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Alternator mods

Fabrication of Alternator from Yamaha Big Bear for 3W 240 iB2 engine

1. Flywheel
2. Stator
3. Clamp
4. Regulator
5. Balancing

Note: Contents of a letter to an enquirer re design of alternator
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  These are roughly the steps I took. I hope the photos are clear enough. If you want more detail of any particular one let me know and I will increase the size. Hope you are accustomed to metric.
1mm = .040 inch.
The finished clamp looks a bit untidy, but it works and you can’t see it with prop and flywheel fitted. I purchased the alternator (from a Yamaha Big Bear quad bike) from a motorcycle dismantler for $150. Rectifier is an aftermarket one from a motorcycle shop.
1. Flywheel.
 Partially drill out the rear of the 6 solid rivets holding the centre spindle and punch them out.
· Cut the heavy bits off the spindle after machining the flywheel side of the spindle down to a thickness of 5mm or less.
· Machine outer half of flywheel to a thickness of 4mm (or less).
· Reattach the lightened spindle using same rivets, punched out into slightly countersunk holes on the inside of the flywheel.
· Using inside magnet surface to set rotation centre, skim excess metal from outside of flywheel, to give a total thickness (magnets, bakerlite and flywheel metal) of 10mm.
· Drill zillions of lightening holes in the diameter face as shown, but leave some metal for more holes for balancing later.
· Find the centre of the flywheel using a dial gauge on inside of magnet surface.
· Press in a tight fit aluminium centre 32mm OD, 5mm thick, and drill out a 10mm centre for the prop hole mandrel then drill the 6 prop holes. (My mandrel came with a 10mm centre, but engine has a 12mm guide, so drill to 12 mm last)
· I drilled out the prop holes for press in inserts 10mmOD x 10mm(6mm ID), to help bear the load of the flywheel on the bolts (after nasty experience wih sheared prop bolts) – having drill a small 10mm recess into prop hub and prop. This may be unnecessary.
2. Stator Set stator in a four jaw chuck, centred on the inside diameter. Machine the centre out to 55mm. Final inside diameter will need to be 57mm to clear the prop hub, best machined while mounted on the clamp. Cut the three stator wires and identify the ends with heat shrink so they join correctly in two 3 pin plugs. You will need to solder on some wire for extra length for the reconnection. Decide where you are going to divide the stator in half as shown and drill the four outside holes for a snug fit for 4mm (or 3/16in) bolts. The heads of these bolts need to be almost flush on the flywheel side of the stator, so countersunk or recessed cap screws would do. (I used countersunk heads – otherwise they interfere with the prop hub). At this point go to the clamp because you need to mount the stator on the clamp before cutting both in two.
3. Clamp.
· Start with 100 mm diameter aluminium billet suitable for machining, face each end.
· Machine out the centre of the clamp as shown
· Set the outside diameter to 2 steps as shown, and mount the stator on the clamp with four bolts (4mm)
· Now the tricky part. Mark the stator and clamp at the diameter for cutting into two halves.
· Drill symmetrical holes across the planned cut line so the two halves of the clamp can be bolted across the nose of the crankcase of the engine.
· Cut a wedge in the clamp at both end of the drilled holes to seat the bolt heads and nuts.
· Cut the stator in two. Cut the clamp in two.
· Bolt the parts together securely then machine the centre of the stator to 57mm
· Dismantle and square up the cut ends of the stator by working them on a oilstone until they mate well. This is acceptable in industrial alternators.
· Finally, with file and hacksaw remove necessary metal from clamp and stator to fit and clear the Hall sensor and the crankcase webs.
· The engine webs may need a groove for the clamp bolts but this helps secure them to the engine
4. Balancing
Balance the flywheel on a long pin (wife’s sewing basket) set in a block of wood. To find the centre of the flywheel make two tapered cones as shown, with a snug fit over a threaded rod secured by wingnuts. Drill a tiny centre dimple in one end of the threaded rod. The idea of this apparatus is to easily move the vertical location of the pivot point to control the sensitivity of the balancer. With this system you can balance to a very precise degree, and the prop can be balanced with the flywheel if desired. Just drill more holes in the flywheel face as required to achieve neutral balance.
5. Regulator
Cut excess metal from the regulator. The three white wires connect with any three from the stator. The Red and Black should produce 14.5 volts DC. Any 2 of the three white wires from the stator should yield 40 – 100 volts AC. The brown wire is for the lighting on the motorcycle and is not needed for our purposes. Finally Fit everything together and make sure no interference / contact points. Place two electrical cable ties around the clamp adjacent to the stator. This arrangement should avoid over stressing the crankcase. The clamp bolts don’t need to be very tight but use nyloc nuts.
Good Luck