Clutch Spring Weight Chart ?

[TrackTen]

Is there such a thing anywhere on the web that compares all the spring weights etc of clutch springs from various sources so they can be easily compared ?

[dickie]

Is there such a thing anywhere on the web that compares all the spring weights etc of clutch springs from various sources so they can be easily compared ?

Not that I know of but if you wait until the weekend I plan to measure the free length and constant (force per unit compression) of the 4 popular ones I have in my garage:

Malossi, gt, bgm, sx200 and some old li150 and li125 ones. The li springs are probably not valid results as they are very old (possible older)

And I know that isn't 4 but I don't care.

[TrackTen]

Cheers Dickie -

Looking forward tomyour results

[nsaints]

I think what you're asking for is the effort required to pull the clutch lever for different clutch springs
If I'm understanding correctly I did some basic tests using a scale that measure suitcase weight. I did ensure each test was identical as
best as I could, by assembling the engine and testing the effort required to pull the clutch lever the same distance

SX150 standard - 11lbs (these are the springs that were in my unmolested SX150 when bought)
MB springs (New) - 16 lbs
MB springs (3000 miles) - 14 lbs
Scootopia springs (new) - 13 lbs
Cambridge Lambretta (ultimate, soft feel) (new) - 18lbs
GT (from Rich Taylor) (new) - 21lbs

I'm not sure in reality what the above tells me in terms of the lightest springs my GT186 would work with.
Thats what I was trying to determine.

What I'm currently using are the scootopia springs, without any slip successfully
EDIT: That said I'm probably getting away with a lighter clutch spring as I'm using a cyclone g/box with a 19t front sprocket. With my limited knowledge in such things, I understand the larger the front sprocket the lighter the load on the clutch, and therefore you can get away with a softer clutch spring

[MickYork]

I've several sets of springs and it's hard to determine which are strong and which are soft.

I think we need to know what the compressed height is of the springs and will this vary from one clutch system to another ?

We can then measure the weight required to get the springs to this level.......the more weight the stronger the spring.

So.....does anyone know the compressed height of a Lambretta clutch spring or a simple method of checking the springs

[Scooterdude]

SX150 standard - 11lbs (these are the springs that were in my unmolested SX150 when bought)
MB springs (New) - 16 lbs
MB springs (3000 miles) - 14 lbs
Scootopia springs (new) - 13 lbs
Cambridge Lambretta (ultimate, soft feel) (new) - 18lbs
GT (from Rich Taylor) (new) - 21lbs

No wonder I keep breaking clutch cables then with my YZ 80 clutch springs as they are rated at 45lbs (each) !

[nsaints]

No wonder I keep breaking clutch cables then with my YZ 80 clutch springs as they are rated at 45lbs (each) !

I can't imagine the effort required to pull the clutch lever for those
do you need to slip a scaffold pole onto the lever to give you enough leverage?

[dickie]

Remember that there are 2 levers between your hand and the spring: on the 'bars; the arm on top of the side case.

Scooterdude was talking about required force at the lever not directly applied to the spring.

Saints; how/where did you measure? There is a consistency problem here. If someone replicates your method they need to apply the force at exactly the same point on the lever.

[nsaints]

Dickie Wrote:
Saints; how/where did you measure? There is a consistency problem here. If someone replicates your method they need to apply the force at exactly the same point on the lever.

Nothing more than marking the lever with a piece of electrical tape 2/3 of the way along and then applying the force at this point pulling the lever back so the lever just touches the grip
the clutch lever was also standard SX without a ball end

The idea of the tape was for a consistent 'lever' length between springs

I used one of these to measure the weight if your unclear what I'm talking about - why did I use this? I had one in the draw upstairs
Mine was an analogue scale. However you get the idea

[dickie]

A hugely important factor here is free length. Springs have 2 main properties: free length and N/mm. It's very easy to think that N/mm (often quoted in pounds) is the only thing of consequence.

Imagine you have 2 springs, a 10lb/inch and a 20lb/inch. The free length of the 10lb/inch is 3inches and the 20lb/inch is 2.5inches.

When installed, they are compressed to 2inches. Therefore they are both preloaded to 10lb. If operating the lever to disengage the clutch compresses each by a further inch then the 20lb spring requires 30lb and the 10lb spring requires 20lb.

You can see that the 10lb spring stops clutch slip just as well but only needs 2/3 of the force at the lever to disengage.

These are completely made up numbers but they demonstrate the principle.

What I'm blathering on about is that you need to consider the entire system.

[Scooterdude]

Scooterdude was talking about required force at the lever not directly applied to the spring.

.

Just to clear this one up. I had the springs from Harry Barlow who tested each spring in a thing that looked similar to a drill press but with a gauge on top, they each displayed a pressure of 45 lbs.

[dickie]

Scooterdude was talking about required force at the lever not directly applied to the spring.

.

Just to clear this one up. I had the springs from Harry Barlow who tested each spring in a thing that looked similar to a drill press but with a gauge on top, they each displayed a pressure of 45 lbs.

Sorry. I swapped you and msaints names around.

[TrackTen]

Hi nsaints

Thanks for taking the time to do those tests , very interesting results.

Also interesting to note how much softer the MB springs became after such a shirt amount of time ?

[dickie]

I was also advised to change my rich Taylor springs to bgm ones due to some slip at peak power. It'll be interesting to see how they compare when I measure then at the weekend.

In case it's not obvious why I'm saying this, msaints results show bgm springs to be considerably softer at the bars.

[nsaints]

The thing is though, there's so many variable's at play doing the test I did one Sunday afternoon, and then conduct your own tests on different springs and draw any solid conclusions
EG - Taffspeed springs are stronger GT springs

There's also variable's within the test I did
the MB springs may have been different batch numbers - different steel used for example
so it's entirely possible there's other contributing factors rather than so many miles of uses = a 2lb reduction in spring force

careful drawing too many conclusions here!

[dickie]

Ok. I've done my testing and as nsaints points out, you need to be careful about drawing conclusions too quickly here. However the following are facts not opinions.

The list below is free length/spring constant in N per mm/preload (force applied to clutch per spring on MY clutch)

Malossi 31.2mm / 21.3N per mm / 249N
MRB 37.0mm / 14.0N per mm / 248N
rich Taylor Gt 33.7mm / 6.5N per mm / 92N
SX 32.5mm / 6.5N per mm / 86N.

The Gt springs slipped on my 5 plate clutch but only slightly.

The Malossi springs were so stiff that it was unusable

The MRB springs have a nice feel but I haven't ridden it yet.

At first glance I was shocked at how similar the preload numbers were for the Malossi and the MRB springs. I think that the massive difference was either due to the Malossi spring becoming coil bound (it has thicker wire) and acting like a progressive spring. Or I'd installed them badly so that one or more wasn't sitting straight; this would increase preload.

[TrackTen]

Thanks for that Dickie

Interestingly after thinking about your findings I wonder if what we actually describe as a 'stiff' clutch is possibly the feel that the preload gives - ie the feeling of the pull required to get the clutch handlebar lever actually moving initially

[dickie]

Thanks for that Dickie

Interestingly after thinking about your findings I wonder if what we actually describe as a 'stiff' clutch is possibly the feel that the preload gives - ie the feeling of the pull required to get the clutch handlebar lever actually moving initially

You're right, it is. Plus the additional force required to move it back to the grip. Which is the spring constant multiplied by whatever plate clearance you need. I've assumed 1.5mm clearance.