The Timing Disc and the Ignition Timing on the Spitfire

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The timing disc and the ignition timing on the Spitfire:

The timing disc (Fig. 1) does not replace a test lamp (for static setting of the ignition timing) or a stroboscopic timing light (for dynamic setting of the ignition timing). It is not possible to set the ignition timing using a timing disc alone. However, you may use the timing disc to put some marks on the crankshaft pulley, to allow a setting of the ignition timing or to control the valve timing (see user’s guide / workshop manual, which are available at every quality Triumph parts supplier).

Fig.1) The timing disc, including some engine settings for the Spitfire. The diameter of the Spitfire’s crankshaft pulley is 15 cm approximately 2

You may find different pointers on the Spitfire engine’s timing cover, according to its year of production: a) Older engines have a single pointer. b) Later engines have a “dented” pointer (Fig. 2).

Fig. 2) The „dented“ pointer of the later series engines of the Spitfire.

If the original mark on the crankshaft pulley is aligned with the single pointer or the 0° position on the dented pointer it indicates top dead centre (TDC) for cylinders 1 or 4. However, the ignition timing has to be set (on the Spitfire 1500 for example) to 10° before TDC (BTDC). Please compare with the technical data of your Spitfire (user’s guide or badge under bonnet).

If you find a dented pointer on your engine you’re lucky. Then, all you have to do to set up the ignition timing is to align the mark on the crankshaft pulley with the 10° before TDC mark on the dented pointer. If your engine has just a single pointer you may use the timing disc to put a mark on the pulley for 10° before TDC (respect the sense of rotation). Aligning this mark with the single pointer allows you to set up the ignition timing correctly.

Ignition timing:

For a static setting of the ignition timing you need a test lamp. If you don’t have a test lamp, you could make one by yourself using an old 12V bulb (see Fig. 3 for a connecting diagram).

Normally, a static setting of the ignition timing is quite sufficient. However, a dynamic setting using a stroboscopic timing light is more accurately.

For a dynamic setting of the ignition timing you need a stroboscopic timing light. If your engine has just a single pointer but you put a 10° before TDC mark on the crankshaft pulley using the timing disc, you will only need a simple stroboscopic timing light. In this case an adjustable (and more expensive) stroboscopic timing light is not necessary (unless you wanted to test the ignition timing advance - but then you could also put some more marks on the pulley). 3

Fig. 3) Test lamp connecting diagram

1 - distributor 2 - ignition coil 3 - low tension cable of contact breaker 4 - test lamp 5 - battery

How to set the static ignition timing ! Stop the engine, switch off the ignition, pull the ignition key ! 1.) Firstly, the dwell angle (contact breaker gap) has to be set up correctly: Contact breaker gap: 0.35-0.4 mm (0.014"-0.016"); dwell angle: 51° ± 5° 2.) At the ignition coil pull off the low-tension cable of the contact breaker (no. 3, Fig. 3). 3.) Connect the test lamp as in Fig. 3. 4.) If your engine has a single pointer, put a 24° before TDC and a 10° before TDC mark on the crankshaft pulley, using the timing disc. Turn the crankshaft (in its sense of rotation) until the 24° before TDC mark (for cylinder No. 1) is aligned with the single pointer on the timing cover. Or, in the case of the dented pointer: until the original TDC mark (for cylinder No. 1) on the crankshaft pulley is aligned with the 24° before TDC mark on the dented pointer. Here the test lamp should light up. 5.) Now, cautiously continue turning the crankshaft until the test lamp just switches off. 6.) If the ignition timing is set correctly, the 10° before TDC mark on your pulley should be aligned with the single pointer (Or: the original TDC mark on the pulley should be aligned with the 10° before TDC mark on the dented pointer). 7.) If this is not the case, the ignition timing has to be set up. 8.) Untie the distributor mounting bolt. Turn the crankshaft to align the appropriate marks (see above). Turn the distributor (anti clockwise) passing the point at which the test lamp lights up. Then, slowly turn back the distributor (clockwise) until the test lamp just switches off. Cautiously tighten the distributor mounting bolt. 9.) Repeat steps 4.) to 6.) to control the ignition timing. If necessary, repeat step 8 to set up the timing correctly.