Single or dual disc clutch replacement, that's the question

[Larry H]

Hi All,

I am renovating my LeMans Mk1 and have found, among other things, that the whole clutch needs replacing including the flywheel as both the intermediate and pressure discs have worn steps in the flywheel splines.
I have had to replace the friction discs and gearbox hub before due to spline wear (the old shallow spline) but then the flywheel spline wear was not deep enough to worry about. Funnily enough the friction pads are not worn much, only the splines.
So I am tossing up between getting the standard flywheel, discs and hub (but with the newer deeper splines) OR a single disc clutch (such as RAM).
I understand the single disc clutch is designed more like a traditional car clutch with a circular blade spring and no flywheel splines. It also has less inertia than the standard flywheel/clutch.

It would be good to get advice on:

1. if someone has had problems with the single disc clutch on a LM 1 or 2?

2. a flywheel/clutch with less inertia obviously accelerates and decelerates quicker but are there also some not so good effects? Like uneven idling?

3. the newer standard dual deep spline discs and hub, do they actually work better and wear less than the old?

Thanks for any info.

 

[john zibell]

I'm not a fan of the single disc clutch. I've seen issues with them. The modern deep spline 2 clutch plate will go over 100K miles without issue. And yes, the lighter flywheel will improve acceleration. Just don't go too light. I had a lightened flywheel on a CA II at just under 7 pounds and it worked fine and no issue with idle. The newer flywheel will bolt right up and is lighter than the one used on the MK 1. I'm not sure of the weigth of a the newer flywheel but it should work fine for you. I think one for the 2000 year EV would be fine.

 

[Larry H]

Thanks for your reply John,

What issues have you seen with the single disc clutch? And were they on a clutch from RAM ?

 

[Moto-Uno]

I installed one of the first RAM clutches (from MG cycle) years ago . Before I made it to work, 15 kilometers away I'd
adjusted the cable 2 times to remove excess play . On the way back home I had to readjust the screw on the end of the
push rod to get free play . After doing this for a few days I looked into the clutch housing and it was full of debris . Contacted
MG cycle and they sent me another plate . Same shit , took the piece of crap out . 2 years later I had a truck shop make
new friction material and they glued and riveted it to the original plate and bingo , all is well with it . The new unit with
the 3rd or 4th update appears to be a metallic friction material (maybe better, I'll never know ) . Peter

 

[GTM®]

See above. The RAM clutch is essentially a racing clutch, and is not designed for a long service life IMO.
I'm sure they've resolved the construction/assembly issue, else they'd have quit making it long ago.
As John says, get the '00-01 Cal 11 and/or the Griso/Breva 1100 assy (the lightest OEM flywheel to date)... Though to note; The heavier one makes for strong/steady pull at speed, which many prefer, unless you are rebuilding it purely for secondary road fun times.

 

[john zibell]

Thanks for your reply John,

What issues have you seen with the single disc clutch? And were they on a clutch from RAM ?

Not only the RAM as stated by Moto-Uno but even the factory single plate units left much to be desired on some of the Spine and Tonti bikes that had them. I can't remember the exact years, but I have converted a few factory single clutch plate to two plate units. Takes a few parts but can be done on 5 speed bikes that used the hub gear.

 

[Larry H]

Thanks Guys,

I will take all of your advice in consideration when deciding. I will wait a little with ordering parts as I first have to open up a few other units to check the condition.

 

[john zibell]

Thanks Guys,

I will take all of your advice in consideration when deciding. I will wait a little with ordering parts as I first have to open up a few other units to check the condition.

That is wise to check everything. I replace every wear component I can when the bike is split. Do check the input and output bearings. They should be steel cage. If plastic cage, replace with 3205 steel cage bearings. The factory went to plastic cage at some point (I don't know the year) to make it quieter, but the plastic cages have been know to fail.

 

[Larry H]

Do you mean the in/output bearings in the gearbox? I have never taken the gearbox apart before but I will do that now as changing the gears could be smoother. Guess the pins or grooves in the drum are worn.
It would surprise me if the bearings have plastic cages, the bike was manufactured in 1976 after all, but we shall see.

 

[john zibell]

Yes in the gearbox. Place the gearbox in neutral. Remove the oil fill plug. You will see a shift collar through the hole. It should be centered. If not, shim the drum so it will be centered. If you aren't familiar with this procedure it may be best to take the gearbox to someone who is. This is also a good time to replace the shift return spring while the gearbox is apart. Once you remove the hub gear and seal you may be able to tell if you have a steel cage bearing.

 

[Larry H]

Ok, will do.

 

[john zibell]

Do you have the special tools for the flywheel, clutch alignment, hub rear, and gearbox output nut? When you remove the output nut and speedometer drive ring be careful not to lose the little steel ball.

 

[Larry H]

I've got all those special tools except for the gearbox output nut. My 27mm socket is too short plus it would provide no access to holding the shaft fixed. Will try to find 27mm boxspanner in a toolshop. If no luck I can probably modify an existing 29mm boxspanner to suit.
By the way, it should be possible to hold the shaft from the input end with a gear engaged, should it not?

 

[john zibell]

I've got all those special tools except for the gearbox output nut. My 27mm socket is too short plus it would provide no access to holding the shaft fixed. Will try to find 27mm boxspanner in a toolshop. If no luck I can probably modify an existing 29mm boxspanner to suit.
By the way, it should be possible to hold the shaft from the input end with a gear engaged, should it not?

I use a deep socket and air impact wrench to remove. I do use the factory tools to install. One tool holds the shaft and the other tightens the nut. Those two tools are not expensive and you should be able to order from a dealer. If you do put the gearbos in gear to hold the shaft, don't get too carried away tightening the nut. Just snug it up and indent the collar into the spline of the output shaft.

 

[Larry H]

Yes in the gearbox. Place the gearbox in neutral. Remove the oil fill plug. You will see a shift collar through the hole. It should be centered. If not, shim the drum so it will be centered. If you aren't familiar with this procedure it may be best to take the gearbox to someone who is. This is also a good time to replace the shift return spring while the gearbox is apart. Once you remove the hub gear and seal you may be able to tell if you have a steel cage bearing.

I can report that the input and output bearings have steel cages. All the gears, sliding shift collars, dogs, splines and bearings are good, no excessive wear. The exception is the needle roller bearing at the rear end of the input shaft (in the end casing), all the needle rollers fell out of the cage and they are pitted. The outer race seems ok. The inner race also but I don't know if it is meant to sit hard up against the hex spacer or not. In any case there is a couple of mm gap to the spacer. So I will replace the bearing.
The selector drum has 0.6mm axial play and the shift collar (near the oil filler hole) is not centered between the pinions (in neutral). If one pushes the collar fwd it is almost centered, but push it the other direction then the pinion dogs and collar dogs are almost touching (0.2-0.3mm clearance). I do not think this is due to wear, it must have been set up like this at the factory. I will re-shim the drum to centralise and remove most of the axial play.