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sebwiers's '81 xj750rh - SECApocalypse - 3rd time's a charm

9K views 33 replies 1 participant last post by  sebwiers 
#1 ·
LOL, so that title came up autocomplete, for reasons. 3rd year working on this, but a good chance at actually finishing this year, as I should have the rolling gear done by January 2015.

Dated photo:


State before start:
Hossack upright fabricated, arms and body work partly done, rear suspension done(?)


State at start - basket case:


Running cost:
Bike - $100
Parts - Under $200 for stuff I didn't fabricate, way to much for stuff I did
 
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#3 ·
Quick pics from work today. Not actually much fabrication, but when I did the fitting I was so psyched I felt high.

The plates align nicely with the supports. Couldn't torque the the bolts on both sides because the shaft running between them won't allow the plates to tighten down all the way, as the holes are not yet reamed to final dims. Had to mill some reliefs on the backs of the plates where they would have pressed against frame and welds, made em big enough to allow weld inspection.


Originally had planed for the plate to be vertical, but for various reasons (mostly me being lazy and careless) it ended up raked back a bit. Upper pivot will be back a bit further than planned, doesn't matter much to suspension. Can always mill another set of plates if it does matter.
If the shock doesn't fit directly above the engine (which seems likely) this is one possible location that would work well in terms of shock rate ETC, but maybe gets in way of steering linkages.


I can't use six bolts per side as planned, but 5 should do fine. Its impossible to get a nut onto the back of a bolt in that hole that is third from the top, and the second from the top needs a shorted bolt than I bought. Top hole the bolt just barley fits, but I can't put it in from the inside like I did on the bottom, for reasons that in retrospect are obvious, but I totally didn't consider in design.
 

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#4 ·
Custom bolt w/ taper for upper control arm. Can't use a full length through rod as on bottom because these bits sit to either side of my head tube. Plus, two full length rods with tapers would mean the top and bottom are both forced to be a specific distance apart ... I'd have to get those to match up (say within .02") in addition to matching the bottom spacing on the tapers to the frame mounting point widths. In the end, this way is just less work, and (hopefully) is strong enough. I figure the side loading on the bolt (plus a good safety margin) to be maybe 4000lbs max.

Started as 3/4" stainless rod, turned it down on the mini-lathe using the little 1/4" carbide tip bits I got for x-mas. Was a slow process, mostly because I suck at setting up the lathe, but it got there. Actually pretty happy with the final fit, though at one point was ready to toss it because the taper was off. Ended up under-cutting the shaft a bit when I fixed the taper, but not enough to weaken it any more than cutting the threads will. Squared the end by clamping the rod on top of some parallels and knocking off .62" in the mill, then turning it 90 degrees so the flat was against the vice, knocking of .62", etc. Do that 4 times, and your 3/4" rod grips nicely in a 5/8" open end wrench.

I'm actually pretty proud of how 'pro' it looks.



Not a prefect fit, but the 'hand wiggle" test feels ok, and the wiggle goes away if you jam it firmly. Should be fine once its bolted up.

 
#5 ·
Made the mate to that bolt above. Lather was still set from my finish cuts, so didn't have to futz with angle. Took about 2 hours, came out even nicer than the first one did.

Rather than take pictures of it, I just slapped it on the bike and bolted everything up with the front wheel in place. TADA!!!! Stance isn't exactly what I expected. Wheelbase is gonna be rather long (is 47 inches from front axle to swing arm).

There's a LOT more space between the wheel and frame than I'd expected there to be, mostly because my pivot points are 3 inches further forward than I had planned, but also because the setup isn't adjusted to get the planned dims (head angle as shown is 25 degrees, not the 20 I'm shooting for; the bottom arm is long, will be adjustable down from as shown, and the trail adjustment is set to max trail). The long wheelbase doesn't bug me to much, and I'll be making used of that space, trying to move some weight forward.

Lower arm is a wood mock up, to help me figure out shock placement. The shock placement in the picture is one option. The other option is to mount it BELOW the arm, behind the wheel, activated by a linkage. The main concern with doing that is the heat from the pipes... there's obviously plenty of space! I may send the exhaust ABOVE the engine through the huge tunnel space I cleared out as a possible shock location, which would reduce heat concerns about the shock being in front of the engine.



'Fork' has an easy 6 inches of travel, and turns 30 degrees to either side (which is how it is pictured above, full left turn... seems rather not enough lock-2-lock, but I'll survive).

 
#6 ·
Reworked the front end dims, did a mock up. Shortened the arms each by ~ 4 inches. Resulting dynamics are not what I'd planned, but do have some advantages. Namely, the anti-dive starts off around 50% and stays flat up to ~3 inches of compression, then quickly ramps up to 100% at ~5 inches (and higher, at 6 inches).


Over-all shape is much improved, I think. More compact, less 'freaky chopper' and more 'street fighter'. Rake is also a bit steeper (was 25 degrees, is sub-20 in this setup)



Lock-2-lock is HUGELY improved. This is a MUCH better way to run the upper rod end. Since there's no suspension load on that arm, this doesn't put any side-loading on the rod end.



There IS a problem with the range of motion on (both) joints. The shorter arms require a larger range of motion to allow the same travel. As you can see, they hit. That can be fixed by angling the tips of the arms down a bit, so that the joints actually use the full range of motion, instead of starting in the centered position when travel is at 0. Adds a little fabrication complexity, but can be managed, and will look trick.



Planned shock location is behind the front wheel, actuated by a pull-link. Photo shows rough location, shock will probably face the other way (so the wheel can't hit the gase resevoir). Its tight, but can totally be made to work. Obviously will require some serious heat management on the pipes in that area (ha, a legitimate reason to use pipe wrap) or maybe routing them above the engine.
 

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#7 ·
Here's the FFE program specs for the new setup. The charts go up to 150mm, but the front travel is probably gonna be limited to about 135mm, so that big spike in the anti-dive at the top end doesn't bother me much. Supposedly for normal riding, anti-dive around 50% is good, I kinda wanted more, but it is nice knowing I have some extra when shoved. I can actually increase it to near 80% for normal travel range if I shave 5mm off the mount for the lower ball joint to bring it closer to the axle. Interestingly, it also means that if I drop the front end, anti-dive kicks in strong earlier in the travel. That may be useful, given I can easily implement adjustable ride height. Other stats look perfect.
 

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#8 ·
Fit some supports beneath the plates, to help pass brake forces back into the frame. Probably way over-done for that purpose, but they will also provide the fit the shock mount to, ensuring that suspension forces feed nicely into the new 'head pivot' structure, not some weak spot on the frame.

To do this, I had to ream down the holes for the taper shaft so that the big ally plates would fit correctly against the frame bolt-on points. Went pretty well, hand reamed about 1mm on each side and it fit up good. I forced the two plates onto the taper as hard as I could by pushing the plates together with clamps, to make sure I wasn't taking off the slack needed for the tapers to snug up. Damn they fit tight and stiff when under pressure!

Fitment (bike is flipped on back)


Welded up. Not my best welds ever (I wandered a bit) but plenty strong; I can grind em down. The ones that really matter strength wise are at the bottoms of the bolt-mounts, because THOSE take the braking force; the ones around the tube are under much less stress, since that joint is already miter fitted and only ever under compression.
 
#9 ·
Threaded the custom bolts today. No pics. Lots of time spent for little visible difference, although it looks less 'sketched' now. Bolts up crazy stiff and snug, should shrug off braking forces with a laugh.
 
#10 ·
Re-built the top arm today. Needed to shorten it from 11 inches to 7, and also rotate the nose 90 degrees.

Planning stage. Basic idea was to take the old upper arm, bridge it near the pivots to hold the alignment with some tack welds, cut it through the bends, permanently bridge the cut with some rectangular tube, and then cut the old 'nose' free and mount it to the bridge.


After much cutting disk and file work, and basic welding, I took it to the anvil and got brutal, wrapping the corners of the tube rectangular around the bent 1" DOM.


Bolted up on the bike for a clearance test. Seems good, may cut out the tack welds and shift the 'nose' down a bit more. Idea is, it points down when wheel is at full extension, tilting the rod end to one extreme of miss-alignement so that when the wheel goes bump it the rod end has its full mis-align to travel through. Ideally is enough for almost 8 inches travel; I'll be using 5, so if I put 1.5" safety on either end I can adjust ride height 1" either way and still have some safety.

The 'nose' sits in a rectangular hole cut in the tube, so the rod end has plenty of space to swivel. I'll probably be cutting some big round 'lightness holes' in the rectangular tube when I get done, both for actual lightness (its pretty much unsprung mass) but also for look and to make painting the inside of the tube possible (to prevent rust).


Don't think I am happy with the results here. The part is awful heavy (especially for something under tension only) and pretty ugly. Will do for now, but I plan to replace with something more like in the Fior patent. That is, a flat plate bridge with lightness holes. Weight matters here because it is both unsprung, and rotates through almost 60 degrees.
 
#12 ·
What I ended up with after doing the mock up.





This is at 4" bump. I'm a bit concerned that 6" bump won't be feasible, but I've got a design in mind that raises the back of the arm some. I also can't really go past 4" with the upper arm hitting the plate, so either need to relief the plate, make a new upper arm, or releif the arm. The last option is probably the least work in terms of what it might fuck up down the road. It means I can't use that arm, but I was already planning to make a new one, and it leaves options for plate alterations and upper arm design open.
 
#13 ·
Managed to bump the wheel movement up by another inch, but more than that and the tire will hit the pivot shaft. The pivots bearings are gonna be kind of like pillow blocks.

Had to disassemble to change parts to rest clearance. What a pain in the ass- between the taper bolts being murderous hard to extract and various regular bolts being blocked by parts I can't get off until those bolts are out.... i had to literally split the fork down. So I've cleaned up some holes to make that easier.

Added some lightness and finish to the upper pivot mount, and also cut some clearance into the bridge. Bridge needs a lot more cut off eventually.
 
#14 ·
Adding lightness and class to the upper pivot mount. Also, can be shifted to allow trail adjustment, instead of threading in and out the rod end.



Horrible pic of it mounted up, ans dome of the relief cutting on the bridge (which will get MUCH shaved for lightness at a later date).

 
#15 ·
Did a bunch of misc stuf today.

went shopping for metal


Started cutting down & finish shaping the bridge plate.


cut the lower arm


Filled in the tack welds on the fork crown and welded the lower arm
 
#16 ·
Metal part above wood mock up, should give plenty of clearance for turns. Had my little helper with todsy.
 

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#17 ·
Went to the shop open house last evening for a few hours, started on parts for the new upper arm. Instead of buying tube inserts, I got some 3/4" x .156" wall dom and threaded the inside for the rod ends (1/2" x 20 tpi). Looks less chunky, and lets me mount the eyes close to the plate because needs less clearance.

Drilling to 15/32 per thread chart


Tapped, with rod end in place.
 
#18 ·
Worked on the lower arm today. Touched up the ball joint eye, bored some bearing pockets in blocks of 7075 t615 on the lathe (had some help w
/ that).
 

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#19 ·
There's a bolt very close to where the bearing will sit on the shaft... sure enough, the head would get in the way of the pivot block pivoting. Can't have that, so I knocked the corner down to make clearance.



Since these bearings will each take a lot of force (though still less than half the force of a head set bearing) I left 3/8" around the bearing, and used a ball end mill to make a transition, to avoid stress risers. Probably over kill, rear swing arms get away with less.



Action shot - first time using a turntable on the mill (or a ball end).

 
#21 ·
Lower control arm is mostly done. Assuming everything bolts up OK, this thing will be getting a bunch of 'speed holes' in it (1-3/8 step drill). The whole point of this crazy lower arm shape is to maximize the space the wheel has to push up into; even so my travel may be a bit short (less then 5 inches).

Each bearing block bolts to the tube with 2 half inch flat heads in countersunk holes (again for clearance, but also a very strong connection) that are 1.50 inches apart on center. The tube has 5 half inch holes that are .75 inch apart on center, allowing 3 positions for the baring blocks, giving arm lengths of 8.5", 9.25", and 10 inch. Configuration shown is the shortest one. Longer lengths obviously give a longer wheel base but also less progressive anti dive; they may also allow more travel both by being longer levers, and leaving more room for the wheel to push into.




Clearance when its all put on the bike is crazy fucking tight. I machined both faces on the bearing blocks down by .125" to get the assembly narrow enough to go where needed with required clearances, allowing the bearing bevels to sit proud. Looks sexy. There's about 1/16" inch between the bearing blocks and those steel uprights the plates bolt to. For final assembly, I will need to bolt everything up with the bearing blocks in place, and then bolt the tube to the bearing blocks, because its the only way I can get clearance to insert all the bolts.

The top of the tube IS resting against the frame in this photo. I'm pretty sure my full-extension isn't more droop than that, but I could make some clearance cuts in the tube top if needed.



I couldn't finish assembly because the ball joint tip hits the fork crown. I'm hoping there's enough material to cut in clearance, otherwise I need to replace the aluminum and modify the steel.

 
#24 ·
Ball joint clears now. 9 inches of travel!!!! Some angles are off, will need some new parts for other clearance issues, but is all stuff I planned to rebuild anyhow. At the very least I now am sure I can get the travel, clearance, and loc2loc I want. Just gotta keep cutting and working.
 

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#26 ·
Cut clearance on the arm to allow nice wide lock-to-lock steering (at least 80 degrees). Shape cam out really odd, but pretty cool (no pic w/o receiver in, sorry).

Drilled holes to mount the ball joint receiver, pics of straight ahead and full lock with full bump.



 
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