Thursday, November 12, 2009

Continuation of clutch trouble shooting update

At this point, the next step is to open up the needle bearings and examine and replace them.

Here is where we started from . . . an email from Paul S.:


I fear that the problem lies with the cush drive. The clutch does not engage smoothly, but snatches and grabs. The clutch basket is perfect, and the plates and corks are new. I have not taken apart an SS clutch, so perhaps there is something I'm missing. I have three areas of concern.

1) no matter how I line up the base plate with the basket, the springs are not 100% lined up with the base plate. I'm not sure if this is how the SS clutch is supposed to work, as opposed to the later style clutches where the springs are in perfect alignment.

2) inspecting the needle bearings on the backplate/gear plate, it appears that there may be some bearings missing. I'm not sure how these are supposed to look. However, my experience with needle bearings in general tells me that there should be no gaps between the needles, and they should cover the whole circumference of the bearing area. This is not the case here. I have not taken off the brass cover to look inside. It appears that there is a special tool required to remove the brass nut. I don't want to whack on it with a punch.

3) if none of the above, then the problem is must be in the cush drive. That would be unfortunate.

Here is what I have learned from Tom G.:

Check that the gear ring is firmly riveted to the back plate of the clutch. Also check the sides of the slots in the clutch basket. In order to properly disengage, the tabs of the plates have to slide freely in the basket slots.

Also, make sure the spring washer that goes on the crank before the clutch is properly installed. The small end of the cone goes towards the crank.

The basket and back plate are not supposed to line up perfectly. The spring depressions in the back plate and the spring cups in the basket are supposed to be slightly offset. If I recall correctly, there is a small hole in both. Align the small holes. Send me pics so I can be sure I'm remembering this correctly.

The needle rollers should take up almost all of the space. Make sure you have the right amount. There is a total of 40 needle rollers.

The brass ring collar, I believe, is reverse thread. There is a special tool that allows you to remove it, but in practice, most people use a small punch (carefully). But you can also find a pipe or socket the right diameter, and grind away enough of the perimeter to just leave two protrusions to fit into the slots on the ring collar. That would be the best way to open the clutch, if you have the time and the patience.

If the clutch is out, you can see some of the cush gear. Rotate it in place, inspecting the rivets for any movement. Push and pull, tap, whatever. If you see any movement of the rivets, or the plates that the rivets hold together, it is safe to say that your cush gear is the problem. If not, continue to focus on the clutch.

I'm slightly concerned about the rust pits in that surface (the rust is gone, but the pits remain) on the plate. They could be creating too much friction against the bottom cork. However, I've run similar plates without problem, so that "probably" is not your problem. Still, if you could find a better plate you might want to use it.

Gene M. posted on the "Vespa Super-Sports Yahoo Group":

Did you install p200 corks with the external tabs on the outer plate? That lurching is common on scooters where the clutch basket is warped and not allowing the corks to slide freely in the cutouts. You can test this by cutting the tabs off the outer plate so they look more like original plates than P2 type.

We've had many many Vespas with "jumpy" clutch. Normally a new basket fixes the problem - but GS/SS baskets are not available new, so the next best thing is to take the pressure off the basket by removing the tabs. the tabs should have no pressure on them to install - they should slide into the basket freely.

**** BUT I have also learned ****

There is a reason that Piaggio started to use back plates with ears. With 125 and 150cc motors, plates without ears was fine, but with the advent of the GS150, the standard baskets could not take the stress, and started to "flower" out under high rpms. The initial cure for this was to put a steel band around the clutch. However,this intervention did not last long. I suspect it cut down on oil flow to the clutch plates, and possibly the bands started to fail anyway. (This is just my speculation). And so, the Piaggio engineers decided to put the ears on the clutch plates to keep the clutch basket from expanding. And it worked. The SS180 has plenty of power -- enough to cause the clutch basket to expand -- which you want to avoid. Keep the ears.

By the way, it is possible that it is correct that cutting off the ears might help solve the clutch grab -- even though it might not be the BEST way. Think about this -- On a lot of after market clutch plates, the ears are not perfectly stamped, and they do bind up when you try to install the plate in the basket. If there is a really bad fit, the force of installing the last plate can make the clutch basket flex slighly. It is possible that this flexing can cause the slots that the other clutch plate tabs slide into become too narrow, possibly causing the tabs to bind up. (Or the problem could be caused by aftermarket clutch plates with tabs too big on the first two plates -- or even that on an aftermarket basket, the slots for the tabs are too narrow). Frankly, there isn't much chance that this is the problem, but it is still worth checking on. One way to check is to fit all of the clutch plates, in order, into the basket (no need to assembel the basket onto the rest of the clutch assembly). Install the back clutch cork, with the ears, and then fit the circlip. Make sure the back plate is pressed up against the circlip. The two intermediate cork plates should be free to slide back and forth, and their tabs should not bind up on the basket slot anywhere along the route of travel. If they do bind up, that's a no-no, and could be your problem.

**** I just got off the phone with Steve B. from MotorSport Scooters and he said ****

#1 - Bench test the clutch with the compression tool. Tighten it till you feel the compression. Give one full rotation by grabbing/spinning the drive gear. It should spin freely.

#2 - Look for wear of the brass bushing in the clutch cover. If the bushing is loose it will cause "jumping".

#3 -- Make sure that the tension washer is facing the correct direction. The "cone" needs to be facing out.

Steve is against cutting the ears off the cork plate, because of the power of centrifical force. It could be very dangerous. He went into a long and detailed reason why it is dangerous and I could not remember all the details when I got off the phone.

He also said, I may be missing some needle bearings, but that would not be the cause of the problem.


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Anonymous said...

To eliminate clutch grab, soak the friction plates (cork) in oil overnight. Also use a motorcycle engine oil, not transmission fluid or car oil.
Clean oxidation from the steel plates, slight pitting will be fine.
I did this today, I found the corks were dry and the wrong oil used when I disassembled the clutch pack.
Also change the transmission fluid at the same time.
Motorcycle technician.