Operation Convert Bike To Sparks: success!

Sacrifice to the Gods of Entropy and they may eat you last.

Things that I have learned:

1. 1.5mm mild steel is arc weldable, but not necessarily by me.
   
2. Sometimes, close enough isn't good enough.
   
3. There's nothing you can damage with an arc welder that can't be fixed with an angle grinder, or vice versa.
   

My first attempt at welding in a section of pipe wasn't a total success. I used 38mm OD 1.5mm mild steel (35mm ID), which is at the lower end of what's arc weldable. Cut to the chase, I got it butchered together, but made a serious snafu: once it was all welded up, the exhaust plain didn't fit, no matter much much I swore, pleaded, or tried to negotiate with it.

I did a fair bit of offering up, then removing, tacking and re-offering but made one fatal error - I didn't tighten up the manifold nuts when offering the exhaust up. Consider that a few degrees of difference at the manifold means an inch or so at the tail joint. One I had it all welded solid, I could choose between a tight seal at the manifold and a clear 1" gap at the tail, or have the exhaust bolted on but spitting from the manifold.

In the event, I called a Mulligan, and decided to do it over. Since I'd burned through so much of the 1.5mm tube, I decided to go bigger. 2mm would likely be OK, but I wanted to be sure and went to 3.2mm, with an OD of 42.4mm = ID of 36mm. This was likely too big; an ID of 33 or 34mm would be a snugger fit, but you can always narrow wide pipe down.

First things first. This time, I'd be doing some serious welding with the exhaust on the bike, so the tank and battery had to be removed and buried 6' deep (well, balanced on top of the bins out the back, anyway):



Then I ground off the 1.5mm pipe section from the left hand pipe. As always, it took longer than I'd expected, and there must have been a small earthquake or similar, as I... uh... ground almost all the way through at one point. Mind Control Lasers, maybe.

Aaaaanyway. Remember the adage: welding can fix anything that an angle grinder messes up, and t'other way around too. A bit of 1.5mm patching over it covered up the evil. Let's never speak of it again.

I cut the the 3mm pipe to 1" longer than the removed section of cat-pipe. Another mistake I'd made the first time round was to make the replacement pipe too long. This meant that it went too far up the curve of the pipe on both ends, which contributed to screwing up the angles. See, I do learn, eventually.

Then each end of the pipe needed notches cut so that I could narrow it in. I'd recommend hacksawing these, rather than grinding them out, since the narrower they are, the easier it'll be to make them gas tight later:




Another lesson learned - this time I bolted the downpipe on solidly before even thinking about fitting the pipe. Note the car jack holding the lower section up at approximately the right height:



Then the ends of pipe section could be gradually narrowed down and offered up until it was fairly tight over both ends. I had to remove the whole assembly to bang it down tight. That's where your Anvil Shaped Object comes in handy. You do have an Anvil Shaped Object, right?

Once the new pipe was as tight as I could get it around the original exhaust, it all went back on again, and both ends of the exhaust were solidly attached. For those playing along at home: solidly attach both ends.

Then and only then did I weld up the joints. Rather than just tacking, I manned up and welded as much as I could manage in place. (Pro tip: remove the brake pedal on the right side to get more access to the bottom weld).

Only when I'd gone as far round the pipe as I could manage did I remove it. The unwelded parts of the pipe ends needed banging down again to get as tight a fit as possible. And the first thing I did then was to put it back on and check that it still fitted. See? Learning! See?

With everything seemingly OK, I removed the exhaust again and finally finished the welding. In my pre-emptive defence, it's a fiddly job, as you have to move the rod in 3 axes: rotate around the pipe, oscillate up and down to cover the joint, and move the rod in as it melts down. Very zen. Then there's the 8 notches in each end, 32 in all, that need sealed up. About 65 amps with a 2mm rod, for those taking notes.

Not the nicest welds in the world, but no, since you ask, I'm not planning on giving up my day job:



Fast forward, the 2nd exhaust went the same way, and a lot faster, since it was just a production line now. The bike fired up fine, this time with the exhausts seated properly. I found a few pinhole leaks, but they were quickly welded over, and some grinding neatened the welds up some:



...although they still need filing, filling and sanding before I paint over them, and I won't finalise that until I get a chance to take the bike out for a run. As usual for this winter, there's a localised Fimbulwinter on the stretch of road right outside my house. Hopefully my de-catted Penguin Murderatron will contribute to this alleged global warming which we could really do with round about now.

Speaking of which, here's one of the offending, offensive cats, the one that I didn't try and drill though:



You might think it wouldn't be hard to drill right through that. Well, think it all you like. It's harder than a scrap-yard dog with a flick knife.

Well, that's us 90% done. If I was doing it again, I'd try and get some 33 or 34mm ID 2mm pipe. Also, I wouldn't do it at all.

But since it's done, all that remains is a road test to see if I've helped, harmed or not done a damn thing to the performance. Nobody laugh; it could have helped it breathe. You'll see. You'll all see.

Catalytic cutting catastrophe

But first, Previously On Bike-in-a-box-blog.

Measure twice, cut once, goes the mantra. Well, in an uncharacteristic display of common sense, I only drilled once before measuring the choke assembly.



The small metal widget in the top right is the actual choke actuator, which rotates to operate the choke inside the carb. Note the shiny new hole drilled in it, where I was going to attach a choke cable. Note also that with the plastic choke lever down (i.e. choke off), the actuator is raised. Annoyingly, it's sprung so that without being held up there in the off position, it would spring down and turn the choke being fully on. This is pretty shoddy design to begin with - if the choke assembly fails for any reason, the choke will come on full. Not good. Note that this is on a Japanese Mikuni carb emulating the behaviour of the Japanese designed CG125: I don't think a Chinese design would be as fail-fragile.

The show stopper is that the actuator needs to be pulled up in order to turn the choke off. However, all sane choke knobs are pulled up to turn the choke on. I'd have to reverse the direction, which could be done by attaching the cable to the plastic choke lever instead. However, the lever isn't sprung, and would require the choke cable to not only pull it up, but to positively push it back down again, which wasn't going to happen.

I tried fettling it various ways but couldn't find an arrangement that would operate the actuator correctly and reliably (i.e. stop the choke from springing on), so I declared it a draw and shelved the idea.

Decatalysing, Round One

Guru Forchetto from defunct TheChineseBikeForum always held that the cheap basic catalytic converters fitted to our bikes were one of the primary causes of the drop in torque and power from their original configuration. Arguments about exhaust baffles and back pressure and two exhausts versus one aside, it's undeniable that these engines were not designed with cats in mind, so it's worth a try. The polar bears can just deal with it. What have they done for me lately?

So I've had a plan for some time to de-cat my bike, and this weekend saw it swing, saw and weld into action. This may turn out to be a mini series in its own right.

First, where and how to cut? From doing a bit of wikiing I'd hoped that the cat would be a relatively fragile ceramic, that I'd be able to drill, chisel or just smash to pieces by going in at one end.

So I decided to make a straight cut just under the cat bulge. First, I drew a couple of lines across the cut so that I could match up the orientation again later - this turned out to be pointless because the amount of handling required quickly erased them, but not a disaster as it's easy enough to offer the pieces back up again and re-mark them prior to welding.

A hacksaw went through quite easily, and I was pleased to find that the mild steel is a good 2mm thick, and thus OK to arc-weld back together again.

It turns out that inside the pipe there's an inner pipe of slightly smaller diameter. I'm not sure what the purpose of this is; probably some sort of circulatory magic gubbins. In the event, I inadvertently lopped off an inch or so of it, which I just discarded rather than trying to weld it back on.

This exposed the end of the cat bulge and the cat lurking inside. It starts 3/4" or so inside the bulge, and looks like... well, I'll take a picture first next time. It's a honeycomb structure that looks to be stainless steel, but very fragile, so in I went with a 20mm wood-hole cutting drill bit, expecting it to shred fairly easily.

Hmm. Er. Mmmm. Nope.

The honeycomb immediately flattened and toughened up and the bit was just polishing it. OK, switch to an 8mm HSS metal bit. That went in 1" or so, and that's all she wrote. I drilled a few such holes, but they weren't anywhere near close to going right through the cat. Pressing hard resulted in another 1/8" penetration and a glowing red bit tip. Oh my.

Next up was a curved chisel, which I whacked into the cat around the edges to see if I could detach it from the pipe walls and just pull it out. It went in 2" or so, and I managed to deform the cat a fair bit and pull some small lumps out with pliers before the chisel, well, snapped clean off while I was wiggling it around.

OK, rethink. If I couldn't get it out from the end, what if I cut the cat bulge in half in the middle? I might be able to chisel the half-cat out from either end and pull them out. So in with the hacksaw, which went through the pipe wall, hit the cat and... that's all she wrote (again). I just couldn't get through it.

After some more bashing, whacking, stabbing and hammering, I had to acknowledge that all I was doing was choking up the cat, and called it a night before I made things worse. These things are tough:



Note the snapped off chisel at the bottom!

That left me with a butchered cat, and a half-cut pipe. I wanted to get the bike back the road, so decided to just weld it all back up, and source some pipe to replace the whole cat bulge with, rather than trying to remove the cat and retain the pipe.

My welding is... well, weld is as weld does. If it holds, it's a good 'un.



Not the best weld in the world, but it's been a while since I did one. That's using a 1.6mm rod and about 50 amps; I didn't want to blow right through the steel. Actually though, I reckon it could stand a 2mm rod and 60+ amps, which I'll use when I replace the pipe.

Getting the main weld right was a bit of a fuss. Putting the pieces back on the bike and marking the join was simple enough, but I'd cut too close to the bulge, and hadn't enough straight pipe on the cat side to get a clamp on the pieces. In the event, I had to hold the pieces together while tacking them, sans face shield, and just wearing clear goggles to protect from weld splatter.



I got it eventually though, and butchered my way around the join, brushing and grinding it down and going around a few times to try and get it solid - I should have switched to 2mm sticks, really.

Well, good enough. It'll only have to hold until I get the pipe.



I'm not even going to paint over it, since I'll just be cutting and re-doing it soon anyway.

Despite the choked up cat, the bike started and ran fine. The weld is gas tight, and the exhaust didn't drop off, so job done.

I'll get some pipe with an ID that matches the OD of the main pipe, so that I can sleeve it over it (much like the cat bulge) rather than trying to weld a piece inline; that's unnecessarily tricky. Having it sleeved will also make it easier to keep it together while I tack it and offer it up.

Well, not a success, but not a disaster either, and I did achieve my real objective: Welding Stuff.

Welding Stuff is all that separates us from the animals. That, and blogging.