Did you use a click stop Tq.Wrench

Did you do a criss-cross pattern evenly incrementally ?

Or did you tighten 1 to torque then another ?

 

Were you only tightening each bolt a couple turns at a time? And you have a good low-range torque wrench? It may be that your replacement already had a stressed/compromised post.

 

Some clutch springs fit differently on the opposite ends of the spring. I don't know why some springs are odd like that. This is a weird deal when it catches you. When they do break, you aren't even close to having them run down to proper position.

If the end wind of a spring starts to bind onto the taper of the post, it snaps the post out of the backing plate. I have broken a few from not checking them on the backing plate before I put it all together. I have run into some backing plates that were repaired with a button head bolt and washer on the back side of the pressure plate. These were found in engines from ride-able used bikes that I bought to scrap out (except the parts I needed for the project). I guess this has happened more often than we think. Sometimes I find serious nicks on the post taper, where springs had bit into the soft aluminum but not quite broken it.

Check the springs, both ends, for fit onto the posts, and make sure you install the "loose" end inward. You CANNOT tell it is going to jam, after you have already put the pressure plate behind the disks. Check for best fit with the plate in your hand, FIRST. Like I said....this is a weird deal when it happens, and I am sure I haven't got the whole answer figured out.

If you run the Barnett clutch and spring package, you never have this problem even though the springs are serious stiff compared to stock (even stiffer than the shortened GL650 springs I sometimes use in 500 engines.)

 

Do this repair, because it works good.

 

That repair is the same as I did when I snapped a post in Eccles' original engine. I used slightly longer bolts because I had them on hand and I smeared them with epoxy before screwing them in to make sure they wouldn't loosen. Don't forget to use 4 screws to maintain balance (not to mention adding extra strength for next time).

FWIW, I always felt that I had something not quite lined up right so that the pressure broke the post before the bolt was seated but Jim's theory about the springs makes sense too...

 

Thanks guys!

 

1) Utmost credit to those who thought of, and had the intestinal fortitude to try such a repair before seeing it recommended. And then thanks so much for passing it along!
2) (Perhaps it's in a different thread, but) I didn't see too much detail in any of the descriptions. As a result, though I know people on this forum are very capable, I thought some might appreciate my experience. I have photos if anybody wants them. This isn't a recommendation, just my way with the tools I had. Full disclosure: I can't assert how it holds up with riding (I've got more to do before mine's a runner), only that it held up for re-assembly and static cycling.

• I only planned to do 2 posts (the broken one, and one opposite for balance), but honestly found it was going so easily that I did all 4. I didn't want one of them to break on the next assembly attempt!
• I used M6x20mm Flat Head Socket Cap Screws for repair, but had to shorten them so I'd recommend buying shorter. The 20mm length (flat of head to tip) was too long for this repair bolt AND the lifter plate bolt that has to come from other end to fit in the same hole. The original 20 mm length left ~0.028” gap when I temp installed the bolts from opposite ends barely snug against each other with lifter plate in the stack, plus I wanted room for bolt-stretch upon torquing. I chose to shorten the repair bolts to ~16 mm (0.630”).
• For the same reason (limited length in shared hole), I was very careful when installing the repair bolts not to put any epoxy ahead of the repair bolt.
• I tapped the threads before countersinking, but would reverse that if doing again (to limit risk of damaging the threads)
• I found no tap-drilling necessary (but found the drill useful for alignment later, see below). The existing holes were sufficient, and actually slightly oversized (somewhat over a #8 imperial drill, which is already about 0.002” diam over the prescribed 5 mm pilot drill).
• I chose to extend the threads from lifter-plate side, rather than start new threads from the flat side. This way I didn’t end up with a region of overlapping and weak/messed-up threads in the middle. It also provided really good guide-threads to start the tap and made a very easy hand operation of it. Be sure your tap shank is long enough. I had to grind (angle grinder & dremel) the shank to undercut and create clearance past where the cutting features ran out. (Maybe you can buy through-threading taps, but I didn’t have one.)
• Be sure the countersink angle matches that of the repair bolt. (90 degrees for mine)
• The countersink required removing very little material and I didn't want to remove more material/strength than necessary so I only went to clean-up.
• I wanted the countersink centered on the hole well, so the bolt wouldn’t side-load when seating.
  • I don’t have a milling machine, but do have an old Shopsmith wood machine that I was able to use. Basically I put the tap-drill in the chuck and slipped the pressure plate’s post-hole over that; clamped everything in place in alignment to the chuck; backed the chuck away; swapped the counter sink into the chuck; cut the counter sink; and then temp installed the bolt to confirm everything before changing setup. Then repeated that 3 times for other posts.
  • If they make a countersink with integral ~5mm drill, you might be able to do it by hand (Heck, somebody better with their hands than me might be able to freehand it, but I wouldn't want to try.)
• After the repair (maybe before too, who knows) I noticed that the pressure plate rocked slightly (few thousandths of an inch) when placed posts down. My repaired post was the high one. I corrected this by buffing on 400 grit sandpaper laid on a flat plate.
• Above prompted me to check the lifting plate too - which I also found to be a few thousandth out of flat. Checking was trickier since the surface has a raised center, but I found a tube with diameter ~equal to the bolt hole pattern to set the 4 "ears" on and check for rocking. Once I ID'd a couple high ones, I buffed them similarly with the 400 grit. I don't know if this was necessary, but I like the idea of even seating and not having to flex the lifting plate into submission.

Regards. Hope this is helpful.