One of the things you quickly learn when working on scooters is that ‘Plug & Play’ is a misnomer. Only Lego is plug and play.
Scooter parts from disparate manufacturers never go together as intended; chiefly because nobody ever builds to the standard specification. If you have an exhaust, carb or ignition system that should work, are you going to spend again to get different ones just because that’s what is in the instructions?
Equally, as a manufacturer, you can’t realistically be expected to test every configuration. It would take weeks on the dyno just to do a selection of exhausts and produce jetting instructions to suit, but nobody would pay extra for this knowledge, so why bother?
In fairness to Max Quattrini, he produces a very basic single-sheet instruction that details all the main specs you need for:
- Assembly
- Carb jetting
- Ignition timing
- Squish clearance
- Spark plug selection
- Running-in
The specs supplied only work for the dedicated Quattrini exhaust (M3-150-S), the carb suggested (Dellorto VHST 34LD) and a Vespatronic ignition.
Since we were not going for maximum power, but a compromise on fuel economy for endurance racing and using a Dellorto PHBH 30mm, obviously the jetting specification was completely out of the window. We did have a Vespatronic ignition to try but the plan was to use the SIP Vape – which has a different retard curve – so the timing figure given could only be a suggestion too.
Leak-down pressure test passed first time with flying colours.
Potentially we also hoped to try using our existing ‘Franz’ exhaust because of its legendary durability and performance at low rpm. We’ve found that the key for our endurance racing successes are ‘reliability’ and ‘ease-of-use’ over all-out power.
Buzzwangling the Vespatronic ignition.
Ignition mission
The original plan was to run a Vespatronic ignition as per the instructions, or rather the descendent of one after our original flywheel (used since 2012) started to show cracks radiating around the rivets. Admittedly this was one of the heavier versions of the flywheel, combined with quite a revvy motor, so there’s no surprise that it began to fail. I’m just happy it didn’t explode mid-race as that would be simultaneously dangerous, destructive and a downright hindrance to a good race result.
I bought another replacement flywheel second-hand but encountered a couple of issues. The first was that it rubbed on the Philips screws and thick washers we used to secure the stator-plate. Allen bolts would have been worse, so in the end I just modified the screw heads in the lathe to increase clearance to the flywheel.
Stator plate screws and washers: pre-mod and post-mod.
After this effort, the Vespatronic ignition worked but misfired at high revs. Something was wrong with the stator, flywheel or CDI and we didn’t have time to solve that problem before the forthcoming race.
TERRY’S TRUISM: No matter how long you set aside to prepare for a race it’s never enough!
The solution was to swap to the SIP Vape ignition that has served us well over the last few races. The Vape is not a straight swap onto the Quattrini engine though because reinforcement in the casings occupies the same space as the aluminium plate for the SIP stator. You can either buy a special stator back plate like the Fabbri Racing version, or you can cut away a great deal of the original SIP one to get it to fit.
With little time left before the race, we got the grinder out.
Fabbri Racing’s stator base plate is the better way to fit a Vape ignition to Quattrini casings.
The next problem is that the plugs on the Vape stator do not fit through the tiny hole for the wiring in the Quattrini casing. We could have carefully taken the connectors apart to pass the wires through but it makes sense in endurance for everything to be standardized and fast to replace. More grinding required…
Sam enlarging the hole in the casing for the SIP Vape wiring.
Finally, we decided to reduce strain on the crankshaft and the fan screws by fitting a lighter fan. The one supplied with the SIP Vape for smallframe is already a CNC aluminium job but it is solid at the back to maintain enough mass for use on road engines. The solution for a race engine is to use another CNC fan which is hollow at the back to reduce weight. Ours came from Casa Performance racer Luca Zani’s new line of Vespa performance parts ‘Ellezeta’.
Original SIP Vape flywheel and fan (left) and the lightweight Ellezeta version (right).
The Ellezeta fan has a revised fin pattern intended to suit higher-revving engines.
Swapping to the SIP ignition also gave us the option of two different CDIs; one with an almost static map, and the racing one with a pre-programmed advance curve. With no time to test options, we plumped for the latter and hoped for the best. Most importantly, the SIP Vape cured our high rpm misfire. We were back in the game.
Words and photos: Sticky
That's all for part 3 but you can catch part 4 next week.
The bearing question
In our last edition, we explained that – contrary to Mr Quattrini’s advice to use two ball bearings to support the crankshaft – we fitted a high-spec 2-piece roller bearing on the flywheel side of the crankshaft. This was chosen to make engine rebuilds much easier since no heat or pullers are required when you have a 2-part bearing.
Max wasn’t as negative about this idea as I expected. The problem with roller bearings (where the rolling elements are cylindrical rather than spherical) he explained, was that they have more mass and therefore inertia. As such, in rapidly accelerating or decelerating engines, rollers are more likely to skid than ball bearings. This is the reason that you aren’t supposed to warm up cold race engines by quickly blipping them up to high revs and back down to tick-over. Making ‘winggg winggg’ noises might sound cool, but the crankshaft accelerates faster in ‘neutral’ than it ever will when driving the rear wheel. This is the condition most likely to cause bearing skid.
Max took on board the reasoning behind our decision to make an engine that is quicker to rebuild, but he’s come up with another solution to facilitate it. In the future, he plans to make crankshafts which are 0.003 to 0.005mm undersized on the flywheel side, so that the shaft simply pulls out of a fixed ball bearing. This means that the engine can be separated without the need of heat or an extractor. Apparently, several minimoto engines are already built that way.
Love a techie article