Mercury Rising: Norton’s Forgotten Featherbed

Comparing the Norton Mercury with its parallel-twin competitors, the Kawasaki W1/W2 and BSA 650 Thunderbolt.


Norton Mercury 650

Years produced: 1969-1970
Power: 47hp @ 6,800rpm
Top Speed: 110 mph est.
Engine: 646cc (68mm x 89mm) air-cooled, OHV parallel twin
Transmission: Chain primary, wet multiplate clutch, 4-speed, chain final drive
Weight/MPG: 408lb dry/NA
Price now: $4,000-$12,000

When the 750 Commando was launched at London’s Earls Court motorcycle show in 1967, cynics were quick to point out that Norton had ditched the best feature of its heavyweight motorcycle range — the sweet-handling Featherbed frame — and retained its main liability — the 20-year-old parallel-twin engine. But the Commando, with its vibe-killing Isolastic frame, was such a success that by 1969 the remaindered items in the company’s parts inventory included Featherbed frames and a quantity of 650cc engines from the Manxman and 650SS. What to do?

The result was the Norton you’ve never heard of — the 1969-1970 Mercury 650. Although no doubt intended to clear out Norton-Villiers’ stock of pre-Commando parts, the company created what is sometimes described as the nicest Norton ever. The long-stroke 650cc engine was considered the best development of Bert Hopwood’s 1949 parallel-twin. The largest capacity version, the 750 Atlas, produced such teeth-loosening vibration in the Featherbed that it was first sold as a mild-tune, low-compression tourer. The 750’s tuning potential had to wait for the Commando’s Isolastic frame. But the 650 worked beautifully in the Featherbed chassis, either in standard 650 Manxman form or as the dual-carb 650SS.

The Featherbed famously started out as a race chassis for the Norton Manx. It was a full duplex cradle frame made from chrome-moly tubing, strengthened with cross braces, triangulated around the headstock, and bronze welded. A rear subframe was welded on to support the swingarm suspension and dual shocks. The Featherbed was more expensive to manufacture than traditional lug-and-braze frames, so its introduction to Norton’s production twins wasn’t completed until the late 1950s. The production-bike frames adopted mild steel tubing rather than chrome-moly, and (after 1960) featured top tubes that swept inward behind the gas tank for more comfortable seating. The earlier frames were known as “wideline,” and the later as “slimline.”

The 650cc engine fitted to the Mercury’s “slimline” Featherbed frame was a development of the 1949 Model 7 Dominator 500cc OHV parallel twin. Unlike Triumph’s 500 twin, the Norton engine used a single camshaft driven by chain from a half-time pinion, making it mechanically quieter. Pushrods were fully enclosed in the cylinder casting, and the cylinder head incorporated the rocker boxes, reducing the opportunity for oil leaks. The 500 became the Dominator 88 in 1953 (in the Featherbed frame) and was joined in 1956 by a 600cc Dominator 99 with an alloy cylinder head. The first 650 was the cruiser-style 1960 Manxman, intended for the U.S. market, though a “home” market 650SS with lower bars and twin carburetors followed in 1961.

1/30/2020 1:15:26 PM

I had an early W1 for a few years. You're right -- essentially a copy of a British 650. No electric start. Strong and fairly easy to work on. Kept blowing out condensors every so often. Would have loved to have had the twin carb version.

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