A different opposed piston engine

[Brian Rupnow]

Thanks Pete.--Merry Christmas.---Brian

[Brian Rupnow]

Okay--Here's what I did for my ignition, and why I did it. Having the magnet embedded in the flywheel sounds like a great idea. Trouble is, the flywheel will be keyed to the crankshaft, so there is no real handy way to adjust the ignition timing. To keep things simple, the green disc on the front of the engine is aluminum with the magnet Loctited into a pocket in the face of the disc. The disc is located rotationally on the crankshaft with a single flat ended socket head set screw. The hall effect sensor , mounted in the D-tube (the red thing) is supported by one bracket mounted to the face of the front bearing support. I have chosen to not make the bracket adjustable so consequently I can't change the engine timing while the engine is running. If I want to adjust the timing, I stop the engine, loosen the set screw, and turn the disc one way or the other, then retighten the set screw. This has no effect on the valve timing, because the relationship between the crankshaft gear and the timing gear is not affected by doing this. On the previous engine I built last summer, I had the bracket adjustable, but I found that once you get the engine running the first time, you never adjust the timing anyways.

[Brian Rupnow]

As always, I find that the hardest part for me to build is the crankshaft.--So---That is where I tend to go first. If I can build the hardest part, then everything else is (or should be) downhill from there. The crankshaft is 3/8" diameter. The outer "webs" are 3/16" thick, and the center web is .469". The space between the webs is 9/32", and the actual "throw" of the crankshaft, from the centerline out to either of the con rod journals is 0.5". The con-rod journals are also 3/8" diameter. The webs are all 1/2" wide. All I have to do now is decide whether to machine this all from one piece of hot-rolled steel, or to do a built up and silver soldered crankshaft. Both have their own unique difficulties, and each represent a lot of work if I screw it up----

[Brian Rupnow]

This is the crankshaft, and if I was feeling really bold, I would machine it completely from one piece of steel. I lay in bed last night, and decided to take the cowards way out and build it up from pieces, in a rather unorthodox fashion. I have the material on hand, and if it works, it will be one of the easier crankshafts I have made.---If it works!!!

[Brian Rupnow]

Center section of crankshaft

[Brian Rupnow]

Then if I was to make the two outside ends of the crankshaft, press fitted together as shown-----

[Brian Rupnow]

Then, in a perfect world, if I could make a good fixture to align the two ends of the crankshaft, I should be able to silver solder the last two joints to end up with a perfectly aligned crankshaft. A point to note, is that the last two joints to be assembled would not be a press fit.--I do want the silver solder to "wick" into the joint. When mig weld solidifies, it has a tendency to pull the welded components out of alignment. Silver solder doesn't do that, because the entire joint has to be heated to a uniform temperature for the silver solder to melt and flow around, so there are no thermal stresses trying to pull the metal to one side or the other. I have never tried to build a crankshaft like this before, but it certainly has an appeal to me. I will build one and take a few pictures to let you know how it goes.---Almost makes me wish I had an old lathe so I could grip one end in the 3 jaw chuck and the other end in the tailstock chuck before doing the final silver soldering!!!

[gerritv]

Would a jig made from angle be a solution? Bolt the angle to 2 blocks mounted on a base, cut out middle to clear the web section of the crank. The angle would then stay aligned. Clamp crank arbors to the angle, heat, solder.

At least you have power, south a bit is not so fortunate.

[Brian Rupnow]

An angle wouldn't give the accuracy I require. I am thinking more of two 2" square aluminum blocks drilled and reamed on the milling machine while clamped to the vertical side of an angle plate. This would give a very precise "backing distance" from the center of the reamed hole to the base of the block where it was clamped to the angle plate. Then bolt the two blocks to a short piece of known "true, flat surface", align them with a longer piece of 3/8" cold rolled, and tighten down the bolts. Slide the set up shaft out, slide the ends of the crankshaft in. That way I can rotate the whole set-up so the shafts set vertically to give me a nicer shot at the silver soldering.

[Brian Rupnow]

So---We've made a start. That is a piece of 1018 hotrolled steel, 1/2" square. The two very outside holes are drilled and reamed to 0.375". All of the other holes are reamed to 0.3735" diameter. All done in one set-up.

[Brian Rupnow]

Now we have a step #2. After recoating the side of the drilled part with layout dye, I take a piece of 1/2" dia. cold rolled steel, and turn one end for a "good fit" into the .3725" reamed holes, set it in place, then scribe around the outside of it with my scriber. This gives me my "reference" lines for trimming to length and radiusing the ends of the 3 crank webs. Why didn't I make the end webs out of thinner material?---Because I figure the thicker material is less apt to move when I weld it, and it can be turned to finished size in the lathe after welding, by turning from the non welded side.

[Brian Rupnow]

So----Nothing is welded yet, but it sure do look good!!! The hurting time will come tomorrow after the welding, so I can see how much it pretzels. Actually, the initial mig welding shouldn't move anything. Then I will have to build an alignment fixture before I do the final silver soldered joints.

[Brian Rupnow]

Tomorrow morning I will build a crankshaft jig, to align the 3 sections of mig welded crankshaft for final silver soldering to join the 3 mig welded sections together. The pale green blocks will be drilled and reamed to 0.375", and bolted to a piece of cold rolled steel flatbar 3/4" x 1.5". I will use an 8" length of 3/8" cold rolled round rod to align the two green blocks before bolting them down to the steel flatbar, then after the bolts are tightened  will slide the alignment bar out and fit the 3 pieces of crankshaft in place. I have drilled and tapped the green blocks for a single #10-24 set screws to hold things in place. Then I can turn the jig on end and set it in my vice for the final silver soldering of the remaining two joints. I will let it cool in the jig, then unbolt the green blocks from the steel flatbar and slide them off over the ends of the crankshaft. If I have lived a good clean life, I should end up with a perfectly straight and very strong crankshaft.

[swilliams]

I really like the look of this engine Brian. Hope to build an example of it one day. Good luck with the crank silver soldering!

Steve

[Brian Rupnow]

Alright--That part went well. I love my mig welder!!! Now I'm working on my jig.