2-14-2021

This information was compiled by the late
Bill Mohrbacher

FOX 78 RC was added by Randy Linsalato

** The 60 RC Line***

In the April 1960 MAN, Fox advertised coming soon was a 59 Mark IV with a 19/32 dia. crankshaft running in 2 ball bearings, fully counterbalanced crankshaft, glass hard cylinder, machined aluminum piston with 3 rings….; “It costs twice as much –worth 10 times as much”. An airbrush illustration showed the engine. We never saw this engine, but saw a series of throttled front intake 59s.
Then, in 1967 we saw the 60 RC (95). A huge beautiful engine with the 19/32 dia crankshaft running in twin ball bearings, needle bearings on both ends of a fabricated steel connecting rod, a glass hard steel cylinder, a machined aluminum piston with 2 rings, a 3 jet carburetor, blue anodized twin plug head, blue anodized spinner nut, and gold plated prop driver and throttle parts. “60” was cast on the bypass of the tumble polished case. It was expensive, $49.95 when the 59 RC was $29.95. Its .907 x .937 B&S has been used on all Fox 60s since. I really think this is the engine Duke had in mind when he announced the 59 MK IV years earlier.
At the same time Fox introduced the .74 RC (96). Essentially the 60RC, but bored out to 1.000. It came with a red anodized head and spinner nut and “74” cast on the bypass.
Fox had planned to come out with a .90 using this case, 1.070 x 1.000 B&S and actually advertised it in 1969. This engine was never actually produced as far as I know. Also about this time, the AMA clamped a .61 displacement limit on pattern planes. Duke was furious since he had invested heavily in the 60 and 74 and really expected pattern fliers to use the 74 with its huge (at the time) power.

The 60 and 74 were never very popular. Scale fliers were building larger, heavier planes and in 1971, Fox stroked the 74 to produce the Fox 78 RC (113), 1.000 x 1.000 B&S. Maybe he had the crankshaft tooled up from the .90? Externally, it resembles the 74, but “78” is stamped on the bypass, the prop driver is a slightly different style gold anodized aluminum, there is a plain prop nut and washer, and a pronounced gap between the head and the case. The increased stroke required a thicker lip on the liner. Internally, the fabricated twin needle bearing rod was replaced with a more conventional bar stock aluminum rod.

The 78 was much more successful; scale fliers liked it. It went through various changes. The 3 jet carb was really excellent, but choked the engine too much (I think) and was too complicated to adjust for pilots who didn’t read instructions. Originally the twin plug head was thought to be required for reliable idle, many other manufacturers also used them. As throttle design evolved, the twin plugs weren’t found necessary. In fact on the Foxes, the plug on the bypass side sits square in the middle of the baffle slot in the head. You must use a SHORT plug as a long plug, especially with an idle bar, will definitely hit the piston baffle and tear it up, tear the plug up, or both and may leave bits and pieces churning around in the engine.

The Fox 78 RC case bypass was enlarged removing the Fox face and engraved.

Muffler bosses were added above and below the exhaust flange. Head was fitted with a single plug. And it was fitted with a new prop driver.

 

 

 

The last version of the 78 was produced in 1981 (217). By now it had a single tilted plug head, a heavier bronze bushed bar stock aluminum rod, a heavier bottom end on the crankcase*, and was fitted with the newly developed Fox MK X carburetor. This is the largest single cylinder engine Fox ever produced and is the final descendant in the 60RC Line.

 

*Note from Randy: I am not sure this is correct