Modern Vespa

I think it was around 2018 that there was a big to-do on a two stroke motorcycle forum. The short story was that the manufacturer of the cylinder head was very heavily promoting his product, and lots of the riders were calling his bluff.

Very slowly over time some of the riders ended up using his head design and it worked well for them. Usually it would be riders who rode their bikes at high elevation (such as the colorado mountains). Customers could order up the cylinder heads that would boost up their compression to around 220psi! Which would work well on high octane gasoline at high elevations. But if the bikes were ever ridden at lower elevations, then of course instant destruction.

I had a different guy reprofile my stock combustion chamber and narrowed up the squish quite a bit. It boosted up my compression from a lowly 140psi~ish to a more respectable 170+.

There's definitely an art to profiling a combustion chamber.

I can, but if we want dead nuts accurate, we should do it with squish.
I will either need to cut a cavity, or a spacer for my existing head, and bolt it on. Likely the latter.
Plan on some shop time this weekend.

Best way, since you have the piston and cylinder installed at the right height would be to:

rotate the piston some say off TDC
put a flat bar across the face of the cylinder
rotate the crank till the piston touches the bar
record the deg BTDC
calculate the distance based on deg.

(could also use this to find how far above the deck the edge of the piston is)

Good one.
Simple.
Will do.

Is there something that stops this idea from working? With your welding experience I'd have to think it was pretty easy.

It would probably benefit from a lead-in ramp (think stuffer type of thing) on the inlet side of the reed block. That would work in with your duct.

Also you could pick up more cooling at the other end - make sure the flywheel cowl opening is almost touching the fan blades for less loss of pressure.

How do you imagine you would make the cowl? They would not be straightforward I imagine.

It's the picture speaking less than 1000 words for me.
In fact it's nearly tongue tied.

Remembered I shot an "flowing air's eye" view snap shot with the borescope. Have it on my phone so will post below.

The intake manifold itself is a big part of the problem. Cutting the flange may not do much.

I see some of the GSF guys seam to be adding a sheet metal to steer the air around it - which is smart. But I think it's going to still cut off 40% of the pathway? That will actually increase velocity- so maybe not an issue, but it will also increase back pressure. I think your idea is along those lines. It seams like a minimum to avoid totally disrupting the flow.

Fan cowl. Again, kinda hard to believe no one has a close fit cowl cover? A Venturi or bell mouth entry instead of the flat edge ? Fan tech is pretty ubiquitously known. Surprised someone not selling an unreasonably priced piece of plastic that improves air flow.

Why I care: I can likely jet around heat issues, but it may take me richer then I want to have to run/ kill my MPG. I've got weight and wind resistance working against me at highway speeds. I'd like to set myself up for success with optimized air flow - then jet as required.

There's this shroud, supposedly for Quatrinni cylinders, which looks like it kind of tries to angle the air around the manifold.

The clamping bolts are pretty much smack bang in the centre of the airstream, setting you up for turbulence first thing out of the gate. My idea gets rid of that. Then make a "stuffer" to flow around it.

Egig's flywheel cowl comes as close to blades as possible without touching. Increases efficiency. On the smallie, there's basically no space between the cowl and side panel so bellmouth is out of the question.
He also makes a fan that pushes more air, but takes a little power to do so. Supposedly is the operative word! I have one sitting on my shelf that just wouldn't fit (it's for a 244 that doesn't have the intake on the barrel).
Unfortunately it's not heavy enough to be a doorstop.



This is much bulkier than a stock cover coming off the fanwheel and probably less turbulent. Maybe you could do something like this instead of staying tight then going around. That cylinder has the same reed on cylinder.

Original cowl -

Or you could just go full water jacket??

He's already said he didn't want to do that, but I bet he could make it work. There's even space in the sidecar for a radiator.

It slipped my mind he said that already... I blame the heat and sun in the UK right now... im not used to it 😉

Thanks.
The Egig solution seams the simplest in some ways.
Simple is good.
I think the snug fit of the cowl though may be part of it's magic - much like the blades of the fan being close to the cover.

The blockage is real - but it doesn't mean a heat gun and some pressure couldn't help resolve the cylinder cowl issue.
At the bare minimum, 50-100 MM of material will have to come off.

Found a few pics - everyone likes pics.
These are from the GSF forum.
I'm sure there are many more.

Anyway - good course of bench racing.
I don't have the motor in front of me.
I will assess my true needs once I am back in front - and keep browsing the GSF for existing solutions/refinements people have made.

Everyone knows, I'm a traditionalist at heart. 🙂

Which brings us to our custom head concoction - whose goal is to run at 5x the original HP, while remaining cool and stable (the traditional part).

Patrick has put up with my ruminations and bad math, to deliver a very cool design - some alchemy of double secret tuning tricks, savvy 3D CAD, and radiuses that fit my tooling!

Will it work?
Seriously, I have no idea.
But man, it looks cool.

Woke up to a new model marked "VMC" and began to query Ai on how I could harvest the machining programs I had previously created. At which point I realized, Patrick had already transposed them for me.

The collaboration is fun.

He's modeled a cavity that incorporates modern geometry that we think will work inside the trashed VMC chunk.
I wanted to do a test cut on some scrap if I could.

Managed to wrap work up a little early t'day and rolled past the metal supply store to see what was in their bin.

Side note: if u've ever wondered exactly why California is the home to so much innovation, its places like these, probably spurred by industries, which were fed by aerospace, that now residing just around the corner for us to shop at. You can just stop in and buy a chunk of T6 aluminum to fabricate your head, for $25. It's kinda incredible.

So I shopped for a few scraps and took the program Patrick transferred over, and had a go on a flat piece to see what we got.

Fun bit of shop time.
More work to be done.
Think we can do something nice in the end.

That looks really really nice. Nice teamwork OCTCM2.

This is WILD Impressive stuff!! Ned and Patrick team up!! Fantastic first pass

Brilliance - the team up is going to work dividends (as they say)

RK Tek are highly textured. Or would that be scalloped?

This is freakin' amazing work. I can't wait to see where y'all wind up with this.

Patrick is riding around the world on a 50CC bike he built from scratch, or something like that, so I'll just say thanks! From both of us.

Who dat - I would definitely say "scalloped".
I looked up the heads - see its a thing.
Apparently the consensus is it's legit.
Also - the owner designer has some, let's just say, strong opinions.

Next steps here.
I am reprograming the squish band cutting to cause it to cut in a much more refined manner.
It will have a bunch of microscopic step overs.
See what the mill can produce for accuracy.

Im increasing the step over (opposite) for the rough cut of the dome.
That thing took forever to rough in (was a lil late for dinner and not everyone was as pleased as I was).

I will also take some measures today to see how close we are to spec./ out of round.

It would be create to just cut this CNC and then polish on the lathe.
If we need to though, I can cut the squish on the lathe to get a super accurate shape and roundness - I think...

Off to play around the the programming and cut some squish bands.
(after a small pot of coffee).

Little more time in the shop today.
Ran a second test cut.
This time with a different program type which, I am told, interprets the information in a manner more conducive to what I'm trying.

Also took some measures.
Ignore the depth measure. I didn't have a good means to do it and knew it was inaccurate - just forgot to erase it...

Took these blind without looking at OCT's specs.
They are remarkably close - within measuring error I would say - of the actual spec.

Getting closer to "ready to cut" the actual head - but I need to wait on Patrick for some discussion on piston -PBT and work it into our model.

Plan is to cut the head deep enough so that it requires decking to tune in the squish. I'd like to also cut an o Ring groove if there's space after I add some pins to center everything!

While Patrick circumnavigates the continental US, I did a little prep work for the next revision.

Head will have a concave feature for the squish band.
See pictures above.

Means I need to do some lathe work.
This is going to allow me to make a centering feature.
More on that to come - but for now - it's all about the tool… so to speak.

I've never actually cut a thread on a lathe.
This "single point threading" has always intimidated me a bit.
The feeds and speeds have to be exactly right.
There are all sorts of knobs and back gears that need to be engaged.
And you have to engage and disengage things before other things crash into them - and vice versa.

Anyway - I've just never done it.
I was lacking the proper tools but managed to cobble a 60degree cutting tool to make the threads.
Few pics below of the goings on.

Nice work.

For a none machinist that you claim to be

Your one heck of a machinist!

You beat me to it! I've been wanting to cut some threads. My buddy used to do it for me when he owned my lathe. At least i know the machine can do it.

Well - I'm glad its not only me!
In truth, a die would likely be quicker/simpler.

But - I wanted to create a tight thread - just a hair over spec - which this method allows.
And
I didn't have the tap...

I tried a method I saw online - where you:
1. Revers cut it - so that it goes from the shoulder out. This took away the likelihood of crashing the lathe
2. Flipped the tool upside down for the revers spin.

Would highly recommend this method if you want to fool around.
One of the better professional machinists I've watched did a demo.

Here is the thread I cut using it: Here's a link if interested in seeing what he shows: ?si=JOI9NawUjlYnX82r

This thread you're cutting... it's not for a selector rod by any chance?
Because they have a left-hand thread. Just wanted to check... after the whole 150/180 head thing. If not please ignore.

(btw it's "reverse")

Chucked.
Indeed it is not.
The backwards cutting with tool flipped still cuts a right hand thread in the Northern Hemisphere.

Said thread is for spark plug hole…

Excellent!

Meanwhile, I'm just watching the water swirl the opposite way down the sink.

Wow this is very exciting!!! Geeking out!!!!

Here's a great video of what's possible...how fast they measured out and did the threads blew my mind...

"Possible." I'm pretty sure that's better than "broken," but only by so much. Like...the break point of that old part was already rusty AF. Was that a previous old repair, or just a hairline crack that had grown until the whole thing finally gave way?

Also, for some reason, I love videos like that where the dudes are all working in their Safety Sandals and not a whiff of OSHA-compliant activity in sight.

Long weekend is here - so have a chance to play.

OCT has whipped up a tool for us to do a few checks.
- Need to confirm exact squish. I've measured and calculated at .688mm, but want to do a physical check
- Will bolt on the tool (below) and run some squish tests.
- I can also use this to get a more precise measure of roundness and overall ID control with the CNC cut.

Think I have enough scrap around to pull it off.
Will post findings here tomorrow.

One thing I need to decide from a design standpoint.
How I will center the head to cylinder.
It will no longer be a drop in.
Pondering some means to add pins.

You don't need pins if you use bushes.

It's a good thought.
I've got a challenge with mine - the case studs are slightly off due to the shim between the cases.
Don't get to type that too often…

I've got an idea on how to get perfect center, but I've got some challenges.

I'll look at the bushes solution tomorrow.
Tks!

but you would still need to line up the head to the cylinder, clamp in place, and drill and ream two of the stud holes to fit the bush.

So ^ this is the issue.
I actually have a plan to address.

It's just not complete…
Which I suppose makes it half baked.
But tomorrow I will do my best to get fully baked. 🙂

Good work! Get Baked brother!! Happy independence weekend!

Few hours in the shop today and managed to push ahead a little.
I'm still learning how to do some things - which is part of my program - so it takes bit of time.

Now, about that mandrel I fabbed last week while OCT was riding up mt Olympus: below was my intent.

The lay of the land:
- The M1XL cylinder is old school 172, not 177. That means its bore is 62mm.
- The Crono head we are putting on had a 63mm bore

Both were drop ins.

The issue:
- The new design is not a drop in - so it needs to have a centering feature.
- It was held on with 8 smaller bolts to the Crono cylinder.
- So it's got 8 holes in it, but only 2 can line up with std cylinder studs.

So I need to do two things.
1. Figure out how to center the head on the cylinder
2. Determine how/where I will bore for the cylinder studs to come through
3. Determine how where I will either pin or bush to keep it on center.

So about that mandrel...
My sequencing is to use the Crono's head's drop in feature to drop into my M1 cylinder, so I can center it.
With it centered, I can pin, bore, or what ever.

Surely you just need to ream for the bush/bushes on the head and cylinder individually? Why would you need to do both at once?
Also would be best if the ream was only ever half the depth of the bush so it can't move up or down once in place. Is there much meat between the studs to tap into? Doesn't need to hold the head down, just locate.

But if the head is inset into the cylinder, that's the centering mechanism, so the problem self-solves. Ream out the stud holes, declare victory, and go on.