Given the Wolseley foray into OHC engines later used by Morris, which were immensely complicated and very expensive to produce, Austin's adherence to a simple well proven side valve engine for a cheap vehicle is understandable.

From pictures, the early BMW chassis has a remarkable similarity to the Austin Seven's 'A' frame.

Cheers, Tony.

Location: Melbourne. Victoria, Australia.

Wolseley's OHC engines are another matter, AFAIK not even Austin considered a production OHC or Twin-Cam engine.

It seems the trend towards OHV engines roughly began sometime during the 30s, with the post-war Morris Minor's potential as a Beetle rival even nipped in the bud as a result of being forced to use the old SV 918cc engine.

None the less, it's interesting to note that the Austin Seven's main competitors in the late 1920s - the Morris Minor and the Singer Junior - were both fitted with ohc engines!

The DA-1, 2 & 3 chassis were pure Austin Seven; the DA-4 continued the basic design but with independent front suspension. But the 3/20 AM-1 chassis was an all new design with a box-section backbone frame with independent suspension front and rear.

Morris upgraded from OHC to sidevalve. Profit upgrade only!

Location: Richmond, Texas

For a detailed account of the twin cam engine, one can do no better than obtaining a copy of " The Classic Twin-Cam Engine " by Griffith Borgeson. This traces its history from the start of the 20th century to modern times. Incredibly detailed and fascinating.

While understanding why OHC was not reliable compared to Sidevalve (especially in the case of Morris), what prevented OHV from taking hold earlier like on the Vauxhall 10-4 or even the Wolseley Eight?

I don't think the problem with ohc cars was poor reliability so much as expensive maintenance bills.
In 1931 there were only four family cars (British or Continental) on the British market under 12hp (RAC rating) that were not side-valve: the long-wheelbase Morris Minor(which retained the ohc engine after the side-valve engine was adopted for the more popular models), the Riley Nine, the Rover 10/25, and the Singer Junior. Even by the outbreak of war, the majority of small family cars were still side-valve (Ford, Morris, Standard, as well as Austin) - they were just so much cheaper to manufacture (and maintain)!