Horizontal Air Cooled Engine

[Brian Rupnow]

Today I did something for the very first time!!! Those reliefs in the face of each flywheel are 3/16" deep, and they have a 1/8" radius in the corners. I have always known that there should be radius there. I know the whole tune about sharp inside corners causing stress risers and are more apt to fracture in use. It's just that I never actually did it before. I have about 40 engines running just fine without a radius in the corners of the flywheels. Today I actually ground an HSS tool and machined the radius. The outer brass rims are loctited to the inner aluminum flywheel body (That's why they look dirty--that dirt will all come off with a "clean up" pass in the lathe.) Drilling and reaming the center hole for the shaft is one of the last things I will do.

 

[Brian Rupnow]

The flywheels are finished except for keyways, and I like this new variation on round holes cut in the webs. This gives the flywheels an interesting look, and it will still make it highly visible when they are rotating under power.

 

[GreenTwin]

Brian Rupnow was one of the folks who inspired me to learn 3D modeling, back in 2012.
Great work Brian !
Its always interesting to follow your builds.
.

 

[Brian Rupnow]

Thanks for saying Hi, Green Twin.---Brian

 

[Brian Rupnow]

I spent yesterday afternoon and this morning preparing blanks for my 20 and 40 tooth gears, and sawing a slab of 1144 stress-proof steel from the round to make a crankshaft. These are all somewhat brainless operations, but they have to be done, and they take time. The gear blanks are finished outside diameter, thickness, hub diameter and bore, but the hub is a couple of inches too long, which gives me something to grip in the 3 jaw chuck on my rotary table while the teeth are being cut. This over-length hub will be cut off after all of the gear teeth are cut.

 

[Brian Rupnow]

Now I've got to ask---Is that a beautiful thing, or is that a beautiful thing!! Both gears turned out fine, the large gear fits into the cavity prepared for it in the base, and they mesh just the way they are supposed to. I always feel good when I've cut a pair of gears and they turn out the way I had hoped for.

 

[Brian Rupnow]

Today, since I had to take the sideplates off to fit the crankshaft and camshaft, I decided to go full ball bearings on the crank and camshafts. I was originally going to run the camshaft in bronze bushings, but decided that since I had the correct size of sealed ball bearing, I might as well add the counterbores to the sideplates and go full ball bearing.

 

[Brian Rupnow]

So, at the end of a long and hard fought day, I have a one piece crankshaft and a cam shaft. It's been a long day!!

 

[Brian Rupnow]

And here we have a video of all the bits and pieces I machined yesterday, working in harmony. This is my horizontal air cooled engine, 7/8" bore. The cylinder is not mounted in this video, although it is finished.

 

[Brian Rupnow]

This morning I machined a con rod. My digital camera shows up things I missed when sanding the finish.--Oh well, I'll sand it a bit more to take out those tool marks. I always have trouble getting a perfect fit between the big end of the con rod and the crank journal. When I bore the big end of he con rod, my biggest fear is that I will go oversize, and there really is no good fix for that except to make another con rod. So, I end up marginally undersize and then have to screw around for an hour with emery paper and lapping compound to get the fit exactly what I want it to be.

 

[Brian Rupnow]

I am rapidly approaching the point where I have to finish the cylinder and make a piston. When I first designed this engine, I never noticed that I couldn't remove the sideplates without first removing the cylinder, which is a giant PITA. I am going to modify the cylinder flange where the grey arrow is pointing, by putting in a couple of clearance holes in the flange, which will then let me remove the bolt which was previously trapped under the edge of the cylinder flange.

 

[Brian Rupnow]

This afternoon I managed to machine a piston. I'm tired, and suppers ready.---Enough work for one day!!!

 

[Steamchick]

Today I did something for the very first time!!! Those reliefs in the face of each flywheel are 3/16" deep, and they have a 1/8" radius in the corners. I have always known that there should be radius there. I know the whole tune about sharp inside corners causing stress risers and are more apt to fracture in use. It's just that I never actually did it before. I have about 40 engines running just fine without a radius in the corners of the flywheels. Today I actually ground an HSS tool and machined the radius. The outer brass rims are loctited to the inner aluminum flywheel body (That's why they look dirty--that dirt will all come off with a "clean up" pass in the lathe.) Drilling and reaming the center hole for the shaft is one of the last things I will do.

Hi Brian, and interesting process sequence. I should have made the centre hole first, then mounted the flywheel on an arbour to machine everything concentric to the shaft centre. But I guess you have done it your way so the loads on the arbour are minimal with only finishing cuts to clean-up the flywheel and true it to the centre?
K2

 

[Steamchick]

Hope your piston ring process works well for you this time. I recall you had a big learning curve on a previous engine?
Enjoy you modelling Brian. We all enjoy your posts!
K2

 

[Brian Rupnow]

The engine is completely assembled except for the cylinder head. Everything has a coat of 10w 30 lubricating oil, and the rod cap bolts are snugged up. It is currently out on my workbench being "ran in" at about 450 rpm driven by my electric motor via v-belt. Every 10 minutes I will go out and snug up the con rod bolts a little more. I will let it run for about half an hour and by the end of that time the rod bolts will be fully tightened.

 

[Brian Rupnow]

And here we have one more step in the evolution of an engine. This video was made after the engine was "ran in" for about half an hour, and the rod bolts were progressively tightened after each ten minutes of running in until they were cinched down tight and everything ran freely with no binding. There are no rings on the piston yet.

 

[Brian Rupnow]

Earlier in this thread I mentioned that I had some cams left over from some other engine build. At the time I made those cams, I remember thinking "Since I have to go thru all the motions to make these cams, I'll cut the stock long enough to get a second pair of cams from." The time has come!! ---and I can't be happier. These cams were bored for a 3/8" shaft, and since I had 1/4" sealed ball bearings on hand, the camshaft is 1/4" diameter on both ends but 3/8" diameter where the cams will fit on. Things are very tight where they have to go, but my computer tells me there is just enough room for the cams to fit in there with enough gap between them to let the con-rod swing thru between them. The cam without a hub (for the exhaust) will be pinned to the shaft, the one with a hub will have set screws to hold it in place rotationally.

 

[Steamchick]

Hi Brian - Love it! Excellent work. But how about some counterbalance for the primary piston/rod/big-end imbalance? - Maybe some weights added to the flywheels? - Now would be a good time to balance the engine, as it is all so free without rings, cams, valve-gear... etc. I'm sure you have approximate weights for the con-rod, piston, etc. from the CAD? - Does that have a balance calculation thrown on the side? Or do you have to do the engineering separately, and just draw stuff with CAD? - Being a pencil n paper Luddite my paper drawings don't do calculations.
Cheers!
K2

 

[Steamchick]

P.S. When I have tried to weigh pistons, rods, etc. I cannot get enough weight to move the kitchen scales! - So I have to take bits to the Post-Office (in a poly bag - with a story about needing to weigh them before packaging). But sometimes I just tape a small weight on the flywheel and see how it goes! - Usually that does it well! Needs the cylinder vertical though, so when you turn the crank to 1/2 stroke both ways it neither drops nor lifts against the bearing friction. Makes slow running really smooth!
K2

 

[Brian Rupnow]

Steamchick--at the speed I run my engines, the counterweights make very little difference to the smooth running of the engine. If I ran at higher speeds, then I would need counterweights. One thing about the engines I design/build---If someone wants to alter the design a bit and add bolt on counterweights, it is very simple to do.---Brian