Subject: RE: Clutch weirdness
Author: Greg Bender
Date: Jun 29, 2005, 10:36 AM
Post ID: 1719093447
Wonderful analysis, Mr Hayes, as usual! Thanks :>
Patrick Hayes wrote:
Kevin Graf wrote:
Careful with the semantics here. The springs sit in "front" of the clutch stack. Always refer to Guzzi parts from the perspective of a rider astride a complete bike. I realize when you are working on the clutch they appear to be at the "rear" from your mechanic perspective working on the back side of the motor but, they are in fact at the front of the clutch. Longer springs don't inherently give longer travel. The necessary minimum dimension of the Guzzi clutch starts with dimension ZERO at the inner surface of the rear or ring gear plate. In front of that surface is a new 8mm friction disk. In front of that is the floater plate. In front of that is an identical second 8mm friction plate. In front of that is the movable pressure plate and then the springs. Stop here. This sandwich stack has a fixed solid dimension when under spring pressure. Guzzi only allows for a ONE MM variation in this stack dimension (0.5mm wear for each of the two friction disks). When the clutch stack is compressed under friction, the length of the spring has no part of the computation, only its force. Doesn't matter if the springs are three feet long (hyperbole). The clutch stack sandwich is a fixed dimension stack under pressure. The springs under installed pressure can be too strong or too weak, but they can not be too long or too short. Pushing forward on the throwout rod, we move the pressure plate forward slightly which compresses springs and releases pressure on the sandwich stack. Allowing for some flex and inconsistencies in part fabrication, we only need to move the pressure plate forward about 1mm or so to get full release. The problem with inadvertent use of a longer spring is NOT its standing length, but its fully compressed length. The relaxed standing spring has space between its coils. You can only compress this spring until the coils bind against each other and it effectively then becomes a rigid cylinder. Can't compress it any further (unless you add literal tons of hydraulic force). Presumably, a spring which is longer than specified to begin with will also be longer than specified when it is fully compressed to the coil stacking point. The only way it can end up being shorter under compression and have "...more travel..." is if it is BOTH longer AND it is made of thinner coil stock so that the resultant, fully compressed, stacked coil cylinder is now shorter. Unfortunately, the thinner coil stock would also result in less rebound force and less friction force to the clutch stack. So, it is entirely possible that springs which are too long, will bind down to or get very near to the coil stacking minimum point during the installation of the ring gear plate of the flywheel. In this circumstance, nothing you do with the throwout rod will ever release the clutch. Although I have never seen such, I suspect it would be easy to notice. The hand effect of the clutch lever would start easily as it compressed the single spring at the outside back of the transmission and then it would stop rock hard as the throwout rod reached the clutch. The clutch won't move at all or it may move only a very little before getting rock hard stop as the springs reach their coils stack minimum length dimension. Greg, is there ANY action or feel to the clutch by hand? Now, if the springs were too short, then the clutch would activate just fine, but they wouldn't be applying adequate internal pressure to the pressure plate and the clutch would slip like crazy under throttle. Not the circumstance we are discussing here. Greg, I know you've done many clutches. The only caution I have is the ease at which one can get the floater plate out of alignment and then bend it during clutch installation and compression. If you bent it, the clutch will always bind, regardless of the nice feel at the hand lever. Just a thought. No answers here, just forum discussion. Patrick Hayes Fremont CA |
Regards,
Greg Bender
1971 Ambassador
2000 Quota
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