need generic clutch springs

[lingeringstin...]

I need some clutch springs but I don't want to use the factory shite, which is terrible and is the reason why I'm looking for better springs.

EBC apparently don't do springs for my bike although in my experience there's bound to be springs for another bike that are exactly what I'm looking for. The problem is, in this disposeable, non-engeering bolt-on internet China shite world I can't just find the measurements of clutch springs. I can find all kinds of clutch springs for all kinds of bikes by make and model, but that's useless unless I can acertain which bike uses the same size springs as my clutch and that information just isn't found.

I'd like to be able to go into a clutch springs warehouse and choose some clutch springs off the shelf that are THIS long, by THIS big around, and about THIS strong. Anybody know where I might find such a thing?






For anybody interested here's the dull details of my conundrum:

It's an MZ 250 clutch.

The factory springs (still readily available) are too weak. I've tried "stronger" MZ springs and they're shite too.

If I put washers under the springs to increase pressure and bolt the clutch together then the springs are already somewhat preloaded so the five plate clutch doesn't separate the plates enough when engaged and you get a grabby, creeping clutch and miserable clunky, grumpy gearchanges.

To get round this I leave one of the clutch plates out and that fixes the problem because it allows the existing four plates to separate better.

This generally works OK but obviously with only four plates you loose like 20% potential friction as opposed to the five plate build. Under normal road use this isn't a problem. The stiffer springs work fine with only four plates if I'm not being a lunatic.

But I've found that if for instance I'm pulling a trailer loaded with camping gear up the side of a steep Scottish mountain on a dirt track in a blizzard in the dead of night being chased by dinosaurs then there are times the four plate clutch would really benefit from being a five plate clutch. So I need stronger springs but I don't know what those would be or where to get them.

The clutch and it's actuating device is designed in a manner whereby it is impossible to modify it to take all five plates with standard springs preloaded by washers, so the obvious answer is to replace the standard springs in a five plate clutch with stiffer ones that would compress by the same amount of travel as standard springs, which I am sure are readily available if I only knew which bike to get them for. But I can't find any information about the actual dimentions of clutch springs for other makes of bike. Some kind of clutch spring chart would be helpful but I can't find anything of the sort.

[stinkwheel]

They invariably fit round an M6 bolt so I bet there isn't a huge amount of variation in diameter.

So you're looking for length which you can possibly work out from a picture. Or potentially even cut/grind down over long ones?

Most motorcycle owners manuals will have a clutch spring free length and the minimum tolerance in the specifications if you can be bothered ploughing through the haynes manuals at your local library or downloading some workshop manuals off the net.

On the Enfield, they have two sorts of spring. Weaker and stronger ones alternating round the clutch basket. I think this causes a slight uneveness in the pressure on the plates which improves bite. If it starts slipping, sometimes swapping the springs round is enough.

Anyway. What size do you want? I bet folks have old clutch springs off various bikes lying around they could measure for you.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[lingeringstin...]

I just had a quick measure of an old clutch spring.

They sit in little cups at either end when installed so the ID doesn't really matter that much but the OD is near as dammit 18mm.

7 active coils.

The one I measured, which may be a bit wore out, is 31mm in length.

I compressed one completely in the vice and got it down to 14mm.

The wire it's made from doesn't look all that sturdy, certainly not like a valve spring. The wire diameter measures just a gnat's ass under 2mm wide.

They just look like fairly standard design clutch springs so I doubt it would be difficult to find something a bit stronger that would work.

As there are six of them it leaves scope for mixing them should I come across something the right size but too strong to use all six.

[Howling TerrorOutOfOffice]

You can use 4 springs on a 6 spring clutch if the springs are too strong.
Correct torque is recommended as they're surprisingly easy to strip.
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The Harry Turner Project

[Snod Blatter]

To give you a bit more scope I once bought some EBC "Heavy Duty" clutch springs for the CB250 that were less stiff than the originals but they were a lot longer, so the preload on them made them stiffer. So it's not all about the length.. Nudge nudge wink wink know what I mean?

I quickly took them out again because they didn't seem to make the plates grip as much as the worn out stock items, but I don't remember them making the clutch drag. I can measure them for you if you want but I'm quite sure they're longer than 31mm, probably closer to 50mm.
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[Pete.]

Spring characteristics is primarily decided by diameter, coil turns and wire thickness. Thicker wire obviously means harder spring.

More turns = softer spring, less turns = harder spring. This is why fork springs are coiled tighter one end, this is the 'soft' section that absorbs normal road travel, the rest of it moves very little until you put a lot of force on it.

A larger diameter spring of given turns and wire thickness is softer than a smaller diameter spring of the same turns and wire thickness.

So, you have a fixed diameter of 18mm, a (more or less) fixed free-length because you're going coil-bound when you add a pre-load spacer, you need a spring of the same free-length but less turns or thicker wire. The problem with less turns is that your spring's working life can be reduced, and a problem with thicker wire is it might bind on the ID and more prone to coil-binding too.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Pete.]

Right, I've found some old Hayabusa inner valve springs. The free length is 5mm too long but with 3 tight coils at one end you could cut off 2 coils to hit your 31mm dead on.

How do these stack up against your OEM springs for wire thickness? I expect they are much stiffer.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

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Why don't you ask the MZ racing club? They won't be using standard springs on their race bikes.

Tuned MZ race motors are far from standard and can be quite expensive.
They race with BMCRC but have a forum.

https://bmzrc.net/

Tuning info...couldn't see clutch springs on a quick glance.

https://bmzrc.net/wp-content/uploads/2014/05/MZ-Tuning-Release-2.pdf
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Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

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