1957 BSA M33 Plunger 500cc OHV
The 1957 BSA M33 Plunger is one of those bikes where the engineering history is written right into the name. The Plunger designation refers to the sprung rear suspension, a system of coiled plunger units that replaced the rigid frame of earlier models but predated the swingarm designs that would become standard through the late 1950s. By 1957 BSA was already offering swingarm models, which makes this M33 Plunger something of a transitional piece. It is historically significant and increasingly rare, as many were upgraded or scrapped when swingarm conversions became popular.
Under the red-and-black bodywork sits a 500cc OHV single-cylinder four-stroke, air-cooled, with a separate four-speed gearbox and chain drive. The engine is fitted with an Amal Monobloc carburettor described by the vendor as virtually brand new. Mechanical notes are refreshingly detailed: approximately 110 psi compression with a good spark, valve lifter functioning, advance and retard working, gears and brakes operational. The clutch slips slightly and will likely need the plates cleaned or replaced, an honest disclosure that any buyer will appreciate and a straightforward job for a competent mechanic.
The bike presents in honest, complete condition. The red tank carries both original BSA roundel badges with the classic piled-rifles emblem and the paint, while showing age, is presentable. The iron barrel and alloy head show the expected patina of a bike that has actually been run. The exposed plunger springs either side of the rear wheel give the bike that perfect mid-50s silhouette that makes BSA singles of this era so photogenic. The solo sprung saddle is the correct period fitment.
The speedometer shows 278 miles though the trip counter reading of approximately 311 miles suggests the odometer has likely been replaced or reset at some point. Buyers should treat the mileage as unverified and appreciate the bike on its mechanical condition rather than the clock. The front fork stanchions show some surface pitting consistent with age. No key is supplied.
This is the ideal bike for a collector who wants an honest, largely original 500cc British single to enjoy, display, or restore at their own pace. With the clutch sorted, it should be a very satisfying runner.
Sold unregistered. No key.
#CCBikes
Location of item: 18 Paradise Road, Acacia Ridge, QLD, Australia
As Standard Auction Practice all Vehicles are Sold Unregistered
As with all vehicles sold in the Classic Car Division, they have been well looked after by their previous owners. This is an Auction Sale. This asset is sold under standard auction conditions, as is, where is. High volumes of incoming product prevent our team from being able to inspect all items individually. All photos, descriptions, odometer readings, hour readings, engine specifications and any condition reports should be used as a guide only and have been compiled after speaking with the owners. To find out more about this lot or to book a live video inspection please contact the Auctioneer Contact which can be found on the Auction Details page. There is no statutory warranty & no cooling off period.
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