Senft "Poppin" engine

[Brian Rupnow]

My ball bearings came in yesterday. They are shielded bearings, not sealed. They should turn more freely than sealed bearings because the shields don't really touch the inner race. I may still have to wash the grease out of them in a solvent bath--will know about that later. Today I hope to make the crankshaft.

[Brian Rupnow]

So, here we have crankshaft phase-1. Everything is cut to length and Loctited together. The shafts are not "press fit" into the square bars. They are a sliding fit. After 24 hours set-up time I will and pin all the joints with 1/16" dowels (Loctited into place), then wait another 24 hours and saw out the center bit.

[Brian Rupnow]

I decided not to use any J.B. Weld on the flywheel hubs. That would have been a bit too barbaric, even by my standards. I made the cam and cam spacer this afternoon, assembled everything and tightened it down as much as I dared, then set the flywheels up one at a time on a stub shaft with their hub assemblies in place and "trimmed" the outer diameter and the sides of each flywheel. It didn't take much, but it did take some. Now the flywheels don't visibly run out or wobble.

[Brian Rupnow]

This engine has a very interesting big end on the con rod. I haven't built one like this before. The red con-rod is silver soldered to the pale yellow part on the right hand end. The pale yellow part on the right is fastened to the pale blue part on the right with cyanoacrylate glue before any holes are made. Then both yellow and blue parts are tapped all the way through. A bolt is screwed through both parts and tightened. Then the hole is drilled and reamed for the crank journal on the split-line between the two pieces. Then the bolt is removed and the assembly is heated to release the crazy glue.

[gbritnell]

I don't see why the screw holes just can't be drilled dimensionally in the proper place, the two pieces assembled then the crank pin hole put in at the joint. My reason for saying this is because super glue is unpredictable. If the joint isn't perfectly tight and has a little glue on it then after drilling and renaming the hole will be too small.
gbritnell

[Art K]

Brian,
I don't want to hijack your thread but, Bent asked a question about the taper lock set up I used, so here goes. I will post the photo and then explain it.

I hope this works, I reposted all my Val photos after Photobucket went  .
OK the easy description. You bore the ID at a 10-15 degree taper, move it to the mill, the rotary table made quick work of this. Drilled & tapped 3 holes on a bolt circle diameter. With the cross slide set at the same angle as the inside of the flywheel turn the taper on the outside, and bore the inside for the shaft diameter. My Upshur engine in the photo has a 5/16 shaft, so I see no reason this wouldn't work on 1/4 as well. On the outside end you do clearance drills for the holes you tapped into the flywheel, when you snug these up it's locked onto the flywheel. In the opposite three holes of this part drill and tap the same size holes as the flywheel. These are used if you want to remove the flywheel. loosen the bolts in the flywheel tighten the opposites & it slides right off the shaft. If I did this again I'd make the thing beefier.
Art

[NickG]

That’s what I did George, didn’t want to mess on with melting and cleaning super glue off. I hadn’t seen this design before either but it worked perfectly well. Think I pinned the rod onto big end but didn’t like the piston arrangement so just made a solid piece from graphite with a milled slot for rod and cross hole and made the dudgeon pin slightly shorter than the diameter. Doesn’t seem to make any difference to performance but was much less faffy to make.


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[Brian Rupnow]

This morning I got up and pinned the crankshaft. In a perfect world, I would have drilled the four holes undersize, then reamed them to 1/16" diameter.--In my world, the smallest drill I could find was 1/16" diameter, so that's what I used. In the foreground on top of the vice you can see the four "pins" prepared to go into the holes. The pins are flat on one end and a small taper ground on the other end, and about 1/4" longer than they need to be. First I tried the pins in the holes for fit and yes, they did fit perfectly. Then a small drop of Loctite on each hole, and the pins are inserted pointy side first and brought down until the top of the pin is flush with the side of the crank journal. In the second picture, the pins have been inserted and you can see the extra length extending below the underside of the crankshaft. If the four pins look a bit like welding rod, that's because they are. I can only buy 1/16" rod as "music wire" which is harder than the devil's horn to work with. However, somebody on the forum suggested 1/16" steel, copper coated welding rod, which is perfect for what I'm doing here.

[Brian Rupnow]

Have been building a whole armada of tiny little pieces. Valve shaft bushings, valve cross shaft, valve lever arm. I still have half a dozen little pieces to make. I just realized that I polished the wrong side of the cylinder head and installed it backwards. The taper in the center should face into the cylinder, not outward as I have it. The crankshaft does indeed fit into the engine frame but barely.  I had to order a 0-80 die and a 2-56 die, as I need them and don't have them. I downloaded these plans from the John-Tom site, and while the mechanical drawings are clear enough to see, the pictures are horrible. If anyone has built this engine, please post a nice clear picture of where the spring that holds the valve open goes. I can't tell from the stuff I downloaded. I think I will try to build the roller and roller carrier that goes on the end of the valve lever this afternoon and then call it a day.

[b.lindsey]

Maybe this will help Brian.

Bill

[Brian Rupnow]

Bill--Thank you very much. That clears it up for me just fine.---Brian

[Brian Rupnow]

I lapped the cylinder this afternoon, but wasn't terribly impressed with the resulting finish on the bore. I used a home made 5/8" lap that I had turned from a piece of aluminum. I had to take a step back and ask myself "Why am I still doing design work for money?"--It was supposed to be money designated for additional tooling in my machine shop. So---I just ordered a set of five barrel laps from KBC. I have one factory built lap that I bought a few years ago for 15/16" bores, and I was very pleased with the results it gave. I ordered a 1/2", a 5/8", a 3/4", a 7/8", and a 1". Sometimes you just gotta spend some money!!

[b.lindsey]

Yep, you can't take it with you Brian. You will enjoy those I know.

Bill

[Brian Rupnow]

This morning I finished detailing the crankshaft. I used a pair of "flush cut" wire cutters to snip of the exposed ends of the 1/16" diameter cross pins , then used my monster stationary belt sander to clean up both sides. Before I cut the remaining piece of shaft out from between the rectangular bars, I chucked one end in the lathe and with my dial indicator on the unchucked end I measured 0.016" total runout. This didn't concern me too much, as these small shafts (3/16") are really flexible fliers. I took my rubber hammer and applied it to the shaft until the runout was only .002" total indicated runout. after I cut away the shaft between the rectangular crank throws, I measured again and it hadn't changed any. So---The crankshaft is finished.

[Perry]

Nice little crankshaft. That is interesting observation Brian- what is the source of measured runout @ 0,016"? Assuming the rod is straight there should not be much more runout than spindle runout multiplied by lenght of rod at measurement point

I like your cylinder btw