I asked what the story was behind the JLO 4 cylinder motor yeterday, and our Bull Sessions resident expert on JLO’s was quick to share his research on it:

“After researching and translating quite a bit of printed matter and German language webpages, I have come up with this summary.There is quite a bit of speculation and assumption here on my part. It is based on the best info I have at the moment.

JLO was purchased Rockwell in the early 60s with the intention of expanding engine sales to the US. Shortly after that, snowmobile builders started searching for lightweight 2 strokes to power their new product lines. JLO had quite a few different designs available to power everything from lawnmowers to motorcycles to small rail cars used for RR maintenance. Basic problem was the current lineup was built for commercial use and they were too heavy. Snowmobile manufacturers wanted a better power to weight ratio.

So a new design was drawn up that would be the most compact and powerful engine available to date. This was introduced as the 339cc and 399cc axial fan which were oddly named the LR series, a name already in use for the centrifugal fan 454cc twin. Along with the engineering work for the new fan cooled line, the free air engine was born. Production numbers and documentation is virtually nonexistant for the free air line. A multi page brochure showing the three free air engines is the only published proof I can find to confirm it was ever marketed to snowmobile companies. The only serious use of the free air line was by Arctic Cat which used the 650cc engine as a fill in for Kawasaki in the King Kat. I believe that AC would not have built JLO or Hirth powered King Kats if Kawi had been further along with their production. [That would have been a shame too!]

Details about the 800cc 4cylinder and 440cc twin are even harder to find than that of the 650cc triple. Production numbers for the 650cc can be estimated by the production numbers of the King Cat triple. No production machines were built using the other two engines. Any use of them would have probably been by privateer racers. The previously mentioned brochure shows the free air engines with a slick fuel injection setup. Don’t know if it worked in actual use.

Questions regarding the durability of the four cylinder would have to mirror the problems seen in the Kawasaki four cylinder engine. The crankshaft being the major issue. The other odd fact I have observed about the 800cc 4cylinder and 440cc twin is that neither of engine has an advance mechanism for engine timing. Look at the scan of the engines below and you will see the triple has a larger magneto housing, apparently to make room for the advance mechanism.”

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