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Bike Review - Posted 11th July 2016
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1982 Moto Morini 350K Sport Front Fork Improvements

The development of Martin Gelder's Moto Morini Three and a Half Sport project continues at the Morini Riders' Club Cadwell Park trackday. How should a classic motorcycle handle?

Are we nearly there yet? Yes, I think we are. Nearly.

A couple of years back Paul 'EVGuru' Compton and I fitted a 'cartridge emulator' kit to the forks of my 1982 Moto Morin 350K Sport. This conversion attempts to give older style damper-rod forks some of the suppleness and control of more modern cartridge forks, improving handling and roadholding.

Moto Morini 'Three and a Half' 350K Sport

The damping in a set of forks does two things; it controls the rate at which the forks can be compressed by the bike hitting a bump in the road or by the rider grabbing the brakes (known as compression damping), and then the rate at which they can rebound to their original length after either of these things has happened (rebound damping). Having the right amount of rebound damping gives the bike good handling and road holding; it controls the action of the fork springs, and without any rebound damping a bike will feel unstable. Compression damping is more subtle, and lets you feel what the front suspension is doing; it helps the suspension transfer feedback from the road and tyre to the handlebars. A bike without compression damping can still handle well, but a bit of compression damping will help the rider feel in control.

In the Morini's era, stiff suspension was considered better than soft and the dampers in the relatively crude Marzocchi forks are compromised, with their only adjustment being the weight of the oil used. Changing the oil affects both rebound and compression damping, meaning you can generally either get one or the other right, but not both. The cartridge emulator conversion aims to separate the two functions, with rebound damping controlled by the weight of the oil and compression damping controlled by an adjustable spring in the cartridge emulator.

1982 Moto Morini 350K

And I think we're nearly there. The first attempt, with re-manufactured damper rods, left us with too much of both kinds of damping, even on the thinnest oil available. Enlarging the rebound holes got the rebound damping into the right range of operation, although still very firm. It was with the forks in this state that I took part in a cold and wet classic trackday at Snetterton last autumn, and the bike surprised me with the amount of control and feedback it was giving on the brakes in the wet conditions.

For track use it was significantly improved over the standard set-up, but for road riding where bumps tend to be bigger and much more unpredictable, the compression damping on the forks was still too firm, giving a harsh ride. This is a classic case of having the right amount of 'slow speed' damping (slow referring to the rate of compression of the suspension rather than the speed the bike is travelling at) but too much 'high speed' damping, making the suspension feel too hard when hitting large bumps.

1982 Moto Morini 350K Using a flexible 'grabber', the compression damping valves can be fished out and adjusted

Backing off the preload on the springs that control compression damping helped significantly, but we're still using the thinnest fork-oil we can get, 2.5W. The next stage in the modification is to enlarge the rebound damping holes to allow the use of thicker oil, and experiment with softer springs for the compression damping adjusters. The aim is to get the damping as soft as possible while keeping the suspension under control, giving a set up that works well on the road as well as on track; we're nearly there.

All of this is fine on paper and when riding the bike in isolation, but what difference have we made in practice? Last week's Morini Riders' Club trackday was the perfect venue to compare my modified Morini with Paul's more standard model. The Morini club trackday is a very mellow and laid back event, with groups for intermediate, fast and Morini levels of performance and an eclectic mix of bikes on the track at any one time.

1982 Moto Morini 350K

I've ridden Paul's 350 on the road before but just rolling down to the assembly area before heading out on to the track the difference in front suspension feel was obvious, with the bike pitching forward and backwards in response to every twitch of throttle or touch of brake. On my modified 350 these movements are there but are much less noticeable, and the bike tends to move and then settle, whereas Paul's would continually be floating slightly. It was much less harsh on the wrists over bumps, but also much less controlled when trail braking into corners. We have different riding styles; Paul tends to do all his braking with the bike upright and then turn it into a corner, while I continue to brake slightly after I have turned in. The modified forks on my bike let me do this with much more confidence, while the softer and less controlled suspension on Paul's bike demanded a more classic style which loads the front suspension in separate stages rather than one single progressive operation; brake, then turn, as two distinct actions rather than merging smoothly from one to another.

1982 Moto Morini 350K A lot of this went on
Bouncy Morinis on Now...

It's not really relevant to this write-up, but the motor in Paul's bike was a revelation, bursting into life in the upper 1,500rpm of the motor's range and coming onto the cam in a way mine never manages. This extra top-end performance, of course, puts more load onto the brakes at the end of the straight, making me even more aware of the suspension differences between the two bikes.

Swapping back to my own bike after two laps on Paul's simply heightened the amount of control and feel from the modified forks; I could brake later and harder and the front wheel felt more... secure, while cornering. Sadly, swapping between bikes also meant that I now missed the cammy-ness of Paul's motor.

1982 Moto Morini 350K Bike with modified forks on the left, bike with standard forks on the right. The 350K already has shorter forks than earlier 350s, but the feel of the two sets is now completely different.

We need to look at setting the damping so that it works with thicker oil, to give a better range of adjustment and there's still some 'stiction' in the action of the forks which is giving a harsh ride on the road, but both in theory and in practice, we really are nearly there.

Words and Photos: Martin Gelder


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