Using the Degree Wheel to Establish Ignition Timing

Converting to an Electronic Ignition

You have finally decided to convert your 1967 Triumph Bonneville to electronic ignition. The instructions tell you to remove the points plate and mechanical advance unit. Not to worry, once the old ignition parts are out of the way, you can start retrofitting your new modern ignition.

Once the rotor and stator plate are loosely fitted, you are instructed to connect all of the electrical wiring, carefully following the instructions. Then they mention setting the engine to the “full advance timing mark on compression”. What does this mean? You open up the factory workshop manual for more guidance, only to learn that the flywheel on your engine’s crankshaft has only one notch, indicating top dead center (TDC). 

This is usually the point at which confusion sets in for the first-time electronic ignition installer. If you are able to read through the series of instructions from Sections B28-B31 in the 1963-1970 Factory Workshop Manual without any confusion, and with a complete grasp of what is being described, then you are probably a genius and will find this article remedial. For the rest of us, I am going to try to save some time by simplifying using a degree wheel to establish ignition timing.

Fully Advanced Timing Position

“If you are able to read through the series of instructions from Sections B28-B31 in the 1963-1970 Factory Workshop Manual without any confusion, and with a complete grasp of what is being described, then you are probably a genius and will find this article remedial.”

The early unit-construction Triumph 650cc engines employed a contact breaker ignition, housed in the timing cover, and driven by the exhaust camshaft. The Lucas 4CA points ignition was used through the 1967 model year and was problematic for tuners to set accurately, which makes these motorcycles ideal candidates for retrofitting an electronic ignition system.

For many years, the Boyer-Bransden was the industry standard for this endeavor, but there are more options now including Pazon, Vape, Tri-Spark, and Sparx. The set-up of these ignition kits is very similar from brand to brand, but they all have one thing in common- they have to be initially set with the engine in the fully advanced timing position, which in our example bike, the 1967 Triumph 650, is 38 degrees before top dead center (BTDC). This the position where the pistons are .415” from their highest point in the cylinder bores, and on the rise towards top dead center (TDC). The Timing Degree Wheel is employed to establish this engine position.

Using a Degree Wheel and TDC

To begin, place the motorcycle on the center stand, if equipped with one. If not, an alternative method of getting the rear wheel off the floor (or lift) must be used, such as using a portable jack, or even a sturdy milk crate to support the weight of the machine. Remove the spark plugs and shift the transmission to high gear.

Now the rear wheel can be rotated to easily change the engine position. Now you can assemble your degree wheel and prepare to thread it into the end of the exhaust camshaft, which will be exposed, having already removed the points plate and mechanical advance unit. In the case of our example bike, the 1967 650 will have a ¼”-26 TPI threaded bore in the exhaust camshaft, provided the camshaft is the factory original cam. We offer the Timing Degree Wheel kit in (2) versions, the TBS-0335 E (with a ¼”-26 bolt), and a TBS-0335 L (with a ¼”-28 bolt). You will be using the earlier ¼”-26 bolt for this exercise.

The next step will be to remove the timing aperture plug from the crankcase, located just below the rear of the cylinder barrel, on top of the gearbox housing. Once the plug is removed, you will be able to see the crankshaft flywheel. With the aid of a small flashlight, you can peer into the hole and while slowly rotating the rear wheel, you will see the slot on the flywheel appear, then quickly disappear from sight. When the slot is again seen by very slowly rotating the wheel in either direction, you will have located TDC. Now is the time to talk about another essential tool, the Crankshaft Timing/Locking tool, which we offer under part number 60-0571.

Crankshaft Timing/Locking tool

Now that you have found TDC, you can thread the Crankshaft Timing/Locking tool into the aperture in the crankcase. The plunger will locate the slot in the flywheel and keep the TDC position from being disturbed while you move on to the next step.  You will need to source a pointer as an indicator for the engine position, calibrated to the degree wheel. I have found a plain 14 or 15 gauge bicycle spoke, with a point ground onto the end, works well for this. The spoke can be bent to whatever position you need to line up with the edge of the degree wheel.

Once the correct pointer has been sourced and bent to suit the task at hand, it must be attached to the engine to make it stationary. You can use one of the timing cover screws to secure the pointer, by bending a loop in the end of the spoke wrapping it around under the screwhead. Since the TDC engine position has already been established, the degree wheel can be rotated on the mandrel to line up with your stationary pointer, then locked down with the knurled thumbscrew. The following picture shows the assembly in place, indicating TDC.

Timing Degree Wheel

The next task is to remove the loosely threaded bolt from the camshaft that retains the magnetic rotor from your electronic ignition kit. Now thread in the Timing Degree Wheel assembly. Once hand tight, the degree wheel can be rotated on the mandrel so that the pointer is aligned with the TDC mark on the degree wheel. Tighten the thumbscrew on the mandrel to fix the degree wheel in place.

At this point, remove the Crankshaft Timing/Locking Tool. You are now ready to turn the engine backwards 38 degrees by slowly rotating the rear wheel anti-clockwise until the degree wheel aligns with the pointer at the 38 degree mark on the scale. You have now located the full advance timing position of the crankshaft to set up your electronic ignition according to the manufacturer’s instructions.

If you have a piston stop tool, this would be the right time to thread it into one of the spark plug holes and adjust it to touch the top of the piston, preventing it from moving any further while you finalize the electronic ignition installation. Since the Timing Degree Wheel was only hand tightened, it should be able to be withdrawn without disturbing the engine position. Once the Timing Degree Wheel is out of the way, the center bolt can be refitted to secure the electronic ignition’s rotor.

“You have now located the full advance timing position of the crankshaft to set up your electronic ignition according to the manufacturer’s instructions.”

If you are performing the same electronic ignition installation on a 1969 or later Triumph 650 model, including some late 1968 models, you will likely not need a degree wheel, as the stock flywheels had an additional notch cut into them for establishing 38 degrees BTDC, however the 61-7022 Crankshaft Timing/Locking Tool will be needed to accurately establish engine position. As the transition to Unified threads was underway, the timing hole threads changed to a coarse UNF thread, necessitating the updated 61-7022 Crankshaft Timing/Locking Tool.

It is worth mentioning that both versions of our Timing Degree Wheel kits, TBS-0335 E and TBS-0335 L are intended for use on ignition timing through the camshaft, which spins at half-speed of the crankshaft. There are occasions when ignition timing is called for on a vintage Triumph with magneto or distributor ignition. I have a Crankshaft Degree wheel that was originally included on a page in the early unit-construction Triumph 350 &500 Factory Workshop Manual. I cut it out and pasted it onto a piece of cardboard. As you can see in the picture below, it is mounted directly onto the end of the crankshaft. I hope this article has been helpful and interesting, thanks for reading it.