As far as machining the casting for the Dake, I would use the same aproach that I used for the green twin, which is as folows:
1. Machine the inside of the crankcase, using the lathe for accuracy.
2. While the crankcase is still mounted in the lathe, face off the mating flange surface.
3. Machine the face of the crankcase cover in the lathe.
4. Fit the crankshaft assembly to the crankcase, making sure the crank disk is flush with the interior surface of the crankcase.
5. Measure the interior depth of the crankcase, and machine the inner piston thickness to match to the exact dimension of the crankcase interior depth, plus perhaps 0.003".
6. Machine the outer piston to match the thickness of the inner piston.
7. The original Dake engines (as I understand it) were supplied with a range of metal crankcase gaskets/shims, in increments of 0.001".
The fit between the pistons and the crankcase cover was adjusted using these shims/gaskets.
This tells me that the original engine must have had pistions that were a bit taller than the crankcase, to allow for wear adjustment.
8. I think the original Dake engine internal parts were precision ground.
I can't precision grind my parts, and so the plan is to machine the pistons, dye them along with the interior of the crankcase, and then assemble the engine, and rotate it slowly by hand.
By observing the high spots (the spots where the dye is scraped off), on can scrap off the high spots, much like scraping the bed of a lathe to achieve a flat surface.
9. The pistons could be lapped to the crankcase using a bit of 600 grit lapping compound, being careful to avoid getting compound on the crank pin, or in the bearings.
The engine will wear-in to some extent, so I don't think lapping is really critical.
It should be noted that a Dake crankcase wears unevenly, and it wears more as you move away from the centerline of the crankshaft, since the velocity of the pistons is greater as you move out radially.
With the correct lubrication, the wear of the Dake internal parts does not seem to be a problem, and I have seen some very old Dake engines that still run perfectly.
10. The funnel-shaped crankcase housing should have the flange faced first, then it should be mounted in the lathe with that finished face hard against the lathe chuck. I plan to press in the bearing into the crank housing, and then with the housing in the lathe, final bore the bearing.
As has been mentioned in some of the Dake sales literature, there are only 3 moving parts to a Dake engine, which is somewhat correct.
The three moving "parts" are the inner piston, the outer piston, and the crankshaft/flywheel assembly.
From the sandpoint of machinging parts, this engine should be quick to machine, since there are really very few surfaces and parts to machine.
The key to success with this engine is accurately machining each part.
I tried to make a few parts for a Dake years ago (not for this build), just to practice machining techniques, and I discovered that my mill lacked the rigidity to make accurate engine parts.
For this Dake build, everything will be turned in the lathe, with no critical surfaced machined by the mill.
An actual Dake engine inner piston has an external flange, and an internal flange.
I omitted the internal flange in my drawings, but for accuracy, I think I will add it back in.
The engine runs fine without the internal piston flange, but the flange gives a larger bearing surface to ride over the crank disk.
Below are a few of my practice Dake part machined pieces.
I recall getting one Dake piston at about 99% complete, and then the part slipped out of the jaws, creating huge gashes in the piece.
It took me a lot of ruined parts to figure out how to machine metal accurately.
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