PTO problem

[Bert]

I'm wondering if anyone could help me diagnose the problem with my Rockford PTO. The PTo is on a power unit that runs my circle mill. The problem is it is eating the teeth off of the fiber friction discs where they engage with the ring on the flywheel. I've gone years without changing them, but now have put 3 sets  in in the last 3 months. My first thought is bearings but there is no increase in heat from what I have in the past. The engagement  is also crisp. Im not sure where else to look for problems. When I put  new set in it seems like all is good for about 12 hrs of run time and then one by one the teeth start chipping and breaking off until there is not enough left to hold the torque and they all clean off.

[hardtailjohn]

Does the throwout fork have any pressure against it when it's engaged?  I've seen them have problems from a heavy lever hanging on them and trying to make them slip..... Just a thought.   
John

[drobertson]

Not familiar with your set up, but when teeth get to binding and wearing, clearance and adjustments (alignments) are a large cause of it.  hope you get it figured out..

[Bert]

It just has the normal Rockford lever on it. Maybe 12-18 inches in length. Not much weight to it. Im thinking it is an alignment issue but nothing has changed. Due to no heat etc in the pto bearings, im thinking maybe the pilot bearing. My thought is, once engaged, the pilot bearing in the flywheel would spin at the same speed as the pto. The only time that would come into play is when the pto is "out of gear". The bearing is not a real tight fit on the end of the pto shaft where it rests in the flywheel. Could this cause the tooth wear problem?

[ddcuning]

Bert,
When I did mine there was an option of no pilot bearing or with a pilot bearing. The one I have is without the pilot bearing and has two bearing in the case that are separated from each other to stabilize the shaft. Does yours have a pilot and have you checked to see if it is bad? Do you have an outboard bearing on a stand? If it is bad, it may also allow some movement of the shaft. I would think that movement of the shaft somehow is causing your issue.

Dave C

[DMcCoy]

Groves worn where the old disc teeth rubbed the flywheel?  With the stack of new discs, the teeth  have a new 'location' due to being thicker and the teeth are getting side pressure on the slope of these groves that they don't align with.   Built up hardened crud shaped to the old discs can do the same thing

[Bert]

Dave,

Mine looks a lot like yours other than your missing the over center part. :D Mine does have a pilot bearing. There is no bearing past the pulley. Always seemed to me that their ought to be but its been that way since the beginning of time. I don't know if I require a pilot bearing or not, but im leaning that way. Just from the comments so far, it seems that the shaft is jumping around due to a screwed pilot bearing wiping out my teeth. This may require some machine shop work as the little stub shown on the end of your pto shaft that rides in the pilot bearing is not a tight fit.

[blade69001]

Ugh pilot bearings. If the pilot bearing is out of alignment in the pilot hole or old grease and crude is in there with it, then it can cause a constant spin pressure to be placed on your input shaft.  This can cause the problem you are having. I put several clutches in a trow truck before I figured this one out.
Sean P.

[ddcuning]

Bert,
Installed, mine has the sheave between the bearings. You can see the keyway on the shaft where the sheave goes.



Since I had that big outboard bearing, I didn't worry about a pilot bearing. Below you can see the clutches in the PTO and there is a small nub for a pilot bearing if needed. When I put the PTO on the engine, it was a very snug fit with the drive ring. I tested the drive ring fit on the clutches before I bolted the drive ring to the flywheel to make sure it was ok and that I had the clutches aligned since I had a double clutch set up. Like DMcCoy mentioned, there was some crud built up on the drive ring that I had to clean all off. 



Dave C

[ddcuning]

Bert,
Re reading your post, if the shaft does not fit in the pilot tight, then that might be the source of the problem. It may be in a bind even when engaged.

What I have seen on cars and I don't know if it would work on a PTO is the pilot bearing is just a well greased piece of brass. With that set up, you can machine the inside of the brass pilot to match a worn shaft and the outside to match your engine crank.

Another alternative is to get a true roller bearing for the pilot and then make a shim out of brass to make up the difference between the pilot bearing and the shaft tip. It may only have to be an inch or so long with an id the size of your shaft and od the size of the bearing. The shim may only be a couple of thousands thick and would need to be machined. This would allow you to get an "off the shelf" roller bearing to use as the pilot bearing.  If you went that route, I would make the shim a tight fit on the shaft so it does not walk off during operation.

Just some things to think about.

Dave C

[Bert]

Dave,

I appreciate the look at your setup and the idea. I think that is what Im going to do. Ill get a sleeve to go on tip where the wear occurred and a bearing to match to tighten up the fit and see if this deal will quit eating teeth. I also have a spare drive ring so I might change that out too.

[TimGA]

Bert,   What happened to the original set ?  Did the teeth break off or slipping issues ? You say you have run for years with no issues. Did something happen when you were milling? Is something causing a vibration coming back to clutch unit?   
       It just seems odd to have to put in a pilot brg when there has not been one.  I might go back to recheck my double brgs. I know this is frustrating hang in there.

                                                 Tim

[Bert]

Bert,   What happened to the original set ?  Did the teeth break off or slipping issues ? You say you have run for years with no issues. Did something happen when you were milling? Is something causing a vibration coming back to clutch unit?   
       It just seems odd to have to put in a pilot brg when there has not been one.  I might go back to recheck my double brgs. I know this is frustrating hang in there.

The teeth are wearing off the clutch discs where they sit in the drive ring that's attached to the flywheel. It always had a pilot bearing. What I'm saying above, is that the pilot bearing might be the root of the problem.

[bandmiller2]

Bert, I think our brother Mc Coy  has the answer, with the wear on the friction surface and no wear where the teeth ride. Put a straight edge on it. New friction sections would put a strain on the teeth when clamped. If the flywheel could be surfaced flat or take the new friction sections and grind just a little off the side that rides on the unworn area. That way you won't be trying to break the teeth off when you clamp. Frank C.

[Bert]

Maybe Im not picking up on what McCoy is saying? The flywheel is really a moot point in my opinion. There is a drive ring that is bolted to the flywheel. The actual clamping occurs within the PTO. The teeth are always engaged in the drive ring. ITs when you clamp the friction disks to the output shaft that turns sheave. The disks do not touch the flywheel in any fashion. Im think what some are describing is like truck clutch. That's not what I have here.

[Bert]

Ill try to get some pics this weekend. I hate to tear it apart until this latest set of clutch discs junks itself.

[ddcuning]

Bert is correct, the clutches never engage the flywheel on the engine. There is a drive ring that receives the teeth on the clutches. The drive ring is bolted to the flywheel and the clutches never come in contact with the flywheel. In my last picture, you can see the end friction plate which is part of the PTO itself. The clutches are sandwiched between the friction plates in the PTO and as Bert said, the teeth of the clutches are always engaged with the drive ring that is spinning on the flywheel. While disengaged, the clutches are spinning at the speed of the engine via the drive ring and the shaft and friction plates on the PTO are stationary. When you engage the PTO, the rear friction plate is forced into the clutch which compresses the clutches between the two friction plates and power is transmitted to the PTO via the teeth on the clutch and power is transmitted to the PTO shaft via the friction plates. In my case three friction plates since mine is a double clutch. They also come in three clutch set ups which have 4 friction plates in the PTO. 

Bert, if you have a picture of the drive ring that may be helpful to explain the concept. I didn't know anything about PTOs before I bought and rebuilt mine and I found pictures of the drive ring over the clutches which didn't make sense to me looking at it. Once I went and bought mine from the salvage yard and they let me take it off, it made sense.

I think you are on the right track with the pilot bearing. After thinking about it further, I would not use the brass method like in a car. In a car there is no side load on the pilot bearing except to stabilize the clutch plate so there isn't a lot of force and the brass can be used. In the PTO, there is a lot of side load due from the belts so a sleeve over the tip of your PTO shaft and a roller bearing for the pilot are probably the way to go. If you had to, you could have the PTO shaft smoothed down a little but that would require a complete disassembly of the PTO. I did a complete disassembly with mine but that was because I bought it from a salvage yard and it was completely frozen up so I started from scratch.

Good luck and let us know how it goes.

Dave C

[DMcCoy]

See what happens with the crud removed.  It could be the pilot bearing, I won't argue that.  The way I understand the problem is everything is exactly as it was before except for new clutch discs. 
My guess is that crud or wear is preventing proper plate movement or once engaged the new teeth are riding on a surface worn to match the old teeth.  This mismatch (new square full width teeth riding on worn metal or crud) has the new disc teeth trying to adjust. When you pull the new destroyed discs are the teeth pressure flaked off?  Do the teeth show uneven compression across the tooth face, where one side of the tooth is possibly riding on a wear ridge?  Ideally the teeth need full face and uniform contact.