Modern Vespa

@Robbie, I'll be upgrading my PX150 from DR 177 to VMC 187 over Christmas. I'm using the Super G kit that I bought two years ago but never used because I didn't have a 60mm stroke crank at the time. Now I have a Polini longstroke crank, so the fun can begin. It's my city commuter scoot, so reliability, reasonable fuel economy and keeping the elestart are priorities. From a performance perspective, I need it to cruise at 65mph+/104kmh+ for 15 miles/24 km on the motorway, and it needs good acceleration between traffic lights on urban roads. I'll probably go 23 clutch/68 primary, 24/24e carb and my BGM BB Touring pipe. Based on FMP's video, I'm expecting to raise the cylinder by 2.0mm in total, to give 118-119 transfer duration and 174-175 exhaust duration. In theory this will keep 1.1mm between top of piston and top of bore, which becomes the squish clearance with the zero squish CNC head.

A straightforward build and hopefully a great all rounder

I'm excited to see how this turns out!

Thanks for the info. 👍
Really interested how this will run.
Let us please know the results and how you get on…
Cheers

Also curious to see how your tourer vmc 187 comes out. I'm currently doing the stelvio but in much higher tuning to see how it runs. Depending on how both my higher tuning and your touring version come out, I may redo my malossi 166 stella to be a tourer with a vmc kit.

Hi there!
Can anybody help with advice?

I building engine for my friend and what we have is:
- LML reed cases
- VMC Super G with CNC head
- 60mm Mazzucchelli crankshaft

What spacer size I need to put under cylinder?

measure the distance from top of cylinder to top of exhaust port and top of highest transfer port then report back.

how much base gasket depends on how much top end you want?

For example (different cylinder) on my vmc stelvio with 60mm crank I needed a 1.5mm base gasket to get everything to line up with my desired timings and squish: 128/195 0.8mm squish.

If I recall FMP said the Super G needs a 60 crank with a 110m rod, taken down 3mm and use a packer to work well. For starters do what Sean said and report back…

I agree, I like to put it together with no gaskets, measure squish and see what I have and go from there.

If you're not familiar with squish measurements, it's a 50cc minarelli, but same concept.

I do this more simply while it is apart. Measure the squish of the head similar to how the guy did in this video (i just use a digital caliper right on the edge of the squish measuring down till the caliper is flush on the gasket surface). This gives just the squish measurement of the head. Then I put the cylinder on with piston on and no base gasket, set the crank to TDC, and similarly measure the distance the piston sticks out of the cylinder by measuring with digital caliper same way as for head. The head squish will be something around 0.6mm (guessing), and the piston will stick out the cylinder something like 1mm (guessing).. so with no base gasket your total squish is 0.6-1.. or -0.4mm. So if you want a 0.8mm squish.. then you know you have to raise the cylinder 1.2mm. raising the cylinder 1.2mm would mean going from piston sticking out the cylinder 1mm @ TDC to piston sitting below cylinder deck 0.2mm. Hence now the combination of both the head (0.6mm) and the piston below deck (0.2mm) equals your desired squish of 0.8mm.

This is pretty accurate, and I've double checked after assembly by doing the solder squish measurement and its close enough that I don't bother measuring with solder anymore as long as I make sure my measurements are correct before final assembly.

wish I had something to put this on! sounds excellent

I think it's a nice kit for the money. You have to be very careful on the running in phase though since I think the cylinders tolerances might be a tad on the tight side for a cast iron one. I've soft seized mine for three times now Just cooled off a moment and fired right up again.

Might need to run it a bit richer on purpose?

Just pushed it too hard on a hot day the last time. It's still in the running in phase

Could give it a tweak though but have not gotten around since I have the 200 lump in progress for that frame.

Thanks a lot friends.
Maybe I wrong but here is what I got.

I checked again and saw that we have crank with 60mm stroke and 105mm rod.
I also need to say that we don't want to squeeze all juice of this kit, just want to have a good reliable touring scooter.
We also have 24/24 drilled carb, Polini box exhaust, 22T and 23T clutch cog and 65T input shaft cog, short 4th gear cog.





Last edited by roland87 on Thu, 18 May 2023 20:23:42 +0000; edited 1 time

Need the measurement of how much the piston sticks out of the cylinder at top dead center. And the head squish measurement. Most likely you are just going to have to get the base gasket to the right height to give yourself a decent squish and you get what you get in terms of power. That kit is already designed for higher rpms, so you won't be able to get a lower timing than 126/178. You'll probably end up around 128/179 with 26 degree blowdown which is not peaky high rpm but strong enough. If it were designed a little less performance oriented you would have lower timings by default which would give you more room to work with in terms of base gaskets and squish.

There are way more knowledgeable guys on here regarding timings for power and torque and why one timing works better vs another for power vs torque. I just go by the info on this link and try to get the max rpm where I want it for the usage.

https://martysgarage.info/reference/two-stroke-port-duration/

And you can play with your measurements to see the timings and experiment with making changes to the pbt and exhaust port to see what making those changes does to your timings.

http://ddog.at/stz/rechnen.php

Here is how I filled it out with your info... Piston level is piston below or above top of cylinder. If above you put positive number, if below you put negative number. Making changes to the piston level number is equivalent to changing base gasket thickness. So I filled it out with piston level with cylinder top.. which is probably the lowest you can go with a base gasket. The actual base gasket thickness you would use to make the piston level with the top you would have to measure without base gasket and see how much piston sticks out.

Question for all you guys who have used the vmc kits. Did you loctite the exhaust stub plate screws on? If so, blue or red?

My VMC cylinder melted in our garage fire before I had a chance to install it

That said, I am using the CNC head from the Super G, in conjunction with my venerable DR177 cylinder + 1.0mm base packer. Honestly, it's a blast, and it pulls the 23T clutch no problem. This summer, the scooter has been my goto.....it's my only working Vespa

swa45 oh I'm very sorry for your loss.

Sorry for my dumb question but is it worth to straight put VMC Super G on my non-ported P150X motor?
Is no ported case is ok for cylinder?
Will it give noticeable better performance than my current motor?

The specs is:
- DR 177 with Malossi head
- Mazzucchelli racing crank
- Polini Box exhaust
- SI 24/24 drilled
- 22/68 primary
- Sip lightened flywheel.

The big gain is the squish clearance, because the VMC head is zero squish and I could raise the cylinder/ports by 1.0mm. It runs really well and much better/faster than with the DR head

Sorry for my inaccuracy.
I meant to put the whole VMC Super G cylinder kit.
Not only the VMC head.

So DR out VMC straight in.

Ah ok. Sorry I was getting off a train when I responded, so didn't read your question carefully enough. Yes, a VMC Super G is a great upgrade from a DR177. That's why I bought the VMC kit, but the cylinder and piston were destroyed. Luckily the head was already on my PX which was not involved in the fire.

The recommended crank for a Super G is 60mm for much better port timings

Yes I understand that Super G is better than DR. But can I put Super G straight to my engine without porting and change crank to 60mm. I have healthy fresh rebuilt motor.

I'm sure the VMC will be an improvement for you, but not optimised. The base transfer ports are quite big, and so restricted by your unported crankcase. In my opinion the BGM 177 would work really well on an unported engine with 57mm stroke.

Yes.

I did Super G on my Bajaj since the kit was only 150eur.

Gasket compared to ports


Sketchy adapter plate


But it works

Thanks for help friends.
I don't consider BGM because I can buy Super G for a very good price.
When the time comes for overhaul my motor - of course I match ports on crankcase and maybe go to 60mm crank. Just don't want do it now as motor works nice.

Today I worked with engine for my friend and put cylinder on LML reed case.
And realised that we choose wrong crankshaft.
It have 60mm stroke but 105mm conrod. So I don't need to put spacer under cylinder.
I measured 1.07 squish.
So. Now I'm confused with what right crankshaft I must choose in future for my P150X rotary cases.
60mm stroke and 110mm conrod? Something like this? With this gudgeon pin bearing? And is this type of crankshaft will fit straight in 150 rotary cases or I need to do some modifications?

I run the BGM touring crank (57mm stroke) in my PX150 cases with the VMC top end. Pretty sure it went right in.

200 rotary crank won't fit in 150 cases. Reed crank will

Sorry for my stupidity. You mean 200 reed crank? E.g. this?

So if I want to stay with rotary intake on my P150X I need to choose crankshaft with 60mm stroke and 105mm conrod?

That 200 crank won't fit because it still has the 200 lip.
This 200 reed crank fits in a reed 150.
https://www.sip-scootershop.com/en/product/bell-shaped-crankshaft-mazzucchelli_45041000

And so does this one
https://www.sip-scootershop.com/en/product/full-circle-crankshaft-malossi_53161760
And for certain many more.

A 110 conrod can be fitted to any 150 crank but is a special job requiring more money.

thank you Jack

Hello Everyone. Im doing some test for GFS Dyno with an Hand Made expansion made by one friend. This is full throttle in 3rd gear

Jetting: Idle 48 - JLJ 1st Clip, 138MJ

here is the recorded audio

http://sndup.net/jrz6

Im having some bog from 3000 to 5500 rpm

Can somebody tell what is difference between two VMC cylinder heads?
Is CNC head really worth the money?
And is central spark plug is better than offset? Why?

I like a central spark plug, because you can mount a piston stop in head and put it in a lathe or drill press to remove some material to adjust squish.

The difference is likely the surface area of the fins. The lateral fins of the CNC head would be difficult to produce by casting.

Off center spark plug compromises some performance for better accessibility. Cylinder heads on performance engines are symmetrical to maximise the chances of even burn where the flame front propagating from the center of the head reaches the sides at the same time. Of course threre are many other factors affecting this so I don't think there is a noticeable difference in our engines.

Thanks for help friends!
Here is first start of VMC Super G on LML reed cases which I built for my friend.

ONE

TWO

THREE

that's a pretty good engine stand there - and the engine sounds healthy. nice work.

Thanks John.
Stand is not so good - you can see the jack under exhaust😂 stand was handmade and cracked after few starts of smallframe engine.

I missed that!