Well, this is turning into a build thread, although that wasn't my intent at the start. The latest work was making the crankshaft support bracket.
For a couple of reasons, I didn't like the Duclos' approach and this seemed like a good part to redesign. Why didn't I like it? Two main reasons. First: he lets the flywheel shaft, 1/4" steel rod, just rotate on aluminum and one thing I've learned about these engines is it's worth it to remove as much friction as you can. I wanted to use ball bearings, which causes the uprights of the part to be bigger than Duclos used. Second: he makes this part from a solid 2-1/2x1x3/4 chuck of aluminum and turns most of it (about 65-70% by my calculations) into waste chips. So I decided to make it out of three pieces of 1/4" aluminum (all you're left with in his design). Two uprights and a bottom piece to hold them in place. Some time with CAD resulted in this drawing:
My CAD model on the left and Duclos' drawing on the right. You can see where the ball bearings sit, in the counterbored holes at the left. I got a set 1/4" shaft and 3/8" OD overall from Boca Bearings.
I then created a drawing with two of these brackets side by side, spaced far enough apart to put a 3/8" EM between them. A little time spent with both Rhino and Deskproto (my CAM SW) and porting it all to the mill ended up with this:
I won't bore you with the side story that popped up here, but I had to re-tram my Z-column. The spindle was perpendicular to the table, but the Z-column wasn't. Which made me do both.
So while these are smallish pieces, the center (deep blue in the 3D model) was 0.75 wide by 1.00" long, and a bit tedious to work on, it all went as designed and went together the way I planned it.
Would it help if I said the back looks just like this side?
30-some years ago, an older engineer told me that "engineering is the art of compromise". There are rarely ever perfect choices that everyone agrees are the best way to do anything and this design is like that. The three piece bracket does what I wanted. All the parts worked out just as modeled. The drawback is that it's three parts and they need to be aligned properly during assembly. When I first put it together, the flywheel spun, but also made the characteristic scuffing sound of something rubbing. The parts aren't perfectly aligned, but I improved that by loosening the four screws on the bottom and putting a shim between each side bracket and the flywheel hub (I used one of my old business cards - still useful after retirement!). When I retightened the screws and pulled out the shims, the scuffing was gone. The flywheel still wobbles which argues that the two sides aren't exactly the same height.
I think I need to come up with an alignment fixture to hold the base and the sides while I indicate the shaft to make sure it's level and not offset side to side.
If I give the flywheel a good flick, it spins for about 45 seconds. Is that a good number? I think it can be made better, but how long should it spin?
My next project is going to be the piston, and I have a small piece of 1" diameter graphite (1.030") I was thinking of using instead of the CRS bar I bought (longish story). Duclos' drawings call for hollowing out the piston until it's left with 1/32" thick walls. Is graphite strong enough for that? I can just envision it shattering as I hollow it out in the lathe chuck.
