Datsun 240Z buyer's guide: the six places rust hides

The 240Z has none of the mechanical fragility its reputation suggests. The L24 is a robust engine, the gearbox is strong, and the running gear is simple. What kills them is rust, and because the S30 is a unitary body, rust is structural rather than cosmetic. A rotten sill on a body-on-frame truck is a panel. On a Z it is a load path.

01The six places, in order of severity

1. Floors and the front frame rails. The rails run under the floor from the firewall forward and they carry the suspension loads. Rot here is the difference between a restoration and a parts car. Lift the carpets — all of them, including under the seats — and look from underneath at the same time. Daylight is a bad sign; so is a floor that flexes underfoot. 2. The battery tray and the area around it. Decades of acid. It rots through into the frame rail below, which is why this small area matters far more than its size suggests. 3. Rear wheel arches and the dogleg. The dogleg is the section between the rear of the door and the arch. It rots from the inside, it is visible early, and it is a common place for a cheap repair to be hidden under filler. 4. Sills and the jacking points. Structural. Press hard on the jacking point with a thumb; if it moves, the sill is gone. Original sills are a double-skinned section and a repair that only replaces the outer skin is cosmetic, not structural. 5. The rear hatch surround and the spare wheel well. Water gets past the hatch seal, sits in the well, and rots it out. Lift the spare. 6. The windshield and rear hatch frames. Rot under the seal is common, expensive to fix properly because the glass must come out, and frequently hidden by a fresh strip of sealant.

02Why the monocoque changes the maths

On a body-on-frame vehicle you can replace almost any panel independently. On a Z, the panels are the structure, so:

• Repairs must be done with the shell braced, or the openings move.
• A car that has been repaired badly may have a permanently distorted shell, which shows up as doors that never quite fit and a car that tracks slightly crab-wise.
• Rust in two of the six places usually means rust in all six, because they share the same water paths.

The practical consequence: a Z needing structural repair is nearly always more expensive to fix than to buy already fixed. This is the market where "buy the best one you can afford" is genuinely true rather than a cliché.

03Mechanical

The engine is durable. Check for the usual: oil pressure when hot, smoke on the overrun, and a timing chain that rattles on start-up. A stretched chain is an established wear item and a well-understood job — the front cover has a wear groove that also needs checking while you are in there. The carburettors. Round-top SUs on the earlier cars are correct and desirable. Many cars have been converted to downdraught four-barrels, which usually runs worse and is worth less. Original carburettors, even tired ones, are rebuildable and worth keeping. Cooling. These run warm and the original radiator is often past it. Not a dealbreaker; do budget for it. Suspension is struts front and rear. Check for leaking struts and for corrosion at the tops. Insulators and bushings will all be original and all be finished.

04Originality and matching numbers

Series 1 cars — the earliest 240Zs — carry a real premium, and there are identifying details that are widely known and occasionally faked. If you are paying series 1 money, get somebody who knows the specifics to verify it. Otherwise, originality matters less than structure. A tidy later 280Z with a solid shell is a much better purchase than a rotten early car with the right badges.

05The viewing checklist

• Carpets up, spare out, before anything else.
• Thumb on the jacking points.
• Magnet along the arches, doglegs and sills.
• Look down the flanks in raking light for filler ripples.
• Check both doors shut cleanly and the gaps are even top to bottom.
• Cold start it. Listen for chain rattle in the first few seconds.
• Look for a fresh bead of sealant round the windshield, and ask why.

If it has been standing, expect the fuel system to need attention throughout — tank, lines and carburettors. That is normal and not expensive; it is just work.