Modern Vespa

I probably wouldn't have loc-tite'd the case bolts, but to each their own.

don't think I've ever used a tool to install a piston pin. usually just a little heat or cool if needed.

good that it closed easy!

Yeah, loctite on the case bolts seems a bit overkill.

The washer/wave washer/nord-lock should suffice.

18nm seems on the high side for m7 bolts, but it is a tuned engine. So suppose can try that.

I'd usually double check final torque after 24hrs of the gasket set in place. Might as well, you have the engine on the bench

You can try install without the piston pin tool… some just slide on by hand. Tougher ones you can use a socket and a strong grip and it'll slide in.

Parmakit and malossi kits usually just slide into the piston.

Usually only use the tool for people who mess up their engines.

C clip tool.

Jack,
Thanks for the tip for the pin!

Fingers crossed I don't have an oil sucker. I am going to use a 1.5mm base shim with gaskets to accommodate the 60mm stroke. Squish is specified at 1.0mm +/- 0.1mm. Nothing else is being done to the top end.
Question for you. I have a newer 24/24 SI carb that will be mounted inside the P125X 20/20 SI air box . The 24/24 carb has the long hex (fine thread)idle air adjustment screw vs the short (coarse thread screw). Is there a special air box plug or grommet to seal around the screw? It sticks out past the air box. Do I use the original rubber plug and make a hole in it for the screw?
This weekend I will drilling the carb bowl inlet and possibly grinding out the 20/20 air box to match up with the 24/24 carb.


Hec

I'm exactly the same way, especially when closing up an engine case. Just keep at it and make sure everything spins freely as you assemble and before starting. After that, there are always gremlins to shake out.

Sorry for the confusion everyone. I was referring to the C-Clip installation tool. The tool arrived today and it won't work. I ordered the 12mm size since the pin diameter is 15.0mm. My other size choices were 15mm,16mm and 18mm. Those sizes are bigger than the wrist pin bore. If I try to push that C-Clip into that 12mm bore in the tool I think it will fold up.The C-Clips are 15.59mm I.D. So I installed one C-Clip by hand. It wasn't as hard as I thought it would be. The wrist pin slides in easily into the piston with no issues too.

Marching onward!

Hec

I'm happy any time it passes a pressure test and I don't forget the kickstart gear.

I've never used anything but needle nose pliers and maybe a pick to get C or G clips in and out, and I've done more top ends than I can count.

There can be a fine line between "use the right tool for the job" and "use the right tool as an excuse for not just doing the job."

1.5mm base sounds better but would be good to put the measurements in a calculator to check it's ok.

There is a special rubber for the spaco mix screw. Shorten the screw by about 8mm and cut a screwdriver slot in what's left. Can even be adjusted past the starter motor.

Tonight I installed the piston on the connecting rod. I did not use the Mazz Gudgeon bearing per FMP's warning. I purchased 3 different Piaggio Gudgeon bearings and found the perfect fit it was part no.90132000 (15x19x20 mm) Part No. 90131000 and 90133000 were also tried. 90131000 was a little loose and 90133000 was too tight.
I checked squish without piston rings installed and used Cush gear springs on the cylinder studs. I only tightened the nuts until the springs just got fully compressed and no tighter.
The head lip measured 0.22mm.

First try: I used the 0.55mm green paper gasket supplied in the Stelvio kit and the 1.5 mm spacer. The result was 1.29mm PBT. Add the head lip 0.22mm measurement and I get 1.51mm Squish.

Second try: I used the 0.20mm aluminum gasket and the 1.5 mm spacer. The result was 1.13mm PBT. Add the head lip 0.22mm measurement and I get 1.35mm Squish.

Third try: I used the 0.12mm brown paper gasket supplied in the Stelvio kit and the 1.5 mm spacer. The result was 1.07mm PBT. Add the head lip 0.22mm measurement and I get 1.29mm Squish.

How much additional squish can I expect after torquing down the head and cylinder? Should I stick with the third try combination? What do guys think?

Hec

Sorry, lost track… what exhaust are you using?

Personally for me, your choice depends on port timings and aiming for a matching exhaust.

Measure the ports. Then decide.

You have everything there, why not bolt on head and squish a piece of solder for squish test? Then you'll know what you have assembled.

I agree

As you start learning, keep in mind, adding spacers to bottom of cylinder, moves power up the RPM range, removing moves it down.

Timing should be setup for your goals, mine was power in 5700 rpm range while cruising at 60 mph. People kept telling me to put spacers under cylinder, increase timing of ports etc. This can increase overall power, however it can also move peak power to a spot up the rpm range that isn't desirable for your application.

Like you I wasn't familiar with timing and really didn't know what I wanted for numbers. Measure everything so you know what you have, learn how to do the measurements. Unless you get some really off timing numbers try it as is. Doesn't take long to remove cylinder make adjustments reassemble. Then you know what each change feels like.

108,

I have a SIP Road 2.0 Exhaust with the twin pipes.

Jack,

Please educate me. I don't understand how port size would impact the squish specification.

Christopher,
Using solder and torquing down is my next step. I wanted to see what the best gasket combo was so I only have to torque everything down once. It probably doesn't matter.

All,

Do I also need a gasket on both sides of 1.5mm plate? If so, my squish clearance will increase a little. Any preferences on gasket material? Paper or aluminum?

Thanks again!

Hec

You can adjust cylinder timing by moving gaskets and you can adjust squish by moving gaskets. As you're trying to balance the two it may require a bit of sacrifice. Such as, you put a 1.5mm spacer under cylinder. You measure cylinder timings and find them high for daily use. You only want 0.75mm under cylinder now what?

I think you're overthinking again.

You need to get some short spacers or stacks of washers you can put on the tops of the studs and then torque the stud nuts to spec with the cylinder and piston, but no head. That'll let you get actual measurements of what you have.

I don't like paper gaskets on cylinders, personally, but it's more personal prejudice than any real reason. A smear of hi-temp RTV on the sealing surfaces works just fine.

Measure it up good and get some numbers. So long as your TD is in the 123-124 range, you'll get plenty of power with a box exhaust on that top end.

Paper I'm ok with… thick paper less so…

As said by CM and Chris, port timing is more important than squish edge clearance.
Paper gaskets are not the first choice, as over time they can shrink and leak. Aluminium and sealer works.

The power delivery of a 2 stroke engine is determined by the transfer ports; duration, flow direction(s) and velocity(s). Each of these factors can be changed. And there is overlap between factors. The easiest factor to change is the transfer duration ie. by length of stroke/rod or base gasket thickness/machinining.

Exhaust ports, exhaust systems, inlet duration and boost ports etc. are support for the transfer ports. Changing any of these can make the transfers work differently, without actually changing the transfers themselves.

'Squish clearance' affects the turbulence built into the head (....too complex), which is managed by the ignition timing.

In summary, what makes a build like yours go strongest, is transfer duration adjusted to suit the transmission, balanced with reasonable squish clearance/ ignition timing.

Ah something a bit more pedestrian.

Hmmm you might want to reconsider a 1.5mm base then… if not, my guess is it might struggle off the line…

+1 on the TD timing.

Whenever I am about to finish an engine, I need to buy another tool, a better part, take more measurements or do more "research". Then you close it up and think you're going to start it in that afternoon…then come the port timings….Ugh.

Jack,

Thanks a million! That is a great explanation which cleared things up. I was struggling with the acronym TD people were using. I know it wasn't a reference to Touch Downs! Now I know it refers to Transfer Duration.

Build Components for reference:

Crankshaft
https://www.sip-scootershop.com/en/product/long-stroke-crankshaft-mazzucchelli-k2d_45046000?q=Long%20Stroke%20Crankshaft

Gearing
Stock P125-X gears with Malossi Up Gear Kit.
https://www.scooterwest.com/malossi-gear-kit-23-64-for-p125-150cc-m673730.html

Carb-24/24 SI Carb

Ignition - Stock points

Exhaust - SIP 2.0 Road Sport Style
https://www.sip-scootershop.com/en/product/racing-exhaust-sip-road-20-sport-style_24156300?q=SIP%20road%202.0

So if I understand the basics of port timing (Please correct me if I'm wrong!)

* Adding shims to the base raises the port timings which raises the RPM at which the engine develops full power?

* Removing shims from the base lowers the port timings which lowers the RPM at which the engine develops full power?

For my needs, I will be using the Scoot primarily around home and in town under 50 MPH. There will be occasions where I will need to run above 55 MPH for 10-15 miles to get to town. I live in the country so I would have to keep up with highway traffic for at least 10 miles. Then my commute would be all under 50 MPH. I will occasionally have a passenger as well.

I will get the cylinder properly torqued down this weekend and get some better measurements. I'll also do some research on how to measure the Transfer Duration and report back. I have a degree wheel, feeler gauges, Micrometer at the ready! Then follow that with an actual squish test using solder and see what I got. Then take it all apart and apply sealant to the gaskets and retorque and recheck squish. After that, Pressure Test! Unless I missed something.


I appreciate everyone's comments! This has been a learning experience for me. For those who don't know I am a Mechanical Engineer so I am cursed with OCD and trying understand exactly what is going on mechanically and electrically. There it's out there!

Hec

I thought I defined the acronym...my bad... That's close enough for now. i.e. it's correct, but obviously not all there is to it. Okay...I realize it's a little late to throw this spanner in the works, but here's the issue...that gearing is going to be too long for what you're wanting to do here.

You're going to make it (much) harder to carry a passenger, plus you don't need that sort of top speed, it sounds like--you'd be doing close to 75 in 4th when you hit end of your power band at just over 7,000 RPM's, assuming you have enough power to push that much air.

Unfortunately, that also means you're not really going to get INTO your powerband in 4th until you're at about 55 MPH. So you're going to be doing a lot up shifting between screaming 3rd and struggling 4th, depending on the wind (which you have enough of to make up for the lack of hills) and is not a fun way to ride, IMO.

Others can jump in and tell me I'm wrong, but the VMC (And BGM) both have a power band that really runs from 5,000-5,500 RPM's out to just over 7,000 (more if you're running reeds, but that's out-of-scope here).

Ray8 has a similar build to yours. Hopefully he will provide firsthand advice on his experience on the power band RPM's because I don't run one, so have to go with what I've read/heard from others. That's it exactly. Lotta dry fitting, measuring, then disassembling, tweaking, rinsing & repeating when you build a motor deliberately.

Oh damn…

Bang on with gearing CM.

I'm always assuming people are running the stock PX200 gearing at least with a short 4th on any tuned engine.

Need to remind myself about stuff like this too…

Sometimes, I hate it when I'm right.

Got too distracted by "time to close the case"………

I did not flow the cases, just plug and play the top end with a stroked crank. I attached the results of stock configuration vs. stock configuration with Malossi 23/64 Up Gear Kit. I am hoping I can maintain 5,500 to 6,000 RPM's on the highway riding solo.

Hec

You need to post the two images separately. Those are impossible to read.

I hope this works.

Hec

My quattrini 181 has nearly identical gearing. Pulls 4th really well, and rolls on from lower speed too.
No panic with the gearing BUT need the port timing to match it.

Measure your cylinder. Main transfer to deck. Exhaust port to deck. And the rest can be calculated. From slightly inside the port to the top with 0.00mm accuracy.

That's better. Thanks!

It doesn't change the fact that I still think you're going to struggle to make those speeds at that gearing, though. You're going to start getting short of power in 4th gear by 5,500 RPM's, when you're going to need about 16 HP to overcome air & rolling resistance.

That's a really big upgear. I would be hesitant on a first time build to make such a big change in gearing. Most upgears are modest. My Stella with a Polini 177 (187 with 60mm crank) has a 22t clutch cog, which only brings the speed up 2-3 mph at 6000 rpm. I am still getting the jetting dialed in, but is will easily hit 60 without much effort and feels like it has a lot more to go. Since it's only the clutch cog that has changed, it's easy to change it back. Changing the primary is more work to reverse and a bigger commitment.

Jack,

Main Transfer to Deck=50.01mm
Exhaust Port to Deck=35.01mm

Stroke=60mm
Con Rod=105mm

Did my best to measure.

Hec

How far above/below deck it the piston at TDC? Can't calculate without that.

-chandler

Update

Sorry it's 1.35mm PBT with cylinder torqued and 1.50mm spacer with a 0.20mm aluminum gasket on both sides of the spacer.

Main Transfer to Deck=50.01mm
Exhaust Port to Deck=35.01mm

Stroke=60mm
Con Rod=105mm

Hec

You need another 1.25 mm spacer under the cylinder to get to 124 TD.

At 2.60 Piston Below Top, you're 124 TD/187 ED/31 Blowdown. That'll be respectable.

Peak RPM's a little over 7,500 peak RPM's on the TD. ED & Blowdown are really for a higher peak, but it'll be fine with a box exhaust.

better hope that bit of highway where you need that power is F-L-A-T or you're gonna be back and forth on the gears.

two up should be interesting.

Hey, it's Nebraska. The topographic maps there are graded in inches.

plot twist: there's a 3.5 mile 5% grade hill to get out of beaver river to the town of two mountains.

chandlerman

In the calculator's I've seen you have to enter the Piston Crown to Top of Barrel dimension. Do we need to add the 0.22mm recess dimension of the head to the PBT distance? The head is not flat. It has a recess or cavity that is 0.22 mm deep. With a calculated 2.6mm PBT my calculated squish would be 2.6mm+0.22mm = 2.82mm. This is no where near the 1.0 mm squish spec. So does this mean I would need to mill 1.72 mm off the head to achieve the 1.10 mm squish requirement?

Hec