Go Guzzi Go
by Alan Shipton
Question: What does 4340 and Titanium have in common!!
Answer: Nothing at all apart from the fact that I have some of each in
my shed at home.
Having decided that I would like a lightened flywheel and ring gear for the
Mk4 I decided that I did not want to lighten the original in case I did
not like it. I needed to be able to put the stock item back in place.
With that decision made and after asking a few questions on what may be the
best steel to use I put my lathe to good use and turned up a blank flywheel
out of 4340 alloy steel (also known as chrome moly). This was then normalized,
(‘what the?’ I hear you say as often quoted by Rove). Well, this is where the
steel is heated above the upper critical range and cooled in still air at room
temperature. This process is intended to put the steel into a uniform, unstressed
condition of proper grain size and refinement.
Rough turning blank in my lathe
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Roughed blank after normalizing
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The blank was then rough machined and finish machined, milled,
drilled and internal gear cut to come up with the item below. The start weight
of an original Mk4 flywheel and ring gear assembly is 5.5kgs as weighted on
the other half’s trusty kitchen scales after a lot of machining I reduced the
weight of the assembly to 4.2kgs (as measured on the scales) or a reduction
in weight of 23.64%. However I feel I can reduce this even more but that’s another
one-day job.
Finishing touches
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Lightened ring gear
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The assembly was balanced and only required 10 grams to be removed to achieve
100% balance, which made me pretty happy. As you can see below it has all been
assembled into the motor and so far I have been happy with my results. The motor
spins up quicker on startup and seems to spin up a lot quicker generally (seat
of the pants feeling) as well as making the gear changing smoother. All this
has resulted in me having to adjust my riding style somewhat (what style I hear
the critics cry out).
Finished flywheel bolted on to crankshaft
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Clutch assembly completed
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Would I do it again? Yes! I would! Remember the Titanium I have in the shed
(every man needs a shed is what I say), well if it’s the right grade for my
purposes just imagine how light I can go with a flywheel. If not it would make
really neat brackets and top and bottom fork triple trees etc.
However the next job on the agenda is to twin plug the heads, so until the
next exciting development keep the rubber on the road where it belongs and the
shiny side up!
Ciao for now,
Alan
(Oh and by the way I am still looking
for that long lost relative to pop off!!)
