ElectricMotorcycleForum.com
Makes And Models => Zero Motorcycles Forum | 2013+ => Topic started by: BrianTRice@gmail.com on July 11, 2016, 08:57:35 AM
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I've alluded to concerns with the mechanical design of the tail subassembly on Zeros. Unfortunately, what fueled my concerns reached a small crisis today, so I'll try to lay out an argument and what to do about this situation. My priorities: (1) fix this for me, (2) document it on the wiki manual, (3) hopefully prevent others from the same mistakes or vulnerabilities, (4) raise the attention of someone at Zero so the 2018 models are better. I can't expect to influence 2017 models at this point.
My DSR's current demands on the tail design are (in order of loading demands): (1) the tail rack, (2) the Corbin seat, and (3) the OEM side racks. It's possible that the problem I'm experiencing requires all of these interacting at once but I can't say.
My Corbin seat will not settle into its intended position the way the bracket is mounted; the bracket is at least positioned 1/4" aft of where it would align properly, which means the seat must be structurally compressed to thread the seat bolts. This means that my seat bolts have been experiencing some shear for about six weeks, and with all the troubleshooting and teardown I've been doing, threading and unthreading the seat has been a bit of a time bomb that I haven't made time to fix because I've been focused elsewhere.
I will figure out how to communicate this problem to Corbin but I don't expect my current seat to be fixed (moving the holes that little will just weaken the pan), and as of today, the holes for the seat bolts are now nearly fully stripped(!), which I need to address ASAP after little more than a month of usage.
There's this thread to reference for a fix: Quick removable seat (http://electricmotorcycleforum.com/boards/index.php?topic=4612). I've avoided that design out of structural integrity concerns, but am considering something like it now.
Also: wiki manual entry for the tail removal (http://zeromanual.com/index.php/Unofficial_Service_Manual#Tail_Plastics)
Now, I need to lay out why this whole scenario is even possible, and how no larger motorcycle manufacturer has this problem: the seat is mounted to the frame with load bearing bolts. There is no justification for this other than "they haven't gotten around to designing something better".
What is the seat loaded with? Everything listed above, into the tail assembly itself which is separate from the frame. I'd say if Zero intends to reach a broader market where third parties support accessories more widely, the frame or tail assembly needs to integrate the top plate or at least the grab bars that it mounts to. Any loading on the top case has both a static and dynamic effect on all the bolts involved, and seat bolts that must be operated more than twice per year should not be part of that structural equation.
Some have carried extra charging capacity in a top case, most notably Terry, but it's worth noting that Terry's tail rack has extra bracing running from the lower center part of the frame out to the plate itself (part of a custom-welded side rack concept that I'm trying to emulate shortly).
I'm motivated with some urgency because my situation is complicated: I'll be commuting 80 miles per day instead of 20 miles per day starting tomorrow, my 2013 DS has been unavailable for months because of insurance issues after a car knocked it over in January (it was intended for supercharger testing and fabrication testbed, so that fell through), and I still need to test the supercharger further, helping test software tweaks mainly. This year has been a bit of a drag in many ways...
With all that said, can someone recommend suggestions that won't impact the structural life of the vehicle? Let's assume I can get a reasonably priced tail assembly replacement soon and swapped, and that I will make some quick compromise for now for safety until this is sorted.
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(http://uploads.tapatalk-cdn.com/20160711/ac5c98dce23c28eeda6d4da73e3fbcd1.jpg)(http://uploads.tapatalk-cdn.com/20160711/3b7c029ecf1deb47a83e27c1cc16fbf1.jpg)
Photo evidence of the stripped threads. The bolts are intact, of course.
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For a quick fix you can Helicoil that. It will actually be stronger afterward.
As for the redesign... no ideas.
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Helicoil is a thing I was stumped trying to remember, thanks! I'll just try to see about a separate seat mount, then.
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The aluminum tail section is not threaded. The seat bracket is threaded. The "threads"you see in the aluminum are just the imprint from screwing the bolts in.
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For a stronger fit you'd want a bolt that has a shank where it meets the aluminum, instead of threads that will deform the aluminum?
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The aluminum tail section is not threaded. The seat bracket is threaded. The "threads"you see in the aluminum are just the imprint from screwing the bolts in.
Harlan's right, that's just a through-hole in the aluminum frame rail. It took me a while to figure that out too. If you look at the bracket, it's actually got a nut welded (braised?) on it to secure the bolt...which is also the point that's so difficult to get properly aligned to install those bolts. The rider's weight on the seat causes the bolt's threads to dig down into the aluminum. All the weight is borne in shear, there's not enough clamping force created by the bolt to keep the rider's weight off the shaft of the bolt.
Shadow is right, a bolt with a shank would be better at taking the weight of the rider without grinding into the aluminum. That's what the aerospace guys do. Next time I have the seat off I'm going to measure it all up and figure out exactly what shank length and thread length it needs, and get the perfect bolt for that application. Or maybe the time after that.
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Thanks. This makes more sense now. I didn't have luck trying to switch back to the original T45 bolts, but will recheck. I'll definitely aim to decouple the seat from the bracket, though.
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To clarify (my takeaway): the tension because of the seat not fitting is putting a lot of pressure pushing the bolts aft which is digging into the softer tail subassembly aluminum.
The bolts aren't in danger, and the tail has a lot of room to allow some digging in, but the whole thing should sit better and I'd rather decouple the seat from the bolts and make the bolts more firmly mounted and able to dampen tail loads better.
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I didn't quite follow all the technical stuff, but I already have the OEM side case brackets, and I'll probably get a Corbin seat. Am I asking for headaches?
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I didn't quite follow all the technical stuff, but I already have the OEM side case brackets, and I'll probably get a Corbin seat. Am I asking for headaches?
Check the seat as you first mount it on the vehicle; if the holes align without putting the seat under much tension, you'll have no wear. I'm going to double check versus my stock seat to see how it's off for smarter feedback.
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I didn't quite follow all the technical stuff, but I already have the OEM side case brackets, and I'll probably get a Corbin seat. Am I asking for headaches?
I don't have the side cases, but I do have the rack, and my Corbin bolted right on. There's always a little shimmying and shaking to get the nuts lined up, but it wasn't a problem for me, at least. I'm not a big fan of having to capture a nut completely blind with the end of a bolt like that, but I've always been able to fish it through.
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Yes, it's not going to happen for everybody. Mine turned out off enough that it started aggravating the arrangement.
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Update: my dealership service guys noticed that one of the vertically-mounted bolts for the top rack had its head snap off.
After thinking about it, I realized that I heard it break while on the road, because I remember a bit of an alarming "ping" sound while approaching the Dumbarton bridge from 880 less than a week ago. I've put 10,600 miles on my DSR now in about 7 months on some highway stretches with rough/bumpy areas, so I'm getting a little ahead of the wear threshold when combining that with various tinkering.
That means right now my top rack is primarily anchored by the side rack bolts and seat bolts until I drill, tap, extract, and replace it. Well, I'll replace both bolts to be careful because now I'm sure the second bolt is under greater strain.
I'm also about to switch to the Happy Trails rack which is much more robust and might be more suited to holding more cargo, so hopefully it'll be better anchored:
http://www.happy-trail.com/find-your-bike/zero-motorcycle/su-side-racks.html (http://www.happy-trail.com/find-your-bike/zero-motorcycle/su-side-racks.html)
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If you can remove the bracket from the seat pan, then attach bracket to frame with mentioned shank bolts. Maybe you could rivet a plate or glue a bunch of rare earth magnets to the bottom of the pan. Magnets dude!
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If you can remove the bracket from the seat pan, then attach bracket to frame with mentioned shank bolts. Maybe you could rivet a plate or glue a bunch of rare earth magnets to the bottom of the pan. Magnets dude!
I do have magnets extracted from the tank bag I'm using.
I'm not sure what you mean by shank bolts - illustrate with a photo or diagram or something?
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A bolt with a non threaded portion (shank). That way it won't rub the frame.
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I know what kind of bolt you meant, but didn't understand where or what you were implying by magnets or use of the bolts. :)
I've spec'd matching shank bolts from McMaster but haven't pulled the trigger. Even quick release pins are available but not in a way that clears the tube for the top rack mount.
Magnets to hold the seat on? Presuming the seat is disconnected from the bracket.
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Anyway, yeah, I'll try it; thanks for the encouragement.
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I was wondering about the magnet comment, too...everything's aluminum on this bike! It's not a bad idea, though, might even be worth bolting on a steel pad for the magnet to grab onto. Of course, then anybody could pull the seat off, and the seat might not be held forward hard enough to keep the tabs engaged in the frame.
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Seat bracket (steel) bolted to frame with shank bolts, steel plate fastened to seat pan with screws or rivets. Place some magnets betwixt and you've got a quick release seat. That's what I was thinking may work.
http://m.ebay.com/itm/181880934761?_mwBanner=1 (http://m.ebay.com/itm/181880934761?_mwBanner=1)
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To reduce compression from the seat, add 1 or 2 washers between the bottom of the seat and the seat bracket itself
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Seat bracket (steel) bolted to frame with shank bolts, steel plate fastened to seat pan with screws or rivets. Place some magnets betwixt and you've got a quick release seat. That's what I was thinking may work.
http://m.ebay.com/itm/181880934761?_mwBanner=1 (http://m.ebay.com/itm/181880934761?_mwBanner=1)
Yes, that seems reasonable, although I'll consider a mechanical catch as well.
I've ordered quick release pins as well as shank bolts, to try both options.
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To reduce compression from the seat, add 1 or 2 washers between the bottom of the seat and the seat bracket itself
Good point. I can try that, too, although the compression is to the rear of the bike more than vertically as far as I can tell.
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It looks like the second bolt went recently. I unloaded my top rack and got replacements with washers from a hardware store.
I think this all just resulted from an aggressive touring test phase this year where I had cobbled together a tail arrangement that put too much stress with not enough reinforcement back there. It's salvageable, and I have projects scheduled to make it quite a bit better.
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Success! I installed socket head hardened bolts with deeper threaded length (M6x25mm) and sandwiched the rack bracket with washers.
The top rack now rests on the tail tab and no longer can regularly be displaced at speed. The Corbin seat barely cleared the socket head height with the washers but was okay. On a regular seat, I'd recommend a mushroom cap bolt and still use washers to eliminate play.
The broken bolts were painful to remove, so be aware of they show signs of strain (particularly when the top rack does not rest fully on the tail when unloaded).
I've removed my hanky side racks and am switching to Happy Trail racks shortly for sturdier bracing.
(http://uploads.tapatalk-cdn.com/20161001/2d6b684c0b49354fd95a1ad4fec68cd2.jpg)
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Some updates after tinkering this weekend:
I've "resolved" the seat bolt issue by installing the most massive seatbolts possible, which are 90mm bolts with a shank right up to the last 25mm, and include spacers that help anchor the access hole on the top rack bars themselves. I did have to grind at the holes in the bars laterally to allow the spacer to sit flush against the frame side of the interior. The bolts are not going anywhere.
Why do this? Because it's part of the sturdiest side rack I've ever installed: Happy Trails SU Side Rack for Zero Motorcycle (http://electricmotorcycleforum.com/boards/www.happy-trail.com/find-your-bike/zero-motorcycle/su-side-racks.html)
I'll check later on making a latch for the seat - right now to unlatch it, I unbolt by just enough to let the latch off and leave the rack mount hardware in place.
I also added some padding between the tail plastics and the tab that rests on it for the top rack, because there was still some play in it while riding which caused the washers to make a squeak sound against the bolt head - a concerning symptom if not at least distracting.
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Some illustrative photos:
(http://uploads.tapatalk-cdn.com/20161004/d4930fb5c7901905faa57b96fd9a72d4.jpg)
(http://uploads.tapatalk-cdn.com/20161004/2d7a2c71b7f109d903b0da2bce062edf.jpg)