A Clutch Story

[billyt]

After many years of riding trials it finally happened to me, the dreaded “clutch drag”.

I guess it was inevitable, I had read about, heard people talk about, but never actually experienced it for myself. Can it be real or just a myth? I had read with much respect and interest Dan William’s research and solutions to his clutch dragging issues and read all the testaments to this being the miracle cure.

Being faced with the issue for myself I soon came to realize after all the years of riding trials bikes I have never had a need to really dig in and understand what is actually going on with a trials clutch.

But if I want to cure this dragging clutch on my new 2013 Beta 300cc Factory then I better educate myself on the clutch workings.

Standing upon Dan’s shoulders of the great work he has done it was a good starting point for me.

So you take out the plates and clean up all the glue crap between the fibre steps!

Okay, no doubt this works, but why? Surely there must be more to it than that?

Some people although in the minority have claimed this did not work for them,

Some people use ATF some use purpose made clutch/engine oil all with various results, but why?

So let the research begin.

Lets break clutch drag into three basic culprits:

1. Mechanical
   
2. Viscous Coupling
   
3. Physics
   

1. Mechanical:
   

The following fall into this category

Warped friction plates

Warped clutch plates

Swollen fibre plates

Notches in the outer clutch basket

Notches in the inner clutch basket

Nicks on the metal tabs of the friction or fibre plates

Not enough travel on the clutch push rods

A race clutch that has tight tolerances resulting in less clearance between plates when disengaged.

The clutch not separating evenly due to machining imperfections

1. Viscous Coupling
   

For those of you not familiar with Viscous coupling it is basically a fluids ability to transfer motion between two plates a slight distance apart through the fluid itself. It is used on various 4WD systems and machinery.

1. Physics
   

The viscosity of the engine oil used

The temperature at start up affecting engine clutch oil viscosity

The temperature of the engine clutch oil once the bike is warmed up.

Centrifugal force

Shear of the oil surface between two plates. Vacuum. Surface tension

Excess glue and residue in between the tabs causing the above

So lets clarify some of these things from a technical perspective.

1. Shear of the oil surface between two plates, Vacuum, Surface Tension
   

If one takes two sheets of glass and places some oil in-between them and the presses them together the next person who comes along trying to separate them by pulling them apart in lateral (equal and opposite) manner will not be able to do so. They will have to slide them apart one surface going up the other down.

This is due to the oils surface tension and the air that was forced out upon squeezing them together has now created a vacuum. Multiple that by several clutches friction plates to fibre plates and one can quite easily see how the potential for a friction plate to stay stuck to a fibre plate is there. What is needed is a surfactant. A surfactant is basically what soap is, it breaks the surface tension on our hands, dishes to let the water actually get to the surface etc in essence making the water wetter by breaking down the surface tension.

But who in their right mind would put soap in their transmission or clutch LOL

2.0 Centrifugal force

Have you ever seen or tried the gyroscopic trick where you sit on a free moving rotating chair, you are given a bicycle wheel to hold at the axle. You hold the wheel upright an assistant spins the wheel and you try to turn it side ways. It tries to fight you and wants to stay upright spinning in its own orbit both axle and radial.

Well a spinning clutch is basically a gyroscope. It is spinning and wants to stay in its own radial orbit. You pull the clutch in, wanting it to separate in the axle direction by basically friction plate’s fibre plates moving away from each other. But the gyroscope effects are fighting it wanting the plates to stay in their own orbit.

Couple that with the above sheer friction of the oil and it is a wonder that plates actually separate at all.

So if your clutch drag issue is caused by surface tension, sheer of the oil, vacuum then Dan’s procedure or ATF is the way to go.

I propose that Dan’s procedure works by reducing the sheer of the oil surface tension, and helping break the vacuum. This is achieved by the filing of a ninety-degree angle when you are filing away the glue and crap. The sharpened ninety-degree angle edges helps break down the oil sheer, breaking the vacuum as each plate is spinning trying to slip against the other and the oil in between. The excess glue build up only adds to the problem by keeping the oil shear and vacuum going. With no distinct hills and valleys it is detrimental to plate separation.

I will also propose that this is the reason ATF works without the clutch mod as it sheer strength and vacuum causing characteristics are much different than regular clutch/engine oil.

And now for the caveat:

How does one know what one of the three basic areas i.e. Mechanical, Viscous Coupling, Physics or combination of all three is the culprit?

Well that's where my experimenting came into play.

Temperatures in the high 80F Dry weather, Sea level. Bike came with Motul engine oil. Changed to Mobile One Motorcycle oil after a few rides. I have used Mobile One for many years.

He is my scenario. With the original Motul oil the clutch dragged. The clutch continued to drag after changing to Mobile One motorcycle oil.

The clutch dragged inconsistently as I was riding it. It was good it was bad all through the day.

In the past with other Beta’s I have owned I could place the bike on a bike stand start the bike let it warm up and put it into 1^st gear pull the clutch in and the back wheel would stop or be very easily stopped by placing a hand on it. This was not the case with this Factory 300cc

What I needed was away to logically break this down into which one of the three main areas (Mechanical. Viscous Coupling, Psychics) was causing my issue.

Mechanical:

Brand new bike…. The reality of warped clutch plates or fibre plates hardly likely. Swollen fibre plates hardly likely. Notches in the basket not likely. Other wear or tear not likely due to age of bike (barely broken in).

But until I took the clutch apart I would not know for certain.

Viscous Coupling:

Trying to find out the Viscous Coupling characteristics of Motul or Mobile One was a long shot at best so I put that one to rest.

Physics:

There was nothing I could do about gyroscopic effects.

I was contemplating to dump a bottle of washing up liquid into my Mobile One engine oil. That would surely be a great surfactant it would break down the surface tension letting the plates separate. Okay bad idea! I needed another way to test the surface tension theory. As stated earlier I think Dan’s process works on reducing the shear and surface tension effect so why not try it out.

So off comes the clutch. Checked for all the mechanical potential issues warped disks etc no issue there. Checked out the clutch for Dan’s excess glue etc.

There was excess glue all right but did not really look that bad. But I followed Dan’s instructions, painstakingly removing all traces of glue etc from between the plates.

Re-assembled the clutch pack and re installed. Another 500cc of fresh Mobil One motorcycle oil and fired her up. Got her good and warm and…….. and …….. the clutch was still inconsistent. ****……… now what. Short of calling Dan I proceeded.

What other Physics issue could there be that I can actually control?

I still had the nagging notion that viscous coupling was not eliminated from the equation but I needed a way to test my theory. So why not dump all the oil out of the cases, with no oil in the bike Viscous Coupling would not be an issue and therefore I could verify or eliminate Viscous Coupling as a culprit.

I needed to do this in such a way as not to burn up my clutch or seize my gearbox.

Dumped the oil, put the bike on the stand, started it up revved it slowly, pulling in the clutch to fling off any oil in between the plates, letting the clutch go in a VERY gentle manner as not to burn the plates. Pulled the clutch in, Put the bike in 1^st gear let the clutch out slowly. The back wheel started to turn (of course) pulled the clutch in and PRESTO the back wheel stopped turning all by itself. Repeated this several times with constant results.

What the crap I thought! I do have some viscous coupling in this equation.

Now what? I cant run my bike without oil! So it was off to Google to find out what oils for wet based clutches where out there. No motorcycle oil manufacturer out there talks about viscous coupling specs of their clutch engine oil. So it was trial and error. To cut a long story short after testing many different oils I tried a bottle of Castrol 5W 40 RS 4T engine Clutch oil and it did the trick.

I can put my bike on the stand now start it, pull the clutch in and the back wheel stops. The clutch is consistent. I am happy.

But the story does not stop there.

Why is that Mobile One has worked for me all these years and now it does not?

Why is that Dan’s process works for some people and not others?

Here is my take on the whole clutch drag issue.

One has to first determine if it is Mechanical, Viscous Coupling, or Physics at play or a combination of all of the above.

No amount of glue removal will help if the clutch plates are warped or friction plates are warped. No glue removal will help with swollen fibre plates or notched tabs.

However if oil shear, vacuum, and surface tension are at play Dan’s process is the cats meow.

I feel I had two issue on my bike since it is a factory spec bike and the clutch is somewhat changed for this newer model it has a 2013/2014 factory clutch

“A race clutch that has tight tolerances resulting in less clearance between plates when disengaged”. This amplified the oil sheer and vacuum effect and surface tension.

Due to the tighter tolerances on this clutch the viscous effect was coming into play as the clutch plates do not separate as far and the Mobile One and Motul oil viscous coupling characteristics what ever they where contributing to drag while the Castrol Oil did not show signs of viscous coupling.

Dan’s process alone did not eliminate this effect but I am sure if one does his process on an none race clutch or one that has some wear on it will do the trick for you.

So before you trouble shoot your dragging clutch, do some homework and determine if it is mechanical, viscous coupling or physics at play.

So, if your bike does not show signs of drag on the ground, can you put it on a stand start it up put it into gear pull the clutch and have the back wheel stop all by itself?

If so you have great clutch.

Cheers

BillyT

Edited July 1, 2013 by billyt

[0007]

Quite thorough

Question: Did you measure the total movement of the pressure plate (curious if our bikes are consistent)

And did you measure for the correct shim as per Beta's service manual

As for consistency maybe change the hydraulic fluid, contamination/slight bit of water may cause some excess fluid expansion

Would change the disengagement point when extremely hot

I also wonder if less oil capacity would result in less dipping of the clutch and less oil on the plates

And I wonder if 90 degrees on the friction plate pad edge is right, maybe 45 would give the oil a little ramp angle (this is a measurable effect in engines)

[billyt]

Jeff

This is a new bike. One month old Factory 300cc. There is no spec in the way of a Beta service manual as yet. The clutch in this bike is a little bit different than my 2013 Beta 250cc. Not quite sure how different but the advertising spec says it is different and when you look at it the clutch plates are different colour and different thicknesses.

There is no water in the clutch line. I have tried clutch oil levels from 400cc to 550 cc with no effect on clutch performance.

There is nothing more to try as my clutch is nice and soft, disengages as and when I want it to, even on a stand.

It is a story I posted for those out there with clutch issues. May or may not help them, but I do think it is very important to trouble shoot what the clutch issue is by the three main areas, i.e. Mechanical, Viscous Coupling and Physics.

That way you are more likely to get to the root cause.

If you want to wonder then go experiment on your own bike.

I know I enjoyed the experience and learned a lot of about trials clutches in the process.

Edited July 1, 2013 by billyt

[billyt]

Not sure If Andy will allow me to post this oil bottle. But here goes.

PS: The RS on the label stands for "Reduced Slippage".

Edited July 1, 2013 by billyt

[b40rt]

Two questions :-

Why didn't you take it back to the dealer as you would had it been a car ?

No,make that one question.

[billyt]

b40Rt

By dealer I assume you mean a brick and mortar store with full time mechanics and a sales staff? I am in the USA, brick and mortar trials dealers like in the UK or parts of Europe are very few and far bewteen over here.

The closest brick and mortar Beta dealer would be the importer or the importer's rep. That would be a 400 mile one way drive. Other than brick and mortar stores we have somewhat local dealers who work out of their homes and/or back of their trucks and sell trials bikes as a side hobby.

In many cases a rider knows more about bike mechanics than the hobby dealer.

I am fortunate that I have good dealer (a 100 mile one way drive away) who is good with the spanners (Bill Merrit) but I prefer to do all my own work when I can as I enjoy it.

Edited July 1, 2013 by billyt

[axulsuv]

Great info for the memory banks . I like it ! Like I found with my old Fantics , Redline gear oil works best for me ...

Glenn