Page 22 - LHR Biker September 2025
P. 22
REAL CLASSIC
was a serious test of both earlier, by 1928-29 they rigid rear, with a spring saddle,
machine and rider. That returned to well-developed were standard. The frame
Sunbeam’s Model 90 could OHV (pushrod) engines for the geometry was tuned for better
compete — and win — there, Model 90, in part due to handling on the mountain
alongside continental rivals, reliability and wider usability. circuits and open roads. Lighter
confirmed that Sunbeam had e x h a u s t p o r t i n g , b e t t e r
achieved a high level of The twin exhaust ports (one carburettors (Amac twin float
performance and reliability. e x h a u s t v a l v e b u t d u a l chambers in some cases), and
exhausts) allowed more improved lubrication system all
Other Races and Hill Climbs: efficient scavenging. Hairpin contributed.
The Model 90 dominated many valve springs were used, which
national and international were more resistant to valve Later Development and
events, including hill climbs float at higher revs. Decline
(especially in France), and other The Model 90 had its heyday in
Grand Prix where road and Compression ratios were 1 9 2 8 - 2 9 , b u t o v e r t i m e
track conditions were harsh. modest by today’s standards, Sunbeam’s involvement in
but high for the era. Optional works racing diminished.
The Engine in Detail higher compression was offered Several factors contributed:
To understand why the Model for racing. Also, special
90 succeeded, one must dig into attention was paid to the shape Emerging competition: other
its engine design and how of ports, gas flow, valve timing, manufacturers improved OHC,
Sunbeam, with input from and machining of critical parts, twin-cam, multi-cylinder
engineers such as Harry which gave Sunbeams their designs. Sunbeam’s pushrod
W e s l a k e , o p t i m i z e d reputation for “smoothness” and OHV could only be pushed so
performance. durability. far before responding becomes
increasingly difficult.
While Sunbeam had briefly tried The chassis and ancillary Financial pressures and
OHC / overhead cam designs components: girder front forks, ch a n g e s i n o w n e rsh i p /
20
22
LHR Biker Magazine October 2025
