Clutch Basket Lighting

[alno]

Hello,
I was looking at Pear0' blunder (yes, I've made mistakes too) Is it worthwhile to lighten a Clutch basket and where do you remove material?
Al

[Moto Chuck]

Al,
I have not done any lightening on any of my bikes but from the comments I have seen it is one of the safest ways to improve performance without increasing stress on the engine.

There is this website called motoscrubs.com and they have blueprints on the secret formula for lightening Ducati singles parts.

Check this out! http://www.motoscrubs.com/Ducati_Engine ... eprint.gif

Guard the information with your life! This can not be allowed to fall into the wrong hands!

[LaceyDucati]

Personally I wouldn't bother doing the Swiss cheese bit, on a road bike you are unlikely to notice any difference. As for the timing gears I never bother even on my race engines, for me it is effort against any tangible worth.

As for the porting recommendations on this sheet, cutting the guides and bosses too short is a sure fire way to cause rapid guide wear, loose guides and subsequent replacement issues. Also a dip in the floor of the inlet port (as it appears in the drawing) and enlarging the exhaust port is from my experience a good way to bugger up flow! Only my experience and opinion

Regards Nigel

[Rocla]

Hello,

About lightening the clutch, I've asked the same question few months ago in this forum, because I was changing the clutch disks and nobody replied. I've asked the question because I was not certain to get a big difference. Of course lightening anything that rotates is beneficial for any engine and I lightened the crankshaft of my car and of some of my bikes, it is clearly very good for getting better acceleration and engine brake.
But lightening something that is rotating maybe 2 or 3 times less the engine is 2 or 3 times less efficient.

So, it could be fine if somebody that already lightened a mono Ducati clutch could testimony bout it real effect... Is the difference obvious once the clutch is lightened?

[ducwiz]

Hi,

here is an extract from a french manual. Lightening the clutch basket is described, as well as other measures. Sorry, but I can't translate the text, my french is rudimentary.

[StewartD]

Hi All,

That looks like a very comprehensive article, I remember a little French and have a very small French/English dictionary. Here's what I make of the clutch lightening part of it:

Clause 3 is about lightening (Allegement); (a) Clutch bell (or basket as we would say).

The text just says bore 16mm diameter holes in each 'creneau'. I assume creneau means finger or dog, and I think the english word crenellation derives from it. It then says continue the opening to the 'exterieur' along two lines ('deux traits') tangential to the hole to the 2mm point.

(Clause (b) is about the gearbox.)

It is a lot more effective to do this than just boring the holes as the volume of material removed is a lot more. As the forces the clutch plate dogs exert on the clutch dogs are tangential the dogs can be considered as cantilever beams taking a distributed load along their length. The bending moment that they experience is greatly decreased at the free ends. For this reason the 2mm left at the tip will be quite adequate. It is important to stick to the big radius at the bottom of the cutout. Cast iron is quite prone to stress concentration failure. Larger radius = less stress concentration.

I tend to agree with Nigel about lightening components, specially on a road bike. I doubt it will greatly reduce rotational inertia; skimming the flywheel would be a lot more effective as it is runs at 0.4 times the crank speed and is of smaller diameter. As Kinetic Energy of a flywheel equals:

1/2 (Moment of Inertia*) x (Rotational speed squared) then the effect of the clutch reduction of weight will be (0.4 squared =) 0.16 compared with taking weight from (at the same radius of) the flywheel.

Lightening the flywheel this way will have a negative effect on the engines idle speed. If you were building a race bike I would consider removing the alternator rotor instead of skimming the flywheels. This would reduce the machines overall mass by maybe, more than the mass of a battery and not greatly effect idle.

*Simplistically the moment of Inertia of a flywheel is basically the mass of the flywheel by the square of the radius. It can be roughly calculated by adding up the mass x radius squared of all the flywheel's annular rings. It needs integration to calculate accurately. The important thing to note is the 'radius squared' part of the equation. Mass at the outside diameter is far more of a contributor to inertia than the mass toward the centre.

On the side issue of the porting in the article, I agree with Nigel also. The article in Cycle World of December 1965 and February 1966 gives a very good description of the modifications for racing. The porting they do is very well described and contradicts this article and is consistent with what Nigel says.

Cheers,

Stewart D

[LaceyDucati]

Hi all

As an aside, on the subject of weight, Inertia and race bikes, a mistake most people seem to make is "light is always best". Just because a road bike weighs a certain amount doesn't mean to make a race bike you have to lighten everything! Consideration needs to be put into strength, stiffness and in some cases whether inertia may actually be a good thing.

Before you start lopping weight off your Ducati single crank for racing especially a narrowcase crank take a look at a Manx Norton or 7R crank. Yes, in a 250 the Widecase crank is a bit heavy but in the 350 and 450 I don't consider the crank to be heavy. In fact I always add a sizable external flywheel to the 450's and Narrowcase 350's for racing. To me the bikes seem much nicer to ride and I suspect it is kinder to crankcases and other components.

On a road bike, I have swapped between original primaries and light straight cut primaries and apart from noise I couldn't really tell any difference.

I have Dyno tested a 350 Narrowcase race bike with and without an external flywheel (solid race type) back to back and there was no perceivable acceleration difference. I also cruelly played a game with one rider by removing and replacing a flywheel throughout the season. Needless to say results didn't change and no comment was made, apart from how much better the bike started with the flywheel fitted, guess what....

Finally, these bikes are old and the parts are getting scarce and I personally am very reluctant to “bugger” any good original parts. Yes replace parts with new replica or performance parts if you wish, but please lets not continue with “in the day” modifications, which will ultimately limit the life and availability of good original components. If I do any serious head modifications these days I will always use a head that is already modified/butchered in some way. Lets have a bit of respect and Sympathy for our aging steeds.

Regards Nigel

[Rocla]

Hello guys,

I perfectly know the French procedure to lighten the clutch, it is an extract in "La revue technique". I have it, I've red it and it is very smart. It is the reason I wondered about doing such modification when I've planned to change my clutch disks.

In fact, the subject is very simple : it is always very efficient to lighten rotating parts but only if they rotate very quickly and if there are many variations of rotation speed.

The problem of lightening the clutch, is that the clutch doesn't rotate at the same speed as the crankshaft, it rotates 2 or 3 times less quickly (I don't remenber the ratio in number of teeths).

Lightening a flying wheel is very efficient for accelerations (and only for accelerations, never forget that it doesn't increase the power at all, and if you drive only on motorways with a steady speed, it is pointless to lighten, it is obvious) but it is not interesting to lighten something that is not rotating very fast. You can gain only if the difference between low and high speeds is very important and if the speed variations are numerous.