340 Static Compression Numbers and Test Procedure
If you don't notice a vibration and the motor has been running this long already I would just leave the balancer on for now and remark it. If you don't want to get a piston stop to find exact TDC then try to find approximate TDC. Take all the sparkplugs out of the engine so it rotates easy. Look in the sparkplug hole and turn the motor with a wrench or socket until you can see the piston at TDC. Carefully rotate until you see the piston just start to move down the bore. Put a mark on the balancer that lines up with the zero mark on the tab. Next reverse rotation and do the same. Half way between these two marks is approximate TDC. Run the procedure again to see if your results repeat within a couple degrees. If it does you should have a good enough mark to time the engine with for now. This is not ideal but should get you closer than you are now. Set timing to about 35 degrees at around 4000 to 5000 Rpm. Add race fuel to the tank and see how it runs. Also mark the balancer with a straight line from inner to the outer hub so you can tell if the outer ring slips.