How a ro­tary en­gine works; strengths and weak­nesses

Practical Sportsbikes (UK) - - Norton Rotary Racers -

The Nor­ton ro­tary en­gine was, in all its forms, a de­vel­op­ment of the Ger­man Sachs twin ro­tor Wankel en­gine (which pow­ered the DKW/ Her­cules W-2000 pro­duced from 1974), a li­cence for which was orig­i­nally bought by Bsa-tri­umph (who then owned Nor­ton) in 1972.

In prin­ci­ple, al­though still an in­ter­nal com­bus­tion en­gine, in­stead of con­ven­tional pis­tons and con-rods ro­tat­ing a crank­shaft, it uses two ec­cen­tric, three-sided (or tro­choidal) ro­tors, driven by com­bus­tion pres­sure and geared di­rectly onto the crank, to cre­ate ro­tat­ing mo­tion.

There are no valves. In­stead, sim­i­lar to a two-stroke, the gases are drawn in, pres­surised and ex­hausted by the move­ment of the ro­tor.

The ad­van­tages are essen­tially three­fold: It’s a very sim­ple de­sign with just three mov­ing parts and as such is com­pact and light. That means it’s rel­a­tively cheap to make and easy to pack­age with the han­dling ad­van­tages that of­fers. Sec­ond, as all parts ro­tate in one di­rec­tion com­pared the a re­cip­ro­cat­ing pis­ton en­gine, it’s both very smooth and ca­pa­ble of very high rpm, with the power ben­e­fits that brings. Third, and per­haps most im­por­tantly, three power pulses are pro­duced per ro­tor revo­lu­tion com­pared to the one of a two-stroke and one ev­ery two revo­lu­tions of a four-stroke, which means it’s in­her­ently pow­er­ful.

On the down­side: they have high emis­sions lev­els due to un­burnt fuel en­ter­ing the ex­haust (and caus­ing the flam­ing char­ac­ter­is­tic of the rac­ers); they’re thirsty on fuel for sim­i­lar rea­sons; heat gen­er­a­tion is ex­treme as one side of the mo­tor is con­tin­u­ally ig­nited and man­ag­ing the wear of the seal­ing ro­tor tips is dif­fi­cult, lead­ing to even greater emis­sions, power loss and un­re­li­a­bil­ity.

A fur­ther ma­jor dis­ad­van­tage ex­pe­ri­enced by the Nor­ton in par­tic­u­lar was the con­fu­sion and in­con­sis­tency about mea­sur­ing its dis­place­ment or swept ca­pac­ity. While Nor­ton mea­sured their bikes at 588cc, the FIM at first de­creed that it should be rated at twice that (tak­ing it up to 1176cc mak­ing it in­el­i­gi­ble for 1000cc rac­ing) be­fore re­lax­ing it to 1.7:1 (or 999cc). And that was be­fore it was barred from pro­duc­tion­based rac­ing and Euro4 and worse came in…

Yep, that’s a belt pri­mary drive you’re look­ing at there

So sim­ple in prin­ci­ple, but huge amounts of pre­ci­sion-ma­chin­ing re­quired to make it work

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