Modern Vespa

Confusing the snot out of people with old and slow looking yet fast scoot is the fun part so fast road will be the thing.

Shooting for 205° (120/85) would mean lenghtening the pad about 5mm on the back and just slight adjustment of shape in the front. I think I'll have to place an order on the crank to get grinding.

Big thanks to Jack for advice!

This project is amazing! I love it.

This right here

There's nothing quite like a shifty little rat that blows the doors off everyone else on the road.

Well, it proved my calculations were indeed correct. Measured timings with Mazzu and untouched pad are 108/77. Time to get grinding

Started by marking out the port lenght and scribing some no-go lines with some give, since there will always be slip-ups and it's always easier to grind more than to add some critical misplaced chips back.


Rough shape opened up with coarse rotary burr


Shaped a tad from the back too for symmetry and the cast seems pretty porous there. Also broke through into the carb bolt hole, but it's nothing that a dab of epoxy wouldn't fix.


Now the intake timings measure at 198 (121/77) so around 6mm more could be ground from the crank lobe to reach the 85 closing ATDC.

Friend of mine sent me couple of pictures from the books of Graham Bell and Gordon Jennings.

According to Jennings a rotary intake is more sensitive to closing time and much less sensitive to earlier opening.




Bell prefers opening time to be 5-10 degrees sooner than Jennings








The last part might explain why our Vespa engines like the later closing time after TDC.




I'm beginning to think I'll leave the closing time at the 77 ATDC for now. This way I get a baseline on how the engine works and how adding more critical closing time affects the engine behaviour. Hope these snippets help other rotary tuners as well.

The port timings for the old Malossi cylinder with different cranks and height adjustments:

57mm stroke crankshaft
181° exhaust
29° blowdown
124° transfer

60mm stroke with 2,10mm spacer under the cylinder
187° exhaust
27,5° blowdown
132° transfer

60mm stroke with 2,10mm packer between the cylinder and head
171° exhaust
30,2° blowdown
126,5° transfer

I think I'll start with the tamer timings with the packer between cylinder and head to see how things start to work out.

What no 62mm crankshaft numbers?

Just have 57mm and 60mm rotary crank on hand so didn't even think about calculating the numbers for 62mm one.

It's a good thing to do a mockup build and check that gear cogs, shaft grooves and cruciform align as they should. Especially if you are using slightly sketchy parts made in India

I started out with a sharpie and blacked out one sector of main shaft, added gears and gave them a spin to wear out the marker where the cogs touch


Lining up nicely with original gear selector? Not First I thought that maybe I have a wrong type gear selector, but no. The old PX type selector pawl goes even further and bottoms out against the gearbox spacer on fourth gear.


Added 1,5mm washers between the cases and selector box


Alignment is a lot better. Have to take into account though that my dry build did not include gasket for selector box or between the cases. Have to whip up a 1mm spacer for the selector box.


Also noticed that the Indian gear selector rod included with gearbox has 0,3mm wider groove for the selector arm pawl. Not a real problem but extra slop is always extra slop. Original selector rod 9,15mm


Indian rod 9,46mm


Pawl itself 8,92mm

1mm spacer whipped up from sheet of alu and added the gasket between the cases.


I'd call this about perfect

You're just observing through the clutch side opening with no primary drive installed?

That's a great way to do it. Never thought of that, but I love it

Exactly!

It was an engine rebuild video from SIP that instructed this method to check for gear selector alignment.

Buttoning up the stuff at last. I redid the primary the second time since Indian spring set did not include the smaller inner springs. The RMS spring set had lot less spring tension on the main springs so no real change there. Practice is good though. Second time it turned out neater than the first time.


Heated up the case and dropped in the bearing from my freezer. Tapped in the oil seal, carefully warmed up the block again and grabbed the crankshaft too from the freezer. Dropped right in and followed by hot bearing race. It's nice when things just assemble without any friction thanks to temperature differences.


Taped and lubed up the crank end for you know what.


Taking some extra steps to not end up with gearbox oil sucker (thanks to mr. Freakmoped)


Siliconed up the other half too


Case closed

Yeah it's great to check on fresh parts…

Learnt from a SIP video where they do that.

Something wrong with these numbers. If these durations are correct then the blowdown is only 22.3.
As you're just about to fit the cylinder, make sure the cylinder port timing matches up with the inlet port timing and the chosen exhaust target timing. If all are in balance the power band will be wider.

I'm with Jack. That transfer time almost has to be too high. I've never run a VMC, but 126 would be too high for a box exhaust in any case.

What exhaust is going on it?

I'll have to redo my measurements to see if I made an error there. I believe the port timings on the cylinder are untouched, but it's an old malossi.

I only have the stock exhaust for this one at the moment and it's good for getting the first smokes out of the engine. I've been thinking about going for Polini box due to nice overall power it should deliver, but the timings on the cylinder are really a concern.

I thought you were putting a VMC 177 on it.

Either way, check your measurements. Looking at what I *think* is the port timing sheet for the Malossi 166 w/60mm stroke on my SprintV motor (It might be the Polini 177. But it's a good target setup either way ), I got:
Measurements:

Exhaust Height - 32.5mm
Transfer Height - 47mm
Deck Height - .5mm

Giving me timings of:
Transfers - 123.9
Exhaust - 185.2
Blowdown - 30.7

Which would be just the ticket for a box like the Polini.

An OEM box exhaust. It will go terrible but it will at least run. Change it later.
The old malossi 210 is very sensitive and looses torque easily.
Measure again and calculate the range of blowdown available.
What did your inlet timing end up at?

The 177 VMC is currently in use on the Bajaj 125 engine which was basically just thrown together to get the scooter registered. The engine now in the works is the Motovespa Iris 200 lump with old Malossi 210 and 60mm stroke Mazzucchelli crankshaft.

And Indeed there was something fishy with my previous measurements. The timings for now, calculated with ddog.at calc:
Exhaust 178
BD 29
Transfer 120
Intake 199 (122/77)

No worries Jack, the OEM box will not be staying with this engine for long

Can you get the transfers up higher and keep the squish under 1.2mm?

I think that is doable. I got the original head burred to 69mm diameter so the piston does not touch it on TDC. I'll measure the squish today to get an idea on what kind of spacing I need. I have a feeling that it's now well under 1mm.

Buttoning things up after lapping the head and cylinder on top of glass. Using 2x 0,20 and 1x 0,10 metal gasket under the cylinder I now have 1,15 squish measured with solder wire and the following timings:

Exhaust 182
Transfer 125
Blowdown 28
Intake 199 (122/77)



Head on, pressure test and rock on, eh? Fabbed up a plate to place between carb and airbox to seal off the intake side.


First test leaked from base gasket so off comes the head again. Lift the cylinder a little to add some silicone. After that, bubbles from the other side of the gasket stack. Head off, more silicone and re-test.

Third test had a leak from my bung attaching to exhaust stub. Tightening the clamps got the pressure to keep on the right side. But still, needle slowly creeping down. Uh-oh... no... please no... Yep. Pressure coming out of the clutch cover breather

On the positive note, it's easier to split the cases again while the engine is still on the table.

A leaky bung hole is always an issue.

That's a tiny bit high, but you can run with it. I feel your pain! I've been fearing a leak on the cases where I had to repair the lip of the crank case during the smallie build, but thus far, it seems to be holding tight.

I need to go see if last nights efforts fixed it, or I'm going to be doing another round of leak chasing.

I was thinking ting bit low. So, I guess where it is is good. Just about to do a leak test too. Somethings going to leak. Let's hope its easier than a re-split.

My sketchy engine stand got even more sketchier. Added some extension mounts to fit largeframe engine.


Makes life easier when there is no need to balance the engine on a wooden frame


Well this is kinda obvious. Heard a hiss and chased it with cleaner spray.


On the video from Vespa Motorsport they knock the oilseal with metal frame into the case dry. Should something like loctite thread lock be used between the case and oil seal frame? On SIP oil seal installation tutorial it is shortly shown that something is applied on the seal edge but not described what it was.

I always use Loctite 603 on both seal types…

+1
The one I did today has 603 on the metal seal too. Test gear leaked but engine not so.

The last oil seal I have left loaned from Malossi VR-One baggie


Made a big honking washer out of plate steel, drilled 10mm hole in the middle and used it along a bolt, nut and socket to pull the oil seal in while gently tapping it in. Used Loctite 290 because it was the closest thing to the good stuff I had.


Pushed in one frozen crank


Attached the gasket on the flywheel side case, squeezed excess silicone out around the crank and put a blob for supporting the weak spot.


Smeared some more silicone on the big half and joined the cases with fingers crossed


Fast forward to the pressure test and no more leaks rigged up a syringe to feed some fuel and kicked the engine to life.


It's alive! -video


Story of this engine continues on the Fast Orange thread because it needs a temporaty engine before VR-One build is finished:
https://modernvespa.com/forum/post2573300#2573300