Awesome info guys. I need to do this to my 610 at some point, I will thread and bolt mine too. In a proper bolted joint, the fastener doesn't see any shear load, up to a (fairly high) point. The bolts, torqued to spec, squeeze the two mating surfaces together, and the friction between the two surfaces resists the shear load, thus none of the shear goes into the bolts themselves. 3 M8 bolts torqued appropriately probably generate enough friction to resist several thousand pounds of shear load. This joint also has basically zero shear load. All you're doing is holding that thin "spring retainer" plate to the backside of the clutch assembly, which keeps the springs from working their way out the back over time. There's no real "load" imparted onto this component. It's really more a matter of making sure time and vibration doesn't work anything loose. I think it is IMPERATIVE that a good, strong loctite, applied to a cleaned and prepared joint, be used for this application. However, assuming that is done, it seems like a great way to solve this problem.
All true. There is a significant load on the plate though, due to the spring cups resting roughly centered between the basket flange and the plate. When torque is applied, it is distributed over the 6 springs, and therefore applied to the basket and plate at 6 points each. So if the springs are centered, then roughly half of any torque passing through the shaft is applied to those three bolts/rivets. Just something to keep in mind before someone thinks the plate is just there to hold the springs in.
I disagree (or I'm not understanding your explanation correctly). The cutouts in the (thin retainer) plate are larger than the cutouts in the gear and the outer basket. The torque is transferred between the gear and the basket by the springs, but the ends of the springs (or, rather, the spring cups/washers) don't touch the thin retainer plate, so they can't/don't transfer any load in. If the retainer plate was installed such that the edges of the "spring hole" was "misaligned" such that the end of the spring was resting on that INSTEAD of the inside face of the hole in the gear, then they would take a torque. They would also take torque if the cutouts were exactly the same size or smaller than the cutouts in the gear (or basket). You can see it in this picture, although it is subtle: http://i22.photobucket.com/albums/b320/nomad650/P1010011.jpg Note the holes at about 6 o'clock; you can see that the cutouts in the plat ye are larger than length of the spring, and thus the ends of the spring(s) do not at all push on the plate. You can see it here too: http://i22.photobucket.com/albums/b320/nomad650/P1010022.jpg Note especially the ones you are "perpendicular" to from the point of view of the photo, roughly 5 o'clock and 11 o'clock.
It's not contacting sitting static like that because the springs are sitting flat on the faces in the basket and gear, but unless the basket supports more than half of the spring cup face, the cup won't stay flat if the spring is compressed and the cup is no longer in contact with the gear. Can you see a shiny wear spot on the inside edges of the retainer plate and in the "ears" where the spring cup would contact? How much the spring flexes, and how much the cup actually contacts the plate, we will probably never know.
Kyle is correct. The holes in the plate are larger than the holes in the gear AND basket. No amount of spring compression will make the cups touch the plate and apply a rotational force.. The plate's only job is to keep the spring assembly centered in/out on the basket/gear; any force on the bolts/rivets would be in tension, not shear.
Oh, I get what you're saying now! You're talking about how, when the end of the spring "tilts," it will/may contact the retainer plate. That's a legitimate point, but given how thin the plate is, it would need to tilt a lot to make contact, I think? The retainer clips probably keep that from happening... That being said, the spring bending probably does put a little bit of force on the retainer plate, trying to "push" it off the back of the basket. The force is probably pretty low, though. I would still definitely be comfortable using bolts in this application, as long as proper precautions are taken!
I did not think that a M8 bolt would be similar in size to the rivet or that it would fit. If all precautions are met, this should be fine. Use a high grade bolt. McMaster Carr should have what we need. Clean out the freshly tapped hole with electric motor cleaner. Disk brake cleaner should work fine. Use red thread lock. You only need about 6 threads inserted to get the full strength of the bolt. 1/2 inch thickness of the clutch basket should be enough. Let the thread lock set before you reinstall the clutch. I would not even bother staking the bolt afterwards as the red thread lock should be enough to make sure the bolts stay in there.
My inclination would be to install rivets again. Especially if you can get the indy guy to do them for $50 if a guy can't do them himself. No question they are going to stay put.
+ 1 on the rivets, if you use the updated Indy cups you will never need to open it back up and will ride concern free.
I think the jury will be out for awhile on how the bolted clutch baskets hold up. It will vary by the application. Safety wire is a good idea. The clutch basket thickness is at a minimum for threading 8mm fasteners in aluminum-in this application IMO. Don't forget that aluminum expands twice as much as steel when heated and the basket needs to flex with those steel threaded bolts inside from the load.
I've seen the number "half an inch" thrown around here, is that really how thick the basket is at this location? With a button head cap screw, you're limited as to how much torque you can put in. A quick back-of-the-envelope calc says that you ought to be way below a stress level that would be a risk at a torque to 50% of yield. For 200 degree F temp rise over 1/2 an inch thickness, the expansion is less than a thousandth of an inch. Also, the whole engine is aluminum on these bikes (and any other decent bike), and they use steel bolts everywhere else. Doesn't seem to be a problem for holding the head or the cylinder on, so I don't see why this would be any different. Edit: Obviously, if people aren't comfortable with bolts, just use the rivets, they ought to be fine. However, it seems like the idea of using bolts is sound, if applied properly.
I haven't been in there in a while, how much clearance IS there between the retainer plate and the gears behind it? Is there room for a standard hex bolt with safety wire?
I can't remember either. That would be SWEET, for sure. I wonder if a low head socket cap screw would fit in there... it is possible to safety wire those. Normally not my choice of fastener, but it's no worse than a button head, which I think works fine in this application. A low head is only 0.5mm taller than the button heads used here... Of course, safety wiring isn't straightforward either, since the bolts are far apart with springs in between them, but you could figure something out. Might be possible to wire each bolt directly to a small hole drilled in the spring retention "tabs."
My problem with safety wire in this application is because it is a spinning part of the engine. With enough vibration fatigue on the wire and centripetal force some could break off and become its own problem.
I've sure safety wired an awful lot of internal fasteners in motors and drivetrains over the years, never once had a problem... When done properly, there's not a lot of room for flex in the wire, and I've rarely seen any break that wasn't broken on installation. Also, safety wire is soft, and won't damage gears and such like a bolt would. It would just get chewed up and sit in the pan.
Just did mine a week or two back and had a local brake and clutch shop rivet them - cannot really see the point of bolts ... if ever one needs to do them again it really is no biggie to drill/grind them off again. May take an extra 5 minutes if that - to get the locktighted bolts out you would need to heat them anyway which takes time. I just feel the rivets are a safe bet IMHO.
Sorry in the last post that is a piece of PVC pipe cut to cup the spring while you just touch lightly with the press. Then clamp the spring with vise clamp preset for proper fitment. Slowly add pressure with press watching to be sure springs are lined up. I also used the basket under it to keep the springs centered . USE A PIECE OF PINE UNDER THE BASKET! Hopefully I won't have to do this again. I was lucky I had a1/3 piece of a spring cup stuck to my drain plug magnet with 10,636 miles. I have noticed others on here with multiple washers mashed with less miles.
