Clutch Push Rod

[Chris & Nean]

The last time I had the clutch push rod pulled out from the its tunnel in the primary shaft on my bike, I noticed that it had picked up and scored on its rounded end where it contacts the pressure plate in the clutch!

I polished these marks out and put the rod back in the engine. Now I can easily imagine that the same damage has reoccurred over again and that it’s only a matter of time before the rod will friction weld itself to the bearing (maybe very unlikely on my bike though… as it has a wet clutch?). This would cause the rod to spin and wreck the slave cylinder, causing quite a bit of expense.

I have an idea for a simple fix to pre-empt this common fa-liar of the ‘spinning push rod’. But I need a bit of advice about case hardening mild steel to be able to implement this fix?

I should think that the rod is mild steel and the bearing pad in centre of clutch would be made of much harder material -probably a bit of alloy pressed in to the bearing. Obviously the end of the rod is not hard enough or it wouldn’t have picked up in the first place.

I want to try case hardening the end of the rod using a bit of artists charcoal stick. I understand it’s simply a matter of heating the metal to cherry red then dunking it in powdered up charcoal and letting it cool.

How many times would I have to dunk the rods end in the charcoal to get the desired depth of case hardening (and without making it so hard that in becomes brittle)? Or might I be totally wrong and that hardening the rod might exacerbate the problem. Looking forward to your thoughts folks :)

[Dookbob]

Why not just change the bearing

[Dukedesmo]

Whilst I've not had the problem (yet) the Evoluzione slave cylinder on my 916 has a bearing in it to help prevent damage if the shaft picks up at the pressure plate end.

[Chris & Nean]

That thrust bearings a special, it’s got an insert in it that locates the pushrod. I’m not even sure it’s available as a spare part from Ducati? It’s part of the pressure plate and I have a bad feeling that the whole clutch is only available as a single unit.

I had the clutch unit off the bike one time when I removed it for purpose of checking out the condition of the cush drive that’s built in to the primary ring gear (there’s been cases of these cush drives breaking up and destroying the whole engine) cush drive on my bike was OK.

I wish I had paid some attention to this pressure plate and it’s bearing when I had the clutch apart. If it buggers up I got a nasty feeling that it’ll be a complete new clutch assembly (someone plz correct me if I’m wrong on this!) this is why I want to get the end of the push rod hardened up, if its not scoring and picking up running against its bearing it might = problem solved.

[crust]

On the proper air cooled clutches its just a normal standard bearing.

You can push them out easily and replace them.

I cant see the oil cooled ones being that different.

If the rods picking up in the end then the bearings screwed, replace the bearing job done.

[utopia]

I'm not familiar with the assembly, but I would say that you're on dodgy ground if you make assumptions about the materials used. Other than low cost, there's no particular reason to assume that the rod is mild steel...it could be one of many grades of steel, which presumably will have been selected for functional reasons, though I do agree that it seems like a relatively understressed part, so cheap mild steel might be appropriate, but who knows?
As for the case-hardening, this is a two step process, where first the mild steel is heated and dipped into carbon rich powder which is absorbed into the surface. Then the steel is reheated and quenched, to harden the carbon rich skin. This will give a hard/brittle surface, but the mild steel core will remain soft/tough. However, if the rod is made of a higher carbon steel in the first place, then the result will be a rod that is hard/brittle to the core, and more likely to crack.
Furthermore, after the hardening process, it is common to reduce the hardness somewhat by tempering. This would entail more guesswork.
I'm not saying don't do it, but I do think that it's likely that the original spec was chosen for reasons other than just cost, and tested over many years of manufacture, and it might be folly to wade in with a simple notion about how it might be improved, without knowing exactly what you have in the first place.....and why.
And there is always the danger of distortion from the heat treatment process.

There are other methods of surface hardening too, eg cyanide hardening, nitriding etc. It could be that one of these is used in the original spec. I'm not sure whether that would lead to further complications or not.
I suppose there is some likelyhood that an original, thin surface treatment has become ineffective, giving the problem you have now, but this is just guesswork.....but a new, std pushrod might be a safer way of rectifying the situation. There have been zillions of monsters made...the basic design of most components will have been well tried and tested by now and few if any major design gliches are likely to exist by now.

Apparently, a particularly good case-hardening compound is a mixture of 60% wood charcoal with 40% barium carbonate, not that I've got any idea where you would get that from. Proprietry mixtures are available, and may be more predictable...I seem to remember a name like 'Kasenit'.

[Starter Sprag]

The 'insert' is available on it's own,

Purchase a new bearing, and a new 'insert'

Polish the rod end smooth with very fine emery, then apply a thin film of grease

Fit new 'insert' in bearing, supporting the inner race, then fit bearing into pressure plate

Job done

[jerry]

The bearings are easily sourced and replacable on all Dry and wet clutch U can use KOYO,SKF ,TIMKEN etc etc the insert is available from Ducati

[Chris & Nean]

Obviously there’s more to it than I imagined. I’m changing the engine oil soon so the best thing is to wipe the clutch cover and have a look at the insert in the pressure plate. If it’s not too bad I might as well have a go trying to harden the tip, it might work and it’s good to know I can get new replacements from Ducati if needed.

[Chris & Nean]

Thanx for advice on this folks :thumbsup:

[Dookbob]

Thanx for advice on this folks :thumbsup:

Here,s a bit more advice, change the insert, dont harden the push rod end. If it,s going to sieze up it will , hardening wont prevent it.

[Pomp1]

Got one of those insert from MotoRapido, they had one in stock when I ordered it..

[Chris & Nean]

Well I did whip out the push rod and pressure plate while I drained the bikes oil. On inspection the round shaped end of the rod where it locates the pressure plate insert was ok.

Thinking about it I recon that putting the rod back in its tunnel one time previously and without greasing its end must have caused the “picking up” in the first place. I didn’t use grease when I had the rod out the engine before because it’s a wet clutch engine and I didn’t think lubrication was needed or a factor. But looking at diagrams of the system: the rod and thrusters run almost dry with minimal oil feed and no splash.

I lapped the parts together using a bit of fine carberundum powder -using palms of hands to spin the rod -like doing valve lapping and stuck it all back together again. I didn’t bother trying to harden the tip with carbon.

Also looking carefully at the set-up it’s easy to see that mostly the push rod spins along with the primary shaft its located in, it also spins against the thrusters in the slave so I greased that as well.

[Chris & Nean]

I'm bumping this thread because having had chance to get the bike out recently with weather being OK-ish, I discovered the gear's shift fast and silky smooth (faster than I can haul bike up on its brake's anyway)... this could be due to service done to push rod and thruster in the clutch hub? or more probably its that I changed the engine oil same time doing inspection and service to rod and thruster.

I used 5w40 full synth rock oil as opposed to 'Shell Advance Ultra 4 Stroke'! Everything seems fine and the bikes a joy :spin:

[Chris & Nean]

I should have also mentioned that the oil in the bike was more than 3 years old! and it makes me wonder about the oil in my cars gear-box thats supposed to last the whole life of the vehicle???

[analogue_rogue]

Car gearbox oil should be changed every 2 - 5 years depending on make model etc. If that helps...

[Capo]

Also looking carefully at the set-up it’s easy to see that mostly the push rod spins along with the primary shaft its located in, it also spins against the thrusters in the slave so I greased that as well.

I dont think the rod is designed to spin

[Starter Sprag]

It isn't, it's designed to push, so as to spred apart the clutch plates to disengage the drive

[analogue_rogue]

Mine doesn't spin.... although mine borrowed up and practically welded itself in there.... nothing. Small techie tap didn't fix....

[gary tompkins]

Pushrod shouldn't spin if the pressure plate release bearing is doing it's job properly. If it does spin due to a seized bearing it'll damage the slave cylinder piston and seal at the other end. I've seen a few slave cylinders get trashed when this happens - far cheaper to replace the bearing

[bialbero]

Pushrod shouldn't spin if the pressure plate release bearing is doing it's job properly. If it does spin due to a seized bearing it'll damage the slave cylinder piston and seal at the other end. I've seen a few slave cylinders get trashed when this happens - far cheaper to replace the bearing

Gary,

that hits the nails smack bang in the middle of it's head and could not be any clearer

[Chris & Nean]

If the push rod did spin for any amount of time relative to the gearbox primary shaft! it would soon burn out those two little rubber sealing rings that are provided to keep the engine oil away from the clutch slave.

Because there’s two halves to the clutch i.e. one bit fixed to the primary drive ring gear, with the other half splined to the primary shaft and then with them both rotating at differing rates relative to each other when the clutch is slipping means that the rod and pressure plate bearing will be spinning differently relative to each other. As soon as the rider pulls the clutch lever the slave piston and rod contact each other and then these parts will also be spinning at differing rates relative to each other too.

For the most part I recon the rod runs at equal rate to the primary shaft but it also is a floating fit within the primary shaft tunnel too. I’m sure that greasing the rods ends cant do any harm when servicing the system.

[Capo]

The push rod does not rotate, the pressure plate has a bearing in it the inner of which is fixed to the push rod so the plate rotates around the push rod. And, there is a needle roller bearing in the layshaft which allows it to rotate around the push rod.

The two O rings will be destroyed in a very short time if the rod is allowed to rotate.

[Chris & Nean]

I didnt know about that needle bearing Capo, I can see from the diagrams that there's little friction between rod and primary shaft because of that bearing. I thought the rod was quite a close tolerance fit in its tunnel but its obviously not as its supported in that needle bearing and shouldn't be spinning with the primary shaft at all.

[Starter Sprag]

Now you've got it

BTW, the inner space of the clutch slave piston, should be 1/2 filled with grease, this is to provide a smoother operation, just like the rubber cush drives in your rear sprocket

[bialbero]

finally..........

[analogue_rogue]

finally..........

bit harsh?

[Chris & Nean]

LOL yeah I love mechanical puzzles like this, they help me get to sleep at night when i wrestle with em in bed. But you gotta admit that the valve lapping technique I used on rod tip and thruster was a good idea though! Also I did note that the thrusters ball bearing spun a bit rough when I examined it, thinks I'll dump that bearing next time I have the cover off.

[Dukedesmo]

But you gotta admit that the valve lapping technique I used on rod tip and thruster was a good idea though! Also I did note that the thrusters ball bearing spun a bit rough when I examined it, thinks I'll dump that bearing next time I have the cover off.

I might be wrong but I think the 'tip' on mine has an 'O' ring in it? if so I'm not sure lapping it to the rod is a good idea.

But the bearing should be free and the shaft should definitely not turn, ever.

[Chris & Nean]

Its a wet clutch on mine Dukedesmo, because your 900 has a dry clutch I suppose some way of sealing off the lubrication from the dry part of the clutch would be needed, I bet its even more important providing a bit of grease now and again on the dry clutch system Ducati use.

[Capo]

Its a wet clutch on mine Dukedesmo, because your 900 has a dry clutch I suppose some way of sealing off the lubrication from the dry part of the clutch would be needed, I bet its even more important providing a bit of grease now and again on the dry clutch system Ducati use.

Indeed in addition to the needle roller bearing there is also an oil seal.