When I recently came to reassemble the timing case side of my 1951 G3LS engine I found that the cams and pinion were not ‘correctly’ marked as described in any of the books or manuals. It was therefore necessary for me to check the exact inlet and exhaust valve opening angles manually to ensure that these were correct.
In order to be able to do this I need a timing discs which showed the angles before and after TDC (top dead centre), but as I couldn’t find one suitable for my classic Matchless, I decided to make one up myself. I also added colour segments showing exactly where each valve should open and close to make verifying their angles much easier whilst on my hands and knees at teh side of the bike.
The timing disc also then came in very handy again when I can to set the ignition time. Previously I had set the firing point based upon piston position via the spark plug hole, but being able to set it by the exact crank angle is obviously much more accurate. I added marks for the correct ignition timing to the disc alongside the valve timing segments to save needing to remember or read off exact angles when working on the bike.
Please ensure that you download the correct timing disc for your model and year of motorcycle as the valve opening and closing angles vary slightly. You can of course check the correct timings for your particular bike by referring to the appropriate Owners Instruction Manual which can also be downloaded free of charge.
The various versions of the timing disc I have created are available for free download by clicking the appropriate link in the table below. Again, please ensure that you get the correct one for your motorbike.
The first timing disc in the list is a generic blank one (i.e. no valve or ignition angles marked) so can be used for any motorcycle. You can draw on the required angles in pen once you have printed the disc out on paper.
|Years||Models (click to download)|
|1945-1953||350cc and 500cc models.|
Once you have downloaded the required timing disc, print it out (preferably in colour) at full size on A4 paper. You will then need to stick it onto a cardboard or plastic backing sheet to give it rigidity before cutting round the circular disc. You may also like to have the disc laminated or coat it with sticky-back plastic to make it easier to wipe off oil fingerprints later on.
The finished timing disc can then be fixed to the end of the left (clutch side) of the crank shaft of your engine using a sticky fixer, BlueTak, magnet or something similar.
You will also need to set-up a pointer to the edge of the disc so that you can read off the required angles. I initially used a piece of thick wire (part of an old metal coat-hanger) which I bent around the rear brake pedal and out to the timing disc. That was a bit too ease to knock so I changed to using a hex key attached to the brake pedal with a magnet (as shown in the photo) but I’m sure you can come up with your own solution. Just make sure it doesn’t move so that the angles you measure and accurate.