Ignition timing is the most important ignition adjustment — and the most misunderstood. Here is what it actually means, why the spark fires before the piston reaches the top, and how it is set.
What timing means — firing before the top
Setting the ignition timing means setting the exact instant the spark fires, measured against the piston's position. And the spark fires before the piston reaches the top of its stroke — before top dead centre, or BTDC. Why early? Because burning takes time. The mixture does not explode instantly; it burns over a few thousandths of a second. Light it just before the piston reaches the top and the pressure peaks just after, right as the piston starts back down — pushing hardest at the most useful moment. Fire too late and you waste the push; fire too early and the rising pressure fights the still-climbing piston. Getting that instant right is what timing is.
Why the timing has to change — advance
There is a catch: the burn takes about the same time whatever the engine is doing, but the piston moves faster as revs rise. At 3,000 rpm it is travelling far quicker than at idle, so to have the pressure peak in the same place you must light the fire earlier — more degrees before top dead centre. That progressive earlier firing is advance, and it is why an engine needs more of it the faster it spins. Load matters too: on a light throttle the mixture is thinner and burns slower, so a little extra advance helps; under hard load it would cause pinking, so the timing pulls back. This is exactly why the distributor carries its centrifugal and vacuum advance mechanisms — to serve the right timing automatically at every speed and load. What you set by hand is the starting point they build on.
Static timing — setting it with the engine off
The base setting is the static timing: the number of degrees BTDC at which the points should just open, with the engine stopped. You turn the engine to the marked position — a mark on the crank pulley against a pointer — then rotate the distributor body until the points are just breaking, often checked with a test lamp. That fixes the foundation the advance mechanisms work from. The exact figure is engine-specific; take it from your workshop manual.
Dynamic (strobe) timing — setting it running
The more accurate method uses a strobe timing light. Clipped to a plug lead, it flashes each time that cylinder fires; shine it at the spinning crank pulley and the timing marks appear frozen, showing the actual timing. Run the engine at the specified rpm — usually with the vacuum advance pipe disconnected and plugged, so you are reading the base plus centrifugal advance — and rotate the distributor until the marks sit where the manual says. Strobe timing catches what static timing cannot: worn advance mechanisms and a wandering shaft, because you are seeing the timing the engine actually gets.
Reading the symptoms
Timing too retarded — late — gives a flat, gutless engine that runs hot. Too advanced — early — brings pinking under load, a light metallic tinkling as the mixture detonates rather than burns smoothly, which left alone hammers pistons and bearings. A well-timed engine pulls cleanly, does not pink on a firm throttle in a high gear, and runs at a sensible temperature. If yours pinks, a touch of retard; if it is flat and will not rev, a touch of advance — but always return to the manual's figures as your baseline, and set the base timing before chasing symptoms.
A note on modern fuel
Old timing figures and modern petrol do not always agree — an engine set to a 1950s figure can pink on today's fuel, and a small adjustment, or the right high-octane ‘super’, usually sorts it. If yours pinks on the book setting, that is often why. See Fuel, Oil & Additives for the wider picture.
With thanks to Andrew at AG Classic Car Tuning, mobile classic-car tuning specialists in North Yorkshire.