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Roy Rice                      Atlanta, GA                                  3/1/2003

I have just started  Phil Duclos' "Gearless Hit 'n Miss Engine" which was serialized in Home Shop Machinist for 4 issues starting with the May/June 1993 issue. It is a 3/4" bore, 1.25 stroke engine. As the title says, it does not have a cam gear. Instead there is a toggle mechanism that opens the exhaust valve every other stroke - unless of course the governor is holding the exhaust valve open. The intake valve, like other hit and miss engines, is operated by vacuum. I will add photos as the construction progresses. The photo attached to this note shows boring the cylinder sleeve which will carry a cast iron liner. The material is 6061 aluminum.

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The photo above shows boring the cylinder sleeve which will carry a cast iron liner. The material is 6061 aluminum.


Here is the cylinder jacket after milling the base to size. The next operation is to cut recesses and grooves for the valve mechanisms.


After milling the slots and recesses in the cylinder jacket, I bored the cast iron cylinder liner to 0.748", to be lapped to .750 after the sleeve is shrunk into the jacket. I then mounted it on a mandrel and finished the OD to .001 larger than the ID of the jacket. after heating the jacket, the liner dropped right in, and on cooling was locked tightly into the liner. In this photo, I have mounted the assembly on the mandrel again in preparation for cutting the fins on the outside of the jacket.


Yesterday I cut the fins on the cylinder jacket. This photo shows indicating the parting tool perpendicular to the lathe axis, a very good  idea offered by Stuart Rolf, one of the instructors at DeKalb Tech, and a first class machinist. I had always set the parting tool by eye, but  my calibrated eyeballs were of by over .015 in an inch. The fins went beautifully as shown in the next photo.

Here we are about 2/3 finished cutting the fins. The parting tool is .125 wide, and was ground from a 1/2" lathe tool bit.

A nice radius on the fins really dresses them up. I used a dentists' diamond burr to grind about a 3/32 radius on a small lathe tool bit. The flash rather over illuminates it, but it cut very smoothly.

With the cylinder jacket fins done, I made the cast iron sleeve about .001 larger than the bore in the jacket, then heated the jacket and it  dropped right in. I had left the bore about .002 under size, and lapped to a pretty exact .750 bore. Here the finished cylinder sits atop the 4 pillar shafts. It is looking more like an engine!


Per Phil Duclos' advice in HSM, I slotted the head with a 1/16" slitting saw. He specified .063 slots, .047 fins, so there was no calculation required after the initial setting of the saw. Just crank the mill table up .100 after each cut, and after a while you're done!

Here is the head after a bit of cleanup. The valve housings fit into the slots on the sides, a rather unusual arrangement, but it allows the exhaust valve (and the intake, too) to point downward and make a more compact mechanism.

Here the head has been assembled to the cylinder. The piston has been  started, it is in the lower left, the crankshaft was finally silver  brazed (after 3 tries!). The Oilite bearings are in place, and it is beginning to look a lot like an engine. The piston is next on the agenda.


I had to turn the connecting rod between centers because it was so long and slim, but then I could not turn the compound around enough to turn the taper (I don't have a taper attachment). so I just calculated the tool offsets and step cut the taper. Ater applying layout dye, I filed the connrod smooth, and in the next photo, you can see the happy result.


I like to make split collets for my flywheels, so I had turned the taper  in the flywheel when I made it a few weeks ago. Now is the time to make the collet. I began by drilling and reaming a pieceo of 3/4 drill rod to fit the crankshaft.

Next, after setting the compound to cut a 4 degree taper, I turned the taper to approximate size. I just took off enough to have a very thin section at the small end and advanced the compound about .063 further than I had cut the internal taper in the flywheel.

I then trial fitted the collet in the flywheel, and adjusted the length of the taper so that I had about .063 clearance between the flange of the collet and the flywheel hub.

4/15/2005   Here is the Gearless on the run-in stand. After about 90 minutes of running in all seems free enough, but I have low compression. Looks like a leaky gasket on the exhaust valve housing.

More to come later...



Copyright 2003,  Florida Association of Model Engineers and engine builder as noted above, All rights reserved.