Timing Belt and Water Pump Replacement Subaru WRX/STi:
23. The timing on this side is the exact same as the other side. You have to line up the side, middle, and top and keep the belt tight. It was a bit of work to get it all lined up as this side is under tension and you are now running out of belt free length. Any slack in the belt up to this point will show up by the lines on the belt not matching the timing marks on the side and the top. They all have to line up! It actually may be better to start on this side as you’ll have the entire belt free.
24. Install the belt tensioner. Torque to 29 foot lbs.
25. Recheck ALL your timing marks. Anything amiss should be fixed. I’m not a Subaru tech, but with motorcycles, being off a tooth will cause it to run poorly and being off a few will definitely cause piston to valve contact. This is catastrophic failure!
Once you’re satisfied that the timing is correct, remove the allen key that’s been holding the belt tensioner pin in place.