Modern Vespa

I see. Makes perfect sense. Thanks.

Bearings are going back in today. I have the roller bearing spaced 1.0 mm off the base of the crank and am getting some light contact between the crank counter balance and the case, when the case is horizontal though not when it is vertical. Should it be further out?

Also, Is it safe to assume that the gear stack tolerance for smallies is the same as for large frames: 0.15mm - 0.40mm.

Thanks.

Thanks again for all of your help.

Got the gearbox back together. The "cruciform" spring and bearings were interesting, read a fucking ball buster. I know I wanted to half ass this in the beginning, but I am glad now that I stripped it all the way down. On to the clutch......

just seeing your motor pics makes me miss building a small frame engine. will have to go there again sometime, but I have at least 1-2 large frame projects in the queue.

Definitely more fun to wrench on than my VNB5M.

Got the clutch rebuilt today. At 21:45, the rebuild video above shows the guy applying RTV to the cylinder head: No, correct?

Why are you using the Polini head? Usually you want the piston crown to relate to the squish band.

I recognize the individual words you have used as being from English, beyond that, I have no idea what you said. Seriously though, I don't understand your comment. Can you explain "squish band"?

Here's what I have to work with:

1. Polini cylinder with some rust in it. Will need to be bored out.
2. Polini head in great shape.
3. Polini piston. Heavily scuffed with stuck rings.
4. PK125 cylinder. Looks new-ish.
5. Piagio 125-90 head. Looks to be in good shape.
6. Piston on engine. New, never used.

Thoughts on how to configure, based upon the above? Thanks.

The squishband is the area of the cylinder head between the outer bore and the combustion bowl. It is shaped to match the dome of the piston. Most stock heads don't have squish bands, the later PK ones might, not sure. The kits had squash bands particular to their pistons.

4. PK125 cylinder. Looks new-ish.

Does this have the internal 3rd port? Picture please?

Here is the bore of the PK125 cylinder.

So, to use the Polini I would need the matching piston and cylinder. Thanks for the education!!

The Polini head will work just fine with the PK cylinder. In fact, it's an upgrade.

^^^ that's exactly what I'd use, you already have all the parts. Your 3 port PK cylinder looks mint but be sure to chamfer the port edges and maybe smooth the exhaust port if you like to fuss. It looks like you have the tall Primavera primary gears, so it's not gonna jump off the line like a rabbit, but will have long legs and should go pretty fast.

Now if it's fast enuff, you're done, just enjoy. But if not go ahead and sort that Polini stuff in no hurry, find a good pipe and maybe even a bigger carb while you can still ride it around. But I'll bet you will be happy w/ that fresh PK 125 top end, I'm kinda jelly. Probably the last unticked bike on my bucket list is a lo mile stock late model PK125. A blue one, please.

Thanks gents.

Making progress on the reassembly. Kinda struggling to find an exhaust elbow that fits the PK125 cylinder though. The studs are 8mm on 56.3mm centers. Bought both of these...no joy.

https://www.scootermercato.com/Scooter-Parts/Exhaust/151152 - stud holes are too small and too close together

https://www.scootermercato.com/Scooter-Parts/Exhaust/151152S - fits the studs but interferes with the bottom fin on the head.

Anyone have insights on the proper part? Thanks.

Your motor looks so gorgeous now! What muffler are you planning to use? I think with most aftermarket pipes you don't need that part anyway. But you could try enlarging and elongating the holes - I had to do that once.


Very nice example, not mine.

Thanks. All I needed to do was clean off half a century of shit and neglect.

I have this stock exhaust.

https://www.scootermercato.com/Scooter-Parts/Exhaust/SITO209

I have the mill all back together except for the exhaust elbow, which I am still struggling to find. Any help would be greatly appreciated. I think it turned out ok. Thanks for everyone's help.

Looking at SIP, it seems like the PK has a different stock exhaust, too. Maybe the cylinder, elbow, and exhaust are all PK specific.

SIP has it, but it kills me to pay $40 in shipping from Germany. Mercado is out of stock. Anyone have one they are willing to part with? Khajiit?

Here's an eBay listing from India that's a lot cheaper. Might be worth a shot.

https://www.ebay.com/itm/274665553209?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200818142055%26meid%3D667670ea955b4aa8a53b3d7415cae21a%26pid%3D101113%26rk%3D1%26rkt%3D12%26sd%3D363256818909%26itm%3D274665553209%26pmt%3D1%26noa%3D1%26pg%3D2563228%26algv%3DDefaultOrganicWeb&_trksid=p2563228.c101113.m2108

Got the headset rebuilt. Lots of rust needed to be resolved inside. Turned out ok.

Rebuild the front end. Needle bearing removal was a mofo. Making progress.

You can order it from Mercato, they place SIP orders every week.

I bought one from mercato. Just need to grind down the fins.

Got the front end back together….after a short detour to "replace every moving part" town. I'm convinced this scoot was under water at some point.

this is great work man. keep it up!

Thanks. I think I have every repaired, now I need to reassemble it all.

Now it fits.

I got the lump back in. Definitely get why they are called small frames. That engine is just shoe horned in there.

Yeah but you can basically one hand it, it's small and light

You gonna fire it up?

Muffler and tail light (not MM, I know) in. Hoping to get fuel to her and timing set for a weekend start attempt.

So, I put the carb air bellow in backwards and tore it up removing it. I ordered another but am wondering, what's its purpose how should it be properly installed? Thanks.

Doesn't it stop dust/stuff getting into carb area? Until it splits of course!!

This thread, starting about here:

https://modernvespa.com/forum/post2555882#2555882

And yes, it's a pain.

Yes, that thing is terrible! I followed V oodoo's advice and just took the aluminum retaining clip off the outer sleeve so that it floats freely. I can't imagine how anyone gets everything in there properly otherwise.