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| kvom:
I had a couple of hours before the Halloween visitors start arriving to tweak the cam housing issues. I discovered upon inspection that the front cam was not seating flat against the driveshaft flange. With tight tolerances on all the parts, the clearance holes were not large enough to allow the screws to enter perfectly straight. I drilled them out with a #43 drill as opposed to the original #42, and with some careful tightening both cams set flush. Since the camming surfaces are so close to the inner diameter of the cam housing, it's important that the shaft and cams be as perfectly centered as possible. How the bearing carrier is screwed to the housing is important, as it seems that the slightest cant in the carrier can cause the cams to rub. So tightening the screws evenly all around going in circles was necessary. I marked both the carrier and housing to ensure that any reassembly matches up the same set of holes. When assembled, the bearing preload seems good, so I don't think any adjustment will be needed. I cleaned up the pushrod holes, and now the supplied ball bearings and my brass pushrods fit nicely. I also parted off the crankcase and turned the back flush, so that I can start thinking how to build a base. Darren, The size of the parts hasn't been as intimidating as I thought at first. Having soft jaws on the lathe, vise, and rotab really helps, as otherwise clamping would be an issue on some things. One fiddly issue for me is the size of the screws; I have to be really careful not to drop any as there are not a lot of extras in the kit. |
| NickG:
Yeah looks far too fiddley for me! Well done, can't wait to see this in action! |
| kvom:
Got into the shop around noon, and decided to verify that the pushrods would correctly activate the rocker arms and valves as designed. The pushrods are just 1/16" drillrod 1.4" long, so I cut off a couple with wire cutters and filed the ends. Here's the assembly with one cylinder: It seems to work! At least the plungers that activate the valves go up and down. It takes a fair amount of force to turn the shaft with just fingers. As Liney suggestes, I will need to attach a small chuck or the equivalent to turn it manually with all 5 cylinders mounted. I may need fewer turns on the springs as well. Given that assembling further without something to hold the engine securely would be difficult, I spent the rest of the session making the first part of an engine mount. First, I took the piece of aluminum from which I parted the crankcase, faced it on the lathe, and then drilled and tapped 5 holes to match the rear mounting surface of the crankcase. Next, I found a piece of aluminum plate that had a hole in a useable spot, and with the aid of a little trig and the DRO, I drilled holes to match the jig. Then after enlarging the hole a bit on the mill, I mounted the plate on the jig... ... and milled the hole to match the innder diameter of the crankcase. Successful test fit: Some more milling, flycutting, on the rotab and vise yielded this: A test fit of the crankcase and a couple of cylinders to show that there is clearance for air supply: I won't be able to complete the mount until I get a propeller and determine the necessary height above the base, but this part will be very useful in assembling and testing. |
| kvom:
Since I blew a start cap on the RPC this week, the lathe was out of operation until this weekend. Once I got things back together, I finished remaking the crank, and it now sits square on the shaft. I also managed to file the ends of the conrods so that they will assemble with the master rod and the crank pin. So now comes the problem of assembly. I discovered that there is no way to insert the assembled conrods/pistons with the cylinders attached. So my plan is to insert the pistons into the clyinders with the conrods attached, and try to assemble the rods inside the crankcase. If that proves too hard I can try it without the cylinders and and/or pistons, and then install the cylinders over the pistons. |
| kvom:
After a lot of unsuccesful fumbling, I finally figured I would never get the conrods attached while they were in the crankcase. So I disassembled everything, and was successful in pinning the rods together. The pins themselves were a bit of a struggle: 1/16" drillrod .150" long. In order to get them cut to length I made a "jig" by milling a small piece of aluminum .15" thick and drilling a 1/16" through hole. I inserted some drill rod, cut it off close with a wire cutter, and then filed it flat to the jig. Still, these are the smallest "parts" I've ever had to deal with. With the rods assembled, they can be inserted into the crankcase via one of the cylinder holes: Then I attached the front section to the crankcase and screwed the crank pin to the crank. I discovered that I needed to file the profile of the master rod so that the screw attaching the crank to the crankshaft is accessible with the rods attached. This is because the timing is adjusted by rotating the rods relative to the cams. Next session I'll attach the pistons to the rods and then the cylinders to see what kind of friction there is in the works. |
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