Longboy's "TWIN REDEMPTION" Model Engine.

[Longboy]

Last year's "SPLIT MONO" engine was a unique effort and a successful build. What would a two cylinder version look like? There are two ways to go here......and inline twin with both cylinders on one side of the crankshaft or a cross cylinder design, like an opposed engine with one cylinder each side of the crankshaft. I got to play with a lot of gears in the process.....and it ended up in a surprise finish! The road to the T.R. engine starting this week!

 

[Longboy]

This is a couple months into the build. 4x4 aluminum angle, 4 in. long time 2 pieces. The cylinder hole on the horizontal is offset on the length from center to accommodate the camshafts. Two screw attachment. A pair of valve lifter holes at the front top.

Brass lifter body, steel lifter with 4-40 socket head adjuster screw lock in with 6-32 set screws coming in at the frame edge.

Two bearing carriers per cylinder are necessary for a split rod engine for the crankshaft stubs and are mounted in their bore throughs from equal off set to the center of the cylinder mounting in the vertical leg of the 4x4.

And mounted in place on frame.

 

[Longboy]

Using a different part number for the Traxxas spur gears and less $$$ at the time ordered. Milling the raised areas on the hub off for flush fit to the webs.

4T less and an eighth inch shorter in diameter. Cutting back the diameter of the web round stock for the fit.

Fitted to the backside of webs with three 6-32 machine screws.

Piggy backed to the backside of gear and web to balance the piston/ rod assembly, a half moon shaped brass counterweight.

One machine screw with blue Loctite. Additional weight reduction of the steel web will complete the primary balance.

 

[Longboy]

Making up a pair of cylinders and their heads. Cyl. get some DOM one inch bore liners for that size piston.

Matching one cyl. head to the other. Central spark plug location.

 

[Longboy]

Twin port valve blocks are made up from quarter inch bar stock.

Self contained units with brass guides, leaded steel valves, o-ring seals. Four corner bolt together. A single fine thread 1/4 in. screw mounts blocks to head.

A flat is machined to lower side of heads. Drilled for both ex. and in. ports at 5/32 in. Brass tube inserted with o-ring seal between head and valve bock. Upper half of valve block drilled for mounting bolt to head.

And as it appears projecting out from head/ cylinder assembly!

 

[Longboy]

The pistons for a dual rod engine are somewhat weird. They are longer and have a more solid core as the rods are attached to their lower third, therefore heavier. A flat is machined across the bottom for the rod attachment. The depth of cut determined by the rod centerline to match piston centerline.

A couple of parallel 4-40 threaded holes for the small end attachment. A standard plumbers O-ring for the combustion sealing.

Rods have the same strangeness to them. With the crank webs offset to the side of the cylinder, you get steep rod angles at their 3 and 9 O'clock positions. The outside cut aways in the rods are to clear the bottom of the cylinder liner in motion.

 

[Longboy]

The two halves of the engine mockup. Have to square up with end plates to the frame. Run a 5/16 in. transfer punch across through web to web to come up with a critical shaft centerline.

With the lower crank endplates in place, how the bottom end will look with six bevel gears. I did not particularly like the vendor's gears here. They are dark end to end with the heat treat. I order 6mm hole thru and re-drill to 5/16in. A couple would not drill cuzz of the hardening. Ordered others from a different provider after the experience.

The cams come into the frame at 90 degrees to the crank/output shaft. My lobes crafted in brass this time, the easiest to cut and file a profile to. Slipped onto a transfer punch and by line of sight location to the vertical leg of the 4x4 pieces.

The marking drilled and bushed and the lifter adjust screw range will take up the valve timing needs.

The upper end plates have the distributor and cam drive shaft. MXL sprockets will mate the crank and cams.

 

[Longboy]

The cams driven by some .5Mod, 24T brass bevel gears. Three up front and two more for the distributor.

The bottom shaft will get a shaft stop collar to keep the gears in mesh.

The ign. points will sit on the vertical leg of the 4x4.

And its cam will be the shaft stop collar for the other side.

Thinking about distributor being in center of the shaft valley........but no. Needs another crossmember to support the dist. body and further limiting access this area.

Cam drive shaft will head to the back of engine and mount to top end plate. Some relief for the gear teeth milled in the end plate.

And the assembly ready to go.

An aluminum bracket for the insulated stud on the points bolt down with a couple of 2-56 screws to the top deck.

And from the top side......the geartrain connected.