Identifying a Part from a Photo
A photograph is often the fastest path to identification. The key is knowing what to photograph and how.
What makes a good identification photo
Show the whole part first. A single clear shot of the entire component from its most recognisable angle — the profile view — gives context. A water pump looks like a water pump from the front; from the side, it could be anything. After the profile shot, take close-ups of any visible markings: stampings, cast-in numbers, manufacturer logos, and date codes.
Include something for scale. A coin, a ruler, or even your hand next to the part tells an identifier whether they’re looking at a 2-inch fuel pump or a 6-inch brake servo. Scale eliminates entire categories of wrong answers.
Capture mounting points and connections. How a part attaches to the vehicle is often more diagnostic than the part itself. Bolt patterns, hose connections, electrical terminals, and gasket surfaces all narrow the identification. Two water pumps can look identical until you count the bolt holes — and then one is for a 1275cc A-series and the other fits a 1500cc Triumph.
Open CarSpanner’s chat, drag and drop your photo (or paste from clipboard), and describe what you know: where it came from, what vehicle, what system. The AI will analyse the shape, mounting points, material, and any visible markings to identify the part and tell you where to source a replacement.
Part Number Decoding Basics
If the part has a number stamped, cast, or printed on it, you’re already halfway there. The challenge is knowing which numbering system you’re looking at and what it means.
BMC / British Leyland
BMC and its successor British Leyland used a prefix system that identifies the vehicle range or engine family. The prefix is followed by a sequential number. Learning the common prefixes unlocks identification across MG, Austin-Healey, Triumph, Morris, and Rover parts.
AHH— Austin-Healey 3000 (BJ8)11G— MGB engine components (1800cc B-series)13H— MGB gearbox and transmissionAHB— Austin-Healey Sprite / MG Midget bodyGHN— MGB GT body shell and structure
A number like 11G 297 tells you it’s an MGB engine part, number 297 in the sequence. Cross-reference against the factory parts catalogue (available as reprints from Moss Motors and British Parts Northwest) to find the exact component.
Lucas Electrical
Lucas parts carry a plain numeric code — typically five or six digits — sometimes followed by a suffix letter indicating a revision. 25022 is a distributor model; 25022A is its first revision. Lucas also stamped date codes: a letter for the month (A=January through M=December, skipping I) and a digit for the year within the decade. C7 means March 1967 (or 1977 — context tells you which).
Bosch
Bosch uses a structured numbering system. The first digit identifies the product group: 0 for ignition, 1 for starters and alternators, 2 for fuel injection. The remaining digits specify the exact part. Bosch numbers are consistent worldwide, making cross-referencing straightforward — the same number in Germany, the UK, and the US refers to the same component.
GM Casting Numbers
General Motors used two parallel numbering systems that confuse people to this day. The casting number is cast into the raw component — it identifies the casting pattern. The service part number (often starting with a letter or group code) is what you use to order the part. They are not the same number and are not interchangeable.
GM casting numbers are typically seven digits. 3970010 is one of the most common small-block Chevrolet blocks. These numbers are found on machined pads or flat casting surfaces — rear of the block for most V8s, valve cover rail for heads.
| Manufacturer | Format | Example | Where to find it |
|---|---|---|---|
| BMC / BL | Prefix + sequential number | 11G 297 |
Stamped on machined surfaces, cast into housings |
| Lucas | 5–6 digit numeric + suffix | 25022A |
Stamped on body, printed on label |
| Bosch | Product group + specification | 0 231 170 034 |
Label, stamped on housing |
| GM (casting) | 7-digit numeric | 3970010 |
Cast into block, head, intake manifold |
| Ford | Alphanumeric engineering code | C5AE-6015-A |
Cast or stamped on component |
Cross-Referencing Part Numbers Across Suppliers
You have a number. Now you need to turn it into something you can actually order. The problem: the number on your part may not match the number in any current supplier’s catalogue. Parts get superseded, renumbered, and cross-listed under different systems.
Where to cross-reference
- CarSpanner — enter any part number and it will cross-reference across suppliers, identifying the current availability and correct modern equivalent
- Original factory parts catalogues — reprints are available from Moss Motors, SNG Barratt, and British Parts Northwest; these remain the authoritative reference
- Hollander’s Interchange Manual — the standard cross-reference for American classics, covering GM, Ford, and Chrysler interchange fitments across model years
- Marque-specific forums — community-maintained supersession lists often catch cross-references that suppliers miss, particularly for obscure late-production changes
- Supplier online catalogues — Moss Motors, SNG Barratt, Rimmer Bros, and NPD all have searchable online systems; try the original number first, then known supersessions
When a number draws a blank everywhere, try searching for the description instead of the number. “MGB water pump gasket 1800” will often surface results that “GEG 238” won’t, because suppliers have catalogued the part under their own reference system rather than the original BMC number.
Using Casting Dates and Date Codes to Verify Authenticity
Casting dates are the forensics of classic car parts. They tell you when a component was made — and that date should make sense relative to the vehicle it’s fitted to.
How casting dates work
Most cast components — engine blocks, cylinder heads, intake manifolds, exhaust manifolds, brake drums — carry a date code embedded during the casting process. The format varies by manufacturer:
- GM — typically a letter-digit-digit sequence:
K 2 7means October (K=10th month) 27th. The year is inferred from context. A casting date should precede the vehicle assembly date by days to weeks, not years - Ford — uses a year-month-day format encoded in the engineering number: the first character of the prefix indicates the decade and year (C=1960s, D=1970s, E=1980s)
- Lucas — month letter (A=Jan, B=Feb, skipping I) plus year digit:
F3means June 1963 (or 1973) - Girling — similar letter-digit system, often stamped on the body of brake cylinders and calipers
What date codes tell you
If someone is selling you a “numbers-matching” 1965 Corvette engine, the casting date on the block should be late 1964 or early 1965 — a few weeks before the car was assembled. A casting date of 1970 on a “1965 original” block means it was replaced at some point. Not necessarily a problem for a driver, but critical information for a concours build or an investment-grade purchase.
Date codes also help identify genuine NOS parts versus reproductions. An original Lucas distributor from the 1960s will carry a period-correct date stamp. A modern reproduction will not — or will carry a date that doesn’t match the claimed era.
Identifying a Part from a Failure Symptom or Location
Sometimes you don’t have the part in hand — you have a symptom. A leak, a rattle, a grinding noise, a warning light. The identification process works in reverse: start with what’s failing and trace it back to the component.
Working from location
If you can see where the problem is, describe the location precisely. “Leak from the front of the engine” narrows things to the water pump, timing cover gasket, front crank seal, or oil cooler lines. “Rattle from the driver’s side rear wheel area at low speed” points to a loose brake drum, worn brake hardware, or a failing shock absorber mount. The more specific the location, the shorter the list of candidates.
Working from symptoms
Fluid colour matters. Green or orange coolant from the front of the engine is water pump or hose. Black oil from the rear of the engine is a rear main seal. Clear hydraulic fluid at a wheel is a leaking brake or clutch slave cylinder. Red fluid under the car is probably power steering or automatic transmission. These are rapid diagnostic starting points that any experienced mechanic uses instinctively.
Tell CarSpanner the symptom — the year, make, and model of the vehicle, where on the car you’re seeing the problem, and what it looks or sounds like. It will identify the most likely component, confirm fitment, and point you to the right supplier.
Commonly Misidentified Parts — and How to Tell Them Apart
Some parts are confused so routinely that it’s worth addressing them directly.
Brake master cylinder vs. clutch master cylinder
On British cars with separate hydraulic systems, these can look almost identical. Both are cylindrical bore-and-piston devices with a reservoir on top. The brake master cylinder is typically larger bore (0.75″ or more) and may have two outlets. The clutch master is smaller bore (usually 0.7″) with a single outlet. Check the bore diameter and the number of hydraulic line connections.
Generator vs. alternator
Early classics came with generators (dynamos in British terminology); later models switched to alternators. They mount in the same location and look superficially similar. The giveaway: a generator has a commutator at the rear (visible as a segmented copper ring) and two field terminals. An alternator has a smooth slip ring assembly and typically three terminals (B+, D+, W) or an integral regulator. If someone’s selling “the original generator” and it has a built-in voltage regulator, it’s an alternator.
SU carburettor variants
SU carburettors across the H, HS, and HIF series share the same basic layout but are not interchangeable without modification. The body size (given as a fraction — H4, HS4, HIF4 are all 1.5″ bore) determines airflow. The float chamber arrangement differs: H-type side-mounted, HS side-mounted with a different needle design, HIF with an integral float. Identifying the series from a photograph requires checking the float chamber position and the dashpot damper configuration.
Shock absorber types
Lever-arm shocks (Armstrong, Girling) and telescopic shocks are fundamentally different components that mount differently. A lever arm sits inline with a suspension link and acts through an arm. A telescopic shock mounts between two fixed points and compresses/extends in a straight line. Both get called “shock absorbers” and neither is interchangeable with the other without significant modification.
When to Check with Marque Clubs and Registries
When standard references fail, the marque-specific clubs become essential. These are not hobbyist social groups — the serious ones maintain technical archives, parts registries, and access to factory records that simply don’t exist anywhere else.
- Jaguar Enthusiasts’ Club and Jaguar Drivers’ Club — maintain parts databases and factory build records for matching components to specific chassis numbers
- MG Car Club and MG Owners Club — extensive technical archives covering MGA through MGB GT V8
- Corvette registries (NCRS, Bloomington Gold) — the definitive authorities on numbers-matching Corvette components, with casting-number databases cross-referenced to production dates
- Mustang Club of America — maintains detailed technical resources for 1964½–1973 Mustangs including part number supersession guides
- E-Type forums, MG forums, Mustang forums — decades of accumulated knowledge from owners who’ve seen every variation
Club tech advisors have collectively seen thousands of these cars. If you’re stuck on an unusual variant, a late-production change, or a part that doesn’t appear in the standard catalogues, they’re the next step after CarSpanner.