Reconditioning a Porsche 964 cylinder head

The background

The customer had noticed the engine no longer ran as cleanly as before. A compression test showed uneven readings between the cylinders, and on inspecting the cylinder head we could see that the valve seats were worn and the mating faces needed attention.

The Porsche 964's boxer engine has two cylinder heads, one per cylinder bank. In this case both heads needed reconditioning. The customer wanted to keep the engine original and avoid buying used cylinder heads of unknown condition.

Face machining and new cylinders

We started with a thorough inspection. The cylinder heads were stripped and cleaned of all carbon and dirt. Then we inspected every detail:

Valve seats: worn and uneven, needed recutting

Valve guides: acceptable clearance, but at the limit

Mating faces: slight warp, resurfacing was needed

Camshaft bearings: within tolerance, could be kept

Crack testing: no cracks found in the casting

The verdict was clear: the cylinder heads could be reconditioned to full function. Nothing needed replacing except the valves, guides and gaskets.

Porsche 964 cylinder in the lathe — Checking and machining to match the cylinders and the seal

Porsche 964 cylinder head being machined — Fixture + dialling in = the same dimensions on every head

Valve guides and three-angle cutting

The valve seats were cut with precision to restore the correct angles and sealing. We used a three-angle cut that gives optimal flow geometry, crucial for an engine that breathes through its ports.

New valve guides were pressed in and reamed to exact size. New valves were fitted and lapped in against the seats to achieve a perfect seal. Each valve was checked with a vacuum test.

Three-angle cutting of a Porsche 964 cylinder head — Three-angle cut seats after guide replacement = correct contact pattern and sealing

Camshafts: wear, profile and grinding

The camshafts were inspected carefully. We found visible wear on the cam lobes that needed attention. The camshafts were ground to the correct profile in our camshaft grinding machine.

Worn camshaft for a Porsche 964 — Visible wear = action required

Porsche camshaft in the camshaft grinding machine — Controlled grinding to the correct profile

Resurfacing and pressure testing

The mating faces of the cylinder heads were machined to remove the warp. The Porsche specification calls for tight tolerances so the gasket seals correctly against the cylinders.

After machining the faces we pressure tested the cylinder heads. They were put under pressure to check there were no leaks in the coolant passages or chambers. Both cylinder heads passed the test without fault.

Assembly and result

With new gaskets, valves and guides, the cylinder heads were refitted. Valve clearances were set to Porsche specification.

The engine regained even compression across all six cylinders, quiet valve operation and clean running with full power. The original build was preserved.

Why recondition instead of replacing?

Used cylinder heads for the Porsche 964 are out there, but their condition is often unknown. Reconditioning your existing cylinder heads means you know exactly what you have. Every critical surface is measured, machined and checked.

It is also the only option if you want to keep the original parts, which matters for the car's value and authenticity.

Do you have a Porsche or another car that needs cylinder head reconditioning?