Modern Vespa

From time to time I'd have a lot of difficulty starting, and that's why I used the drill. Sometimes there would be a mismatch between speeds when the motor fired it felt for a second like it was going backwards. That's where I think the extra stress came in... basically using the drill to try to stop the flywheel (intermittently for a very short time), so that stress would presumably be felt at the junction of flywheel and crank. That's my theory anyway, doesn't explain yours!

The only info I have on flywheel weight is not to use anything much more than 1.6kg with a Mazzuchelli bell crank, but I think you were staying with rotary?

I would imagine misfiring had a lot to do with your break. Not so sure why mine broke though. I ride quite hard but all smooth. I can only think there was a micro vibration issue. It broke while cruising along. It does rev quite violently and had a 1.9kg flywheel, which may have been a bit heavy in hindsight. Sure this is it.

I don't think the general 200 flywheel guidelines have changed for decades, 2kg flywheel for touring, 1.6kg flywheel for road and 1kg flywheel for track.

As the flywheel weight doesn't affect the max power very much, it would seem the decision is made. 1.6kg it is.

taking note of flywheel guidelines;

How much do PK flywheels weigh?

What has been said here only applies to PX200s. The PX has the clutch on the other end of the crankshaft and a PK has just a tiny cog. The PX needs more weight to stop it shaking itself to pieces.
PKs (smallframes) can get away with much less flywheel weight. Others know way more than me about those.

I believe PK flywheels fit, actually think I use one. 1,8 kg?

Might be wrong, it has haoppened.

They do fit and people do put them on, but the keyway is in a different position than the P stators require.

There's the 1.8kg dual key PK/PX flywheel:

https://scooterlab.uk/dual-keyway-vespa-pkpx-lightweight-flywheel-news/

https://www.sip-scootershop.com/en/products/flywheel+sip+touren+for+vespa+_51003000

Jack, I wonder if your image shows corrosion around the keyway, which prevented the two tapers from meeting fully, and concentrating the torsion forces around there, where they would bind, rather than along the full length. Any high spots and you'll still torque up, but not be completely pulled on to the taper. Just a thought from taking my flywheel off outside in the rain so many times this year.

Yes, I've got the dual keyway type.

Yes, this is what I just put on my P as well. The slot timing was a tiny bit off, I did have to retime my stator a smidge. And no, I didn't use the wrong keyway, that would have been a much bigger change .

I see what you are getting at and was certainly not helping any. They always seem to go a bit rusty. Something to do with the metals and magnets I guess. Insulating grease either puts them on too tight or too loose. Will need to decide what to do with the new shiny crank when it comes.

The broken off part was still very tight in the flywheel. I think it had been breaking for a while, quite a lot of rub marks on one side of the flywheel, which for this build means its no good. New one will be 1.6kg, so looking forward to that.

How's your set up going? Nice and well behaved trouble free Summer?

You can always lap it with valve grinding paste if you want a good taper match.

Ahhh, shiny new bits to play with; what'll be the next weakest point to crack though?
No problems for mine over a great Summer (the beach isn't far though), and safe for the frosty morning runs for a few months now; I'll update in New Year.

Home soon. Parts ordered

We have progress.
All stripped down and washed. Good news is the casings are no more battle damaged than they were. Less good is the Crucifom is prematurely worn out. Didn't order a new one as I was expecting it to be fine. What a mistake that was. I don't think this double hard one has lasted any better than the Piaggio one. Won't be wasting money on another hard one.

Nice shiny crank to put in and a 1.6kg plastic flywheel. Going to do some slight dremel work on the cylinder and change the packer to raise the transfers a tad. Just wan't a few more rpm in the porting to match with the lighter parts. Hopefully no more than 9000 rpm in gear but we will see.

That's disappointing; how many miles did you get out of the hard crux? You can buy three Piaggio ones for your £60, and it's less damaging on the loose gears - are they all still OK for this build?
I note you say these casings are battle damaged, so another build will be on the cards soon anyway I imagine - a standard crux will probably last between rebuilds!

So, as it turns out, both SIP's and BGM's cruciforms are crap. I wonder if the one by Crimaz is better than these two...

Gear cogs are fine. All look good enough to go back in. Wasn't jumping gear or anything suspicious. This seriePro one actually didn't last so bad. It did 4500 miles.
The way it failed seems like it was only case hardened. Once worn was as soft as any other.
The Crimaz one is worth a try. And cheaper too.

Engine is back in. Not running yet as still waiting for some parts. Busy weekend with real life so should burst onto life again about Tuesday new porting looks good. Dropped compression to 11.2 :1
Pressure test was good even though I had to seal it twice after forgetting to put in the kick-start cog. Yes, I do dumb stuff too.
Just hope she doesn't rev to high.

Was running again last Wednesday. Been quite busy since. Doesn't seem to be as quick top end as before and revs out to 9500 (only in 3rd). Still pulls 4th but not as strong as it did. Turned the timing up as far as I dare and still not enough to get the hard pull back.

New flywheel fell off (like they do). No major damage but annoying. More grinding paste and a new key and we were going again. Been fine since and done at least 200 miles. Hopefully thats the end of that.

I think the porting is too high. Since we're between festivities, I'm going to drop the packer later today and see what happens.

Definately seems like there is more bottom end with this crank and flywheel. If it take off hard she floats up in 2nd. First time it happened I was exiting a roundabout (traffic circle) and it was quite exciting.

Jack, what gearing do you use in your 221? Gearbox, 4th cog, primary, clutch?

Yikes. Did you think for a second the crank had broken again?

swa45 standard 200 gearing with a 22, 35 tooth and 350/10 tubeless. normal compared to your set up.

Ginch, it was just rattling when I got home but yes. Done another 50 miles today. All going great. Got slightly hot, so back on 175 main jet for next time out

My flywheel sheered another woodruff key Was revving down from 9,500 when it happened.
That's three keys sheered and three times with the griding paste. The keys are sheering clean. One was DRT key too. Definately holding tight and extracts with a pop.
I have ridden again since and seems to be holding again. Can't make my mind up if she revvs too violently or it's just a c**p flywheel (pinasco btw). Any ideas?

I know with the Wideframe Vespa Pinasco Flytech flywheels you have to use an extra washer under the flywheel nut otherwise without the extra washer it doesn't matter how much you tighten up the nut it bottoms out on the threads before the flywheel is fully tight on the crankshaft taper.
This sounds like what yours is doing, remember the rule about woodruff keys only being a locator and not designed to take any load.

I would suggest that your flywheel isn't being fully tightened down, not from you incorrectly torquing the nut but I suspect you need a thicker washer/s under the flywheel nut.

Thanks,
Rog

Was so hoping you were right. I had to have a look but the taper stops 1mm under the flywheel. The nut (hardened serie pro) will screw right up to the taper.
Rode around for another tank of gas today. All going great with no further incident. It might hold, we have a chance.

Those black streaks or witness marks (?) emanating out from the flywheel hub caught my interest. It almost looks like the rivets are 'working' i.e. a small amount of movement causing some wear either of the rivets or the holes.

Even a tiny amount of movement will cause a minuscule lag and huge extra stresses.

Maybe you can do a little test and clean off the streaks and see if they come back after a ride? I'd be worried if they do. Of course it might be remnants of some dirt/paste/oil from somewhere..

I wouldn't worry if they don't come back.

I do hope not. I've cleaned them off and we'll see what happens. If the rivets are loose, then the new flywheel really is junk.

Did another tank of gas today. Flywheel still on.
Gets up to 8000 rpm in 4th pretty easily and often now. Even when slight uphill or into headwind can still make the 8000 rpm. Feeling impressive to ride.
And the downer of the day is the clutch has started juddering. Probably the steels have notched. Bugger.

Is there any particular reason you have to rev the guts out of it. Is it not producing enough torque down low that you need to have it right up there in the revs to produce any power.
I had this issue before i went to the variable ignition, where the MHR would not produce any low down torque with the static set 18 degree timing.
With variable static is now at 21 and gives a much broader powerband and i can lug it in the lower revs and have plenty of torque and dont feel i need to be killing it in the higher revs all the time. Mind you its nice to let it rip.and feel that power hit in the upper revs.
The other advantage is you can lean out your jetting, so it becomes nice to ride around town without all that 4 stroking going on.
Im not sure if you have variable ignition but its definatley worth it, will just make it much more relaxing to ride.
But still have the power hit when you want to play

Jimscoot, I appreciate you have been doing this a long time.
I have stock P200 gear ratios and a Kytronic (no.2 after Kheper no 3) with static 26 degrees. Running a 175 main jet with a nice tan coloured WOT plug chop. There is certainly no 4 stroking anywhere on any of my carbs.
8000 rpm is not really revving the guts out of it as she will go to 9500 (70mph GPS in 3rd ). Torque is good since I dropped the packer can 4th roll on with no issue. I have done everything I know to make the power band as wide as possible. You are onto something though, I was thinking I might up the gearing slightly next time in there but fingers crossed that's a long way off.

Yeah sorry Jack i went a little off track there.
What i was getting at is its great that it revs so high. But if you keep killing it it might be better to go for a more touring set up where thr powerband is stronger at say 2000rpm lower so it starts coming on around the low 6's and tops out around the 7.5. That way keeping all those spinning forces lower

Done exactly that on my PX200 tourer. Power comes on about 5000 and tops out at about 7500. Ideal for two up and long distance.

One issue with power is that it and rpm are linked together. The more power there is the more rpm there are. Can't have one without the other. Reducing the porting reduces rpm and power but increases torque, to a lesser extent. I think this scooter is close to the power/torque balance limit for 4 gears, a single exhaust port, air cooling and rotary inlet. Flywheel aside, this is it for this scooter's tuning.

Jack, just a thought. Is there any chance that your Kytronik could be misbehaving? I think Ginch's crank snap was timing related.

I'm interested because I'm planning to transfer my Kytronik to my MHR 221 build as I cannot stretch to a SIP Vape ignition. I have the original KT with the built in spark booster thingy, and I know some people have had issues with the early units.

I have strobe tested the timing accross the rev range many times in the past few weeks. Its working fine. No reason to doubt it. This Kytronic is a 2016-2. I think there is a newer one now but much the same overall. Mines probably the same one as yours.

Seeing how difficult it is to get a taper to hold on this build, its most likely that the crank snapped because the old flywheel was heavy and the taper hold was too good. And it was 6 years old and highly abused. The MHR revs quite violently (as you will find out) more like a motorcross bike than a scooter.

Jack maybe a lighter flywheel would be better.
I run the malossi flywheel that weighs in at 1.2kg.
Its not riveted made out of one solid piece so would be nicely balanced too.

The MHR likes to rev and i think a lighter weight flywheel might give you more reliability

For a 221 used on the road, I feel a 1.2kg is just not enough. Possibly a mistake buying this Pinasco 1.6kg but it is holding fine for now. Even at 1.6kg there is already a very lumpy tickover when compared to the 1.9kg flywheel.
The marks on the rivets never came back, so at least that is holding too but one peice gets over that issue. Will investigate better when I buy the next one.
I am certain I am going to up the gearing before the Summer. Will probably need to lose a few rpm too but plenty of movement in the MHR cylinder packer. The reasoning for this is the exhaust. I have a JL RZ at the moment and its doing most of its running coming off pipe at the top of the power band. Until I buy a new pipe, higher gearing will be more appropriate.

Maybe you can get away with a slightly lighter flywheel on the 177 compared to the 221 Jimscoot.

I talked to a guy a while ago who had had lots of clutch trouble... not entirely unexpected because he rides it hard. But he went through 3 in a year and each was slightly more robust than the last. When it came time to buy the 4th one, he swapped the HP4 (1.1kg from memory?) back to stock, clutch back to stock and hadn't had any issues for a couple of years since.

Ginch thats kinda weird that the heavier flywheel had saved his clutch, i would have thought the opposite.
Something to consider would be to have the clutch weigh in the same as the flywheel, to try and exert even forces on both sides of the crank, especially the power a 221 would put out.
My clutch weighs in approx 1.3kg thats a sip ultrastrong with cr80 plates.
Its not the same as the 1.2kg flywheel but its getting close and maybe somehow there is a theory behind it and definatley worth putting on the table when on this subject.

About time for an update. I have been quite busy with this behind the scenes.
I changed the gearing higher to 24/65 35 4th and dropped the cylinder packer as low as it would go. Giving 184/126. Was no good, she went fine but 4th gear was a struggle and even when she got into the bigger power at 7000rpm and up it was actually no faster than with lower gearing. And with less acceleration in 4th she felt slow.

Put the gearing to stock 23/65 35 4th. As it wasn't new anymore I decided it was time to play with the MHR. I did some general porting on the cylinder. Cleaned up all the defects, there wern't many like in the old days but still more than a few. Opened up all the base tunnels in the cylinder. Done some work on the boost exits. Widened the exhaust port a little. And left the cylinder in German mode at 184/126.

Now she goes ok. Not over the moon but ok. Pulls 4th uphill and makes over 8000 rpm in top on a two way run. A T5 4th would improve this but I'm not splitting again for a while...........however, I did prefer the cylinder at 187/129 and I think I will go back there with the lower gearing.

Since bolting it up and going over the data. I now understand better what Malossi are doing with the new MHR scavange pattern and think it doesn't work optimally as a 221. It works obviously but could be better. Luckily there is metal to fix it, by the time I get home again I'll have worked out a porting plan to try

Why is that do you think? As in welding???

Well, this set up has higher crankcase compression by being rotary and having a plastic packed Pinasco race crank. This is going to make the mixture squirt into the cylinder fly up the back wall and loop straight round and out the exhaust. At high rpm there is no time and its on pipe, so this feature is better and makes more power (ie why its a race crank). At low rpm this is awful. On a 57MHR cylinder on a 57 crank the ports are much lower and the entry angles are adjusted for lower duration. Put in a 60 crank and the durations are way longer. The entry angles are then not so appropriate for a rotary. Going to take a punt and re-angle the scavenge pattern. I'll do anything not to buy a reed block As in enough metal in the cylinder to re cut the ports without making the durations too long.