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1950s Ariel Square Four 1000cc Valuation Report

Date: August 2025

Historical Overview

Ariel’s Edward Turner–designed Square Four became a 1950s UK classic for its smooth, torquey 1,000 cc four-cylinder and distinctive engineering. Within the decade, values and desirability split between the Mk I (1950–1952) plunger-frame machines and the updated Mk II (1953–1959) with its revised alloy head and four separate exhaust downpipes. Originality and completeness are critical; correct tinware and undamaged alloy castings make a big difference at sale time.

UK Valuation Summary (by condition and variant)

Condition	Mk I (1950–1952)	Mk II (1953–1959)	Example External Source (non-link reference)
Project / Restoration Non-runner or incomplete; often needs engine work, exhausts, wiring, and cosmetic metalwork; missing alloy parts suppress price.	£3,500 – £5,000	£4,000 – £6,000	Iconic Auctioneers – 1958 unrestored sold; eBay UK completed results
Roadworthy / Presentable Running and usable; tidy paint/chrome with age; largely stock; history helpful but not essential.	£6,500 – £9,000	£7,500 – £10,500	Iconic Auctioneers – 1951 example sold; Car & Classic – UK sold listings
Restored / Excellent Very original survivor or high-quality restoration; matching numbers; correct exhausts/tinware; strong documentation.	£10,000 – £14,000	£11,500 – £16,000	Bonhams – Stafford motorcycle sales; H&H Classics – Ariel results; The Saleroom – multi-house archives

Notes: Verified UK sales include unrestored late-’50s examples selling in the mid-£4k range (project tier) and early-’50s running bikes around the £7–8k mark. A post-war Square Four sold at Bonhams Stafford in April 2025 for £8,625 (context for roadworthy outcomes). Asking prices on dealer/classified platforms commonly sit above achieved auction results; bands here reflect sold prices where available.

Value Influencing Factors

• Variant & year: Mk II (1953–1959) with the four-pipe head typically commands a modest premium over Mk I.
• Originality & completeness: Correct tank, mudguards, four-pipe exhaust (Mk II), intact alloy castings and instruments are key.
• Mechanical condition: Cooling/idle stability, oil tightness and charging are common buyer checks; rebuild evidence helps.
• Provenance: V5C, period paperwork and restoration invoices lift confidence and results.
• Venue & timing: Major UK motorcycle auctions (e.g., Stafford) and well-photographed online sales achieve stronger prices than winter classifieds.

Conclusion

In the UK, Mk I Square Fours from the early 1950s generally realise £6.5k–£9k when roadworthy, with excellent examples at £10k–£14k. The later Mk II typically sits slightly higher at £7.5k–£10.5k for tidy riders and £11.5k–£16k for top, documented machines. Projects span roughly £3.5k–£6k depending on completeness and alloy/tinware condition.

Source attribution (non-link references): Bonhams – Stafford motorcycle sales (Square Four sold £8,625, Apr 2025); Iconic Auctioneers – 1951 Square Four sold; Iconic Auctioneers – 1958 unrestored Square Four sold; H&H Classics – Ariel results; The Saleroom – multi-house archives; Car & Classic – UK sold listings; eBay UK completed results.

All Valuations