I have been running a turbo short block 3 rotor for years now, and want to start wicking it up a bit. My issue is that with a custom made crank and using a standard front pulley, I am not sure if the timing mark is at 5 degrees as standard or whether it is actually TDC. Is there any way to physically check the timing? ie if you can see the apex seal thru the top plug hole it is so many degrees before of after TDC? I hope this makes sense to someone, and any help would be appreciated.

Remove the plugs from the front rotor housing.



With a mirror and strong light turn the engine clockwise until an apex seal is centered in the trailing plug hole (the top one).



Mark the pulley under the wire pointer.



Turn the engine backwards until an apex seal appears centered in the leading plug hole. (the bottom hole).



Mark the pulley under the wire pointer.



Measure the distance between the marks.



Calculate 1/2 of that distance.



Measure the 1/2 distance from each of the first two marks toward each other.



If both measurements end up at the factory pulley mark, then that mark is TDC.



If the pulley is blank where your measurements predict the TDC mark should be, the factory mark is an unknown. Make your TDC mark on the pulley.



Measure the pulley diameter.



Find the circumference of the pulley. Calculate it. Don't try to measure it.



C=3.1416 X the diameter.



Divide the circumference into 360 to find the degrees per inch.



Use that data to lay out timing marks on the pulley.



Do it several times to be sure you understand what you are doing.



Use a fine 3 corner file to score the timing marks on the pulley engine side flange.



Fill the marks with different colored paint to indicate which mark it is.



You can now measure from the TDC mark to determine what that existing mark is. 5 degrees 10 degrees etc.





This will pretty accurate. But you should know that Mazda moved the plug holes up and down over the years to gain some advantage in polution control.



So, your TDC mark may turn out to be off of dead on accurate by a degree or so one direction or the other. This will have no effect on performance.



There is a very accurate method to measure for TDC if the engine is apart shown elswhere on this site.



Lynn E. Hanover

Thanks very much for that Lynn, I knew there must be a way to verify it but wasnt sure what it was.