The Craftmans Shop > Model Engineering

Rockerblock engine--something a little different--

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Brian Rupnow:
Pete--There is no pressure in the water reservoir. As long as it doesn`t cut thru and leak water, there isn`t any problem. Speaking of the water jacket, my plan for sealing the jacket to the o.d. of the cylinder is shown in this section view of the water jacket. An annular groove cut at each end, just slightly shallower than the cross sectional thickness of a .094 Viton o-ring. Hopefully an o-ring in each groove will seal any water leaks. I will be able to get two or three bolts thru from the flange on the cylinder  into one end of the water jacket to keep it from turning on the cylinder.

Brian Rupnow:
Well Hot-Dog!! I even managed to sneak an ignition cam and my old stand by Chrysler ignition points in behind the offside flywheel.

Brian Rupnow:
There. That's a solid 8 hours playing. I have to dwell a bit on whether or not I have the crankshaft counterbalances on the correct side of the crankshaft or not, but other than that and a gas tank, the engine design/modelling is finished. Now I have to go shovel out the end of the driveway. We got 5" of April Fools last night. Yuk!! I was hoping we were done with that white stuff!!

Brian Rupnow:
I always think it sucks to design a nicely proportioned engine, and then stick a gas tank on it. Gas tanks don't leave you with a whole lot of options. They have to be near the carburetor, they have to set below the carburetor throat (but not too far below), they shouldn't block any other equipment which needs frequent adjusting, and they shouldn't be directly in line with the exhaust. That being said, you just do the best you can and hope it doesn't ugly things up too much. This is not an improvement over the normally configured gas engine. It's just a different, artsy fartsy way of doing it.

Brian Rupnow:
--I've been trying to wrap my head around your concept of reversing the crankshaft counterweights. I have three books here that deal with balancing of small engines, and they are all rather vague. In a vertical cylinder engine, if you remove the piston rings and assume no friction whatsoever, then when the piston is at mid stroke, the counterweights on the crankshaft should, theoretically balance the piston and connecting rod perfectly so that the piston doesn't fall any farther under the influence of gravity, and so that the weight of the offset in the crankshaft doesn't cause the piston to raise back up in the cylinder due to gravity acting on the offset weight of the crankshaft throw.--When you have a horizontal cylinder, then a lot of that reasoning goes out the window, because gravity isn't really acting to move the rod and piston one way or the other, although it still acts on the offset weight of the throw on the crankshaft.  Indeed, the biggest job of balancing that the crankshaft counterweights have is to balance the con-rod journal and the portion of the "throws" that support it on the far side of the crankshaft centerline. In a perfect world, if you set the crankshaft alone on a pair of knife edges, it should be perfectly balanced with no tendency to roll one way or the other because of a "heavy" side. If there is a heavy side to the crankshaft, or due to the weight/drag of the piston in the cylinder, the twin flywheels should compensate for that. The fact that the engine is intended to be a "low speed" engine also does a lot to nullify any great "out of balance" issue. The bottom line is that I don't really know. I'm just running my mouth here. I know that the counterbalances make the crankshaft "look better" to my eye anyways. I think in the end the only way I'm going to know is to build it and run it, and then perhaps I'll know. I always bolt my engines down before I fire them, so even if it is out of balance, it won't run off the end of my reference table and fall on my foot.

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