Its been awhile, but I'm back to consult the experts.
After checking the base timing at the garage, I noticed it was about 2 deg different from what I set it months ago. (usually run at 12-13 deg BTDC, but it was sitting between 10 and 11 deg BTDC.)
I then checked the Crank Pulley TDC mark against the piston TDC using the screwdriver method.
The TDC marks were clearly off by about 1.5 deg. When Piston was at TDC, the crank pulley marks were at least 1.5 deg Before TDC. (2 deg maximum, checked it 5 times).
I reset it to 13 deg BTDC, per Haag's recommendation. After my first day of racing on Saturday, I noticed it was back at 10-11 deg BTDC. I reset it again to 12-13 deg, and will check to see if it moved again today.
I've heard stories on this forum of the harmonic balancer rubber getting old and slipping. I have no idea how old this engine is, and if it got a new harmonic balancer when it was rebuilt by Haag Motorsports in Northern California.
How real is this harmonic balancer slip? Does it happen all the damn time? Or just once in a while after 150,000 miles? What is the word from the experts here?
Trying to refrain form buying a new balancer from Mazda Motorsports for $100.
I will check the TDC marks on Crank Pulley vs. Piston TDC with dial indicator and see if it moved more.
Jut looking for guidance on how often these things slip.
Luckily the 1.6 doesn't have crank position sensor attached to this area so I'm not suffering any performance loss, but I don't want to advance the engine too far. which is what I'm worried about.
If it didn't move again, it could just be a loose adjuster bolt on the cam pulley timing adjuster.