The spare parts supply for Puch Maxi is already very extensive. However, there are certain parts that are either not available or only exist in inadequate quality. What began with replacement clutch shoes for the Puch E50 Surflex is continuously being extended with new parts. Quality is of the utmost importance in this regard. Read More about our the evolution of A.S.P

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How does the E50 engine driveline work in general?

To understand how and why the ASP clutch and driveline internals help, we first need a basic lesson about how Puch clutches work, (please skip if you already know this)

Put simply, as the engine spins so does the clutch, this spinning motion causes either 2 or 3 clutch arms to fly out and grip against a metal ‘clutch bell’ which is connected to the rear wheel via the primary gears and the chain. Rev the engine…the arms fly out and away you go… Easy!

Now to add a little complication… Just like a car or a conventional motorcycle we want the clutch on our Puch maxi to take up gradually allowing us to ride away smoothly and under control.

Because the forces caused by something spinning are very strong Puch also needed to add some strong springs which act against the spinning force and allow these arms to come into engagement with the clutch bell in a slow, smooth manner.

This combination of the arms and springs allow the clutch to act smoothly and automatically. As the machine gets faster the increased centrifugal force pushes the clutch shoes increasingly hard against the bell until they stop slipping and the clutch grips fully, transmitting all the engine’s power to the rear wheel. Now we get our smooth controlled start and complete power transmission once we are speeding along.

All that complication for a clutch on a 45kph 2bhp moped! If you are reading this, you have either tuned yours or are about to tune it. What clutch are you going to need for 2… 4… even 5 times that power?

Luckily, we are here to help you to have a clutch that will slip progressively when needed and grip hard when the machine is at speed.

What are ASP "Aramid Sport Clutches" good for?

Why do I need an ASP modified clutch?

Simply put… Because eventually the standard one won’t do the job… but if you want a technical explanation, here we go.

At the standard Maxi top speed of 45 kph (28 mph) the engine and the clutch are spinning at around 6,500 rpm, it is all very happy and will last for many miles, the forces on the clutch are fine.

Our problem here is that the laws of Physics do not work in a linear fashion…  We begin tuning, just a little at first, an exhaust for instance and we get up to 50 KPH (31mph) now our motor is having to spin at over 7,000 rpm. Although we have only increased the rpm by around 10% the forces on the clutch have increased by over 20%.

As we tune further our engine revs more and more… It is great, we go faster! The issue is that we are now starting to increase the forces through the clutch to a point where things might bend or break.

As an example, one of our test Maxis revs to 12,000 although this is below twice the standard revs, it puts nearly 350% more force though the clutch than at 6,500 rpm, with a standard clutch this is more than enough to start bending and breaking things. But, by changing to the lighter ASP clutch shoes we go a long way towards preventing this.

How does this work?

If we go back to the Physics lesson, we realise that the force produced is a combination of Mass (weight), Velocity (revs per minute) and the radius of the clutch bell.

We can not do anything about the radius of the clutch bell (it needs to fit!) and we don’t want to reduce the revs we achieve, so we only have one factor we can control, the Mass…  Our clutch arms are lighter (they have less mass) so the forces acting are a little less.  Here Physics begins to work with us, small changes in the mass of the components makes quite big changes to the forces involved.

Why do I need ASP clutch shoes?

When compared to the standard shoes the ASP Aramid lined versions offer several advantages.

1.      The Large Aramid friction areas allows the clutch to slip smoothly up to the engagement point and then to grip efficiently when the engagement speed has been exceeded.

2.      The shoes are lighter, reducing the need for very stiff springs if later engagement is needed, this protects the clutch pillars, helping to prevent them from bending or pulling out of the backing plate. (This can happen when the heavy standard shoes fight against very stiff springs in the more conventional set up)

3.      These lighter shoes continue to reduce the bending forces put into the pivot pillars in high revolution applications, an ASP clutch brace should be specified when really very high revolutions are envisaged. (One of our test machines is often to over 12,000 rpm with such a brace)

4.      In very extreme revolution applications, the forces can be so great that the shoes can begin to spread the clutch bell, opening it up like a flower, While ASP’s lighter shoes and increased contact area will not entirely prevent this, they can delay its onset until even higher rpm.

5.      A lighter than standard clutch assembly helps the engine to accelerate and decelerate more freely, the engine uses its power to accelerate the machine not overcome the inertia from heavy assemblies.

In the clutch... What parts do we recommend?

1.      Standard machine or mildly modified machine (for example just a sports exhaust) Our standard Surflex ‘repaired’ clutch shoes with the extra Kevlar re-lining, these live longer and allow some scope for tuning with stronger springs for later engagement.

2.      More modified machine needing even later clutch engagement (for example 70cc with larger carburettor and exhaust pipe such as the mid-range power ‘circuit’ designs) … Our lightweight shoes with larger Aramid frictional area.

3.      Modified and very high rpm application (for example 70cc with larger carburettor and when using very high rev exhaust pipes such as Homoet 6p/8p, Simoni or similar) … Our lightweight shoes with larger Aramid frictional area. PLUS, our additional brace.

Why do I need a new gear-set?

Here we need to consider some of the considerable advantages offered by the ASP gear sets.

Extra strength.

Our Primary gear is laser welded into the clutch-bell for maximum strength and the clutch housing itself is lighter and stronger.

Remember, the original transmission for the Maxi was designed to cope with 2 bhp, and around 6,500 revolutions per minute at top speed. As soon as we start to modify the motor we need to consider that we can quite easily have up to five times the standard power and nearly double the RPM.

At 10 bhp and 12,000 rpm do you dare trust the standard components designed for 2bhp?

Lighter weight

Lighter Clutch bell, with reduced weight, more of the engine power is used to accelerate the machine rather than having to also accelerate the heavy standard clutch bell. 

Our secondary gear and shaft are around 10 percent lighter than the Puch one.

Reduced Drag.

Reduced oil-drag from all over machined surfaces when comparted to the rough cast areas on the standard set, oil drag equals lost power.

The Difference between helical and Straigth cut gears.

Your machined gear sets come in 2 versions, either straight cut or with a helical tooth form. Why is this and which one do I need?

ASP Straight cut gears…

Advantages

• The primary advantage of straight cut gears is that unlike helical gears they produce zero side thrust, preserving the thrust washer and the critical crankshaft circlip which can be forced out of place by very high horsepower applications.

• Straight cut gears while slightly nosier than their helical counterparts need slightly less power to drive them and produce less frictional heating.

• Reduced oil-drag from all over machined surfaces

Disadvantages.

• Noisier than the Helical set

ASP Helical Gears…

Advantages

• Because of the way they mesh helical gears are quieter,

• They can transmit as much power as their straight cut equivalent.

• While helical gears are cited as being less efficient than their straight cut counterparts, they are still over 90 percent efficient.

• Reduced oil-drag from all over machined surfaces.

Disadvantages

• Produce some side thrust, so not recommended for very high horsepower builds.

In the drive line, which gear-set do we recommend?

1.      Regular use, where extra strength and reliability is desirable, but lack of noise is of high importance... Our Lightweight helical gear set

2.      For Sprint/ race use, for very high power, where optimum strength is of greatest importance (and where there is any concern that side thrust might damage the thrust washer or dislodge the crankshaft circlip) … Our Lightweight straight cut gear set 

If you are in doubt… Buy the straight cut and ignore the extra noise!!

How to: Setting up a Puch maxi clutch 

The spring inside the Puch clutch acts against centrifugal force and delays the point that the clutch begins to engage. By changing these springs, we can choose the point at which the clutch engages. Simply put…  The stronger the spring the higher the RPM that the clutch engages.

Why is there also a screw? The screw gives us a range of adjustment with each different spring, the further the screw is turned in the later the clutch engages…

What happens if I turn the screw all the way in? If you go crazy on the screw it will reach the point where the coils contact each other… this locks the clutch solid… It will not work!  If the screw starts to get more than say 2mm below the surface, and you have not reached the revs you desire, it is time for the next stronger set of springs.

Why do I need later engagement?  Later engagement is desirable on tuned engines, which do not produce much power at very low RPM, indeed they may even be producing less power than the standard engine at say 2,000 rpm. If we allow the clutch to engage this low it will barely pull away, it might even stall the engine. If we make the clutch engage later rpm (when the engine is producing far more power) we will pull away smartly.

How high should my clutch engage?  This is a difficult question to answer so let us give two examples from our own test Maxis

Maxi 1 has a reasonably tuned engine, it has a 19mm carburettor Proma circuit exhaust and a 70cc barrel. This begins to produce its best power at 4,400 rpm, in this we have the ASP brace (Maybe not necessary, but as we make them why not!) our Kevlar lined shoes and the 50Nm set of springs, the screws are set make the clutch engage at 4,200 rpm, this machine steps away very well and then almost instantly accelerates very hard as the engine hits its powerband.

Maxi 2 is very highly tuned, with a 21mm carburettor, Polini Reed valve barrel and a Homoet 6p. exhaust, in this we have the ASP brace (definitely necessary, as this one revs to 12,000) our lightweight Aramid lined shoes and the 50nm set of springs, the screws are set make the clutch engage at 6,200 rpm, notice we still only use the 50Nm springs as the lighter clutch arms balance against this. Although we engage at 2,000 rpm before the power really gets going, this is deliberate because we had to think about how we are going to use the machine. We wanted a strong clutch set at the point to give us reasonable acceleration without having to ride through the town with a maxi that has to be screaming at over 8,000 rpm before it drives!

If Maxi 2 was used for sprinting where all that cared about was the maximum acceleration, we would be setting the clutch for engagement far higher, at the point where the engine really begins to hit the power, that would be 8,200/8,300 rpm, this would likely need the 100Nm set of springs.

Remember, unless you are racing, try and set the clutch engagement with how you want to ride. The higher the revs it engages at, the more annoying it can be in town and of course more wear involved.  Our big Aramid friction area does a lot to mitigate the wear, but they are not magical, they will like all things, eventually wear out.

 Is there an easy way to guess my clutch setting?

The short answer is no, not really

We would recommend that unless you want the clutch to engage where it was, that if you are mild tune you start experimenting with our 50 Nm springs and the screw flat with the arm on standard shoes (about 4000 rpm?)

For those high rev pipes… again start with 50Nm springs but with the lightweight arms (and don’t forget a brace!!)