Belated build thread; upgraded Suzuki DR350 flyweight air-cooled ADV bike

OK, now we are onto the meat of this thing...the one you have all been waiting for...the swingarm swap! I've been asked about this aspect of this project far more than anything else, so I can get a few things out of the way right now. No, it is not a bolt-on. No, you can't do it yourself at home if you don't have decent fabrication skills and welding skills/equipment. Given some of the pitfalls I encountered along the way, I wonder if there is a better candidate for a swap than the one I chose, but if nothing else, I learned a ton along the way. The swingarm in question is a 2012 Honda CRF250R swingarm, which is undoubtedly quite a bit stiffer and lighter than the stock DR unit. It is also substantially similar to many other Honda CRF swingarms from the past 20 years or so, 125, 250, 450, both R and X models. I'm sure there is some small difference in some dimensions, but the basic architecture is the same, and many dimensions are the same as well. I was inspired by a blog post on a blog called Tiny War Machine about a guy and his DR350 upgrades:

Tiny War Machine DR350 Swingarm Post

I don't know that he ever followed through with it, but I took the idea and ran with it. Here are some of the images from the blog linked above. I am not sure how my measurements differ exactly from the ones below (if at all) since he used a 2004 CRF450X arm and I used a 2012 CRF250R arm, but they aren't massively far off, however, I didn't write all the details down and have now long since sold the bike, so if you are planning to duplicate my work, you will have to do some measuring...sorry.

Both the 2021 CRF250R and my DR350 share the diameter of the swingarm pivot, which is confirmed by fitting the Honda pivot bolt to the Suzuki frame. You can see that the Honda bolt is longer and bottoms on the threads before tightening on the frame, so the options include washers under the bolt head, welding spacers to the outside of the DR frame, or just using the DR hardware. I elected to do the latter. The Honda swingarm is also a touch narrower at the pivot point, so there will be some spacers on the inboard side as well. More on that in a bit. Also note the stock DR rear suspension linkage mounts visible just below the swingarm pivot bolt as these feature prominently soon.

So, let's review what we know about the two swingarms:

-Same pivot diameter

-Same lower shock mounting bolt diameter

-Slightly different lower shock mouting width, but easy to make up for with spacers when using a DR shock on a CRF arm/linkage/dogbone.

-Different rear axle diameter

-Ballpark similar, but slightly different rear hub spacing

-Different rear brake mount design that will require matching brake caliper/mount to the swingarm.

-Different rear rotor diameter (but the Honda CRF250 diameter matches a DR650 stock rear rotor, which bodes well for a Suzuki hub/rotor that will play nicely with Honda arm/caliper/mount.)

-The drive side/brake side is the same between both bikes.

-The brake line routing is roughly the same between both bikes.

-The rear brake master cylinder diameter is the same between both bikes, which bodes well for a DR master, CRF slave setup.

-The Honda arm is slightly longer, but I did the math, and it isn't so much so that it will have a huge impact on axle travel or rising rate. Spring rate I didn't do the math on...more on that later.

-Completely different attachment point for the linkage (top vs. bottom, and different dimensions)

-Completely different attachment system at the frame/swingarm interface. The Suzuki arm is distinct from the motor mount, and has a full-length sleeve that is part of the arm over the entire pivot within the frame. The Honda arm splits around the rear motor mount, and has a big ol' open space in the middle of the arm where the rear motor mount lives on a Honda.

I started out by making a jig that could accommodate either swingarm on the DR frame, with both lower brackets matched for dimensions around the center of the rear axle, but built for the different rear axle diameters. In addition, I made sure the length would reach from the rear axle all the way up to the rearmost and highest fixed mounting hole on the DR rear subframe with the rear wheel at the stock location for full droop. This jig will allow me to compare DR and CRF swingarm measurements, and more importantly, determine how they relate to each other. I wish I had a couple more photos of this process, but history is what it is, so bear with the long-winded explanation.

The photo below shows the CRF arm mounted on the frame. The preceding step I didn't document was to remove the spring from the DR350 rear shock, and remount it on the frame with the stock DR swingarm, linkage, and dog bone on the bike and attached. The rear wheel was removed, and I attached the jig with the DR axle adapter around the DR rear axle. Without manipulating anything, the setup was at full droop, and I clamped the jig to the DR rear subframe, marked the center of the rear subframe hole for rear droop, and drilled a corresponding hole in the jig. The hole in question is at the very rear of the subframe and is clamped with a vice grip in the photo below. Then I swung the stock DR setup all the way up to the bump stop to the full-compression position, and once again marked the center of the same subframe hole on the jig, and drilled it for a full compression position.

By using these two holes drilled in the jig, only with the CRF swingarm/linkage/dogbone on the bike, and the CRF rear axle bracket at the bottom of the jig, the jig would allow me to compare the behavior of both rear suspensions at full droop and at full compression. Before rigging up the CRF setup on the DR frame, I also measured shock shaft exposed at full droop and at full compression, and then mocked everything up with the rear axle one inch closer than full droop to the rear subframe bolt, and remeasured rear shock shaft exposed. I then compressed the rear to two inches above full droop at the axle, and measured the rear shock, and then did the same at three inches at the axle, and so on. I continued all the way through the travel with the stock DR setup, which gave me a map of how wheel rate compared to shock rate, i.e. rising/falling/or whatever.

After extracting all the DR data, I put the CRF rear swingarm, dogbone, and linkage on the bike, along with the jig (now using the CRF axle-sized lower bracket) and left the front linkage attachment point loose for the time being. With the jig, I knew where I would want the axle (and therefore essentially ride height-ignoring slight axle length differences) at full droop and at full compression. What I didn't know is where I wanted to attach the linkage to the DR frame to get this all to play nicely together.

During this process I did lots and lots of math. I didn't keep all the numbers, and I am not sure what the numbers below even mean, but one thing is certain, the whiteboard in the shop sure got a workout in this era. The other thing I determined is that if I combined the CRF swingarm/linkage/dogbone with DR frame and rear shock, and replicated the stock DR positions for full droop and full compression, plus each one inch rear-wheel-travel increment along the way, the rear wheel rate wasn't more than a tiny bit different between the two, and the front of the rear linkage that was unattached at this point looked as it could probably find a happy home if I just fabricated one not too far from the stock DR point...in other words, the linkage didn't need to occupy the same space as a hard point on the existing frame throughout the range of travel.

Now that I knew the extremes of travel with this custom setup, and that the points between weren't going to be too far off the map, I needed to create the linkage mount that would work across the entire range of travel. I got some heavy cardstock and left the CRF swingarm/linkage/dogbone plus the DR frame and rear shock bolted together with the jig.

The idea here is that if I can find the linkage mounting location that satisfies both full droop and full bump with this setup, I can build a mount there, and everything should work. I set things to full droop and moved the linkage through the resulting arc.

I simply put a ballpoint pen through the front linkage hole and scribed a few arcs on the card stock, figuring to take an average. Then I set everything to full bump and repeated the process. The intersection point of the two arcs is the linkage mouting point needed to make this setup work.

Initially I had fantasies that I might be able to either repurpose the DR mounts by cutting them off and respacing them for width and/or reclocking them around the cross tube they were mounted on, or possibly use them as an anchor point for fabricating a new mount. To that end, I was pleased to see that we ended up only a little bit behind the stock DR linkage mounts.

I realize that it is a slightly complex process to follow. If you have questions or want me to try re-wording the explanation, let me know and I'll be happy to do my best.

Initially I was hopeful that I might be able cut off and reposition the stock DR linkage mounts to repurpose them for the CRF swingarm. The dimensions just didn't really work out, unfortunately. In any case, the stock mounts have to go, so I got busy with the cutoff wheel. One down, one in progress...

Et voila! Just as easy to forge ahead now as it would be to go back, right? Time to grind these babies smooth and fabricate something new.

Above is the topside view. I stopped short of the factory crosswise reinforcement between the still-existing motor mount tabs, and the now gone swingarm mount tabs, figuring it could be useful to tying everything together in the end.

Even so, I did tidy things up a bit....

I found some metric washers that were the perfect i.d. and the perfect thickness for one spacer on each side of the inside of the swingarm pivot to bring it down to the Honda dimensions. Woohoo, saves me time on the lathe! Here's one side tacked in and ready to test fit the swingarm. It worked a treat, and I fully welded them and ground them back.

Keep in mind that most of the photos in this post are of the frame upside down with the new swingarm installed. Now that I knew where the new linkage pivot needed to be, I just had to translate cardstock to metal. Rather than use the cardstock as a template transferred to metal, and then try to deal with any warpage, shrinkage, or displacement due to the processes of fabrication and welding, I decided to simply redo it once again in metal. The other benefit of doing things this way is that it would allow me to confirm that it wasn't practical to reuse the old mounting tabs. I tacked a sacrificial bit of thin plate in the correct spot to cozy right up to the linkage.

Perfect! The linkage is touching the plate, but can still swing freely...and I still have my jig for rear suspension travel.

Here we are at full bump with the Honda swingarm, linkage, and dogbone, plus the DR rear shock with no spring, and the jig mounted. I added some straps to make sure that the damping of the rear shock wouldn't try to move things while I was working.

Given the challenges of trying to perfect center the scribe in the oversize hole at the front of the linkage (or at least oversize as far as the scribe is concerned) while marking an arc, I decided to play it safe, and figured I would scribe four arcs rather than two. Instead of two perfectly-centered arcs, I would do front arc at full droop, front arc at full bump, back arc at full droop, back arc at full bump. The keen-eyed among you might spot some new hardware welded on the foreground. Stay tuned for details on this in a future post.

Here are the resulting scribe marks for the arcs, and the center of the diamond is the exact spot we need our linkage to pivot.

Like so. I center-punched the dot, and drilled a hole in the correct size for the linkage pivot hardware.

Here's the hole. At this point you are probably wondering how this will work with only one side of the linkage supported. Great question...I won't be riding the bike with this flimsy plate, just fabricating, so all it has to do is be stout enough to stay in place and hold the linkage in place while I get the first final piece tacked to the other side. Then the final piece on the other side will hold everything in place while I grind this temporary bit of plate off and fab a second final piece to take the place of the plate, and tack it on. Then I will remove the swingarm and weld everything.

You can see the plate in the top of the frame here, and see how it snugs right up to the linkage. I test fit a bolt for this photo, and will need to find a longer one to reach all the way through and get a nut on the other side to keep everything fixed while I work.

Here's that longer bolt, complete with nut on the other end (not visible in this photo.) On the other end, I have bolted on the stock linkage mounting tab, and then swung the cut-off end around to meet the frame, and you can see that it just isn't going to work to re-clock these and weld them on. Not enough surface area or structure to withstand dual-sport abuse. Ah well...

Teaser for the next post...

I gotta admit, that's a pretty clever way to figure where the linkage mount needs to go. This is a fun project to watch come together. 

In reply to thatsnowinnebago :

Thanks, it was a fun project to put together. I should have done a build thread at the time, and had intentions to, but didn't get around to it. At least I took a ton of photos so I can upload one after the fact. I don't know that I've ever been asked more questions about a project than I have with this bike!

I figured I could have started with sheet and made a bracket as close as possible to the original Suzuki one in terms of structure and shape, only with the correct length and angle to attach to the frame in the correct position...or I could just cut something vaguely the same shape out of angle iron that is just a skosh thicker, save some bending, and call it day.

Not really all that different as far as the important stuff is concerned.

Here is it is mocked up and bolted to the linkage. The plan is to keep the jig and swingarm on the frame and locked into place while tacking the new bracket, which is also bolted through to the temporary plate on the other side of the swingarm. It isn't as heavily braced as a proper jig would be, but it should really help keep the bracket in the right spot while tacking. The swingarm was centered in the frame between the washers on the inside of the frame pivot...and yes, I also confirmed that that both bikes have rear hubs centered relative to the swingarm pivot while hatching this plan. An asymetric swingarm setup isn't unheard of, and could wreak havoc if not accounted for in the design phase. No such worries here.

Looks pretty good from this angle. I'm my own worst critic, so I see the fit, champfer, and welding prep issues. Given that I was cutting out the brackets with a bandsaw, hacksaw, and cutoff disc, I could have been a bit more conservative on the cutting phase, and put in a bunch more time on the filing/fine-grinding/fitment phase and made this a more precise fit, but I didn't. I can always hold down the trigger on the MIG for an additional second or two and fill up the gaps with my hot metal glue gun, right?

OK, one side tacked, swingarm and linkage removed, and welding underway.

One side now welded, frame back upside down again, and the initial temporary plate has been cut off in preparation for putting things back together and tacking bracket number two.

And here's both sides welded on. You know the old saying, "Grinder and paint make me the welder I ain't!"

I was quite pleased with how well these interfaced with the existing motor mounts and the amount of that bracketry that I left on the frame, which should make it easy to tie everything together. It was becoming aparent at this point that installing the linkage bolt in this location and working around the factory DR rear brake pedal mount and the kickstand mount on the other side might be a bit of challenge, but more on that later...

Here's a top-down view from the front of how the new brackets fit with the original brackets/motor mounts, and also gives a view of the washers/spacers on the swingarm pivot.

I just realized I neglected to post some pictures of my mockup on the rear wheel end of the swingarm, so let's hop back a bit before we get too far ahead of ourselves.

As I alluded to early, lots of measuring, drawing, and math went into the swingarm swap. These paper notes have since been lost to time, and at the time I knew the context for everything, and didn't intend it for anything other than working out the possible issues, so sorry for the lack of detailed specific notes for what each number means. It looks like I was using the inside face of the rear swingarm on the disc brake side as a baseline, which I think I did just to have a reference for how different the Honda and Suzuki were, rather than because I was using that as a fixed point while fabricating. If my memory serves, I was going to use all stock Honda, but then switched gears and decided to fit the Suzuki hub (with modifications) to the Honda swingarm with custom bearings and axle spacers, and with a Honda rear caliper and caliper mount, plus a Suzuki DR650 rear brake rotor. If you are wondering why, and the time I had a stack of DR350 hubs, and wheels, including supermoto wheels, as well as stacks of DR rear sprockets, and even with thinner custom bearings for the oversized Honda axle, the Suzuki bearing setup was beefier and easier to service than the finicky, tiny Honda setup. Once I knew what I was in for, I proceeded with spacing by getting the rotor centered on the caliper, and found that the difference in chainline on the drive side was so tiny I didn't end up worrying about it, and then just laced the rear wheel to make sure the rim was centered over the hub/spacers/axle assembly, and made custom axle spacers to fit it into the swingarm. It wasn't quite that simple in the end, but more on that later...

Here's a side by side of the two rear brake calipers, Honda up top and Suzuki at the bottom. Good news includes the same basic type of brake, and the same size fitting on the brake line. The Honda is a little lighter, and the Suzuki might have some more heat-shedding capability, but not a night and day difference either way.

Here's a hub comparison from overhead, with all stock Honda setup bolted to the swingarm, including a 2012 CRF250R rear hub and the stock Honda spacers. The powdercoated black hub below is stock DR350SE, with the brake rotor mounting faces aligned along a straightedge which I then removed for the photo.

Here's the difference in the position of the rear sprocket mounting faces with the brake rotor faces aligned. I think it was right around 2mm, not enough to worry about in my book.

At risk of hopping around a bit, the other project going on concurrently with the swingarm swap was a kickstand swap. The DR350 has a heavy steel kickstand which bolts on to a heavy steel bracket that is welded to the frame. When it is up, it points pretty much straight back, which means it will scratch up the swingarm if it gets bent, and is at just about the worst angle possible for potentially bouncing in bumpy terrain. It is highly unlikely it would bounce all the way down, but not unheard of, but it will bounce enough to kill the engine if the kickstand cutoff switch is still intact. Even if you remove the switch, it most likely has never been maintained, and the pivot is also the mounting bolt, so they get sloppy and flop around, which makes them wear out faster and flop around more, which....you get the idea.

In the center of this picture is where the stock mounting plate once was, just to the right of the footpeg mounts. I cut if off.

I bought an aluminum TrailTech (another local company!) aftermarket kickstand for some KTM models, which is an aluminum arm with steel mounting bracket, perfect for my purposes. It is one of the more modern designs that swings up high, tucking behind the side panel, and angled up far enough there is very little chance of bouncing down on accident. Brackets, stands, springs, and feet are all replaceable as parts from TrailTech if needed. If something wears out, it can be unbolted and replaced, instead of being a welded part of the frame. In the picture above, I put two longish bolts through the mounting holes, and put sleeve nuts onto the backside of the bolts.

The frame is now upside down again, and what do you know...when held up to the frame at the correct height to work with the kickstand in the down position, these KTM bolt holes line up really nicely with the frame...awesome!

ZAP ZAP, and we're on!

Couldn't have planned it better, but to be honest I looked at one and said, "Ehhhh...that looks like it is about the right size/shape and might fit."

Tucked up nicely out of the way...this thing is looking more and more modern by the moment! The kickstand also weighs a fraction of what the stock one did.

It felt like it could be more solidly-mounted, so I decided to add one more fastener in another plane. It just so happened to work nicely to keep building down below the two bolts I had already installed, and weld another nut onto the frame where the rest of the original kickstand mounting plate was attached. I added a third mounting tab to the kickstand bracket, and it was like it was made to go there!

A bit more welding and we are in business. I can't believe how well this all worked.

I put the swingarm on and mocked up full bump....just clears the swingarm, just clears the side panel (not installed) is at just the right height and angle when lowered to hold the bike up like stock. Looking back, I have no idea how I would build a jig to replicate this. It was all eyeballed, and it really is better to be lucky than good sometimes!

Here's the clearance at full droop. Plenty!

This is really cool.  I enjoy following along with the changes.

In reply to wawazat :

Thanks, glad that you are enjoying the build. I enjoyed building it, and I am reliving the fun by sharing it with others!

One additional aesthetic change I wanted to make was to replace the 80's/early-90's-style droopy rear fender with a more-modern looking higher, longer fender, and preferably one that would match my front supermoto fender in terms of style as well. The common go-to for these bikes is the Maier fender, while it is an improvement in the looks department,  it still looks a bit dated, and a bit too rounded, and doesn't match the idea I had in my head, or my current front fender. I found an early-2000's RM250 fender that looked about right (and it was only about the fifth fender I bought on a wing and prayer!) and it fit into the DR frame with only a tiny bit of flexing inward. Even better, once in there, the holes lined up...it was also nearly perfect match for the look of my front fender, and it came in white...it was meant to be!

The two holes that lined up were only two of the mounting points, and the fender was so radically different in the front portion, I couldn't exactly figure out where to trim, or where to make some holes for an additional couple mounts, so I started by covering the stock DR350 rear fender with painter's tape, and marking the mounting holes.

I peeled off the painter's tape skin and draped it over the RM fender, lining up the existing perfectly-aligned holes, to see what else I might need to cut, drill, etc. The fit of the tape contours wasn't perfect, but worked really well as a rough cut guide.

I did a little cautious snipping, and tried a test fit, and it went in waaaay better than before...progress!

Here's the second or third test fit from underneath...getting there. Easier to measure 17 times and cut once and all that. I decided to leave the stock RM front mounting points on for now, and see if I could make them work somehow, which ended up being a good decision in the end.

Getting it fitted nicely, careful bit of trimming by careful bit of trimming.

So the front mounting points aren't too far away from the subframe, and I could probably whip up a couple of brackets pretty easily to connect these existing fender mounting points up to the existing subframe structure, which would ease replacement of the fender down the road if needed. Buy another, trim a bit, and bolt it on.

I hopped over the purple-framed bike for more complete context and whipped the stock fender off for a test fit of the RM unit. Yes! That's the look I'm going for!

Here's what the RM fender looked like post-surgery, and ready to bolt on once I add a couple quick mounting tabs.

Now that the rear linkage mounts were in place, I went about tying them in to the existing structure, which might be overkill, but if it is, it is an overkill I feel better about than just leaving them as is. I went back to the scrap heap to dig for cut offs and found some that I was able to trim to fit nicely.

And here they are welded in. Good to get more welding practice, but the results are still not ideal. Grinder and paint make me the welder I ain't once I again.

I didn't do any sort of calculations or FEA or anything, but the seat of my pants says that looks strong enough for any normal riding circumstances.

Now I could finally get everything bolted together, flip the rolling chassis over, mount some wheels, and see what it looks like. I was really excited to have reached this milestone, but as I got to it, I noticed that the clearance to the spring was pretty tight. When I mocked all of this up with the jig, I had the spring off so I could work the rear shock up and down, and silly me didn't think about clearance with the spring installed. Well, let's keep some fingers crossed and keep working ahead.

It is starting to resemble a motorcycle again! The "primary/original" purple chassis can be seen on the left.  Very handy to have both side-by-side for reference, measuring, etc.

I stood in the glory of my creation and cracked open a beer. in part to celebrate, and in part to drown my sorrows for the remaining work ahead. Now that I had all the major rolling chassis components on, it became apparent that the clearance on the rear spring wasn't going to work without more modification.

Here's a closer look.

Here's the angle that tells the complete tale of woe. There is just no way this is going to work with the stock DR frame cross-brace. There isn't really room for smaller diameter spring on the shock body, either. Relocating the lower pickup point or the pivot point would mean going back to the drawing board on every other aspect of the rear suspension. Another rear shock wouldn't be likely to match critical dimensions like length, eyes, and width, and/or would likely foul the DR350 airbox and intake boot, which is very tight to the shock already.

The short version of the to-do list on the whiteboard at this time.

In case you were wondering what I was riding, if not the purple-frame DR, I was spending a lot of time on the red GSF400 Bandit, and my buddy with the Husky 701 was undergoing surgery and asked me to ride it from time to time to keep her battery topped off, fluids circulating, and such. I was only too happy to oblige!

Even though I lost the numbers, I did just find my photo of the visual representation of the very small difference in the wheel rate versus the shock rate with the stock DR setup being the bottom line left, top line right, and my custom hybrid setup the top line left, bottom line right.

While working on everything else, I was also working on the rear rack.

At some point along the way, I acquired a rack from an inmate at advrider.com, which had already been discontinued at that time. It was made by two members on the forum, 2sos & Ro0K. At one point they did short run DR350 upgrades in their spare time, and this elegant, lightweight, bolt-on, folded and powdercoated steel rack was one of theirs. It can be seen above. While it was a nice basic design, it had a few issues for me:

-The front edge (fairly sharp stamped and bent thin plate steel) was uncomfortably close to the back of my overstuffed and custom-upholstered dirt-model seat, causing me to have to shove the rack all the way rearward and hold while tightening bolts, and shove the seat all the the way forward while tightening bolts to keep the rack from potentially cutting into my upholstery over time. Things might have been different with a stock dual sport seat, or maybe just any stock seat, but I wanted to increase clearance.

-The rear turn signal mounts are round with a couple flats on them to keep them in the correct orientation. The rack had a couple round holes for mounting, and not quite the right size.

-Using this rack meant losing the stock tool kit mounting.

-The rear turn signal wiring had to be extended and was dangling, and the solution was to zip-tie to the rack...how gauche!

-Gloss black is innocuous and is probably the best color for short-run custom parts, but I wanted something that blended a bit better and didn't look so aftermarket.

-The front corners were cut and folded, which I'm sure was the perfect process for production, but resulted in some sharp edges that were going to make short work of my new soft luggage.

I stripped the rack of the black powdercoat, and here is the the bag's-eye-view of the sharp edge.

Easily enough removed!

Nice; now I just need to fill in the gap somehow.

That should do it. I'm finally beginning to wrap my head around chamfering, going slightly undersized, and leaving a trough to fill when welding, instead of stacking up an ugly, weak raised bead up top and then spending forever grinding it down and therefore removing most of the strength.

Progress! Stack of dimes, row of tacks, basically the same thing, right? I am also beginning to realize that when welding on small bits of thinner stuff, taking one's time and doing a lot of tacks might be preferable to blowing a hole in the work. You might also be able to see that I ground back and radiused the forward edge of the rack to minimize potential damage to the seat upholstery.

Looks great once linished back!

Plus the other side.

The problems with a belated build thread...I just found some photos for the rough repair (but an improvement) on the ugly previous weld repair on the battery box mount. The old repair was out of alignment in all three planes, and completely out of round, as some material seems to have gone missing in the middle before they tried to patch it back together.

I got it level in the up-down sense, if not perfect in the left-right, front-back sense, and good enough to accept the factory rubber battery box mount...good enough!

In order the create clearance for the rear shock, I broke out the Sharpie and marked the crosstube that was in the way before removing the shock.

A little bit of work with the cutoff wheel later, we have a bit gaping hole, and hopefully, clearance.

While I was in there and welding, I wanted to add captive nuts for the rear rack. The mounting the rack designers envisioned cleared everything on a stock bike nicely, with a spacer between the rack and subframe, and a nut on the backside of the subframe. Since this bike is custom, I have a welder, and I make my own rules, I figured it would be slick to replace the spacer with a captive nut, and avoid the whole loose nut on the backside arrangement. I installed a sleeve nut with the correct threads (after removing the plating that might mess with my welds) by using a bolt from the backside to hold it while welding.

Yarp, we have  clearance, Clarance! That'st still pretty tight, but this was my first mock up post-cut, so I resolved to do some judicious grinding of the hole, and plate it on the inner face, not the outer, to ensure enough room for the spring. This photo is taken at full droop, which is where the rear shock is closest to the cross tube.

It sure makes things easier to have two bikes side-by-side, one stock, and one a modified work-in-progress. Great for reference on how it all goes together, great for measuring as you customize....highly recommended with a project of this nature!

I took the rear spring off again, and used my tried-and-true painters masking tape when trying to make a pattern for a part that will end up curved, but will start with flat stock. I got the tape in there, and used the Sharpie to clearly mark it out on the outer corner. I will cut to meet the outer corner, just as I have marked here, but then will grind it down a bit to precisely fit the patch inside the hole for maximum clearance before welding on the inner corner. Measure seventeen times, grind five times, weld once, grind the weld a couple times, and all that...

The final task to tackle on this stretch was marking, drilling, and tapping the upper triple clamp for the Britannia Composites Lynx fairing and lighting...came out nicely! The two bolts/washers on the front side are new and will line up with the fairing mounts. I seem to recall that Britannia Composites supplied either a template or at least a set of measurements for marking and drilling the holes. You can see that I have started a tiny cut on the old motocross-style single center-mount tab thingie that is now useless to me, because I am not attaching a plastic numberplate where there should be a headlight, and the tab is in the way. After snapping this photo, I finished nipping it off with the Dremel.

Since I took a chunk out of the frame, I figured I should add back in some reinforcement via a gusset on the front side. I found an appropriate left over slice out of some tubing in the scrap pile at the shop, and cut 'er down a little further on the bandsaw, and then cut out a little wedge and bent her into shape:

Eh....not my best work, but close enough for this exercise...While I was at it, but not something I captured in photos until after the fact, I drilled a hole in the gusset and added an M5 or M6 captive nut on the backside before welding it on, in order to roughly replicate the mounting point for a wiring harness clamp that went AWOL when the grinder came out earlier.

Here's the captive nuts welded for the rack welded on. A double benefit of these is that they will also serve as two of my rear fender mounting points. The sleeve nut is long enough for rack hardware to thread in about 2/3 of the way from outside, and fender hardware to thread in about 1/3 of the way from inside. M8 should be up for the job, and both rack and rear fender will have two more additional attachment points as well. I seem to recall I was thinking of Colin Chapman and his relentless pursuit of double-duty parts in the interest of weight savings when I came up with these.

Here's the shock clearance cut and gusset welded on and linished back. The pre-grinding photo of the weld wasn't quite so tidy.

Woohoo!