Scooterotica

I generally use MB springs, and then either Surflex B standard or Surflex Green 'thin' plates, depending what clutch I'm building.

Thought i'd have a look at the Readspeed 5-plate 'supergrip' clutch kit, the red plates look good, 1.2mm steels are fine, and springs looked very similar to MB ones. So i did my usual test......i popped them into a vice so i could measure their length when fully compressed. On the outset the MB spring is 36mm and the RS is 35mm, so very little in it. They both compress to roughly 13.7mm, but when taken out of the vice.....only the MB one returns to its original length. The RS one is now 4.5mm shorter!

I don't have equipment to test the pressure needed to compress MB vs RS, but when done unscientifically by hand the RS feels like it needs more pressure, which whilst being heavier on the lever will result in less clutch slip. I carried on with this and pre-compressed a full set of RS springs in the vice, so they are all the same length now......i'll carry on with the clutch build and build one with MB springs and RS red plates, and the other with RS springs and RS plates......so 2 clutches, same plates, different springs.....and will see how they both feel and perform.

MB spring on the left @ 36mm, Readspeed pair of springs on right @ 35mm:

Untitled by Scooterotica Scooter Garage, on Flickr

Both in the vice uncompressed:

Untitled by Scooterotica Scooter Garage, on Flickr


Both in the vice, compressed to 13.7mm:

Untitled by Scooterotica Scooter Garage, on Flickr


MB back to 36mm on the left, compressed RS spring in middle @ 30.5mm, and uncompressed RS spring on right to compare (still @ 35mm):

Untitled by Scooterotica Scooter Garage, on Flickr


Just an observation at this point, its the grip of the clutch plates and the correct free play which concerns me mostly, followed by pressure and coil-bound length of spring. The lack of return to form on the RS is just an observation at this point, and may or may not be a problem, i'll soon find out.

My clutch was built with extra strong springs which was hard on the hand, I replaced them with the MB ones and its spot on...

Timbo wrote:My clutch was built with extra strong springs which was hard on the hand, I replaced them with the MB ones and its spot on...

Yes, i like them and use them on nearly everything....but on big BHP motors slippage is more of a concern.

Hi Dan,

Looks like you have reached the elastic limit of the spring if it does not return entirely to it's "Free length". This could be for a number of reasons, design limits or poor heat treatment. Whatever it is, if the spring does not return to it's free length I wouldn't use it as the pre-load you will be applying in the clutch will not be consistent. Have a read here, it is Hooke's Law http://en.wikipedia.org/wiki/Spring_(device)

It should be of interest that spring strength is dictated by material, number of coils and wire diameter. It is entirely possible that the RS spring reached it's elastic limit before it went "coil bound". However, any spring manufacturer "worth their salt" would 1. publish the Nmm rate 2. publish wire diameter, free length & number of coils 3. have some advice about elastic limits if the coil bound state was not reached first. So at the very least you should be able to get this information some how.

If you do want to work it out yourself it is actually quite easy. You need to put the spring in a guide (for example place it on a M10 x 75 socket head bolt) and clamp it in the vice vertically. Slid a piece of tube over the top of the bolt which is a suitable diameter to compress the spring. Fix a plate to the top that you can place a weight on. Measure the "free length" in this condition (say 34mm). The place a known weight on top (say 1.5 Kg for example). Measure the length again (say for example it has compressed to 31mm). The calculation for spring rate is 1.5Kg /(34-31) = 0.5kg p/mm. It then becomes easy to compare spring rates and calculate pre-loads etc. In fact I made a spread sheet to do this years ago and it works a treat.

Like everything with Lambretta engines, there is a balance to be struck with clutch springs, it is not just about the biggest fattest spring you can fit in there.

Time for bed...

Could be the pictures but the MB spring wire looks slightly thicker, also (again could be the picture) the MB appears to have 7 turns whereas the RS has 6.......or is it me ?

Rich_T wrote: In fact I made a spread sheet to do this years ago and it works a treat.

Would it be rude of me to ask for a peek?

Absolutely no problem, send me an Email Dan and I'll forward a copy to you and give some further explanation etc. If you want to edit the document or make it available to everyone feel free.

Funny that you are using these 2. I never did find (or bother to look for... oops!) the clutch spring chart that I compiled, with the help of a French pal, a few years ago. This chart identified coil-bound length being a real problem for many of the springs available if you try to use them with multi-plate clutches in deep crownwheels. The Readspeed and MB springs, along with some of the Cambridge springs were among the best for not going coilbound too early.

Having successfully used the Readspeed springs in a couple of clutches, I've recently been trying the MB ones and they do seem to be good and strong, don't suffer early coil-bound limitations and retain their spring.

My French pal has recently discovered that he can accurately test the spring pressure in his R&D division at work. He would be very interested in doing a like for like comparison with any springs that are available so this may or may not happen at some stage. I've just had no time to help him with this quest. I have asked him to email over the old chart if he finds it.

Regards,

Adam

In my home tune 245 I Have been using these which have worked well.

Although Ive just put Richard Taylors springs in my GT kit to try