Whats in a Name?

For those not living in the Southwest USA, the Lobo may not be a familiar name. The Lobo is the Spanish name for wolf, and in particular refers to the Mexican Grey Wolf. The Lobo has many of the same traits as model engine builders. It is a solitary animal, seldom seen with others of its kind except during mating season, or in our case the occasional model engineering show. It is an endangered species, but with it's reintroduction to the wild it is making a little bit of a comeback, although less than 100 exist in the wild.

As related to my hopes for this engine, the Lobo is known for being a steady runner. Not the fastest, but very steady.

As related to me. When things go wrong in the shop, I go out the top of the sand dune that I call a back yard and howl at the moon when it is up, the stars when it is not, and otherwise just for the fun of it. Unlike the Lobo I almost always have a companion when I do my howling, my 3 year old Papillon shop dog who looks nothing like a Lobo, but does enjoy the howling with me.

Design

The general design considerations were to make a fairly low tech twin of fairly small displacement. The design would be considered fairly conventional - if we still lived in 1955. The stroke/bore ratio is 1.17, a little long by today’s standards, and a little short for 1955.

A 3-piece crankshaft is used to avoid having split big ends on the connecting rods. The centre two crankshafts are permanently assembled to form one crankshaft which carries both crank pins.

The front crankshaft is driven by engagement with an extended front crankpin. Both crankshafts are running in sealed ball bearing races. The bearings each have two Teflon seals. This is done to isolate the primary compression space of the two cylinders and to seal the front primary compression space from the outside world.

Teflon seals were chosen as I did not know how rubber seals would react to the ether in it fuel. They are also a standard bearing in the radio control car world and are readily available at low cost.

There would be nothing wrong with running both the centre and front crankshafts in plain bearings by removing the bearing cavities in the centre bearing housing and the front bearing housing. If the crankshafts are well polished, they would be fine in 6061-T6 aluminium.

The timing is fairly conservative so this is not going to be a high speed engine. Top RPM is expected to be in the 10,000 range. As with all side port designs with the crankshaft on the cylinder centreline, there is no favoured direction for the engine to run.

The crankcase can be switched front to back at assembly so the exhaust and intake can be reversed. This opens up another possibility of extending the rear crankpin so it is the same as the front crankpin and replacing the rear cover with a second front crankshaft and front bearing assembly. Then the engine would be double ended. Direct drive tether car racing anyone?

With all the preliminaries out of the way, it is time to start making chips. First up will be the crankcase. Click on drawings to download.

Crankcase

Sawed off a piece of 1-3/4 square 6061 extrusion and then squared it up and face milled it to the major dimension of the crankcase.

After making a rough sketch of the holes on the crankcase, I centre drilled, drilled and tapped the 12 0-80 holes and the 8 2-56 holes. (Ed: You might prefer to change 0-80 threads to M1x0.25 or 11BA, and 2-56 to M1.4x0.3 or 8BA - but note these threads are not interchangeable).

The rough sketch is so I would not put the 0-80 hole p

attern on the top edge on one end and the bottom edge on the other end. I like to get all the tapping out of the way as early as possible as a broken tap is a difficult to repair error and very irritating if it occurs after a lot of machining is done. It can become a real possibility if you are not used to doing 0-80 holes. I also put a centre hole in location for each cylinder and on both ends of the crankshaft bore for setup purposes for boring those holes. All holes were drilled using the DRO on the mill for location.

Off to the lathe to bore the hole for the crankshaft assemblies. The blank was set up in the 4-jaw chuck using a wiggler and a dial indicator to indicate the centre of the hole to be bored. Notice the strips of soft aluminium under the jaws to protect the surface of the part. The bore was rough drilled with a 1/2 inch drill which is the largest I have.

The hole opened up the a short stiff boring bar that would just fit in the 1/2 inch hole and the part is now ready to go back to the mill where I will put the 0.118 hole in the bottom and bore the cylinder mounting holes with a boring head. The crankshaft bore was done first because I did not want any holes into that bore that might distort that bore by having an interrupted cut.