A Special "Thank you" to Paul D'Orléans for his help. Please enjoy the second part of this post that he warmly send us.
Norton revised the 490cc 16H engine for 1931, establishing the form that would remain until the end of production nearly three decades later. The magneto was moved from the "vintage" forward mounted position to behind the cylinder and the lubrication became dry sump. These revisions were followed in 1935 by the adoption of the Norton 4 speed foot operated gearbox.
Thanks to : The Motorbike search engine
The 16H was Norton's pre-war workhorse. Its 500cc side-valve engine produced only 16bhp but the ultra-low compression meant it would run on anything vaguely connected to petroleum
PRAISE FOR THE HUMBLE 16H c.2008 Paul d’Orleans/theVintagent
Until the Honda 'Step-Thru' became the immortal motorcycle of the ages (51 years old and counting, with untold millions produced), the Norton 16H had the distinction of the longest production run of any motorcycle in history, at 47 years. The fundaments of this model have roots in the early days of Norton Motors Ltd (est'd 1898), when James Lansdowne Norton designed his own engines in 1907. One of these designs was a simple 500cc sidevalve engine housed in fairly ordinary cycle parts – this was the father of the 16H.
In November 1914, after years of single-speed belt-drive machines, Norton finally announced an all-chain drive, clutch-and-gearbox model, to be included for the 1915 range. One could still buy direct-drive models, including the TT Model, Brooklands Special and Brooklands Road Special (BRS - with mudguards and toolboxes), the BS now having a guarantee of a 70mph lap and 75mph over the flying kilo. The TT machine had no guarantee, but was claimed to be good for 65mph.
It took until 1919 for the Model 16 to appear (the H stood for 'Home Market' - there was also an export version, the 16C for 'Colonial'), although it used the same engine (79x100mm) built since 1911 (with improvements of course). The new model number heralded the familiar configuration of flat-tank sidevalver we have come to love. Norton raced this model in the TT for the next four years, coming closest to a win in 1920 (and filled 9 of the first 14 places); Tommy de la Haye and his Sunbeam 'long stroke' racer proved faster.
On March 29, 1921, Rex Judd, new to the Norton team at Brooklands (and weighing a very useful 125lbs/57kg), ran an amazing 92.44mph on Dan O'Donovan’s 16H. This was the fastest the 16H would reach in the hands of the Works, for in 1922 the factory introduced the Model 18 (500cc ohv, also 79x100mm), which was, right out of the box, 6mph faster than the 16H. Instantly our humble hero was relegated to 'sporting' status. Still, dogged fans (mistrustful of dropped valves) continued to race the sidevalver even until the mid-1930's, when the indefatigable A.L.Loweth rode his specially tuned 16H to 94 mph at Brooklands, in 1934. It must have been sheer cussedness which inspired Loweth to seek out the last nth of speed from an obsolete design, but we're grateful he did.
So, during the later 1920's and through the 1930's, the 16H was produced in great numbers, as it still had a reasonable turn of speed, and was simply stone reliable. Overhead valve machines had their problems with lack of lubrication, in the days when rocker arms and valves were exposed, but the 16H had proved its dependability, and most buyers who relied on their machines to get them to work valued the Norton's combination of decent power and unfailing reliability.
As the decade turned into the 1930's, the saddle tank frame with lower seat height was introduced on all models, which included thicker wall frame tubing and generally heavier spec on all metal items, giving further boost to smoothness and unbreakability, with a profound minus on performance. The 16H engine gave little additional power even after it gained a detachable cylinder head (1931) and fully enclosed valves; thus the added weight (370lbs) meant performance (65mph top whack) slipped further behind its ohv rivals.
During the Second World War, no less than 100,000 16Hs were produced, fully one-fourth of the entire output of military motorcycles from Britain. It's hard to imagine, looking at the WW2 16H, or the postwar dinosaur model, that in its youth, the old warhorse had been as fleet as a greyhound, and the terror of road and racetrack. By the end of production in 1954, it was simply heavy and slow (although still reliable), all the glamour of its youth having long since faded away.
And yet...there has been a resurgence of interest in the model in the past 10 years; after decades of laying in the shadow of the Model 18 and CS1/International, the 16H, especially those early, light, flat-tank models, have grown steadily in demand and consequent value. After dusting off the layers of history, it appears the old luster is back.