Engine sourcing
Buying Used Cylinder Heads for a Classic Engine: What to Check Before You Pay
A set of used heads can be the best deal in a rebuild or the most expensive paperweights in your garage. The castings all look alike under a coat of rust and old oil, and the problems that matter most (cracks, heavy milling, worn guides, warped decks) rarely show up in a listing photo.
This guide is about buying used, core and "rebuilt" heads for pre-1990 engines: how to confirm you have the right casting, what to inspect in person or ask a seller to show, and how to budget for the machine work almost every used head needs.
Why used heads are worth hunting for
Original heads matter for two very different reasons. For a numbers-matching or period-correct build, the right casting with a plausible date code is part of the car's story. For a driver, certain factory castings simply flow better, have the chamber size you want, or bolt up to the parts you already own. Either way, the used market is where many of those castings now live, since reproduction and aftermarket heads don't always replicate the originals.
The catch is that a cylinder head is a precision part that's lived through decades of heat cycles, overheating, freezing and sometimes neglect. You're not buying the metal; you're buying the chance that the metal can still be machined back into spec.
Step one: confirm what you're actually buying
Casting numbers
Most factory heads carry a cast-in part or casting number, and many carry a date code too. Ask the seller for clear, straight-on photos of both. Then cross-check those numbers against a casting reference for your engine family, rather than trusting the listing title. "Fits small block" or "big valve heads" in a title tells you almost nothing.
If you haven't dug into how these numbers differ, our guide to casting numbers vs part numbers vs date codes covers it, and the interchange manuals guide explains how to find out which castings were used across models and years.
Date codes and originality
If you're restoring to factory-correct, the head's date code generally needs to fall before your engine's assembly date, within a window that marque experts consider plausible. That window varies by manufacturer and plant, so check with your model's club or judging guidelines rather than guessing. Our numbers-matching parts guide goes deeper on how judges look at this.
What the casting won't tell you
A correct casting number doesn't tell you whether the head has been milled, ported, fitted with oversize valves, converted to screw-in studs, or repaired. Those changes can be great for a performance build and a problem for a correct restoration, so ask directly.
The inspection checklist
If you can see the heads in person, bring a flashlight, a straightedge and a set of feeler gauges, and ask for permission to look closely. If you're buying remotely, turn this list into photo requests. A seller who won't photograph the combustion chambers is telling you something.
- Combustion chambers: look for cracks running between the valve seats or from a seat toward a spark plug hole. Hairline cracks can hide under carbon, so treat "looks clean" as a starting point only.
- Deck surface: look for erosion around the water passages, deep gouges, pitting and signs of a blown gasket (a dark track between cylinders or into a water port).
- Exhaust ports and seats: heavy erosion, burned valve edges or recessed seats point to a hard life and possibly expensive seat work.
- Valve guides: with the valve slightly open, side-to-side wobble suggests worn guides. A machinist will measure this properly.
- Water jackets: heavy scale, rust or sludge suggests the head saw neglect. Freeze cracks often show on the outside of the casting near water passages.
- Bolt holes and bosses: stripped spark plug threads, broken exhaust manifold studs and cracked bolt bosses all add cost.
- Rocker studs or shafts: pulled or bent studs, worn shafts and damaged pedestals.
- Machining marks: a freshly surfaced deck suggests it's been milled, which is fine, but find out how much.
- Signs of welding or epoxy: sometimes visible as smooth patches or odd-colored areas. Not always a deal-breaker, but you need to know.
Why every used head needs a machine shop
Even a good-looking head should be cleaned and inspected by a machinist before you build on it. A typical intake for used heads covers:
- Teardown and cleaning: the head is stripped, and cast iron is usually hot-tanked or baked and blasted so cracks are visible.
- Crack detection: magnetic particle inspection is the standard check for cast iron. Aluminum needs a different method, usually dye penetrant, because it isn't magnetic. Many shops also pressure-test for leaks into the water jacket.
- Measurement: guide clearance, seat condition, valve stem wear, spring condition and deck flatness are compared against the factory specifications for that head.
- Machine work: depending on findings, that might mean guides, seats, a valve job, resurfacing and new springs and seals.
- Assembly: installed spring height and seal fit are set to spec, with the results recorded.
Ask the shop for a written list of what they found and did. It's useful for your restoration records, and it matters if you ever sell the car.
Milling, chamber size and compression
Every time a head is surfaced, a little material comes off the deck. That shrinks the combustion chamber and raises compression. One light resurfacing is normal. Multiple cuts over the decades can push compression higher than your fuel and cam can comfortably tolerate, and they can also affect how the intake manifold lines up on a V engine.
If you're buying a head that's obviously been machined, ask whether the seller knows how much was removed. If not, have your machinist measure the chamber volume. That's the only reliable answer.
Cores, takeoffs and "rebuilt": what each label means
| Listing term | What it usually means | What you should assume |
|---|---|---|
| Core | As-removed, condition unknown | Full inspection and machine work needed; may be uncrackable or junk |
| Takeoff / pulled from running engine | Removed from an engine described as running | Still needs crack-checking; running doesn't rule out cracks or wear |
| Freshly rebuilt / machined | Some machine work done, details vary | Ask for the shop name and work list; verify before you bolt on |
| Bare / stripped | No valves, springs or hardware | Budget for all new valve train parts plus machine work |
| Ported / performance | Modified for flow | Not factory-correct; port work quality varies widely |
Our listing terms guide covers these labels across all parts categories.
Smart buying tactics
Buy heads, not promises
Price a used head assuming the worst reasonable outcome: that it needs guides, seats and a valve job. If the deal still makes sense, it's a good deal. If it only works when the seller's "ready to run" claim is true, keep looking.
Shipping and handling
Cast iron heads are heavy, and the deck and sealing surfaces are easy to damage. Ask the seller to bolt a piece of plywood to the deck, or at least pad it, before shipping. For multiple heads or a full engine's worth of parts, see our freight shipping guide.
Swap meets and local pickups
In-person buying lets you check the chambers and deck yourself and avoid freight. Our swap meet buying checklist covers how to handle the conversation.
Researching value
Prices for specific castings swing a lot depending on condition, desirability and whether the date codes suit a particular restoration. Instead of trusting a single asking price, look at completed sales of the same casting number in similar condition. Sold listings tell you far more than active ones.
Tools for a first look
You don't need a machine shop at home, but a few inexpensive tools make a first inspection much more useful: a bright LED flashlight, an inspection mirror, a precision straightedge and a set of feeler gauges for a rough flatness check, and a small magnet to confirm whether you're looking at iron or aluminum.
The bottom line
For most builders, the right used casting plus a proper machine shop job is still one of the best ways to get period-correct heads. Verify the numbers yourself, treat everything as a core until it's crack-checked, and price the machine work in from the start. Walk away from obvious chamber cracks and heavily milled decks unless the casting is rare enough to justify specialist repair.
FAQ
Can a cracked cylinder head be repaired?
Sometimes. Some cracks in cast iron and aluminum heads can be repaired by specialists with pinning or welding, but whether it's sensible depends on where the crack is and how rare the casting is. For a common casting, replacing the head is usually simpler. Ask a machine shop that does head repair for an assessment.
Do I need hardened exhaust seats to run unleaded fuel?
Many older heads were designed around leaded fuel, and hardened exhaust seat inserts are a common upgrade during a valve job, especially for engines that work hard. How much an engine actually needs them depends on the head, the use and the valve materials. Your machinist can tell you what suits your build.
Are 'rebuilt' heads on eBay ready to bolt on?
Not necessarily. 'Rebuilt' can mean anything from a full machine shop job with documentation to a cleaned head with new valve seals. Ask what work was done, by whom, and whether it was crack-checked and pressure-tested. Without that, budget for inspection as if it were a core.
How do I find the casting number on my heads?
Location varies by make and engine family. It's often cast on the top of the head under the valve cover, or on an end or side face. Check a casting number reference for your engine, or our guide to casting numbers, part numbers and date codes.
Should I buy a single head or a matched pair?
For V engines, a matched pair (same casting and similar history) makes machining and setup simpler, because both sides start from the same specs. If you have to buy a single head, match the casting number exactly and tell your machinist so they can equalize the deck and chamber work.