clutch springs

[sydduckett]

Have used MB comp springs in a JB 5 plate and startred to slip on sunday. The gap seems fine but i think i need a stronger/longer spring. The clutch is light prob to light so i dont mind it being a bit harder but dont really want to go down the centre spring route again as that was too OTT. Also tried some andy Francis ones but they were even worse.

ta
sef

[WINTERMODEL150]

Have used MB comp springs in a JB 5 plate and startred to slip on sunday. The gap seems fine but i think i need a stronger/longer spring. The clutch is light prob to light so i dont mind it being a bit harder but dont really want to go down the centre spring route again as that was too OTT. Also tried some andy Francis ones but they were even worse.

ta
sef

Hi,been running MB springs with a centre spring MB dogleg lever and a nylon cable for years with no problems,just recently changed to an AF 6 plate clutch as iv'e gained some more horse power so fingers crossed.

Dean

[Rich_T]

Try some springs from Gran Sport, I've used this type for years. It is very important with Lambretta clutches to have matched springs with ground faces, otherwise they don't run true and that's where you get most of the clutch drag problems from. It ensures all the spring rates are identical and the ground face makes them seat properly.

The other thing to mention about clutch springs is calculating their pre-load. This is done by multiplying thier spring rate (typically neuton/mm) by the amound the spring is compressed from its free length. That number is then multiplied by 5 (the nummber of springs in the assembly).

Typically, the compressed spring length for a stock Lambretta clutch is about 16.25mm. So if the spring you plan to use has a rate of 20N/mm and a free length of 25mm then each spring would have a pre-load of 175 neutons x 5 = 875 neutons.

The next step is to work out if the spring is "coil bound". This is done be multiplying the wire diametre by the number of coils in the spring. The resulting number should be less than 16.25. For example a spring with 7.5 coils and a wire diametre of 2.2mm would be "coil bound" (16.5mm, 0.25mm over size) BUT, if it were 2mm diametre it would be usable (15mm).

That is key is "pre-load" value as this is what holds the clutch when the power is on. What you DO NOT want is a very heavy clutch to dis-engage so this means that you want the lowest spring rate once you have achieved the desired pre-load. Provided the spring is not coil bound or reached it's elastic limit, the spring rate (on a standard spring) is constant and bearing in mind that a stock clutch will require a further 2.5 - 3mm to release fully then you'll realise that if you have selected a set of springs with a combined rate of 600N/mm then your clutch will be no fun to use at all and not help the gearbox endplate bearing (which is the only thing keeping the layshaft in position).

I've use the Gran Sport springs on stock 4 plate engines up to 22-23BHP with no problem at all, even with standard levers.

Hope that makes sense

[Bofs]

Rich, are they the ones listed as "GT Preformance Springs"? Can`t see any others listed.

[Andy Pickering]

I have just fitted mb extra strong springs and they are spot on and sorted my clutch right out, I have also got the yam lever (corrado) and have just fitted a brand new nylon cable as the one in was 4 odd years old and seen about 4k so changed it and clutch is firm but very nice

[DaveTomo]

running a lth 5 plate clutch,starting to slip when it got hot (correct gap in plates,rear & front sprocket aligned and all OK) put a set of these in http://www.afrayspeed.co.uk/index.php?p ... buteID=CLU last week,all good not to stiff.To be honest the amount I've spent on clutches these last few years (crownwheels,plates,spiders,clutch bell) I could have bought a rocho clutch 3 times when I add it all up,so when this gives up the ghost,thats the one for me.

[Rich_T]

Rich, are they the ones listed as "GT Preformance Springs"? Can`t see any others listed.

That is them.

Oops, made a mistake earlier the compressed length of a standard Lambretta clutch spring is 20mm (approx) not 16.25

Coil bound length = wire thickness x wire diametre. This number must be less than the compressed length 20mm minus the release movement (3mm stock) = 17mm.

I made a little spread sheet to work out these loads a couple of years back, if you want a copy PM me.

[sydduckett]

Rich, are they the ones listed as "GT Preformance Springs"? Can`t see any others listed.

That is them.

Oops, made a mistake earlier the compressed length of a standard Lambretta clutch spring is 20mm (approx) not 16.25

Coil bound length = wire thickness x wire diametre. This number must be less than the compressed length 20mm minus the release movement (3mm stock) = 17mm.

I made a little spread sheet to work out these loads a couple of years back, if you want a copy PM me.

Rich, thanks for the info mate. Think I will get both the AF and Gransport ones and try both. I have also spent way to much on clutches and when funds permit will be going for the rocho one.

[tha83]

I have an AF 5 plate clutch pack with their uprated springs in my Rapido 220 with SX 200 gears. They slipped all over the place. I changed back to my Barnett/Yamaha springs and all was good. I live in San FRancisco though and need the extra grip. The springs arent' for the limp wristed though. I've seen hopped up TS1's with 4 plate clutches stand up to abuse with the Barnetts. I believe they are the YZ 125 springs.

[Rich_T]

Coil bound length = wire thickness x wire diametre. .

Doh! done it again... it is wire thickness x number of coils...

My opnion is that you shouldn't need to have a stonking big clutch lever. If the pre-load is too much for the original lever then it is probable too much for the end plate bearing in the long run, and certainly too much for the pressure plate..

If you have to use all that strength to pull the clutch in then all that load is applied directly to that little bearing in the end plate and if that bearing cage breaks up that will make a bit of a mess in the gearbox. additionally, the stock release plate is pressed steel and the springs mounted outboard of the main material, this is a very weak design & construction.

If the springs are too strong they distort the pressing which prevents the clutch disengaging properly. The springs then do not seat properly and the clutch does not run concentric, this will all lead to clutch drag. Next time you're at a parts fair going through a box of pressure plates pick a few up and look closely, bet you'll find some with the spring seats bent upwards.