Clutch plate thickness

[Petr]

I wondered if anyone knows when to change the plates on Beta Evo 2018; in another words what is the minimum thickness of them. The plates are around 3mm each, I run out of the adjustment on the handlebar and the slightest pull on the lever sends clutch slipping. Is it a time? Would adding a few shims to the basket postpone the replacement? Thank you ahead for your wisdom.

[dan williams]

If it’s a four stroke they are all six nominally 3mm. The two stroke uses two 3mm and four 2.7mm. Plates don’t wear on a trials bike and certainly shouldn’t be worn on a 2018. I think your adjustment is just out. To make it engage further out back out the screw on the lever that pushes the master cylinder piston in then adjust the screw on the perch to allow the piston to return all the way out to the snap ring in the master cylinder. I also move my levers in on the bars to give me more leverage and better feel since I only use one finger on the clutch and brake. It has the added advantage of making it hard to bend or break a lever since the bar ends will almost always hit first.

[lineaway]

You do not have enough free play and when it heats up it starts slipping. You obviously have the levrs stopped from going back out. 

 If you have small hands you can slightly grind down the end of the push pins.

[Petr]

Thank you guys for your suggestions.

It may be better to illustrate the problem. The master cylinder push rod gets now activated by the lever itself as the adjusting screw is almost out and only tip is holding the rod in the position. When the rod gets activated it takes about 2-3mm travel (piston covering the inlet hole in the process) before any resistance is felt. It is Beta 2T and before I bought it it was used for a year by expert rider. The problem somehow became apparent after DOT4 oil replacement.

Lineaway is right in saying it gets worst when the thing heats up. There are two thicker plates on both ends of the clutch basket and I have hands big enough to operate the lever. However, if I let the lever out more, it will be more difficult to operate. I can also try to put in that 1mm free play between the push rod and screw if it will make any difference but that will get me into the same spot as described in previous sentence. 

You both think the plates are just fine? I have read somebody's mod about shortening the push pin which makes sense to me but before I take a angle grinder near it I wanted to make sure. BTW I watched the video about japanese mechanic messing with shims but never understood what he actually achieved.

[dan williams]

Experts tend to like their clutch to hit immediate and hard like an on/off switch. First things first though. Pull the lever and the rubber dust cover off to make sure the piston in the master is actually returning to the snap ring. There is a spring above the piston that can be damaged if the lever takes a hard hit. Looking at the photo the adjustment screw should never have to be that far out so that looks funky but maybe those levers are not the correct ones for that bike. People that have measured the throw of the pressure plate report it to be around 1.27mm so there's not a lot to play with. Theoretically the hydraulic clutch is self adjusting as the slave piston only comes back as far as the pressure plate pushes it so its resting position is variable depending on wear and manufacturing tolerances. If the actuator assembly is put back together wrong it's possible the clutch will still seem to work but not work correctly. I think we've all lost the ball bearing that sits between the push rod and the actuator at one time. Replace it with a slightly different bearing and the clutch behaves a bit "odd". Along that line the Japanese video you're referring to uses shims to take up any slack in the actuator mechanism so that the clutch actuation takes place without any slack in the throw. This is to address the problem of clutch drag with the lever pulled in. Referring back to the 1.27mm of pressure plate throw, if you pull the lever at the handlebar all the way in and the piston in the slave cylinder moves 1.4mm over the entire lever travel that is a fixed amount. If the resting position of the clutch actuation mechanism has 0.5mm of slack in it you will only move the pressure plate 0.9mm which may cause some drag as the plates move past each other. If you use washers to take up the slack in the actuator mechanism so there is no slack then you get the full pressure plate movement of 1.4mm and less drag. These are numbers just for illustration, not actual measured values. Bear in mind that free throw at the lever is not necessarily the free throw of the actuation mechanism. The master cylinder must have dead space in its throw to allow the bleed hole in the reservoir to be uncovered. That part of the travel has no effect on the pressure plate as you noted. Since an expert had the bike I wonder if it could have an accessory slave cylinder. Might be worth asking if you can. One other thing I think worth noting is on my bikes I ditch the thicker plates on the ends of the clutch pack for two more of the 2.7mm plates. I just like the feel better being a duffer with no expert ambitions. Or intermediate ambitions for that matter.? Having done the clutch fix on so many bikes I have a stack of various Beta clutch plates in the garage. Some of them given to me by people who thought they needed to replace their plates. 

In theory it's a really simple mechanism but in reality they can be very finicky if the bits aren't all in the right place.

This is where I wish all you guys were local so I could see it in person.

[dan williams]

Here’s mine.

[Petr]

Dan, thank you very much for your comprehensive reply. It is a lot to take in but at least I know what were the shims used for. As you mentioned accessory slave cylinder I believe it has not been replaced with a different or upgraded version - only caps on reservoirs are Apico instead of Beta originals. No idea what benefit that can provide. 

If I may ask you, your replacement of the thicker plates on both end of a clutch basket was to make the action of engagement smoother or it increases the length of throw? As you mentioned, the the clutch is self-adjusting...

There is one thing I have not mentioned. I removed two springs from the pressure plate assembly to ease the operation. Now I can ride without hurting finger but obviously the clutch is slipping in highest gears. Out of interest, would this have similar negative effect for clutch engagement even in the lowest gears? I am now thinking about how quickly can remaining springs push out the oil from the spaces between the plates. There could not be a change in the way the piston or slave cylinder operates but as I have no other adjustment available, I will put them back for the next ride. Fingers crossed ?

Also I would like to acknowledge the helpfulness of this forum. For me it is very useful source of information thanks to many dedicated people who share their knowledge and donate their time to others.