Sloppy Seconds (and 3rd and 4th)
When it comes to traditional scooters, having a precise gearchange is a real bonus. The problem is that it’s not that easy to achieve due to all the linkages involved. Every linkage on a Vespa or Lambretta adds unwanted ‘slop’ until you end up trying to play snooker with a sausage.
One of the firms working to eliminate this slop is Crimaz. Instead of the standard riveted-together linkage that shifts gear in a smallframe engine, Crimaz makes a CNC-machined version that bolts together.
Crimaz gear linkage for smallframe, now with two o-rings!
The unfortunate detail is that our headset runs the small gear wheel, not the large PK type, so we needed to swap the cable wheel on the linkage to the older type.
Smallframe type cable connection (left), and PK type (right).
What you’ll quickly notice from this image is that it’s not as simple as swapping the cable connection because the shafts take tapered pins at completely different angles. The only solution for us was to unbolt the Crimaz linkage and reassemble it around a used gearchange shaft and wheel. Sadly this only left us with 2 o-rings to seal the shaft and not 3!
I’m sure we’ll manage.
One issue we were alerted to about the Quattrini casing is the holes for the gear cables do not correctly align with either the PK-type gear wheel or the smallframe type.
The Quattrini crankshaft is a hefty beast and with wider webs it’s far less liable to twisting than a normal smallframe crank. This crank dimension is now such an established design that many rival manufacturers now make crankshafts that are compatible with Quattrini casings.
Max’s intention is that the crankshaft should run on two 6205 C4 (increased clearance) ball bearings. The advantage is that ball bearings are low friction and capable of very high rpm use. The two ball bearings also hold the crankshaft very stable and prevent it floating side-to-side. The disadvantage is that you always need heat and/or pullers to assemble the engine around ball main bearings.
Tapping an NJ series bearing track onto the Quattrini crankshaft.
Given that we intended to lower the operating rpm of our engine, and also that there was a likelihood that it would get rebuilt quite frequently, we opted for Dave Bristow’s ‘lazy man’ solution; which was to fit a 2-part roller bearing on the flywheel side. The bearing we ended up selecting is a FAG NJ205-E with a C3 clearance. C3 is bigger than standard clearance, but not as generous as C4. The NJ bearing is like the NU series used on Lambretta and T5 flywheel bearings but it has a lip on the inside edge to prevent excessive float. This type of bearing is used in some kart engines. While a roller bearing does have a lower rpm limit than a ball bearing, Dave from Hornet Racing has been running Quattrini engines with this set-up for a while without problems so we followed his first-hand experience.
With one 6-hour race victory now under our belts on this engine, it does seem to work…
Special oil seals and special grease.
One good feature of the Quattrini casings is the ability to change oil seals from the outside on both sides.
One feature of the Quattrini crank is that the seals run against a relatively large diameter (24mm) part of the shaft. The larger the circumference of the crank at the sealing face, the greater the relative speed between the crankshaft face and the oil-seal. In a high-revving motor that means increased heat and wear. I mentioned this issue to Max Quattrini and he explained that the solution both he and Honda use is a very high-quality oil seal material that’s better able to cope. Additionally; Crimaz supplied some special grease for both the seals and bearings.
Again, we are one 6-hour race in and so far so good.
Primary Pick
What you’ll see confirmed in later articles is that changing exhaust can cause a massive shift to the power graph. We also wanted this engine to be adaptable to run on the small circuits generally used for British Scooter Endurance Club events, but also adaptable to large circuits or even road use.
Sadly, changing the primary gearing on a Vespa is not as easy as on a Lambretta with their interchangeable chain and sprockets.
Since the 1980s it has been possible to swap the front primary gear cogs on Vespa smallframes for other tooth numbers. For instance, the standard primary gear kit of 24 front meshing with 72 rear could be adjusted slightly by fitting a special front cog of the same diameter but a different number of teeth. I had several Taffspeed front pinions (‘cogs’) allowing the fitment of 22, 23 or 25-tooth cogs that still meshed with 72-teeth on the clutch.
That’s fine for small adjustments in gearing, but not for major changes like going from tiny kart tracks to Grand Prix circuits like Nurburgring. For substantial gearing changes to a smallframe which required a different cog behind the clutch, that always required you to physically swap the primary gear kit and cush-drive. It wasn’t previously possible to make such changes without stripping the complete motor, but Crimaz has developed a system that works.
On the Crimaz primary, the central part and outer gear are connected by a large-diameter thread, so it is possible to use a special tool to unscrew the centre part in situ, and remove the cog and clutch basket assembly as a unit. It is both ingenious and effective.
Obviously, it’s not quite as easy as that. The cush-drive assembly and clutch bell are fastened around the cog using Loctite on the four Torx-head screws. The only successful way we found to loosen the screws was to use a blowtorch to break down the Loctite. A better-prepared team would have two gear cogs built up with a clutch bell and cush drive on each, but we didn’t think that far ahead. Doh!
Bolting It Together
Typically Max Quattrini’s products come with a single page of instructions in Italian. Thankfully that’s is not as incomprehensible as it once was. With a smartphone and the camera feature of Google Translate you can now live-translate the page in real-time as on your phone screen.
Along with this bare-bones instruction page was another diagram showing where all the Allen bolts to fasten the casing go, because they are all different lengths.
Rather than trying to remember where the piece of paper is each rebuild, I decided instead to engrave the length of each screw next to its hole in the casing with a Dremel. Hopefully, that should speed up rebuilds considerably.
Engraving today, tattooing tomorrow.
The Quattrini casings are precision-machined so that they assemble – like many modern motorcycle engines – without a main gasket. Two small steel pins act as dowels to align the casing halves and it is sufficient just to use sealant. Max recommends a type of Loctite that I didn’t have, but Alan from Diablo Moto suggested using Stag Wellseal; which is an ancient favourite of the British bike rebuilders. The advantage of Wellseal is that it is easy to clean-up and remove with thinners, unlike silicone or Yamabond. Again, we are thinking not of this build, but of speeding-up future ones.
Wellseal is unusual because it should be applied to both mating surfaces and allowed to dry slightly until it is tacky before closing the casing.
Clutching at Straws
Before fitting the clutch we installed the primary drive cog. This is an interchangeable design from Crimaz with a cone-fit like a Lambretta rear hub, and it uses a similar 3-bolt extraction system. The cog fits with a supplied hardened nut which should be tightened to 70Nm (51.5 fl-lbs). That’s a hefty amount of force.
In order to block the gears still while you tighten the nut, Crimaz makes a special tool that looks like a Penguin’s foot. It seems Mr Happy Feet’s dancing days are over.
Punched dots are marked with white Tippex to make them easier to see.
TOP TIP:
Since we may end up doing assembly and stripping with an electric impact gun in endurance race conditions (where every second counts) we have a Top Tip for fastening such nuts. Once the nut has been tightened correctly with a torque wrench you can put a dot punch mark on the shaft and the nut to show how they align at the correct torque setting. In the future, at the trackside, it’s then simply a matter of tightening the nut with an impact gun until the two dots align.
Once the casings are together the next job is to assemble the clutch. When I raced in the 80s and 90s the clutch was always the weak link in the smallframe engine. Since that time, many clever solutions have been developed which can cope with quite outrageous power outputs.
For this engine, we chose the Crimaz CMX5 5-plate clutch. Unlike the lightweight and mainly aluminium Fabbri one we used before, the Crimaz clutch is all steel and relatively heavy. The advantage of this construction is a lack of flex, and less pollution of the gearbox oil than you get with aluminium plain plates.
Sadly, the Crimaz clutch and gear cluster we chose do not have the fancy triangular or square-drive fitting to the clutch of many rivals. The CMX5 uses the traditional conical fit with a Woodruff key. Christian explains that he gets no trouble from the old system if you assemble it using his method. His trick is to pre-heat the clutch centre before attempting to fit it. This makes the conical centre of the clutch expand so it goes on a little further than normal and when it cools it grips the gear cluster more tightly. Again, the proof is in the pudding. It worked for us.
Pre-heating the gear cluster to 120 degrees with a heat gun prior to fitting.
In order to hold the clutch centre still while the nut was torqued, I fashioned a tool from an original Vespa top clutch plate with a strip of thin steel bar welded to it. This bar rests against the output shaft to steady the clutch. You must use a Woodruff key with this method.
Unlike most modern systems the CMX5 uses two large springs similar to the original Vespa clutch, but one inside the other and wrapped in opposite directions. This required a longer bolt for my clutch compressor.
It took a couple of attempts to get the clutch working correctly. It was a simple issue in the end once I discovered the problem. If the circlip is not located correctly all the way around then the clutch centre bearing does not sit flat.
The final part of the transmission puzzle was the Crimaz version of the XL2 rack-and-pinion clutch cover. This cover massively reduces the stiffness of the clutch lever compared to the traditional bronze plunger types.
Words and Images: Sticky
Thanks to: Max Quattrini, Crimaz, Diablo Moto, Hornet Racing and Sam Round for help with this article.
NEXT TIME: We get the engine built, encounter fit issues with the exhaust and finally get it running for some dyno results.
