Cylinders


The cylinders all had the heads secured to them before this page was completed, so I was unfortunately not able to show much of the actual machining and fin cutting while it was taking place. In fact, the cylinders were completed before I even had a digital camera, so I have attempted to show what occurred to make the cylinders a reality.

Before the heads were in place, I attempted to have the cylinders hot-blued at a local gunsmith's shop. The results were disastrous, with no real color and much streaking. I suspect the gunsmith did not to a proper degrease job... the preservatives I had sprayed into the fins probably ruined the blue job. So if you want your own cylinders professionally blued, you must tell the gunsmith to manually brush the fins clean in the degrease bath, rather than simply soaking them which is what I believe happened.

The cylinders started life as slugs of 12L14 steel, 2" long by 1.75" dia. The bore was roughed out to within .0015 of 1.000, leaving material for later removal via lapping. On the left is a starting slug... on the right, a piece which was the "guinea pig" for my fin-cutting tool. It was used to test the cutting ability (and safe fin spacing) for the finished cylinders. DON'T underestimate the difficulty in cutting deep, narrow fins! Broken tools and folded fins are inevitable.

While this operation is simulated, the tool is real... I hand-ground a .032" parting tool which would cut to .125" deep. The only parting tools available commercially in this width are for the "Mini-Thin" tool, but the .032" wide blade can only plunge .093" deep. Maybe they know how tricky this can be. Alignment and a rigid carriage are crucial to success. The carriage must be locked at the correct position, and the utmost care taken to avoid a broken tool and scrapped jug.

After the fins are cut, the jugs are lapped to 1.000" as close as possible. The copper lap is used to cut a truely round and parallel bore to ~.9995". The expanding brass lap is then charged with 400 clover lap and the bore lapped to final dimension with a pumping action on a drill press.

I have TRIED honing rather than lapping, and I always find the hone cutting a bell-shaped bore. Perhaps it is my technique, but I always return tot he lap as a tried and true method of creating a perfect bore.

The heads are secured (screwed) to the jugs with a special wrench. An aluminum washer helps seal, and I also used a special high-temperature loctite, good to 500 degrees f.

After the heads are in place, each jug is secured in this special jig which aligns the head so that I can drill the flange with the 8 holes which slip over the 5-40 studs in the crankcase.

The position of the flange makes deburring of the flange holes impossible in the normal sense, so I slipped each cylinder over a mandrel and polished the holes clean with some 400-grit paper backed by a piece of steel.

After the smoke cleared, I had a total of 10 cylinders and heads, so I was able to keep one for a spare. This after starting with 12 cylinders and perhaps 14 heads. The scrap rate must be estimated conservatively in this type of project!

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