Modern Vespa

Ran on straight teeth for a good 3 years installing it without understanding what I was installing at the time... I had the malossi 24/63 combo and needed to swap my clutch and primary out, so I thought why not...

Theres definitely more noise coming out of the primary and clutch, that's with the full metal to metal contact...

When you cycle through the gears its a lot more crunchy with the engagement, but definitely more solid transmission of power... feels like there's less dip in revs between gears.

I was quite comfortable cruising on short highway stints.

The primary seemed bulletproof, not much metal wear in the oil.

But eventually I went back to DRT helical stock gearing 23/65 the biggest reason because I wanted a shorter gear setup (higher gear ratio) and as far as I can see, there's not that many short gear options for straight teeth clutch and primary (all race use I imagine)

So with helical you get less noise and a smoother, softer shift (which is better for me riding around the city)...

Just my none scientific experience, question hijack over...

I really think it doesn't matter so much. Gearing in mine is total stock. 23/65 with 35 tooth. Helical is stronger and smoother but more friction and higher side load. Straight cut is kinder to the bearings but weaker. And so noisy. Like most things scooter, is personal choice and no right answer.

The funniest thing about the seize was there are no detonation marks. Head still like new. Must have been too weak to pink properly. There was no sounds and it felt a bit dead over 80. While I was thinking 'this is weird' it seized. Can only be fuel starvation. That was the third time it had been over 80 that day. Was maybe just lucky before. Piston marks were straight overheat at the exhaust port. Usual for running weak.

It can only be something between tank and carb. There is a pump and two fuel filters and a load of pipes. Something wrong right there.

Not updated this for a while. New 57 MHR kit on new 60mm crank to rebuild from the seize. 65 helical gear wore loose in the primary too. Changed to 24/62 straight cut primary with 36 tooth 4th, because the 35 had worn out too.
At a guess I've done 3000 miles on this rebuild already and is due another this winter. Going to need new clutch plates/springs soon as an interim fix but that's just a service item on this thing.

Anyway, weird issue. The other day it was making a tinkling noise while idling, like something loose, similar to a primary cush plate starting to come off. Later the same day it started backfiring at 6000 rpm and not revving more. Thinking it was not my day and the Kytronic had failed too, I removed it and took off the flywheel to change the timing to static. To my surprise the spark coil had fell off. Thought that's the issue bolted it up ran it again no difference. Long story short, the pickup has been hammered by the rivet and is broken. Changed the stator to another and all good at 10000rpm again.

It never ceases to amaze me the new and different ways these things break, especially the highly-tuned ones. It's a good thing they're so much fun to ride when they're wound up so tight to make the effort all worth it.

Been riding the 221 often. Would guess a few thousand miles over the summer been going good and solid.
Rode it Thursday all good. Wheeled it out today, wouldn't idle and was racing. Pulling choke again slowed it down. Blocked pilot jet it wasn't. It would appear to be some massive and sudden air leak.
Winter rebuild might be a few months early. Will investigate tomorrow. Pressure test first plan.

Interested to see what it is.

Winter overhaul it is it seems

Took the carb and exhaust off. Disconnected the fuel pump pipe. Installed bungs. Connected the pump. Waited for the big hiss and nothing. 8 psi for many minutes. WTF. Nothing to see here.

Ok, fourth strip down of the 38. Pilot jet clear. Inner pilot jet clear (yes, these carbs have two pilot jets). Blew carb cleaner through the body from the float bowl. Same as yesterday, spraying into the Venturi from both outlets. Starting to struggle for ideas. Held the carb up shining a torch into the Venturi and can't see a clear round hole, there's something in it. Poked around with some soft wire. Looked again and clear. Reassembled and working fine. Drama over. Took for a celebratory thrash round the block, popping over 80 on the bypass.

Edit: Winter rebuild to include a fly side bearing. The one in it is looser than a retired madam.

Wooohooo! 4th times a charm.

EDIT: and I gotta say, I appreciate you going through what the problem was and the steps to make it work. And sometimes it takes going over everything a number of times, even for Jet-Eye Jack!

Ok, it's time. 221 engine is out and split. There is a whole catalogue of stuff wrong with it. However it was still going fine; properly fast, reliable (still going on 50 mile round trips), smooth and easy to ride, no clutch or box issues. It was dripping oil but many do.

Once split it was surprising. Piston (vertex) had a crack in the underside, clutch cover leaking, gear oil minor seeping from one case bolt behind the stator, oil seeping from the head bolts, fly side bearing now badly worn (0.5mm radial), rear wheel bearings both beyond acceptable, low compression, cruciform as bad as the last and kick start buffer nearly through.

Gear oil level was full. Pre split pressure test holding good.

No more tuning, just repair and get going again before one of the others breaks.

I literally explained to people twice this week that the higher the state of tune, the more frequent and extensive the rebuilds, even if nothing has materially broken along the way.

That cruciform has definitely seen better days, though. That's some well-earned wear.

That MJ9 hardened cruciform was new in Nov 21. I'd guess 3000 miles, no more than 5. I'll check the old MOTs.
This time I have a hardened BFA one but that was as the one in 2020, and ended the same way. Surprised the cogs are still good. Last time it had a new 4th though.
It's just so tuned. Fastest PX I've ever ridden. When I describe it to people, the only comparison I have, is just like a stock 350LC. I used to have one and it's a fair comparison. I'm waiting for the cases to break. Have to be so careful I never miss a gear change.

Looks like you found the air leak.

Strange the pressure test didn't spot the leaky head.

That cruciform looks like it's seen a gear shift or two.

That's not just any old cruciform. MJ9 hardened
https://www.sip-scootershop.com/en/product/cruciform-serie-pro-by-mj9_87029100
After the last BFA hardened one didn't last a year, I thought it would be worth a try. Just the same. Back to BFA again.
https://www.sip-scootershop.com/en/product/cruciform-sip-bfa_87095100
The head bolt leaks were spooge dribble. Pretty much nothing stops spooge leaking out when running 13.5:1. Only 4 studs, at full temperature, weren't designed for this.

Any good? https://www.sip-scootershop.com/en/product/lock-nut-m8-mm-gas-tight_87181100?q=gas%20tight

Nice find. Amazing what sip sells. Upper temperature is a concern but worth a try.

Got a high rpm misfire. Sudden WOT on the stand backfires, as the revs increase past 8400rpm. If I ride around under 8000 rpm it is great. Smooth clean rides normal.

This time is not a carb thing. Even with no main jet it still backfires.

Pk50 flywheel
Ducati OEM stator
Ducati OEM CDI
Kytronic 2016

My spare Kytronic is blown up, so if that will need a new one. Everything else I have spares for.

Changed the plug already. Not that. Will have an investigate tomorrow. What are people's thoughts? I have no guess but as usual scooter rules, I expect it to be the expensive part I don't have.

Edit: Just scrolled back up the thread. This happened before. Woohoo, might be the same thing again

lol… answered your own question it seems…

The unsurprising news is that it appears to be the stator pick-up again. Not ridden yet (raining) but seems much better with a spare stator on.

The weird thing is, this is a different stator to the last similar issue. Not only that, different engine cases, now VR-one. New bearings and a different flywheel.
Nothing involved is the same, except crankshaft and that's straight enough.
Pick up was rubbing on the flywheel, as there are heat marks. Turning by hand no rubbing. Why?
All I've got is there must be engine case distortion under load. 40+ bhp at 10,000rpm might need more stator clearance to allow for case twist. Anyone agree? Or other ideas?

One thing that occurs to me is that the taper on that crank only needs to be slightly different to affect the alignment of the flywheel and stator. Same with the stator mount in the case.

Also possible is that the flywheel is very slightly out of round on the inner circumference. A difficult one to check though.

Earlier you said the flyside bearing was badly worn. Clearly that would allow something that was very close to now touch. I have a VBC case (first of the P-style flywheel bearing changeover) which went through a few bearings before I realised the case journal was oval. Far less likely with the Malossi case, but bears investigation.

Of course 10,000rpm will put different stresses on a motor than turning it by hand, and the fact that you can't see the area at the same time doesn't help... but I do find the case twist idea probably the least plausible.

It doesn't solve your whodunnit, but Vape might solve your problem?

Late summer 2023 the 200 casing did crack across the clutch side main bearing. Unrepairable. I changed for VR-one cases. New flywheel, another stator. All new bearings. Same crank though.
Between the first time the stator pick up burned out in 2022 and this time, it's like an entirely different engine. The only common things for the stator rubbing is the high power, rpm, vibration.

As you say, Vape would surely fix it. Other people don't have this issue. 10,000rpm on an original stator is probably too much. I'll rebuild the stator and dremel in an extra mm of clearance. A bit bodgy but worth a go.