Funky Running: Tale of Woodruff Keys (Alternator Flywheel)

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Wheelman-111
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Funky Running: Tale of Woodruff Keys (Alternator Flywheel)

Post by Wheelman-111 »

Greetings:

Sharing an anecdote:

Flash II's performance had fallen off dramatically a few weeks ago. Coincidentally, there developed an alarming noise that turned out to be the fan rubbing on the evidently melted black fan cover. I surmised incorrectly that the LeoVinci pipe had eventually melted the cover, bubbled it up inside, producing said rub.

So I shimmed out the pipe, replaced the fan cover and the shroud without much improvement. In fact the scooter went from bad to worse, where it would barely idle and wouldn't accept throttle at all.

Checked for vacuum leaks, mucked about with jetting, swapped plugs, all to no avail. Finally in desperation I pulled the block and began disassembling. Bore looked great. Compression 155 spinning by hand. Spark was fine. Or was it?

Pulling off the alternator flywheel told the tale. The shredded remains of the little half-moon sliver of what is known as the Woodruff Key lay adherent to the Rare Earth magnets of the flywheel. It seems that during my careless assembly thereof, I presumed the key would remain obediently adhering to the slot in the crank, and didn't check for it.

What had happened? The flywheel got loose - just a little at first. Evidently this retarded the timing more and more, first expressed as a little power loss, and eventually it would barely run. The spark was there, but coming much too late in the compression stroke to produce useful combustion. This also explained why the fan made its acquiaintance with the cover; the flywheel was awobble. New Key ($3. later) and careful reassembly: Voila! Flash II back to the high 50s/low 60s.

Watch out for this "Gotcha" any time you pull the flywheel, kids.
Wheelman-111
Most of my money is spent on scooterparts. The rest is just wasted.
"ISO": '03 Vespa ET4 Malossi187 74MPH
Flash 9: 2001 Elite SR Contesta 72 ZX Tran, 9:1 Gears, Stock Airbox/Carb/Pipe 58.8 MPH
Punkin: 2010 Vespa/Malossi S78, 61MPH
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