Sunday, November 30, 2008

Pic-less progress

Pop did his usual parts-mule job when he and mom came out for a quick visit. He brought a pile of stuff, including the engine for the DZR400 project (which came with most of the wiring loom, the carbs, and other stuff) as well as various bits and bobs for the Ducati. As for the Duc -- I bought two exhaust systems -- a D&D and a staintune, to see if either would work with the MH swingarm. Turns out the D&D won't (and I sold it for a wee profit), but the Staintune would, with some work. So I mounted the rear header pipe and exhaust (a nice reverse - megaphone), and started to modify the horizontal header to work. I will need some 1 5/8 stainless tubing to mate everything up... Cdn Tire has mild steel header bends in this size, but no stainless -- I found some on ebay that should work. I can tack this into place, and then take it to Cycleboys to get finished by a tig welder. Mocked up, it already looks 1000 times better than my home-made exhaust system that you can see on the earlier posts way below.
As well, I was able to get a neat 6-piston FG front caliper and a set of EBC wave rotors for cheap. The caliper needed a bit of machining to fit the fork properly, and so as I am only running a single front rotor, the other rotor went on to the DRZ -- fit perfectly! Radial caliper, wave rotor -- cool! As soon as the exhaust is fitted, I'll take some more snaps of the Ducati.
The DRZ has been a bit frustrating, as I used a crappy cheap caliper to measure the bore of the engine case -- at 16.4mm -- so I ordered some 16mm drill rod to use as a bolt... and its too small. Bugger -- must be 17mm. I HAD a nice 17mm rear axle from a Ducati that would work perfectly, but sold it on ebay. So there I went again to get a replacement. This means the frame will have to be bored out to 17mm (didn't want to bother with sleeving the engine case), as well as the brass swingarm bushes. Bugger! Waste of money, as the minor trimming needed to go from 15 to 17mm coulda been done the first time. Oh, if I only had a lathe!
Did get the engine in situ in the frame (rough mock-up), and it fits a treat -- lots of room on either side of the frame tubes, and tons of room for a nice radiator and the oil tank. Hooray! Pics to come soon.

Thursday, November 13, 2008

More Physics Help

Some shocking ideas...

Originally, I thought to create a rear suspension similar to a Honda Hawk GT (left) -- single monoshock, no linkage. This design allows for the typical 4-5 inches of travel at the rear wheel, and requires a pretty hefty 1050 lb spring, but no linkage -- simple and light!
The swingarm I am using is an Aprilia Pegaso -- it normally has a RHS chain drive, so I simply flipped it for my application. I can conveniently use what was once the linkage tabs on the underside of the swingarm as mounting bosses for the Hawk shock. The 12" ruler is shown as a guide -- the stock Hawk shock is 12" long, and the angle it is set at approximates the angle of the stock frame above. Should use the same 1050 spring, or close, to get the proper travel.

There is, of course, the gaping hole that the original linkage shock passed through. Note that the rod shown will also pass through the rear of the engine case. This got me thinking because if I mount the shock as above, it sits high in the frame -- would like to lower the C of G if possible, and it would be a much "cleaner" solution.
So what I had in mind is similar to the pic at the left. Note that this is a linkage design (hidden under this swingarm), but if I could fabricate a shock mount to weld to the underside of the swingarm, allowing the shock to pass through the hole in the swingarm, the entire design would be stronger -- less material, less weight. However, what would this do to the spring rate required?
If mounted to the underside of the swingarm, the shock will be at a slightly different angle, be about 1" closer (fore and aft) yet almost 3" lower (vertical plane) to the forward swingarm pivot. Conversely, it would be 1" farther and 3" closer to the rear wheel axle. It may make no difference -- some eyeball engineering at work, but I'm gonna get a Physics expert (Ross) to ponder this for me.

Why this is so critical, is that if my new location requires a lighter spring (less than 1050 lbs) I'm OK -- lots are commercially available and reasonably priced. However -- if this new location requires a stiffer spring, heavier than 1300 lbs, I might be pooched. From what I can tell, there is no spring at this length (number of coils) readily available for the Honda Hawk shock I am working with. I learned once the hard way about custom-wound springs and etc -- don't want to go down that road at all! The picture at the left shows the approximate attitude of the shock if mounted according to my idea... we'll see.

Sunday, November 9, 2008

Swingarm Bushings

I got the rear swingarm back from Atom-Jet with the aluminized bronze bushings installed. A nice fit -- might need to trim a bit off of each end to allow for thrust washers. Maybe not -- will let pop take a look and give his opinion. Rod (15mm) still needs to be cut down and threaded into a bolt, but that can wait until later. Will be using the same 14mmx1.5 nuts (locking) from KTM I sourced awhile back for the 450 project. Also was able to finally source a rear caliper bracket from eBay.UK -- hopefully that is in my hands in short order. Still thinking about how I am going to mount the rear shock. Got some specs about the Hawk GT shock online... but of course can't do anything until the actual item is in my hands.
Using a bit of long-forgotten math (sine laws, of all things), I was able to determine that, based on the length of the swingarm from pivot to rear axle, in order to get the ideal 12 degree angle of the swingarm, the pivot point needed to be 111mm above the centreline of the rear axle. SOOOO glad I took the hell that was Math 300 to use the formula... once since I graduated!

Sunday, November 2, 2008

Swingarm silliness

My plan for mating the rear swingarm to the frame and engine was to bore out the Aprilia Pegaso bearing sleeves to match the 15 mm od of the shaft I was going to use. I have since learning that trying to bore out a small diameter, tempered steel sleeve is pretty much impossible. One option was to use a smaller Pegaso swingarm pivot, but I wasn't too keen on that -- it would mean some significant modifications to the frame. I decided to go with another option. Knocking out the torrington bearings in the swingarm, and getting bronze bushings machined to the right specs. A bit low-tech, but worked fine for decades on TZ250s, and 350s. Considering this is going to be a fun street-trackbike in the end, good enough for me. The swingarm and shaft are currently at Atom-Jet where they will work their magic on the CNC machines. I'll choke at the price in the end, but a necessary evil -- and still cheaper than buying my own lathe.
In the meantime, I've been compiling a information and picture resource of interesting singles and parts to suit. Again, all asthetic at this point:

This is the DRZ400-based CCM CR40 cafe racer. Alloy tank, twin shocks, spoked wheels. A neat, retro-looking machine. I'd love to get my hands on an exhaust system... would suit my purposes just fine.

This is a CR&S Vun (one) -- powered by a Pegaso/Bombardier/BMW/Rotax 650 single. Lovely bike. Google it if you want to see the website. If you have a spare $20,000 or so lying around, you could get them to build you one. Customizable down to EVERY last detail. Some neet videos on the site as well.

Airtech sells this BMW Rennsport fairing. Originally for a late 50s and 60s BMW R50. Gustaffson sells a windscreen for it for another $100. I REALLY like the shape of this, and it should be nice and narrow for my project. The issue is the HUGE 8" headlight cutout. I could see if they can build me one with the headlight cutout filled in, or I could do some work on it myself, maybe using a smaller pair of lights or the leftover 5.5" one from the Ducati.

I'm also partial to this seat, actually from a Bimota. The built-in fender extension will double nicely as a place to mount a licence plate, and a small rectangular (LED?) tailight will fit just underneath the ductail. I could get a proper seat made, after moulding a base "pan" from this, and benefit from a real cushion for my butt -- rather than a slab of foam. Perhaps it can even curl down over the side of the seat like a real seat pad. Dimensions seem right (supersize the image to see), but this will be something I would have to get in my hands first, prior to building the rear subframe.