Lambretta steering bearings are only one step up in dimensions and design from pedal cycle parts. The caged upper and lower bearings have a minimal number of surfaces to cope with quite high loads; particularly once you start fitting 30hp engines and disc brakes.
What goes wrong?
The main problems are under-tightening and over-tightening. If you tighten too much then the steering feels stiff and notchy. If you under-tighten the fork starts to rattle in the frame and this hammers the top ball bearings which puts dents in the bearing races and again you get notchiness.
When it comes to steering tightness, there really is a ‘Goldilocks’ setting which is just right, but with less porridge and fewer bears.
So how do I improve the steering bearings?
The old-school method recommended by Dave Webster was to remove the caged bearings and replace them with a full compliment of loose balls held in place by grease during fitting. That improved steering feel but is not easy to assemble.
Several other scooter engineers have had cracks at taper roller conversions – like those used on motorcycles – which share the load over a much greater area, increasing smoothness and reducing wear. Ian Frankland (RIP) was selling just such a conversion before his passing.
Now SIP have teamed together with V2 Edelstahldesigne (V2 Stainless Design) to offer a complete steering bearing solution for Lambretta that is like the one that V2 have already released for Vespa models.
What does what?
At the base of the fork stem is a taper roller bearing with a matching housing that fits into the frame tube.
The usual problem with this solution is that the taper roller is much larger than the ball it replaces in terms of height. So it is also with the V2 conversion but by using a small diameter taper roller, they’ve managed to keep this change to a minimum. With this conversion the fork only sits 2.5mm lower in the frame tube. This will ever so slightly change the angle that the chassis sits at but most people probably won’t be able to tell the difference.
At the top of the forks, SIP did try another taper roller solution but tester Jesco didn’t like it. Instead they’ve gone for a sealed ball bearing solution to keep out the dirt. Instead of centring on the special grooved fork nut that usually forms the top race of the bearing, this system does away with that completely. Instead, the inside of the bearing is conical, and there’s a corresponding conical split ring that is fastened by the top locknut. As the nut is tightened it both compresses to grip the fork tube and centres inside the sealed bearing. This assembly actually saves 1.5mm of height compared to the original so the top fork nut should be in roughly the same space. A special tabbed washer is supplied to bend over and secure the top locking nut after correct tightening.
The only issue that I can see arising from this set-up is that of fork/headset alignment. Obviously, if the fork drops 2.5mm through the headstock then the headset would normally be 2.5mm closer to the legshields and you may get paint rub.
Thankfully, the slot in the fork that the headset clamp bolt goes through normally has enough slack that you should be able to reposition the headset to ensure sufficient paint clearance. At worst you might have to file the slot in the fork top a little wider.
The advantage should be improved steering response and stability. The people who stand to benefit most are those with high-power or very fast Lambrettas, racers and anyone building a chopper.
For the rest of us, the benefits are likely to be less apparent but the price of the conversion is not unreasonable at £82 for both upper and lower sets which makes it a viable option to the often poor quality standard of replacements available.
SIP are sending us a set to try so we’ll let you know how they perform.