westerbeke Corporation. Apparently these little engines made their way into marine applications too and alternators such as the Delco I was using were one the alternators of choice.

The problem is the single lower mounting tab and where it attaches to the mounting boss that's part of the D750/D850/D950 engine timing cover. If this attachment loosens (possibly from vibration), continued use can cause the upper bracket to fail. Once this happens, the extra stress from the unsecured/loose alternator has been reported to break off the mounting boss. If the owner is lucky, then the entire front of the engine (timing cover) must be replaced. If luck is not with you, the busted metal will drop right into the sump and/or timing gears and then the problems multiply.
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The alternator replacement fix is fairly easy once you know what it is. And when you don't, there's endless hours on the internet doing some digging. There's a couple of compact alternators that have double (front and rear) lower mounting tabs that will straddle the Kubota's timing cover mounting boss and provide a very stable/reliable arrangement. Kubota has used an older style Nippendenso externally regulated alternator. I tried one of these 35 amp wonders but ultimately scrapped the idea since it was too difficult to decide on a suitable location for the regulator. Space for such items are at a premium with Centurion.
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A simpler and more elegant one-wire solution is available and it came on the gas sipping Geo Metros and Pontiac Fireflys. Delco supplies a part number but it's a Nippendenso unit:
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If you're using a Kubota D750/D850/D950 strongly consider trying to find (or make) the Kubota optional lower mounting bracket. The bracket will mount to the timing cover boss directly, and set the alternator a bit higher which makes removal of the oil filter a breeze! This higher position also gets the rear of the alternator a bit further away from the exhaust manifold so the alternator won't pick up as much of that heat. (My original reason for wrapping the exhaust manifold)..
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https://www.youtube.com/watch?v=phwiFsiqhoE

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Is it any wonder why fuel logs come soooooo slooowwww for Centurion?
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~CrazyJerry