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Alternator - The Build

From the last post, I've got pictures of the Kubota alternator all dismantled.  Next comes the modification pieces.

I've made an adapter ring plate to which flat bars will be welded to hold the case of the dynamo to the engine block.  This has the challenge of interference with the side of the case.  The cap screws that I will use will have to be ground down somewhat, and the side of the dynamo case ground down to accommodate the screws.  This should hold the case firmly to the engine block.

The next big item is machining the crankshaft adapter.  This will be a copy of the back of the armature, which will allow the magnet of the alternator to bolt directly to the crankshaft.  Here's a picture of it just started out of a piece of roundstock.  I'll need to get a parting tool for the lathe before I finish the part.

Here are the plans for the finished part.

Alternator - Proof of Concept

I'm fed up with the original Sunbeam S7 Lucas dynamo, and the MC45L dynamo that I bought. Neither one produces enough electricity in a foolproof fashion.
I don't want to have to worry about if there's enough battery to get me home anymore, and I want to run the lights all the time. I also don't want an after-market alternator conversion that does not look like the original.

The plan is to create an alternator conversion that produces 6 volts, is fully encased in the original housing, and works reliably.

I've seen others who have used a Kubota tractor permanent magnet alternator to do the job. Its only 3-1/2" in diameter and shorter than the MC45L dynamo. That means it should fit inside the casing. The trick is to mount it up.



It comes as a flange mount unit for belt drive, with its own bearings.

[edit]  I actually did use the bearings after all to keep the stator assembly centered in the magnet.  The magnetic forces are VERY strong radially, and will pull the stator into the magnet if there is the slightest mis-alignment or looseness.  A spacer piece was machined to hold two of the bearings into the stator and then the bearings were placed on the center bolt with their own machined spacers.

The permanent magnet rotor can attach directly to the S7 engine crankshaft, and the stator can mount to the engine block, or dynamo casing. All that is critical is that it runs centered and true. Should not be a problem for a guy with a lathe in his workshop.

Here's the sample fit up.  The center bolt presses out of the rotor cup easily.  This will allow me to make a bolt (left-handed Whitworth of course) to fit in there and mount to the crankshaft.  The question is whether 'tis better to bolt the stator to the engine block, or to bolt the stator to the outside of the dynamo, and put the rotor cup "upside down" against the crank.  I'll have to make an adapter to provide the seal to the front of the engine regardless.  The stator to the front makes it easier for the wires to come out to the terminal block on the dynamo casing.

The final part is the regulator / rectifier from a scooter.  I've bench-tested the rectifier / regulator up to 6 amps load.  It works fine with 14 vac input, and does not overheat.

Here's a VERY ROUGH sketch of the assembly.  I keep changing the design, so my dimensioned sketch is pretty bad.  I will require a minor modification to the dynamo case.  The cap screws will interfere with the side of case, so the case will need to be ground away in two small spots not visible from the outside.  The cap screws can be modified slightly to reduce the amount of grinding to the case.

MC45L Dynamo arrives

Just bought the proper dynamo for my S7 Deluxe.  The one that was on it was from a the earlier S7 model.  This one should have more current capability, since it has updated field coils, and four brushes instead of just two.  I knew it wouldn't include the bolts, so I probably will have to get those elsewhere... or use the ones that are on the bike.  It looks like its in fairly good shape for its age.

The commutator is a bit rough, but shows no signs of arcing.  It should be 100% functional.  The brush wires need routed, and the connector needs fastened down too, but it looks like its all there.  I may have to dress up the seal surface on the back of the rotor if I decide to use it. There's some pitting.  Its kinda a shame that the cover has been bead-blasted.  I would have preferred that it still had the original patina.  That's not to say that I couldn't GIVE it some patina.  Hmmm.

Hopefully, this all works and I can sell the older Lucas MC45O dynamo that's on the bike now to someone who needs it to make their original bike proper. (sold it!)

New Seat Belts

I finally got tired of the single-sided retractable seat belts that were in my Imp when I bought it.  They kept retracting back behind the seats and you couldn't fasten your belt unless the door was open. If you let it loose, it would slam against the door pocket and disappear behind the seat.

I sent away for some new proper ones.  My friend Nick was kind enough to supply me with some Sunbeam stickers for the buckles.  They look pretty snappy!

Sunbeam S7 in the press

I was thumbing through the AMA magazine from September 1955, and I discovered a treasure. Here was an article reviewing the uniqueness of the S7 and then a page or so later a nearly full page advert.

Thinking of warmer weather

Ahh.  If it were only warmer out...  with less SALT in the environment.