Modern Vespa

I'm following intently.

I'll need to do the same soon and will be going in a similar direction.

I'm hoping to be able to just slap a 1.5mm base gasket in there and be good to rock, but it'll take some measuring beforehand.

What crank did you get?

Long stroke Mazz. Best bearings/seals I could get. I like torquier timings but I'm also still learning. We'll see what kind of squish the provided gaskets yield.

I also went with a Malossi box over a Polini or BGM BBT which I have on my All State, basically because I wanted to try it and think it may be often overlooked. BGM all the way though if $ isn't tight. That BBT is incredible.

We'll see!

FYI

You could have also used your SIP crankshaft installation tool to install the bearing race on the crankshaft. That's how I did mine! No heat or hammering needed. Worked great!

Hec


SIP tool for installing crankshaft bearing race And 1mm shim.

Done!

This is how I do it, too. Makes it super-easy to get it precisely 1mm off the cheek, too.

Was unaware of the 1mm myself. Thx

It's so you can get a puller under it to remove it when you replace the bearings. Forgetting about that is a mistake you only make once.

Well, I've chalked up my "once".

The easiest way to solve this problem is to make sure that you whatever you do to merit a rebuild, you kill the crank in the process.

I was afraid of that. Your picture looked like that bearing race was slid all the way on. Ouch..

Hec

Worse things have happened. 🤷

There's this really cool picture earlier in the thread of a real nice crank with no bearing race on it. The title of the thread is "what to know before we close it".

If you go with long stroke make sure you get the appropriate head spacer and/or play with the base gaskets. That's where I'm at now, with no clue how to measure port timings yet. Working on that.

Most definitely.

I went through this with a P200 about a year or so ago - a nice O-tune with a Gran Sport piston...

Getting Bianca, the P200 back on the road

Calculating port timings is not actually all that hard.

Measuring accurately is about diligence and averages.

Figuring out what the timings you're trying to achieve is the trickier part, but we can help with that based on performance goals and specific parts choices, e.g box vs pipe, which top end, cruising vs. stop light racing, etc.

Performance goals: Feels like a P200 running lean haha.

Anyways, case is closed & cyl is on. I didn't realize I would need the long stroke appropriate head spacer until now but basically this seems like a perfect opportunity to learn how to measure and what those values mean.

I know how to set the kit up to function well but I learn nothing that way. I'll feel like I missed an opportunity to progress if I do that.

I need an idiots guide, like set your dial at TDC and then...

So maybe performance goals aren't even the point right now tbh. Overall, I like torquey around town bikes that can stretch their legs on the occasional back road, but I'm not a tourer that loves nothing more than cruising at 55-60 all day.





Last edited by HMC_MT on Sun, 12 Mar 2023 04:31:11 +0000; edited 1 time

I have BGM coming for the swingarm mount. Looks like a bitch to remove compared to other models.

Did you measure anything on your cylinder? It can be set up a few ways on a 60mm crank. The wide flat exhaust port is key to it's torquey reputation.

The timing of any port is quantified in degrees duration. This is the amount of time it is open. And is symmetrical about the stroke.

There are many online calculators. To start this is a simple one. https://lambretta-images.com/tuningh/port-timing-calculators/

Fundamental characteristics of a cylinder are represented in exhaust duration/primary transfer duration/blowdown. Like 185/125/30. If you need to fit a packer to set up a cylinder, then there are upper and lower limits of these numbers. Decisions (and alterations) can be made to suit the user's expectations. However having it all was never an option.

I haven't measured anything yet, just set it up to take them. The kit came with a .2, .35, & .5 base gasket with a .5 head gasket. I should've ordered the 1.5 head spacer to run the .2 base and stroker crank but didn't.

I'll pay some thoughts in the morning when I'm at a real keyboard.

We got ya covered.

Pretty solid forum here I see! No rush, a long with everything else I'm learning patience lol, and working on the swingarm mount. Also waiting for the new mounts & a couple odds n ends.

I'm in Montana so I haven't rode for way too long. Got my P out today and it was 22 degrees, felt fantastic to freeze my ass off lol.

I've always found it very easy to both remove and install swingarm mounts. I use a propane torch to get the swingarm spacer tubes really hot. Then use a pair of channel locks to twist the spacer tubes out of the rubber mounts. Once that's done, i heat up the aluminum portion of the swingarm until it's hot. Then i use a large flat blade screwdriver and jam it between the aluminum swingarm and the rubber. Pry it apart a smidge and squirt some WD-40 between the two. I'll do that in all four corners, then i can fairly easily pry out the rubber. The whole job is less than 5 minutes...maybe closer to 3.

The Stella has a straight through tube, no split in the middle, and the outside edges are peened.

Putting 1.5mm spacer on the head is making a port timing decision. Could put 1.7mm on the base. Could do anything in between.
Identical cylinders are not identical port timing. The manufacturing tolerances are such that it matters. Casings and cranks differ too. This is why the supplied gasket choices.
Measure your cylinder. Check the science. It will go faster.

Haha, well played Jack.

For the Stella, grind the swedging down then stick the nozzle of a propane torch down the center of the tube. Do that through both ends until the rubber starts smoking then use some channel locks to twist tube out. If you can't get enough grip on the end of the tube, use a socket and extension as a drift. Once the tube comes out far enough, then try using channel locks again.


And yeah, the Stella mounts are more difficult to remove than on a Vespa, but lots of heat is your friend!

Pretty much exactly how I spent my night last night. Half way there!

I have a BGM 177 with a Sip RoadXL and a 60mm crank. Port timings are 124/171/23 and it puts out 17 HP. That's on an extended intake rotary, but no reason you shouldn't see something in the neighborhood with your setup.

I have a pretty good gearing & port timing calculator spreadsheet (advanced features require OpenOffice for macro support. Basics stuff all works in Excel) I use which you can download here. PM me your email if you have any download issues and I can just send it to you.

That will give you a "what" to aim for. If you want to start getting into the "why" of it, you need to read "Two Stroke Performance Tuning" by A. Graham Bell and "Two Stroke Tuner's Handbook" by Gordon Jennings. While the start of the art has advanced since either of them were written, they will give you the fundamentals you need to get properly into the weeds.