I thought this would be easy to find.

When I have my engine rebuilt, the harmonic balancer relative position changed. Trying to mark it correctly. Does anybody know the diameter of the harmonic balancer? Can’t really measure it easily once it’s in the car.

 

what model you have? i recently replaced the balancer on my XJ6 S2, the refurbished unit only had one mark, checked true top dead center with a dial indicator, turned out to be 5deg/ retarded, made new mark for TDC and use an adjustable timing light to set correct timing