1981 Piaggio/Vespa Si Build

Picked up ole crusty, after contemplating which route I wanted to take for a kitted speed bike. My poor Grande gets lapped by Tomos bikes in group rides, and I’m planning on droppin a can of variated whoop ass 💪🏼 Frame is pretty true, medium pitting in some areas that may need special attention, but overall the guts are there! First thing first is getting rid of the forks and upgrading to more of a motorcycle look, with a 12V headlight. I’m not a fan of the rinky dink headlights Piaggio used on the Si, Ciao, Bravo etc. They should have used the Grande forks in other models IMO

Also, if you have the front “hood” piece and are looking to get rid of it hit me up! I have no idea what they call it, but it screws on the front of the tank and hides the wires?

This is going to be a slow and methodical build, as I’m not going to dump $1K + all at once, but my idea is to build a low profile bike cafe racer style, but with the comfort of a step through. I’ll periodically post updates along the way, and if you have any pointers, or Si knowledge you can drop on me, please by all means do so!

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Re: 1981 Piaggio/Vespa Si Build

I’m slowly working on one too, but I chopped it in half. I thought that since it has the mono shock it might look cool with the seat floating out over the back wheel.

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I plan on making custom forks from the original forks since they are hydros. I’d rather they be triple trees instead of the stem quill thing so that’s next on the list. The Black Pipes donated some dirt bike forks for me to tinker with, I just gotta find the time.

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

That is a killer build! Absolutely love the stance of that seat, stoked to see the finished results for sure. Since they’re far from saving as a “stock” bike anyway, you might as well go all out! Any idea what forks you have? I like the idea of trying to incorporate the old ones, but much prefer the triple tree with low profile bars look. I’ve been toying with multiple ideas, and may even try to hunt down some Grande forks to modify. Never short on ideas, it’s always time and money 😂

Re: 1981 Piaggio/Vespa Si Build

campeona del mundo /

make sure the tank is sound, i had a crusty one like that and the tank leaked all over the place!!

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

There’s quite a bit of loose rust in there right now, so I haven’t filled it yet to see if it holds. I’m most likely going to do a tank sealer on this one. Probably the more expensive kit that’s epoxy based! I was lucky that they at least had a cap on the tank while it sat outside

Re: 1981 Piaggio/Vespa Si Build

My plan with the forks is to use the upper and lower yokes from the random dirt bike forks I got from WillD and Derek (thanks guys!!). I was going to make the fork tubes myself so I could use all the lower pieces from the original Si forks. I think the tubes would have to taper from a 28mm diameter down to 26mm if I remember correctly. By using the lower parts I also won't have to worry about the rim and brake plate lining up with aftermarket forks.

The head tube on this frame has a larger than normal diameter and it is short in length. I was going to make a sleeve to slip inside the stock head tube and weld it at the top and bottom. The size of the sleeve will depend on the yoke I use, I guess.

BTW when I cut this open I noticed that the seat post must have just filled with water and the top of the gas tank, inside the frame was rusting like crazy. I wouldn't be surprised if a lot of these had phantom fuel leaks inside the seat tube where you normally wouldn't be able to find it.

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Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

I definitely noticed the diameter and length difference from most, I believe the Ciao forks are built the same from my understanding. I was toying with the idea of creating a bushing from Delrin to fill the void. I’m going to ponder about that for a while, may just take the leap and buy the aftermarket EBR forks and be done with it!

Appreciate the cutout shot, that makes sense as to how it all lines up now.. Mine had a seat on it the entire time out in the elements, and because of that the seat pan is absolutely toasted. I’m hoping the seat acting as a sponge for years kept most of the water out of that space. Guess we’re fixing to find out. If there’s a leak on that backside there’s not much of a fix other than building it as a top tank. Im thinking positive thoughts haha

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

Alright, I’m making progress on it! After a gallon of PB, I got the handlebars and forks off. I planned on having to chop the whole thing, so I feel like I got lucky having it finally give up. Seized is an understatement.. Getting the frame all built, then moving onto the motor once she’s a roller. Chunk by chunk folks. Shoutout to those that have sold me parts so far, much appreciated 🙏🏻

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Re: 1981 Piaggio/Vespa Si Build

Don't shoot me for posting this here, but this is the SiBi. A Si and Derbi DS50 mashup, it started as a frame and a dream.

The rack is from a Grillo and the side boxes are old Grande. The seat is actually from a Peugeot or something and held on using leftover hardware from installing my garage door.

Wheels and engine are DS50, handlebars are from a 2018 Tomos, and the forks are EBR, but Grande and needed some custom parts to fit.

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Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

No hate at all dude, I’m all at the vespa vibes, there’s too few of us!! That thing is probably an absolute BLAST to ride. That pipe has to make that thing absolutely blast.. You weld that up?

Also, what the hell was Piaggio thinking not doing a triple tree on a Si? For their sport model they missed the mark on that detail. I’m building mine with a Grande triple, I just prefer the look. Plus the plastic headlight is trash IMO, if I wanted cheap looking parts I’d buy a Chinese knockoff. Trying to make mine look like a cafe racer

Re: 1981 Piaggio/Vespa Si Build

Yeah, super annoying not having triple tree. Of course I didn't even have forks anyway.

The pipe was a Cranks pipe but it's been swapped for something else now.

This thing is amazing. It's a 50 plus ripper on tiny wheels that one of my friends refuses to ride. We also preserved the monoshock so it's just got coolness all over.

I'm looking forward to seeing how your project turns out. Despite their initial lack of speed, and a flimsy subframe, the Grandes are the best Vespa, in my view. The frame is beefy, forks are beefy and smooth, and the seat is unsurpassed.

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

That’s what I’m taking about, I’m looking for that 50+ mark myself! With a nice kit I should be able to achieve that. With regards to the mono, I’m going to do some welding to the sub to make sure that box is rigid. Feels like they skimped on the welds where it seems most crucial. Water tested the frame today and she didn’t leak, so that’s already a big win!

Terrible investment overall, but I love saving things, and it turns out mopeds are my ultimate vice 😂 Can’t take money with you, you’ve gotta enjoy life while you have it! Tell your friend he needs a Sachs since he likes to go slow haha

Re: 1981 Piaggio/Vespa Si Build

Lol actually, he has more kitted bikes than I do and rides faster than me. In fact, he had the SimoSi that was talked about a couple of months ago, which is far faster than my bike. But he says mine is "sketchy." Lol

But I love it anyway.

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

Haha if we’re being honest, mopeds are inherently sketchy. Motorcycles are way more safe! With my Grande, I’m not throttling out of any danger, and if anything, I’d be throttling into danger!

On your kitted Vespa builds, what gear ratios are you using? I’m looking to go 70+cc with a 9.5:1 and obviously upgrading my rear variator with an appropriate contra and cheeks. So many ways to go with Vespa gearing it’s mind boggling!

Re: 1981 Piaggio/Vespa Si Build

If it's a milder kit I'll just leave the stock gears. In that case its better to have the torque than the top end.

I did the cheap CIF set on my 70cc. It's 10.49 I think, which has been plenty.

My blue bike with tiny wheelsended up with the 10.49 as well, at least for now. I have a converted single speed that is 7:1 but it's too much. I think I'd be happier with 9.49.

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

I’ll do some thinking on it then! I was also looking at the CIF set, which I’m assuming are decent. Half the cost has me certainly questioning though. I have a blank slate, as the gearbox I bought had some wrecked gears in it. Not sure how they did it, but the teeth were toasted. My Grande has a 10.7 so a 9.49 isn’t a huge jump if I’m adding 20cc+

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

Grande forks are going to work, after some time on the lathe, my spacer came out pretty decent. This weekend will be some sandblasting! Slowly working through it, however I have almost all the parts for it to be considered a roller, so that’s a positive!

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Re: 1981 Piaggio/Vespa Si Build

I've been goofing with this bike for awhile. Definitely like the tall transmission gears.

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Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

That think looks siiiiick! What kit are you rolling with? I’m a ways away, but most likely going the Malossi 73cc route

Re: 1981 Piaggio/Vespa Si Build

Thanks! That was the previous build with the 65cc Malossi 13/13sha & circuit pipe. I currently have a Malossi DEPS motor for that bike, but the cylinder is roached & I need to bite the bullet $$.

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

That’s where I’m at.. Trying to take it one chunk at a time, but speed cost serious dollars haha I’m ready to be rippin already! My stock Grande runnin at max 35mph ain’t doin it for me

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

Alright Vespa rippers, I need some advise on my build. I already know I am going to be dumping some serious dough into the engine, so at this point I am just looking for suggestions. I don't want to go through this build, and then be disappointed in the results. I've already ordered the Malossi MP One case for CDI, which based on the decision of utilizing a 46.5mm OR 47mm DEPS. Would the DEPS kit be worth the extra few CC I'd gain? Also, if I'm running a 13.13 SHA, what kind of jet size should I expect? Clearly this is all planning stage, I'm just trying to get a feel for it, as reeds and all the other details are foreign to me at this point! Appreciate any insight

Re: 1981 Piaggio/Vespa Si Build

Dirty30 Dillon /

I love a 13:13 on big cylinders, but a 13:13 on DEPS is gonna leave you underwhelmed.

But either way, you splurged for 4-bilt cases with big transfers: get the MP One DEPS

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

I would love to do the PHBG kit for the MP-One cases, but it looks like that is pretty hard to come around these days. I'm looking at utilizing the 13.13 in the meantime. So you're saying since I splurged, I should "go big or go home"? If I can't get the PHBG anytime soon, is there a better option?

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

I lied, looks like it is available from DOS! That's the route I will be taking for sure

Re: 1981 Piaggio/Vespa Si Build

> Josh G wrote:

> -------------------------------------------------------

> Thanks! That was the previous build with the 65cc Malossi 13/13sha &

> circuit pipe.

Great setup! I ran that on my old kinetic for years with the stock gearing and it was a tank.

Which gearset are you running? I'm looking forward to running a similar setup on a bravo, but I've also got one of the polini "racing" 65cc kits floating around somewhere... (edited)

Re: 1981 Piaggio/Vespa Si Build

Mcproparts is making a reed block and intake for a phbg 21

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Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

I saw that, which has me questioning which route I want to go.. Think the 19mm would be holding me back? This started as a “I want to keep up” bike and I’m slowly working my way to highway speeds 😂

Re: 1981 Piaggio/Vespa Si Build

> Bryan Shank wrote:

> -------------------------------------------------------

> This started as a “I want to keep up”

> bike and I’m slowly working my way to highway speeds 😂

That’s what makes it fun. Spend more than a motorcycle to be slower than a motorcycle then break all the parts that can’t handle the extra power. Repair and repeat.

Re: 1981 Piaggio/Vespa Si Build

Bryan Shank /

You’re not kidding! Haha I must be a glutton for punishment, because I’m having trouble keeping one on the road as it is. Speaking of breaking, I’m sure my subframe will shit out sooner than later. What’s the plug on the cnc’d sub frames? Looks like treats has been out for a long time now

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