There are a few old tried and tested methods of finding top dead centre. if there is no mark on the flywheel for instance.
The approved best method is to remove the cylinder head [easier on a 2/ ] and find T.D.C. with a dial indicator. If this is done with a 4/ it is important to make certain that the cylinder barrel is locked down securely to the crankcase. [Is it through bolted]?
The bubble method. Set up a timing disk and pointer, get the piston as near as you can guess to T.D.C. Then get a cake of wet soap, rub your finger on the soap, then over the vacant spark plug hole to form a bubble, slowly rock the flywheel to and fro to form the highest bubble. This is T.D.C.
Of course a 4/ motor must be on the top of the compression stroke. I have frequently used this method successfully.
An accurate method I have used when setting up a timing disk especially when building a motor with different cams etc where I need to check numerous figures is as follows.
Set up a timing disc and flexible pointer such as a piece of wire mounted to a convenient screw into the crankcase so the end pointing to the timing disc can be adjusted.
with the cyl. head bolted on find a bolt with the same thread as the spark plug hole or in some cases a long reach plug with the side electrode removed,screw this into the plug hole with the piston well down the stroke.
Next slowly rotate the flywheel 'till the piston contacts the end of the bolt.
Bend the pointer to a convenient mark on the timing disc and note the reading.
Rotate the flywheel in the other direction 'till it again contacts the stopper bolt.
Remove the stopper bolt and turn the flywheel to a point exactly half way between the two previous points. This is Top Dead Centre.
These techniques as described in the late great Phil Irving's bibles.
cheers pancho.
