Using Great Plains Force One crankshaft on Aerovee

[lutorm]

As I may have mentioned before, when we rebuilt our Aerovee we elected to switch to a Force One crankshaft from Great Plans since it has a seal at the prop hub and it was clear that our engine (tailwheel Sonex parked outside in Hawaii) had taken in moisture through the front. When we first tried to start it up, it backfired, which usually means an ignition timing problem. How could that be, given that the ignition timing is fixed?

When I talked to the guys at GP, they told me that it was compatible with the Aerovee in terms of the dowel pin pattern on the back and the length of the prop hub on the front, which it is. However, when double checking now, it appears that the GP crankshaft has the dowel pin pattern rotated 180 degrees compared to the Sonex one, so the ignition will fire 180 degrees off. I guess the GP guys don't care about this since they are using a distributor ignition, but it creates a big problem for the Aerovee's flywheel-based ignition.

Could someone with a standard Aerovee sanity check for me that when the magnet is aligned with the upper magnetron (per the instructions for setting the secondary timing) it is the cylinder pair nearest the prop that is at TDC (or just before.)

I confirmed my ignition timing hypothesis with a timing light and, after rotating the secondary ignition 180 degrees, I can start and run it fine on that one. However, the primary ignition will be a problem. We'd have to either flip the magnet and the counterweight (but it seems unlikely the bolt patterns are compatible) or flip the ignition leads for the top and bottom magnetrons. The latter would be easy except there is no way the leads from the bottom will reach all the way to the top front spark plugs so we'd have to replace the leads with longer ones.

[Area 51%]

Assuming the holes are indeed 180 degrees off, I would pull the flywheel, remove the dowel pin that indexes the crank/flywheel (and the one opposite), rotate the wheel 180, and reinstall. These crankshafts and the flywheels, as used on cars, have the 8 pins to distribute the shock loads of a firm departure from a standing start.

[lutorm]

That's an interesting idea. It would be a clean solution, but I'm not too keen on pulling the engine off the plane again.

I wonder why the flywheel dowels are indexed at all. In the original application the flywheel is symmetric, isn't it?

[radfordc]

The latter would be easy except there is no way the leads from the bottom will reach all the way to the top front spark plugs so we'd have to replace the leads with longer ones.

Replacing the spark plug wires is fairly easy. I had to replace one of mine when it got up against an exhaust pipe and burned through the insulation. The original wires need to be extracted by force and any insulation, glue, etc left in the hole can be dug out with a sharp tool. I found solid copper core wires of the correct diameter on Ebay (Ford tractor parts as I recall). Screw the new wires onto the stud in the bottom of the hole in the module and glue in place.

[PeterLovell]

I swapped crankshafts, had exactly your problem and found online NGK 7mm spark plug wire connectors, cheap, incredibly easy to use, about 5 minutes per wire. Only have 3 hours on them so far, but perfect, and look neat.
Peter
Onex 120

[lutorm]

I swapped crankshafts, had exactly your problem and found online NGK 7mm spark plug wire connectors, cheap, incredibly easy to use, about 5 minutes per wire. Only have 3 hours on them so far, but perfect, and look neat.
Peter
Onex 120

Aha, so I'm not crazy!

So did you replace the wires on the magnetron so the bottom one can go to the top front plugs, or extend the secondary ignition wires so they could go to the top plugs and put the magnetron on the bottom?

[PeterLovell]

I extended the magnetron wires. 2 NGK connectors and 2 new plug wires which I cut to length.
Cheap and fast and currently working well, put another 30 minutes on them today!
Peter
Onex VH-BHU

[PeterLovell]

Forgot to mention, I did not change the timing wheel of the secondary ignition, I simply pulled out the leads from the coils and swapped them over. This took 30 seconds and the engine fired the moment I pressed the starter which solved the mystery for me !
Peter

[Area 51%]

Didn't know it would be that easy to swap out wires and such (no assembled Aerovee as yet).

As far as the indexed pins are concerned, the later VWs had a magnet on the flywheel for the fuel injection trigger. That's the extra hole you see on the case mounting flange. It held the pick-up.

In a performance application, the flywheel and crank are balanced together and the index keeps us feeble minded from screwing up.

[lutorm]

Ah, the splice connectors. Yeah that seems like the easiest solution, as long as the wires are secure.

Did you use solid core wire? No noticeable EMI?