Modern Vespa

So I've had the original motor from my VBB sitting on the garage floor for two or three years, in part because it's a two-port motor and thus generally not worthy of my personal style of tuning.

Also, and I'd forgotten this, I had to cut it out of the motor because the front mounting bolt was completely frozen into the tube from riding in winter salt, so I had the joy of getting that out.

I rebuilt it back in 2011. It was the first motor I ever rebuilt, and it almost caused me to swear off working on scooters. It probably took me thirty hours to tear it down between having to learn every step of the way and not having any vespa-specific tools other than a flywheel puller.

The only performance upgrade I did was to put a 2-port Pinasco 177 on it. Tame, but decent torque.

I probably spent ten hours trying to get the rear hub castle nut loose, for example, whereas this time with the correct castle nut tool and my impact wrench, it took maybe thirty seconds.

So at this point, other than ordering new mounting buffers and the various other rebuild parts, I have a couple of actual engineering decisions to make.

First off is how much to even try and port this thing. The deck on the motor has almost NO room to expand, so if I do it, it's going to mean adding JBWeld and knowing I'll be cutting into that.

The more significant question is whether I can use the long stroke Mazzi crank I originally bought for my Sprint before switching it for one with a P-series flywheel taper. On the clutch side, though, the sprint crank has the bearing outside the seal.

Is it possible to swap the bearing/seal order to use the Sprint crank?

Either way, interestingly, the prior crank has already been cut to the same timings as the Mazzi (138°/6°).

Finally, I'll go for port timings of 124/172/26, same as my Sprint, assuming I can pull it off. The old port timings were 122/152/14, so the exhaust needs some serious work, but the transfers just need to lose the .25mm base gasket and I'm at like 123.3 on the transfers. The exhaust is going to need to be raised a good five mm to get to 172.

I'm going to aim for peak power at 7,000 RPM's since the 2mm rings will float at 8,000. I need to spend some time working out the intake milling and timing for that, still.

So lots going on, hopefully good


I now include a dog in as many pictures and videos as possible.

I made it look like this

The gasket is an exact match to the meat on the case ::

Crank shoulders

Dunno this crank brand. DE-MI?

Cut n' Color...I mean fill...

There's actually a gate over the port on the right (bottom) side of the transfers, so this would open that up.


Last edited by chandlerman on Wed Jul 01, 2020 12:09 pm; edited 2 times in total

I can't answer your question, but I'm eager to watch your progress and see what you end up doing

I don't see a gasket on the case photo for us to see just how crazy you are...

If you look at the third picture, that's a picture of the cylinder with the gasket sitting on it. The gasket exactly matches the deck face on the cases, so if you look at the marked up image, you can see what I'd have to add.

Basically, the case has so little meat on it, it might as well be a Vegan Vespa.

gotcha

Tofurkey

Surely you've got to get some metal or something in there, so you can open it up. Seems to me a little sliver of JB would be pretty fragile though, especially after you've cut it afterwards. No possibility of getting a little aluminum weld in there? You chaps normally have all the tools and skills for such things. You have the same situation on the casings and barrel too though? If you went for welding, it looks on the second image, below Josie, like a bit of filling might give you enough to squeeze a third port too, but again that depends on the barrel. You said before it was a 2-port kit, so maybe not bothered about that.

I wouldn't cut the base of that cylinder. Open it slightly and match it but no more. Won't make enough difference in performance to be worth the risk of it leaking.
Those 2 port kits have internal transfers for the boost and secondaries. I would open them up and check the angles.
If you can run the 60 crank it will make better port timing. Something like you said 123/175/26 would be age appropriate.

Thanks, Jack!

The Pinasco top end is a perfect match to the ports. I'll have to take a look at roof angles and see what those come out to.

For now, I think I'm looking at raising the exhaust port and deciding if I want to take the risk of fitting the 60mm crank. It looks like folks have done it and used retaining compound to hold it all in place. Assuming I can get away with that, I'll just open up the intake port and flow the airbox down through it, sort the timing on that for 7,000 RPM's, then put it all back together once the gaskets & seals arrive, probably this weekend.

I'm not sure if I'm going to install a 24/24 or stay with the 20/20 that's on it now. Last time, I could never get the mid-range of the 24/24 to really run right, probably due to the carb being a bit oversized for the build, but I also didn't properly open up the intake, so maybe that will fix it.

CM - I had similar shape to work with and took same path Jack suggested. Interestingly - on mine - that meant that the primary transfer aligned with the full case ported area - and the secondary transfers aligned with the slightly thinner area. I took it to paper thin - but keep the aluminum wall between the ported area and the JB weld. Decided it would provide velocity over volume for that small area. Made me feel good about it.

I opted for the slow cure JB - it has a higher compression and heat capability. If you have read any of my posts - you are aware I am not so...uh - careful shall we say - with the way I run the motor.

I have scrapped the 1mm fancy rings and GS high silica piston off the walls of my iron cylinder at least twice (3 times). The JB area with thin aluminum wall have remained as cast ea time I have reset the base gasket.

I did take some extra time in my build to deeply score the surface and de-grease it multiple times before I cast the JB on there. Seems to have held up nicely with little to no shrink.

Like this one.

-CM

I thought I could see something, but wasn't sure; I'll mind my own business now.

This came up from another thread on here about flipping the order of the bearings and seal in a motor, but it's from the old Stella Speed...So you wanna install a P crank in a Sprint.

I think I'm going to give it a shot, assuming that it looks good when I dry fit it.

I'm going to go for it on using the longstroke Sprint crank in my VBB.

I dug back through Sprint rebuild pictures and there's no circlip or lip on the inside of of the sprint's bearing, so they're effectively the same other than the order and the lubrication hole, which I'll just seal up with RTV.

Rebuild kit came earlier in the week, so if all goes well, it'll be running on the stand this weekend


VBB clutch side bearing housing

Sprint clutch side bearing housing

Missed this until now. Love it. Btw, your home Depot pipe engine stand is amazing. I and definitely going to build one of those following your pictures. I actually bought an engine testing stand from scooter mercato 8 months ago and when i finally tried to use it last month to kick start my rebuilt Stella motor, the stand bent in 3 kicks to the point of useless. Was pretty pissed at that waste of money. Your stand looks legit and cheap.

Also just noticed the ingenious peanut butter jar fuel supply with fuel tap in the base. Was also trying to figure out how to set a fuel supply up for stand. I'm gonna copy your setup to the t!

Thanks!

The Home Depot engine stand (and that's totally what it is) wound up costing more than I was expecting by the time I bought all the parts, but it's rock solid and has withstood a lot more than three kicks with no issues. I got the idea from someone else's pictures because I built a previous engine stand out of scrap lumber in the garage and while it worked and weighed a lot less, it was never very sturdy.

For the fuel tank, I used a mayonaisse jar and installed an old fuel tap that had a bent breather tube into it. I use a BGM quick connector for the fuel line, with a second piece that I can tie to the carb and then connect/disconnect as necessary. Whatever container you use, make sure it won't melt when you put gas in it.

I finally started the rebuild tonight after at least a month of procrastination.

I went ahead and installed the 60mm Sprint crank, swapping the bearing and seal order on the clutch side. It's all in and feels like a tight fit. I used bearing compound to glue it in place, but it sits against the lip of the bearing either way, so I'm not too worried about it.

I measured port timings and this jug is going to need some quality dremel time. Raw timings with no base gasket were:
-1.4mm piston over deck
41mm top of exhaust to top of deck
50mm top of transfers to top of deck

This gave me 147/102/22.

Those are some Born To Be Mild port timings right there.

Since the lip of the head is 2.2mm, if I put more than a .25mm base gasket on there, I'm going to be shaving the head down to get proper squish, so I'm going to aim for that to avoid having to cut the head.

If I raise the exhaust port 4.8mm and the transfers 3.8mm, that gets me to timings of 175/124/25, which is almost a little too aggressive for a motor that won't rev past 8,000 RPM's..

So I'm thinking to target max RPM's of 7,000, which means that with the .25mm base gasket, I'm now looking at raising the top of the exhaust to 36.5mm (raise it 4.5 mm) and the transfers to 46.6 (raise them 3.4mm).

That gives me timings of 167/122/22, which is about right for 7,000 RPM's.

Oooh...as long as I'm building a FrankenMotor, I could put a BGM recessed head on it with a 3mm base gasket on it to manage my squish, and do a lot less dremel'ing...that'll merit some exploration once I get back out to the garage.

Regardless of how I get there, if someone wants to check my math on raising the ports by 4.5 and 3.4mm, I'm thinking it'll be Dremel Time this weekend.


Progress at last!

Welp...I finally got a little bit of time and was able to button up the VBB, figure out port timings, and get it running.

Ultimately, the 60mm crank was not a go. The seals didn't want to fit right, so I gave up and went with the 57mm cut crank I had in it.

Initial port timings were abysmal when I checked them: 153/102/25.

I fabricated a 3mm spacer out of aluminum stock (waaaay more work that I was expecting. Not gonna' lie...I gotta get proper tools for that sort of thing if I'm going to keep doing it.), which got timings up to 166/120/22. With the BGM head stuffed down into the bore, I was able to get squish right at 1mm.

I figure that's respectable for this build. It's not supposed to be too revvy, mostly just torque-y and hard to stall, since I'm building it as a learner scoot for my daughter.

One thing I was struck by was how quiet it was compared to my other two motors. I'll have to check the noise level with the decibel meter, but it's a noticable difference.

One thing I'm NOT happy about is that the timing seems to be whacked. I set the stator using the existing timing marks from when I shut it down. I was expecting it to be at about 18 BTDC.

Instead, it seems like it's at, like, 90 BTDC at 4,500 RPM's. I didn't think a motor would even run that far out of timing. Once it started to warm up, I heard pinking, so I shut it down and called it a day.

All in all, I'm happy with the state of it, even if the timing still needs some sorting out.

Obligatory First Start Video

So I had another look at the timing last night. I'm running the original points on this motor, and I haven't really dealt with points timing since probably 2012, but I'm thoroughly confused.

The motor starts and runs, but the timing seems to be at 72 deg BTDC which seems impossible unless I screwed up my timing marks, which would be surprising, but is certainly not outside the realm of possibility.

If I had some sort of Math Fail, that would have me off by 50-55 degrees, which seems like an odd number when dealing with fractions of a circle.

Also, I verified by visual inspection of the piston that it was at TDC when the marks were applied, for added confusion.

I'm going to have another look today, but this one is stumping me

I can't help you with the timing, as points, condensers and coils disappeared from my vocabulary many moons ago. The reduced noise level of a stock/mildly tuned motor is very noticeable compared to higher tuned ones. I had a DR177 and BGM177 kit on the same scoot, with the same exhaust, and the difference in exhaust noise was significant. I guess compression and the pressure of the exiting exhaust gases creates different noise levels. I got an almost stock sounding pop, pop, pop with the DR. Not so with the BGM.

Nothing PK anywhere in that set up? That's about the difference on a PK to a PX. If it's not that I can't imagine

Points timing needs to be a few more degrees than electronic to be the same but not 55 degrees, more like 3.

Nope, it's the OG VBB setup. Good to know about the 3 degrees, too. Thanks for that, Jack!

I also have a Bajaj 12v CDI setup for this motor that I bought several years ago but never got working and put on the shelf. I may drag that sucker back out if I can't figure this out in pretty short order.

Other than the detonation, it seems like it's running well, just rich across the range. so maybe I closed up an air leak on this rebuild. This was the first motor I ever rebuilt, and it's definitely not the one I would suggest starting to learn rebuilding with in hindsight, especially compared to PX motors.

Are you sure the stator is bolted on correctly?

Pretty sure?

I still had the old timing mark on the Stator & case from before the rebuild and matched that as a starting point, then re-measured TDC once the flywheel was on.

And you can see in the video, it seems to run pretty well, no backfiring or any of the behaviors I'd expect from timing being that far out. I just can't figure out why it's reading so far off when I strobe it.

Just incase it's the strobe. Have you tried it with a bulb and battery? If all original VBB it's quite a mystery.

It's my good variable strobe. I have another I can try, along with the ol' bulb n' battery method, which is what I used last time I did it.

Someone with points should contact these guys and see if you can get any interest in a setup for a scooter. I put this setup in a VB Bug and a 1950 Ford truck with a flat head six. I set my points with a dwell meter and had them perfect in my 1950 Ford truck, I thought it started easily. I put a Pertronix ignition in hit the starter button and he fired right up. I didn't even have the choke pulled out, I was amazed at how much better he ran.

https://pertronixbrands.com/products/pertronix-1163a-ignitor-delco-6-cyl-with-mechanical-advance?variant=31797171257380

What are you using for a timing light? Maybe try and get one of the fancy units with built in functions for timing so all you need is a good TDC mark?

That's what I use. Makes figuring out the actual timing a breeze.

And I dug in to see what was going on and have now resolved both the timing & detonation issues.

I fired up the motor, confirmed that the timing mark was at 71 BTDC, then went back to make sure I hadn't messed up marking TDC. I re-measured, went to make the mark, and discovered another mark on the flywheel right where I was about to add one. I had marked the hell out of some other random sharpie mark on the flywheel rather than the correct one.

Timing is now at 21 BTDC at 4,500 RPM's, which'll do.

So, first problem down.

Next, I started trying to figure out the detonation. And realized that what was happening was that the cylinder was touching the engine stand, and what I was hearing was the cylinder bumping against it, because i still need to install the new motor mounts.

So, at this point, things are good on the timing front. Now, it's time to get the motor back in the bike and dial in the carb. This'll be interesting since I have the SIP RoadXL with the AFM bung in it. I'll have to figure out a battery for actual road tests, but that's not a big deal.

Never a dull moment in my garage!