I've ridden about 500 miles since restoring my 1973 Commando 750. After a recent ride I noticed that both fork sliders had devoloped cracks approximately 1" long beginning at the top of the sliders. During the restoration the fork tubes, bushings, seals and springs were replaced and the sliders polished. The springs are Progressive and I used 1" spacers at the top of the springs. I'll replace the cracked sliders, but I can't figure out why they cracked. Has anyone experienced this or have any idea what caused them to crack? I don't want to ruin another set by making the same mistake - they're expensive!
Cracked Fork Sliders
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Mick
No one that I've talked to has heard of this happening. If it was just one slider I wouldn't worry about replacing it. But with both of them cracking in the same place, there most have been something wrong in the parts or assembly. I was hoping someone could shed a little light on this for me. In any event, I'll try it again with new sliders.
No one that I've talked to has heard of this happening. If it was just one slider I wouldn't worry about replacing it. But with both of them cracking in the same place, there most have been something wrong in the parts or assembly. I was hoping someone could shed a little light on this for me. In any event, I'll try it again with new sliders.
I've never heard of this either. Do you recall bottoming out or any unusual bumps or noises? Is the bottom bolt in place? Look inside for areas of impact or contact. Something must have been done incorrectly upon assembly I'd think. You should find out on disassembly. I happen to have 1 slider off at the moment. Here's what it looks like.
My first experience with substandard Commando parts was a set of upper bushings. They fit on the stanchion, they were a tight fit in the slider. When I tried to assemble the forks the crush from the slider was enough to bind them up. If I forced it they would have probably cracked the sliders. The interior machining of the bushes was pretty bad too.Tim said:
There's a remote chance that the yokes or tubes don't line up. Where were the cracks on the sliders, looking down at them.
OK, here is some additional information. The cracks in both sliders are on the same side looking down on them (left side). When I rebuilt the forks I had the same problem mentioned by Bob. The new upper bushings were too tight in the sliders. I carefully tapped them in about 1/2" before deciding they would not work and removing them. I used the old upper bushings and reassembled the forks using new Progressive springs, new lower bushings, seals, etc. I finished the bike and rode it about 100 miles or so and noticed the forks were soft and bottoming. I called Progressive and they advised to put a spacer at the top of the springs. I added a 1" spacer and did not notice any cracks at that time. The fork action was much better, but still bottomed out occasionally when hitting a large bump. I suspect that I need more than a 1" spacer with the Progressive springs. My weight is 220 lbs. I had about 500 miles on the restoration when I found the cracks. My plan is to obtain new sliders and use 1 1/2" spacers with the Progressive springs. Any suggestions? I really like riding the old Norton!
Thanks
Tim
Thanks
Tim
Tim,
I've got no idea whats causing the cracking, but clearly its stress and thus metal fatigue. Try assembling the forks without the front wheel and without the top yoke nut (i.e. let the internal spring poke out the top) push each fork slider up and down and see it there is any binding. Next take the axle and fit it through the sliders. Push up both fork sliders at the same time and see if there is any binding. The idea here is to see if there is any fore and aft misalignment. If there is, this may be caused by a bent bottom yoke, they are not too strong and that puts the fork stanchions out of parrallel. The Next put the front wheel in and make sure you got all the right end cap spacers in place to ensure lateral alignment. Pull the wheel up and down and see if the action is smooth.
If that all comes out good, I can only assume the old sliders may have been stressed in a prang sometime back and the cracks have just formed. Could be the first attempt to fit the tight new top bush just was enough to initiate stress cracking? But it is a good idea to replace them, I'm sure this won't happend again as no one else seems to have experienced this.
Mick
I've got no idea whats causing the cracking, but clearly its stress and thus metal fatigue. Try assembling the forks without the front wheel and without the top yoke nut (i.e. let the internal spring poke out the top) push each fork slider up and down and see it there is any binding. Next take the axle and fit it through the sliders. Push up both fork sliders at the same time and see if there is any binding. The idea here is to see if there is any fore and aft misalignment. If there is, this may be caused by a bent bottom yoke, they are not too strong and that puts the fork stanchions out of parrallel. The Next put the front wheel in and make sure you got all the right end cap spacers in place to ensure lateral alignment. Pull the wheel up and down and see if the action is smooth.
If that all comes out good, I can only assume the old sliders may have been stressed in a prang sometime back and the cracks have just formed. Could be the first attempt to fit the tight new top bush just was enough to initiate stress cracking? But it is a good idea to replace them, I'm sure this won't happend again as no one else seems to have experienced this.
Mick
[reassembled the forks using new Progressive springs, new lower bushings, seals, etc. I finished the bike and rode it about 100 miles or so and noticed the forks were soft and bottoming. I called Progressive and they advised to put a spacer at the top of the springs. I added a 1" spacer and did not notice any cracks at that time. The fork action was much better, but still bottomed out occasionally when hitting a large bump. I suspect that I need more than a 1" spacer with the Progressive springs. My weight is 220 lbs. I had about 500 miles on the restoration when I found the cracks. My plan is to obtain new sliders and use 1 1/2" spacers with the Progressive springs. Any suggestions? I really like riding the old Norton!
Thanks
Tim[/quote]
I think I would call progressive and ask why you need spacers at all if they are new and supposedly made for a Norton's forks.
Thanks
Tim[/quote]
I think I would call progressive and ask why you need spacers at all if they are new and supposedly made for a Norton's forks.
ML said:
seaguy said:
One of the sliders (RH or brake side) cracked in a similar manner. Also, the bottom of the fork on the other leg cracked and broke at the at the axle pinch bolt. My bike was an eBay special and came with some receipts that the forks had been rebuilt by a brit-bike shop in Seattle area, who I think caused the damage. My bike has standard springs. I think (in my bike's case) it is overzealous tightening that caused the fractures. The collar is a fine thread and doesn't need to be tightened to resitance with a pipe wrench, which is what I think happened in my case, judging by the effort required to unscrew it when I dis-assembled the forks.
I ended up buying two new sliders.
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