Modern Vespa

I find myself frequently wanting to know the stud patterns for different engines and never able to find them.

Starting this thread to fill this gap. Please add to this as you measure or discover the missing measurements. If we get enough info together maybe we can consolidate it in the wiki later.

To start, here's the stud and spigot size for the large frame 125-150 cases:

Nice... could've use something like this when cutting gaskets.

Do you have a template or something we might fill out to keep the format consistent?

sketch it on a napkin and post a picture.

my other CAD software let's me output a PDF that is to scale, so may redraw them as we get more

For the GS/SS/Rally the cylinders are tilted and the stud pattern is not square, so those will be a bit more difficult. Same with Lambretta.

Is the Rally is the same as a P200, or at least the Rally 200?

yes, it's the same. I've got an extra head I can pull the stud placing off of, but getting the angle that it's skewed will need to be measured from a set of cases (or wait till I pull the top end off the rally).

I have my 200 apart at the moment, I'll measure it tonight.

heh. I tend to have the problem of not being able to find the cases to measure in my pile of used parts.

are you looking at cylinder conversions?

I started down this road because I've been wanting to cast a cylinder as I'm not really happy with any of the ones out there. combined with this, I've got a Malossi 210 that I've been thinking of sleeving down to 200 for the rally, and I've also been thinking of doing a new head for the GS.

Base/head gaskets, fixtures to profile the head, designing a cylinder all need the stud layout as that's the most limiting constraint (sure you can move them but...)

And it seams like something you should just be able to google, but it's not there.

Very interesting projects... Given the somewhat newly available SS180 barrels, heads would be a nice one to have available, especially given the 190 and 208 pistons now available. Modifying P heads with the one stud slightly offset is kinda ugly...

Here's the smallframe layout.

Sorry I've been trying to work out the 200 one in my spare time and am having trouble getting it right. The non-symmetrical design really makes it tricky as well as none of the studs appearing to be directly opposite each other. I'll keep trying!

It's a pain, here's what I pulled off an old head. How does it compare with what you get?

I'll put it up after work... about 3 hours (but who's counting?)

I really should have paid more attention in geometry! Here's mine measured off the case to the studs.

I just found this on WhiteOne Racing (Italy) facebook page. This was for a 150-200 conversion.

https://www.facebook.com/WhiteOneRacing/photos/a.1020090191425071.1073742007.151893714911394/1026852860748804/?type=3&theater

started playing around with just how much port width could be fitted around the stock stud placement on the 150.

This is a bit off-topic, but do you, or does anyone else, know why there is no gasket between a GS160/SS180 stock aluminum head and stock cast iron cylinder? Should there be a thin film of sealant or grease, or does it just go on dry? I'm just curious.

Do you have anything particular in mind Patrick?

Particular?

I've been following a thread on another forum where quite a few legends of two stroke design share what they can within the limits of NDAs. We are talking people that designed cylinders for GP125-500 before all the bloated 4T stuff were let in. So, greater than 50HP for a 125.

Meanwhile the newer scooter cylinders coming out are much better but they ignore much of the state of the art and still go for max displacement.

The stud placement on a scooter is a huge obstacle and the asymmetrical layout of the vespa 200 and even the lambretta are a total show stopper. So I started looking at the Vespa 150 to see what you could fit. By keeping the bore at 57-58mm it leaves more area between the stud and piston to sneak the port around it.

The exhaust blowdown area is going to be the limiting factor since the studs limit the width of the port. Auxiliary EX ports can still get to ~80% of bore by keeping the bore small. Here's a shot of some earlier work seeing what could be done with the transfers. Also, there is improvements that can be had by radiusing the top edge of the piston.

If you are planning on a cylinder from scratch, couldn't you avoid studs and use the base flange method to hold it down? And screws for the head? That would free up the exhaust.

Not quite sure where you're going with this. Many of the 125/150 kits already have auxillary exhaust ports. And others have wider bridged exhaust ports.

As you say the P200 has a problem here but there is plenty of exhaust port to get up to very high power and for me the practical limits of the frame on the road.

If someone would just make a P200 cylinder that had short base studs like a small frame 50. Then the cylinder could be anything you wanted it to be. No limits. Not sure the rest of the scooter could handle it though.

Bolting the flange does not help as then you need room for the nut and that's a larger diameter than the stud, so now the transfers, and maybe even the exhaust, have less room.

The aux ports I've seen on the DR are minuscule and a center bridge is not ideal as it's prone to overheating. The parmakit is close on the exhaust but the transfers are a very old design.

Anyhow, been kicking the idea of doing a cylinder from scratch thinking the 150 may be worth the effort.

Yeah I guess that makes sense. Is the T5 stud spacing much different? They managed to get some pretty big transfers in there using the same width case.

The other option is a stud-changing packer and long rod. It's being used by a few now, particularly with cylinder conversions. This one is by PLC Corse... you'd use long studs instead of what they've done obviously.

The short stud option might be just possible if using some kind of thin round nut with an Allen key. Going to lose a lot of fin area though. And would be very difficult to work on in the frame.

Stud changing packer is a great idea, as long as it could keep the original conrod. If changing cranks and rods and custom machining is required, then plenty of motorcycle cylinders could be grafted on. The whole point would be a bolt on kit that could have aux ports or a bridged exhaust.

The iron cylinders with aux ports all start quite small but all can be opened up.

The bolt on auxillary exhaust port P200 barrel is the one that nobody does. I'm sure there are plenty who would want a 50 bhp Vespa if you didn't need the resources of SLUK to get anywhere near.

You kind of need the longer rod to allow for the packer. Unless the cylinder was designed to allow for the packer within the length of a stock rod... it would look short with a long skirt.
The packer needn't be just a lump with a hole in it though - it could have a couple of cooling fins as well.

Now this sounds like just the kit. If it had everything like a Malossi Sport, especially the Vertex piston, then the transfers would be no issue. The finned stud-changing packer would start all the transfer ducts and just be like a two part cylinder.
The longer stub would last better if it was an iron lined alloy cylinder. The liner could just continue to be the stub. Sure this would be easier to make.

Imagine something like this for a P200 cylinder.

Now if it could be piston ported reed induction too.....

Yeah but is the exhaust big enough?

The guy that did the boring on my old Polini cylinder makes two stroke sleeves for dirt bike racers. I think he said that he could do one for me for around $300. I see you can buy them ready made for popular models for something like a hundred US. Seems like the best of both worlds with ally cooling and cast reboring available.

Those are proper ports! When you start to worry about the aux ex ports short circuiting through the wrist pin...

That's what 50 bhp ports look like!

Just seems so possible to make. The casting metallurgy probably the only difficult part. Rest is just machining.

You mean like iron sleeve a Malossi barrel? With some welding up here and there first and 8 head bolts tapped in......hmmmm.....might work.

Yes I had an idea to make use of a seized cylinder that someone might be throwing away.

Resurrecting this. Gentlemen, I hope your measurements are correct. I designed these in AutoCAD and Monday morning, I'll print them at work (my printer is acting up) cause I want to build a cylinder head mount tool, for both largeframe engines, so I can machine some heads I've got laying around...

I hope so too Chrys! That 200 is a bastard to measure.
Are you going to make something to hold the head in a lathe?

That's the plan...

Patterns came out to be correct. Tool is ready for the 125/150 & 200 heads...

Nice!!

+1 !!

how did I miss that? nice setup for the vespa heads!

Anyone holding on the small block lambretta stud pattern? I'm starting work on my TV again.

first pass measurements off of the Imola cylinder. Angle relative to crank is not correct.