ball bearing size for clutch pushrod on hydraulic clutch?

Paul LeClair

Paul LeClair

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Location
Calgary, Alberta, Canada
Hi all

I searched and found conflicting answers.

I am rebuilding a hydraulic clutch master and slave system on a series 2 180. When I took the slave cylinder cover off, there was no ball bearing on the end of the clutch pushrod between the push rod and the slave piston. This is not my bike I am working on, and the service history is not known, but it is clear from the wear on the end of the slave piston the clutch has been running without a ball bearing in there for a long time.

one post I found here says the bearing should be 6.5 mm (which is around 1/4 inch?), another post says the bearing should be 8 mm (which is around 1/3 inch?)

does anyone know for sure what the size is supposed to be, before I run out to try and buy a single ball bearing..........  :o

Paul LeClair
 
Paul, you can always get single ball bearings at bicycle shops, at least inch sized ones. 1/4" and 5/16" are standard bicycle bearing sizes.
If you really want to get carried away, Campagnolo bearings are polished to "beyond aerospace standards". Add another 1.5 rwhp to your 1200 :D :D

Ken
 
5/16" Paul.

The 1/4" is the one between the 2 clutch pushrods!

About time you got yourself a RGS parts catalogue!!

piet
 
It's a good idea to put a little dimple in the end of your pushrods to centre the ball. I had a clutch that used to click every time the lever was pulled in. It drove me nuts until I figured out it was the two pushrods popping out of line as the pressure came onto the ball between them. The rods had flat ends. I put them in the lathe and cut a dimple in the centre of each one - no more click!

Cheers,
Cam
 
sfcpiet said:
5/16" Paul.

The 1/4" is the one between the 2 clutch pushrods!

About time you got yourself a RGS parts catalogue!!

piet
Click to expand...

yep - 5/16" or 8 mm roughly for the one in the slave cylinder and 1/4" or roughly 6 mm for the one between the push rods.

I am still thinking of how to improve this sucker. It drives me nuts why all Laverdas with hydraulic actuation (but also many with the mechanical actuation) do weld the parts together if you hold the clutch lever pulled to long. Kawasaki had a similar setup but never ever that kind of issues. I managed to destroy this setup 3 times during dyno runs within 2 days on the same bike...

I think the biggest issue is that the one ball in the center of the two pushrods does not separate the rotating forces enough and there is not enough oil supply to make sure the heat that is produced is taken away from the parts. I thought about installing little tappered roller bearings into both the slave piston (where the 5/16" ball sits) and the square bar that is pushed by the 2nd push rod and make the according ends of the push rods a bit conical so they seat themselves perfectly into these tappered bearings. I am simply not sure that a) these bearings can take that kind of load and b) they are available in the right size...

maybe a ruby bearing like in my watch is the best solution. Just where to get them cheap enough in that size...  :D
 
Lothar, I believe the trick is to pull the clutch at the end of the dyno test, releases the rods from the energy, and avoids 'welding' the ball to them.. Levo has more on this topic, but essentially that's the problem.. gotta save you a fortune in rubies.. :LOL:

8)
 
LaverdaIan said:
Lothar, I believe the trick is to pull the clutch at the end of the dyno test, releases the rods from the energy, and avoids 'welding' the ball to them.. Levo has more on this topic, but essentially that's the problem.. gotta save you a fortune in rubies.. :LOL:

8)
Click to expand...

well - if you pull the lever, you put the energy ON the rods, balls - the whole construction basically. That's why pulling the lever and engaging 1st gear while standing at red traffic lights is a no-no-no for Laverdas...


The trick how not to weld these suckers together on a dyno basically is to
-make the dyno run in 3rd gear, not in 5th
-pull the lever at the end
-shift down twice into idle as fast as you can
-release the lever as soon as possible

but make sure you are really in idle before you release the lever, else you a) spoil the dyno run and b) even worse potentially crack your engine...  :'(

But that's basically just "coping with an existing miss-construction", not solving the problem...  :-[
 
In normal usage there is nothing at all wrong with the Laverda clutch mechanism. I grew up around Velocettes - now THERE's a fucked up clutch mechanism.  PhD Theses have been written about adjusting the Velocette clutch.
Regarding dynos, one should just use a proper brake dyno.
 
breganzane said:
Regarding dynos, one should just use a proper brake dyno.
Click to expand...

...best with an old tire and serious mounting of the bike... But I agree, changing a tire is easier than repairing the clutch...  ;)

If you look at how the components look like in a bike that has done 50.000Km (just like the SFC Classic I have on the work-bench), you come to different conclusion about the day-to-day abilities of the components (from todays perspective)...

However, the question is why does the Kawa stand to the excessive abuse of these components on an acceleration type dyno and the Lavi doesn't? How to improve it?

this in the right size, permanent greased and sealed would be a great solution:

1800f03.gif


or

4036_3d-305x305.jpg


not sure it's existing in the necessary diameter though or with the according load-resistance...
 
Lothar, pull the clutch in and it's disengaged from the drive as the dyno winds down.. IMHO... but you seem to have a system..\

8)
 
Hi Lothar

the Kawasaki 4's from the 70's have exactly the same issue as the Laverda's concerning the clutch actuating assembly cooking and seizing when the clutch is pulled in and held, loaded while the engine is running at high speed like spinning down on a rear wheel dyno. The mechanism is different, it is a larger plain faced sort of mushroon shaped actuator, but the problem is the same as the Laverda's.

the solution from the aftermarket for Kawasaki's, that I fitted to my recent KZ 650 rebuild, is almost exactly what you illustrate in your post, a bearing replacement. See it here    http://www.z1enterprises.com/Kawasaki-Roller-Clutch-Push-Rod-Kit-257.aspx

Hi Ian

on the Laverda clutch mechanism the default position is the clutch fully engaged, with no load whatsoever on the clutch actuating mechanism. When you pull in the clutch lever, it loads the clutch actuating rods to disengage the clutch pack against the clutch pack spring pressure, so holding in the clutch lever, especially at high engine speeds and for long periods of time, causes the friction/heat/spinning on the actuating rods and actuating surfaces. So, lets say you are trying to do spark plug reading on the street, you run the bike up to full throttle, kill the ignition and pull in the clutch and coast to the side of the road, there is a fairly high risk of cooking/seizing your clutch rod actuating mechanism, same as pulling in the clutch on the dyno. As the Laverda uses a silly flat square bar stock inside the clutch pack for the actuating rod to push against, over time as the clutch is held with the lever pulled in, the loaded and spinning actuating rod actually starts to bore through the flat clutch actuating bar. I had to replace mine with a piece of tool steel intended for a lathe after I ruined the original Laverda piece running my RGS "1200" repeatedly on a DynoJet 250i rear wheel dyno. Unfortuantely no proper water brake dyno's available for rental useage anywhere around where I am.

Paul LeClair
 
I wonder how well a ceramic ball bearing would work? Would silicon nitride be better than silicon carbide? http://www.vxb.com/page/bearings/CTGY/BearingBalls?gclid=CM6MvcjauawCFZFb7AodvGWGrA

What about coating the bearing and the ends of the rods (and the "push bar") with low friction coating, titanium nitride or silicon nitride or diamond-like carbon?

More things to spend your money on. But don't forget, if it isn't original, it takes away value from your bike :D :D

Ken
 
Reckon it wouldn't be too difficult to incorporate an axial bearing into the slave piston, got an old Beemer item laying around, looks as if it might fit OK without too much magic.  Problem is sealing the sucker, the Lav clutch slave lives in a murky and hostile environment, not very bearing-friendly.  I'll see if it fits under the dust boot.

piet
 
Thanks Paul, I may have it the wrong way round. I've seen 'bored' actuating bars, on PFC's RGS it was actually bent, causing all sorts of problems..
You learn every day about the magic (and not) of Laverda design.. ::)

8)
 
I know this will go over like a fart in church, but on that other Italian brand that uses a similar actuation arrangement the pushrod are separated with a combination of rollers and balls.  I think the multiple elements may reduce the point to point friction and provide more room for lubrication.I use a thin moly based grease and coat everything liberally when I assemble and haven't had any undue wear or welding problems,even using clutch springs that make an 180 clutch seem Honda like.
 
and on the original topic, I went to my local transmsssion supply shop looking for a single ball bearing in 8 mm or 5/16", they would only sell me minimum quantity of 100 for almost $100, so I passed...... :o

then I went to my local bicycle shop, didn't have any better luck until the bike mechanic came up with some sort of bicycle bearing assembly that had nine 5/16" bearings in it. The bicycle part, whatever it was, was $10, I ripped it apart and salvaged the nine 5/16" bearings, now I have a lifetime supply of Laverda clutch slave ball bearings.

Paul LeClair
 
Ken, clutch was fine, just an expat trying to ride like a yank in Oz was the problem.. and yes it was raining pretty hard as I recall.. :LOL:

8)
 
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