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.



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.