Modern Vespa

What is everyone's opinion on lightened flywheels.

I need a new flywheel. Beedspeed sell a lightened one for a couple of quid cheaper than the normal one?

As I understand a lightened one will spin up quicker and put less strain on the crank. I could be way off here though. There must be downsides as well.

On a secondary point, the lightened wheel from beedspeed has 2 woodruff keyways. Anyone know why? I don't know of a crank that takes 2 keys.

Thanks

Wow - I was contemplating a post very similar to this one

I think I came across a similar flywheel (PL170, 2 woodruff slots, 1,4kg) by chance, and , in addition to pros / cons, I was wondering if a longstroke setup would benefit from less bulk.

The second woodruff slot is for fitting it on a Smallframe (PK).


Normal vs Light

The HP4 flywheels have two slots so you can run it on a P200 or a small frame.

The one I was looking at weighs 1.88kg.

Thanks for clearing up the 2 woodruff slots questions.

I'd be fitting it to a px125e.

Pinasco have a lightened flywheel too. I need one as my woodruff slot in my current flywheel is pants and wiggling a lot. Interested in people's thoughts too. Thanks

I ran those on two of my bikes in the past and really liked 'em at 1650grams. not too light not too heavy.. they're great for some instant zip.. and I never noticed any negative effects climbing hills or whatnot!

if you go too light then you have to up the idle speed a good amount to keep engine running...

heavy = stress on taper = snap
lightening = cheap performance upgrade

Another option is to use a stock electric start flywheel with the starter cog removed.
My stock px200e flywheel with ring removed weighs 1.8kg.

Thanks for the feedback all. Putting bike back together in the next day or two. New clutch side seal I hope solves my issue. All being well I will have some riding in before I fly in Sunday back to Europe.

Especially glad for some feedback on using the pinasco one. For some weird reason I got it cheaper in oz than the list price at sip. The moons were aligned!

light cranks for quick acceleration and more suited to city driving where you want the wooosh factor
On my long haul touring scoot I took it off because I would loose momentum up hills and into the wind...ie loss of inertia.
shaneo

I have heard about balancing issues in the clutch, but not idea more than that

I had a conversation with a guy who had a Pinasco 213 and it was pretty quick. He said he fitted a very light flywheel (1.2kg from memory) and apparently it was very quick off the line. BUT he went through a bunch of clutches... each a little more exotic and pricey than the last. Eventually ran out of enthusiasm for the purchase of new clutches. Put the old flywheel back on, stock clutch and was still going well a year later.

Biggy,

Lots of good information HERE if you missed it, including info on plastic fans and cut down stock fans.


stock fan @ 2.72 kg & plastic combo @ 1.43 kg.


cut down stock fan @ ~ 2.2 kg, turned & balanced by Hot Rod Al

As always, everyone rocks on this forum!

Thanks for the input.

For my style of riding and the kind of roads I'm on, I don't want to go too light on the flywheel! I spend time on open roads and need the ability to pull my fat ass up hills. That being said, the 1.88kg flywheel from beedspeed should suit my purpose and maybe give me better acceleration.

I need a new clutch anyway so I think I'll upgrade to a p200 clutch. This should be able to cope with the added stress of the lightened flywheel.

In theory, JOB DONE!

Thanks everyone

I ended up with his DRT race clutch, and ended up tearing th guts out of it.

With only one cylinder on a 2T you have all the torque and power being produced in 1/4 of a revolution. At a minimum the total mass of the crank, flywheel (and clutch on the largeframe) must store enough energy to complete the other 3/4 of the revolution. The torque and stress that the clutch, primary gears, and cush gear see is not the average from the dyno but the 4X that average that is delivered in the 1/4 of a revolution. Even that is not the max, the torque ramps up and then down so the total stress would be about 8X if there was no flywheel.

So the practical limitation is on the wear that the clutch and cush gear take. I'm sure there are ways to calculate and predict this but it's probably easier to wait till you have a problem and then correct it.

On my smallframe I ran an HP4 flywheel and all the cush springs are broken and the tabs of the clutch plates are chewed up. Empirical evidence that the HP4 is too light for endurance racing.

As for balance, I don't buy any of it. If the flywheel had to balance the clutch in some way then the smallframe (and every motorcycle and lambretta) would be "unbalanced". As long as the flywheel itself is balanced all will be well.

There is some validity to a heavy flywheel increasing stress on the crank. This comes from the fact that the flywheel that's storing the energy is on the opposite side from where it gets delivered. So during the power stroke the fly side taper is stressed in one direction and energy goes into the flywheel. Then the taper is stressed the other direction as energy flows out again.

Time warp/stock '74 VBC here.
Vape DC conversion. Everything off the battery. Works great.

Bike doesn't like the flywheel, 1600 grams vs stock 2400:
Wants to stall at idle.
1st to 2nd flat road doesn't hold rpm.
"Feels" wrong

Saw a German Instagram post with a Vape & OG flywheel.
Anyone tried this?

Is it timed correctly? VBC is 25/26 degrees? Or even earlier? 28?

Wonder if the clutch is that heavy it needs a heavier flywheel?

Vape sport or road? It's not the flywheel weight causing this. Too light is like 1.2kg. With the new stronger spark it will be highlighting some other issue. Timing, jetting, compression are the usual suspects.

It's at 20 currently. Stock (points) is 22.
Tried 22 initially.
Clutch is stock.

Aside from it wanting to stall at the same idle rpm as before and this "feeling" of a loss of inertia, there aren't other issues (other than how it looks there ).
Haven't had any loss of long uphill power as mentioned earlier here. More the opposite.

Road. 2 degrees retarded vs original/points spec.
Nothing else was changed.
Compression is good.

Correction: Stock is 2.8, not 2.4.
Vape is 57%

Wow it's cool to look back and see some of the old contributors in this thread. Damn, I still miss Vader on here.

I think I can see how it was done. It would take a LOT of work, and be considerably heavier than stock
Bailing out of this.

Looking at them together, force isn't equal to scale weight between the two. The weight of the Vape flywheel is much more centered.

Adjust timing/jetting?
I'm at 1300 rpm idle, to prevent the inevitable monthly stall in traffic at any less.

Timing isn't that sensitive at low rpm but the pilot jet is. The spark will now be much stronger. Before doing anything else re jet the whole carb. Sure it's just that.

Hmmmm that's a little strange.

Using stock timing should be the best because the road advances 2.5 degrees as the revs increase to 4000rpm before dropping back down.

The 2.5 degrees will help with off the line stuff.

Stock jetting, right?

But the timing of 22 degrees should allow for richer jetting because it has more time to burn.

One thing I haven't seen mentioned is balancing the rotating mass on Vespa engines. Maybe it wouldn't make much difference, but it sure does in automotive engines…even for non-performance reasons.

Got it.
Stock autolube carb/jets here, but no other single digit pilot jets to try.
I have a 20/20 Dellorto and lots of pilot jets with the air corrector, but no idea where to start on jetting.

Is it possible to plug the air channel on the original carb and use a #/# pilot?

Yes. Lead (unleaded now) solder works great to plug the air hole.

Sure a richer pilot and/or main jet will fix it.

It's "happiest" so far at 19 with stock jetting. This trial-and-error-experience jives with the early P spec from points to the Ducati curve.

"No such thing as PNP."
But the only way to solve the '74 US electrical discombobulation I could figure out.

Better to just plug the air hole on the #/# jet. This is less intrusive.

Waaay old thread that recently got revived but it makes sense: it's a good topic, maybe always relevant.

I just got a replacement crank for my bitsa VBB project that will use an otherwise original VBB motor with a total rebuild. This crank happens to be a Mazzucchelli AMT 132 (indicated as replacement for VBB, GL, super, Sprint etc), but the cryptic literature in the box alarmed me

Referring to its "advanced crankshafts,"Mazz says:

"We recommend the use of a lightened fibre flywheel (max weight 1600 g) to avoid great vibrations and the inevitable breaking of the flywheel shaft, valve widening and lightenings etc."

Does this qualify as one of their "advanced" cranks? I wasn't planning on replacing the stock Piaggio VBB flywheel (2400 g) and stator, though, for now.

And, after re-reading this thread, it sounds like a lightened flywheel actually created problems with clutches for many riders.

So... can this crank flyside taper handle the original VBB flywheel, or not?

(Edited to correct kg to g)

Last edited by zachyzach on Thu, 16 Mar 2023 12:02:26 +0000; edited 1 time

I heard from the mechanic at one of parts houses I buy from, and he said, mainly, that Mazzucchelli routinely includes disclaimers like this. He's used Mazz cut cranks on many dozens of motors and hasn't seen one break.

Making the disclaimer probably is to protect against liability arising with the rare defective part and also because people do all kinds of nutty stuff with tuning, occasionally maybe causing exceedingly high RPMs etc.

I'm not going to worry about it, then. I'm not going for the extreme build here, just a refreshed stock-style restoration.

I've found that the small block engines like the 177/187 like a lighter 1kg flywheel where as the large block 210, 221 232 etc like the 1.4 to 1.8kg.
This is only personal trial and error between my MHR 187 and a mates Quattrini 232.