LONGBOY'S "JUSTABLE" MODEL GAS ENGINE!

Longboy · May 2, 2020

The best way was to pull back from the 2 inch crank to camshaft centerline. Lower and to the right, under where I want the lifters to be.

Belt slot will end before running off the deck and if too much slack in the belt, can reorder. Most likely a MXL78 tooth.

Trying an idler to take up the slack now and it will work fine with the 81T belt. Locate with a couple of transfer punches and drill the frame.

One caveat with the choosen location of cam sprocket is its flange sits right on top of the short deck now. With a slitting saw, I milled a shallow trough in front of the sprocket to the end of the deck for the clearance. Trimming the flange back about .025 in. would have done the same..... but I was looking for adventure with the slitting saw!

Still going to be tight under the lifters. So I re-bush the sprocket for a 1/8 in. shaft now. These cam lobes start form 5/16 in. 12L14 round stock secured with 4-40 set screws to their shaft.

Back on the other side, I shorten the lifter guides to be flush with the cylinder deck underside and cut back the lifter heads so they have some space between the lobes and guides. Of course....I just made it!

Longboy · May 4, 2020

JUSTABLE's distributor sits on the back corner of the short deck. Its bracket is a piece of the angle aluminum milled for the correct angle along the apex.

With the camshaft at 1/8 inch through the brass bushing to end of sprocket, I need a 3/16 in. shaft for these 20T .5 mod gears. They come holed at 3-4mm and I re drill for this size shafting. An inch long piece is drilled the eighth inch and pressed fit over the cam shaft with some epoxy. There is a flat for the set screw under the gears.

These gears are tiny and on an eighth in. dia camshaft.......to prevent flexing and going outta mesh screwing up the ign. timing, an R166 bearing supports the tail end.

Now if you look closely! (

not again Longboy). Oh yes.......the distributor gear........"just fits" between the sprocket bushing and drive gear! (ah- huh

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Longboy · May 6, 2020

Can an overhanging crankshaft be developed for a 360 degree two cylinder inline engine? Perhaps best described has a hybrid as one crank throw supported in two webs, and the other crank throw.....not supported by two webs. What does that look like?

A third crank bearing is supported under the deck between the cylinders. With two bearings in the vertical portions of frame, a transfer punch is inserted.

The bearing block is 1/2 x 1 inch stock. A bearing cap bolted to its bottom, the butt joint is slightly below the crank center line for trimming up to the correct match up with the point on the transfer punch.

There is an Oilite bushing on the crank segment for this bearing block. The crank webs are assembled onto the crank segments with the rotating assembly. The front two webs are pressed fit to the shaft with the Oilite bushing with two thin SS washers properly spaced for some slight thrust movement and capped in the lead bearing block.

The bearing block shank has been reduced substantially as it is obviously too meaty in appearance here. The illusion presented upon completion is that JUSTABLE's crankshaft appears to be hanging out in space under its cylinders.