Modern Vespa

Yes, that's with the .5mm gasket. Those numbers just took a dump and fell off a cliff. I was off a whole mm measuring the transfer ports…at least I think. I will have to find my notes. I would think kit manufacturers would publish their transfer dimensions. I find them hard to measure with a caliper and get numbers all over the place. I think the depth of the caliper in the port creates a lot of noise because of the shape or roughness inside the port. Would it be more accurate to make a rubbing with paper and pencil?

I will go through my measurements again and get them nailed down for realz. Either way, I will button it up and run it as it's easy enough to make adjustments with the engine in the bike.

Thanks!

There are multiple methods for measuring ports. All of them have their strengths and weaknesses.

You can measure them with a degree wheel or inclinometer directly, by placing a feeler gauge into the port and then measuring the depth from the deck to the feeler gauge, or by putting a caliper into the port.

For the caliper method, you really need a set of calipers with the ID arms cut off to fit it into the ports properly.

and whatever method you use, taking multiple measurements and averaging will get you closest especially if you throw out your high & low measures.

But 1mm is a LOT of variation. Definitely re-measure a few more times and average.

Orwell - I have noted this challenge along the way on a few of my 100 pages…
For your sanity, check 72ish.
Vintage vespa with sidecar (**Now In Technicolor ! **) (Page 72)

1mm is a lotta difference in timing as CM noted, but it's a simple differential to have occur when trying to measure.
I couldn't get my mind around such a fine difference making so much difference in timing - but it does.

I show a close up picture shot with a microscope camera that can vary the measure about that much.
The depth that your caliper reaches in the port (with its canted roof) has a significant effect.

To avoid: I have one pair of calipers I've cut the tails off (as cm notes) to allow cylinder fit.
I also, very carefully sanded a taper on the depth gauge rod.
That way, when I have it on the piston top, I don't pick up the crown of the piston.

See if the pics below help

Thanks so much!

HF digital calipers aren't the best way to measure, but should be more than accurate enough. After repeating my measurements a bunch of times, I kind of figured out what was going on. Your info helps a lot.

I found learning to measure was one of the most difficult parts of engine building. It took a long time before I felt confident in my measurements. It's practice and developing a feel for it. When you measure something different enough to what your used to, you have to develop that feel again. Measuring deck height is really familiar, but those ports…It looked easy, but isn't.

Another thing I learned about measuring. When you have been at a project long enough to know what values you are looking for, your measurements are influenced by your expectations. When I get to that point, I have to sneak up on it first thing in the morning before I have pondered it too much.

Tru

Starting to get somewhere. Over the weekend, we shuffled cars and I threw the Stella in the bus, plus parts and got it to the new place.

After following all the helpful advice and many careful rounds of measuring, I think I'm getting there. I ran the numbers using the most extreme measurements I got for deck height just to get an idea. It doesn't change the timings much. There is a fair bit of variation from piston rock even measuring at the wrist pin and the fiddly HF caliper. I was going to break out the vernier depth gauge, but I could end up doing that for months.

Squish is on the high side…between 1.78-1.91mm using a 1.5mm base gasket and no head gasket. I could bring squish down by taking down the cylinder head on a surface plate. I will check it with solder first or play dough.

Squish is kinda big (2.03 mm) I think the timings are pretty close.

What would be the best way to get a tighter squish?

Thanks

That's with no head gasket? What're your current measurements and base gasket?

A page ago, you should've been right at 1mm with squish once you got your port timings up a bit.

And which top end is it? Nothing with the convenience of an inset head, I'm assuming?

These are my current measurements with 1.5 mm base gasket. Squish is a little over 2mm with no head gasket. A page ago, I was way off in measuring the transfers. It's a Polini 177 kit. No inset head.

So to recap, my first calculations were off by a lot because of the way I measured the ports. When I corrected them, the timings went out the window.

So it's looking like using the 1.5mm spacer gives me decent timings, but too much squish (2mm). The Polini kit looks a lot like a stock piston and cylinder in terms of the mating surfaces etc.

Just not sure how to adjust squish without messing up the timings. There is still the possibility that I measured something incorrectly, but I have checked and rechecked, measured 6 ways from Sunday and am getting consistent measurements.

Thanks for bearing with me.

There's a reason most people never get beyond squish in terms of setting up their top end.

Also, for an online calculator, there's the Lambretta Images Archive, which has ads for their stuff spread through it, but is in English, so one less level of translation.

There's also the downloadable Vespmoto excel file which is my favorite (especially after I tweaked it a little) so you can save your work in an editable form. It's also much better for working toward specific timings.

Now getting back to your specific problem at hand...when I built my SprintV motor with a Polini 177, I used a 1.5mm base gasket to get the transfers to 124, then dropped the exhaust to flush with the piston and raised the exhaust up to get to 172 ED. At that point, I had 1.7mm of squish, but no record of whether or not I ever cut the head down that last half mm.

Even if I didn't ever cut the head down, that motor hauled a fair amount of butt. It happily cruised at 65. I have it in the VBB now with the same crank and a BGM177 and even with the down-gearing of dropping from 10"s to 8"s it still cruises at 65, albeit at WOT.

Figure that you can just run it as is. P200's routinely shipped with 3mm of squish, so you should be fine.

Thanks! I was coming to the same conclusion. Timings are decent AFAIK, squish isn't optimal, but shouldn't make it run like crap either.

This is kind of a reliable bread and butter, get a bike on the road and be able to get it home build. I think it should be ok the way it is. I can tinker and tune the next engine once I get one on the road.

So measure ring gap, button it up, leak test, then on to jetting.

Thanks again.

Absolutely! Get it on the road.

It may have room for improvement, but it'll still be so much better than stock that you won't care. You should see at least P200-grade performance out of it, albeit with shorter gearing so it won't have quite the top speed, but it'll get there quickly

I ended up lapping the head on a surface plate…you knew I would…Mostly to clean up the sealing surface as I won't be running a head gasket. I will seal it with copper coat and RTV at the spacer/spigot.

I haven't checked yet what I ended up with for squish, but something under 2 mm. It's not in the tuned bike range, but neither should it be gutless because of excessive deck.

Quick assembly question:

The oil pump drive gear. I know there is a funny slotted washer that goes under the gear.

Is there a washer(s) that goes between the gear and the c-clip. I think the Haynes manual mentions it, but I haven't found it in any diagrams.

Down to the nitty gritty.

Thanks

Good to hear the top end is basically done. I seal the head to the jug with copper bond head gasket spray and RTV at the base, same as you're going to do.

I don't recall a washer under that circlip on any of my autolube motors and there's no reason for one. The gear is driving itself toward the crank.

Keep up the progress. Looks like you almost have this thing across the line!

Yes! Almost there. I am dreading the whole jetting thing, but one step at a time.

Jetting has a much worse reputation than it deserves, especially on a near-stock bike.

You are probably right. My impression of the Polini kit is that it is mostly a displacement increase without much of a power band shift. If I don't end up making it worse, I will be more than happy with it. It already went faster than I had the nerve to ride it. Kind of a good kit to learn the basics.

Plus, it's cast iron, so it's tough as hell. Hopefully you won't need to find out, but you can seize the crap out of it and other than cleaning off any smeared aluminum and sorting out the piston, it'll be good-to-go again.

Or just wait until it cools a tad, kick to fire right back up and be on your merry way again

Did that to it a few times, too. Had a wheel-locking seize doing about 60 on Lakeshore Drive one time when a cylinder stud worked its way loose. Sat basically in traffic for a few minutes, fired it up and rode carefully on down to work, then home again that night.

Another bonus for a beginner.

For sure I have been acting like these engines are delicate flowers after seizing…getting the cylinder honed by a machinist and letting the whole project grind to a halt.

As long as the ring lands are in good shape, the piston should keep doing its job.

Muriatic acid is great for getting off smeared aluminum. Sanding a crosshatch pattern into the cylinder would probably be ok. A couple passes with a cheapie blade hone if I wanted to get fancy.

Moving along…Not one of these shitty little tabs lined up with a slot no matter how many times I tried to retorque it. What are the chances?

Ditch that junk for better nuts

+1000

If your castle nut tool has marks on the clockwise side, you're using it wrong.

Allow me to do a simultaneous translation:

many on this forum (I am told) don't use the castlnut - opting for something else. I'm pretty sure that's what Swiss was suggesting.

CM - Wadda you mean?

Lol. Took me a minute…Only one thing it's good for…

Replace it with this and make your life easier...

https://www.scootermercato.com/Scooter-Parts/Clutch-Misc-Parts/MODERNCLUTCHNUT

Thanks!

A few of those will go in my next Mercato order, but I'm leaving it for now and getting on with it. Not like that ugly snarl will come off easily either by accident or on purpose.

Your life expectancy will increase two-fold from that better nut.

I was bald. Now I'm not.

The better nut gets rid of crows feet, male pattern baldness, takes 20 lbs off your waist, and acts like viagra. (plus the obligatory increased 20mph top end speed)

PS. just realized this is starting to sound like a scoot.net (orig) ad. Email for paypal address if inclined and I'll send you a little baggie of sodium phosphate.

It looks like you got one sort of into the slot. Did you use loctite? It's a good idea. If you did, I'd not worry at all. Clutch nuts always get a dab in my engines.

Last night I got the top end together without breaking any rings. Those c-clips are evil. I managed to get them in with a dental pick type thing. Shmoozed up the cylinder and small end bearing with 2t.

I kind of muffed the fly side seal, it's slightly cocked, but I will replace it if it doesn't pass the leak test.

I didn't use loctite on the clutch nut. Would any flanged nut of the right size and thread pitch work for the clutch? I would use the same type of lock washer used for the flywheel nut. If not I will retorque the stock nut with some blue loctite and a new washer.

Getting there. I had hoped to finish this before moving. Now my basement is a sea of overturned bins from hunting for parts and tools. Hope to have the engine in this weekend.

I have my own means of piston install (piston first, then connecting rod gets attached to already inserted piston)
Try it sometime if you find it a struggle/ are concerned about the rings falling on a land.

Any shoulder nut will do, however, you have to watch the outer circumference for interference between shoulder and any chamfers on your clutch. Shoulder needs to sit flat on flat portion of clutch face.

Motor spins backwards naturally tightening. Unless you are down shifting.

Pro tip: Use gravity to make the fall path for an errant key, so that it would not drop inside the crank case if it gets nudged out. Ask me how I know…

Today I retorqued the clutch with a new washer and blue loctite, buttoned up the engine and called it good. I did an air leak test but couldn't get the plate I made to seal the reed block. As it wasn't leaking from anywhere else, I decided to call that good too, and got the engine in the bike. There's nothing wrong with the reed block and I didn't want to dick around testing it with the carb box. Just wanted to get it in the bike.

The usual stuff left to do. Everything went a lot smoother than the last time around.

You can install the carb box and put a solid rubber between the box and the carb.

I will probably end up doing that. Easy enough to do on the bike. Just wanted to keep it going.

Leak testing is kind of PITA, but worth doing. I also meant to check the timing on the bench. Pretty sure I was off the last time around, but I will get it right this time.

Last thing is jetting. I know we went through this after I seized the engine and the consensus was that it was lean. The seize was definitely caused by a disintegrating big end con rod bearing. I'm not sure if the jetting changes because of the slightly larger displacement.

The PO graciously mailed me a big bag o' jets and carb slides as well as tires, a few carbs and many other gems. What a guy!

So what would I start with for jetting?

I hope to be doing some actual riding by the weekend, but I will be taking it easy. I think I pushed too hard on my first rides. If I get some nice fall foliage rides in before winter, I will consider that excellent. I feel like I have moved a long way along the learning curve. Given how much life has been getting in the way, I am not one bit disappointed with my slow progress and lack of actual riding.

Many thanks!