On a pushrod engine you set the tappets with a feeler gauge and a screwdriver in ten minutes. The Alfa twin-cam is not that engine. Its valve clearances are set by shims, and because those shims sit *beneath* the bucket tappets, adjusting them means removing the camshafts. It is a proper, methodical job — but an important one, because the twin-cam's clearances close up over time, and tight valves are what burn. Here is how it works.
Why it matters
Each valve is opened by a cam lobe pressing on a bucket tappet, and the clearance between them is set by a hardened steel shim under the bucket. Get it wrong in either direction and there are consequences:
- Too little clearance (too tight): the valve is held slightly open and cannot seat fully. It loses its path for heat to escape into the head, runs hot, and eventually burns — costing compression and, in time, a valve. This is the dangerous direction.
- Too much clearance (too loose): noisy tappets, and cam timing very slightly off.
Crucially, Alfa twin-cams tend to tighten with use as the valves recede into their seats, so clearances close up rather than open up. That is exactly why regular checking matters: you are catching a burnt valve before it happens, not just quietening a rattle.
How often
Check periodically — the factory schedule called for a look roughly every 18,000 km (around 12,000 miles) — and any time the top end gets noisier or the running deteriorates. Always measure and set the clearances with the engine cold.
The method, in outline
This is an overview so you know what the job involves, not a substitute for the workshop manual:
- Measure first. Remove the cam cover, and turn the engine over so the lobe for the valve you are checking points well away from the bucket. Slide feeler gauges between the heel of the cam and the bucket, and record every clearance — intakes and exhausts have different specs.
- Decide what needs changing. Compare each reading to the spec. Anything out — especially anything tight — needs a different shim.
- Get to the shims. Slacken the timing-chain tension, and detach or secure the chain to its sprockets so you do not lose the cam timing (mark everything first). Lift out the camshaft(s).
- Lift the buckets and shims. Withdraw each bucket with a magnet or a valve-grinding suction tool. The shim usually stays stuck to the underside of the bucket on a film of oil — take great care, because a dropped shim can vanish down an oil gallery. It is worth plugging the drain passages before you start.
- Measure and swap. Micrometer the old shim, calculate the thickness needed to bring the clearance into spec, and fit a new shim. Shims are sold in graded metric sizes.
- Reassemble and re-check. Refit buckets, cams and chain, confirm the cam timing, and re-measure the clearances to be sure.
The figures
Clearances vary by exact engine and year, so treat these as indicative and confirm the correct figures for your car against the workshop manual. As a rough guide, the classic Giulia twin-cam runs the intakes a little tighter than the exhausts — broadly in the region of 0.45–0.50 mm inlet and 0.50–0.55 mm exhaust — but different references and engines quote slightly different numbers, so the manual for your engine is the authority, not this page.
A job worth doing properly
None of this is beyond a careful owner, but it rewards patience, a written record and the right shims to hand — and if that puts you off, it is a routine job for any Alfa twin-cam specialist. Either way, a set of correct, cold clearances is one of the best things you can do for a twin-cam's long-term health.
*Written for the Giulia Spider archive. Valve clearances and procedures vary by engine and year — always confirm the figures and method against the workshop manual for your car, and set clearances cold.*