Engine turning 101

First I should say I'm not the happiest with these results but from 10' it'll look killer! These are the "engine plates" I made earlier. I knew I would be doing this to them since the beginning. Engine turning is one of many names (all somewhat incorrect for this application) referring to a decorative overlapping pattern of swirls. True engine turning involves cams and precise lathes and good eyesight and is seen mostly in fine watches. The layman's engine turning is no less attractive and can be found on many vintage race cars and is maybe most popularly known from the Spirit of St Louis cowling. There is a lot of info out there but practice is about all you can do. Those who say it's simple are likely happy with anything they get 'cause this isn't a cinch. It is mechanically easy to attempt but just not easy to get perfect results. First you need the base metal as shiny as is reasonable. I have experimented a bit and every shortcut seams to cut into your final results and you can't go back on this stuff. You have to play a bit. Some use lubricants, some use lapping compound, some use wooden dowels, some cork, and some use Cratex sticks. 3M pads for some, wet-dry sandpaper for others. You see what I mean? I wasn't happy with the dowels, corks, or mounted Cratex stick. I used a stainless crimped end wire cup brush. Recommendations are to use a stainless brush with a very fine wire (.06). If you can encapsulate the wires all the way down to their ends all the better to keep them from spreading out under pressure. I used a zip tie and some masking tape. As far as spacing, there are many patterns. Again you have to experiment. I chose to overlap about 1/3 along the row and about the same between each row. You also have to offset each row by a chosen amount. I went with 1/2 the distance used between each circle. Looking at the pics, I would go with a little more offset next time. That tends to give more of a diagonal pattern. There are indicator jigs people use on a drill press but I used a mill. Once set you have to apply equal pressure with each disk. I started dry then added some 40wt oil about half way through on one side and added WD40 after one row on the second side. I used 360RPM on one side and 930RPM on the second but 1100+ is recommended for aluminum. I got different results but they all showed "ghosting" and some galling where patterns overlapped. I think I was going a bit deep. Here's what it will look like on the bike: And from a distance:

Reworked the stand a bit yesterday. Planned on redoing it with channel steel but the tube stand is more what the Cyclone class B stand looked like so I stayed with it. The factory race class machines of course had no mounted stand. I bent the legs wider adding a new cross bar. I also added gussets. The bottom 1" or so on each leg is a solid round plug to decrease wear. I turned a shoulder on each plug to fit snugly in the legs then brazed them in.

Chainline

Here is how it looks on the bike. The 41 chain afforded much more space and the chainline was correct with very little adjustment. I moved the inner axle nuts around and may have added a washer to the right side shim but that was it. Throttle and brake linkage and cable, foot boards, and wiring will wrap up the trial fit of everything.

Sprocket stuff

Well I hope everyone had a great Christmas and a good New Years celebration. I slept through the latter. I have been fitting the sprocket with the Worksman freewheel acting as a carrier. Pics are easier than words in this case(a hard thing for me to admit). I bored out the center hole of the sprocket to a friction fit on the freewheel. As you can see this entered into the original bolt pattern of the sprocket. I decided to use these "partial" holes as locators for four pins(turned down some socket head bolts) tapped into the freewheel sprocket. A slight taper on them helps with location. I would also use four sets of teeth to bolt the sprocket to - thus the sprocket carrier term. Since the teeth aren't that long, I brazed up some half step spacers to complete the surface under the mounting nuts. They are a combo of a smaller and larger washer. I could have ground them to the same diameter but just didn't care to. All in all this will give me eight points of contact with the freewheel. I then used an indexer to locate eight holes symmetrically around the sprocket and made eight 1 1/2" holes. Here's how it all fits together. A quick word on sprocket/chain sizes. It is often said that any #40 or #41 sprocket/chain combo works. Indeed these are both 1/2" pitch but the roller width of a #40 chain is 5/16" and is too wide for the 1/4" #41 sprockets. It would work but these are shortcuts that make for a hack job that will soon fail. A loose floating chain will at best wear out quickly. There is a .0065 inch difference in the roller diameter but that will be okay. In my case the narrower the chain (as long as it's motorcycle size) the less trouble with interference with the seat stay or bottom bracket. My advise would be go with the common #41 sprockets that are common with the jackshaft kits and use a 420 motorcycle chain. This keeps the pitch at 1/2", the width to 1/4", and the rollers to 5/16" Everything matches perfectly, is the narrowest reasonable combo, and is stronger than needed for such a project. An alternative would be to use true #40 sprockets(wider than the kit sprockets at nearly 5/16") and #40 chain for a thicker look that is still stronger than the #41 option. Remember without cush drives on these things, chain wear could be an issue. Whatever you do, don't run a solid rear cog(without freewheel) as the motor breaking will likely unscrew your cog from the hub in quick order likely with violent results.

Merry Christmas!

From the even more obsessed contributor Ed. Thanks! And Merry Christmas to all.

After trying the latest bars, I tried another set, and finally came back to the originals. I had to braze them on as the stem bolt through them was hardly enough. That's okay - I like the look a lot better this way - it's more of a cast look. I scuffed the bars with emery cloth to get rid of that new chrome look. 1" bars are difficult to come by unless you are looking at modern metric or Harley stuff. The new problem will be fabricating an internal throttle. Cheap and expensive 1" versions are readily available but the only 7/8" option would be the Honda CT-70 Monkey Bike throttle, which would work and is often used for Brit chops, etc., but which might be a bit sloppy. We'll see what I come up with. I also plug welded the bottom bracket bearing insert for the "countershaft". I will cut the remainder of the jackshaft once the chainline is determined for sure. The wheels arrived yesterday and I finally got a look at them this morning. They are plenty strong but will add a challenge, which I was anticipating, of making a sprocket carrier. I will likely use the existing freewheel cog, turn off the teeth and make a carrier of that. The chainline along the right side is close and looks like it will work with this idea.

State of the Project Address

So here's what is looks like at this point. I'm still waiting for the new 1" handlebars to arrive as well as the wheels. The jackshaft in place but I have yet to weld it up. I have to double check the offset needed between the pulleys to allow for the shift as they each expand(one way only each). I had to make a spacer for the crankshaft under the clutch as it was not seating against the crank. Also without a spacer the O.D. of the clutch would rub the case. There was also a gap between the end of the crankshaft and the outside of the clutch so I had to make a spacer so as not to have a 1" gap under there. I bought a larger stainless bolt and rethreaded the crankshaft as 9mm isn't the easiest to find. Really there should be only slight axial loads on the clutch as it open/closes so this bold/spacer setup is just to keep it in place while the woodruff key takes all the burden. Here are those parts and where they go. My plans were to move the engine a bit more to the right. It felt balanced already but without those fins on the flywheel and with the pulleys as the new "meatgrinder", I decided to shift it about 1/8" to the right. I know that's not much but every bit helps get that jackshaft shorter(i.e. right shifted). I decided to remove the outside mounting holes and bosses from the case to clean it up a bit more. Here's what I removed and how the block now looks.