An Elf 10 "Corncob" Diesel (?!)
by Stan Pilgrim (July 11, 2001)

Click on a photo to view it full sized.

Recently I attended an engine Collecto and prior to the event I thought it might be nice to display and run something unusual that I had created. I went searching through my pile of partly finished projects and came up with my Elf 10 Diesel. What? you say, Dan Calkin never made a diesel! Well read on...

I always wanted to try my hand at making a miniature built up crankshaft in conventional single cylinder two stroke motorcycle engine fashion but without the roller bearings. I also liked the appearance of the Elf Corncob crankcase so that is where the story starts.

Back in 1996 I'd bought a set of Elf Corncob castings and drawings from John Goodall. They were produced for the Elf Corncob construction article that had featured in Model Engine World. I made some modifications to the drawings, removable head, flanged drop in liner, schnuerle type transfer port configuration, lapped cast iron flat top piston, spigotted crankcase halves, socket cap screw fasteners and DIESEL IGNITION. The engine was going to be for control line use so I altered its capacity to my favourite size - 0.10 cubic inch.

I rushed in and machined the crankcase and cylinder muff. The castings were nice to machine. Next came the aluminium head and steel cylinder blank before I tackled the dreaded built up crankshaft. The engine was starting to take shape and after each session in the workshop I would clean and assemble all the parts then sit and admire my work and dream.

The crankshaft has 1/4inch diameter drill blanks for the main journals. The flywheels are full circle 1inch diameter mild steel discs 1/8inch thick with drilled counter balance holes (refer picture). The crankpin is a hardened and ground shouldered affair with a 3/16 inch big end diameter. The conrod is steel and is bushed both ends. All parts were pressed together using a jig for alignment purposes. It was then that I found that perfect alignment was extremely difficult to achieve. I had two attempts at the crankshaft and my second go was as close as I could get the alignment. Once I knew the shaft would work I lost interest in the project and put it aside until itís resurrection a few weeks back. I did not leave myself much time to complete the engine for the big day and also encountered problems.

No layout drawing of the engine was produced, only rough sketches when needed so guess what happened. Due to the much smaller bore than the original Elf the conrod fouled both the cylinder and piston skirt when the crankshaft was rotated. I had already cut away the bottom edge of the cylinder in two places to give access to the main transfer ports so the only answer was to rotate the cylinder through 90 degrees and cut clearance slots in the piston skirt.

Now everything worked and I had a rear exhaust engine. WOW I think it looks great! Needless to say I did not finish the engine for the Collecto and was only short a venturi (refer pictures).

 

 

The engine feels good and I have had it running in my hand using a small prime of fuel in the exhaust port. I am working on the venturi now and will send further pictures of the engine when it is finished plus a report as to how it runs.

Specifications

Bore:
0.474 inch
Stroke:
0.580 inch
Swept volume
:
1.68cc
Mass
:
136 grams (minus venturi)

 

Ruler

 

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