Motorcycle Monthly - - Knowledge -

Lay­out: Two pairs of two cylin­ders in a square con­fig­u­ra­tion. Ben­e­fits: Nar­row in pro­file, big torque, af­ford­able to build.

Ariel took the de­ci­sion to em­ploy de­signer Ed­ward Turner in the late 20s, hav­ing seen his il­lus­tra­tion for a square-four mo­tor­cy­cle en­gine. Turned away by BSA, Ariel quickly got Turner’s in­no­va­tive 500cc con­fig­u­ra­tion into pro­duc­tion and show­cased a mo­tor­cy­cle aptly dubbed the Ariel Square Four at the Olympia Show in 1930.

Be­tween 1931 and 1958, a to­tal of five dif­fer­ent ver­sions had come and gone, with over 15,000 ex­am­ples of the pop­u­lar ma­chines be­ing sold dur­ing that pe­riod.

De­spite its en­gine ca­pac­ity in­creas­ing from 500cc to 997cc, the square-four lay­out was to prove in­ca­pable of revving high enough or pro­duc­ing suf­fi­cient power to com­pete with the lat­est and great­est op­tions com­ing to light by the end of the 50s and was con­se­quently dropped. Broth­ers Ge­orge and Tim Healey – fans of the square-fours – bought-up all re­main­ing square-four com­po­nents from Ariel and built just 28 Healey 1000/4s be­tween 1971 and 1977, hav­ing tuned the en­gines from 45bhp to 52bhp, be­fore they even­tu­ally packed up.

Suzuki then took up the square four de­sign in the 80s, when it re­leased the two-stroke RG500 Gamma race bike in 1984, go­ing on to in­spire the pro­duc­tion of the RG500 Gamma road bike be­tween 1985 and 1987. De­spite achiev­ing a re­spectable out­put of 94bhp, no fur­ther ad­vance­ments to the square-four were made.

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