:welcome:
Blades that need to be timed to each other run toothed belts like on your car's timming belts
There is a good chance the deck is a little bent
Get under the deck and rotate the blades by hand.
first without the belt attached.
You are looking for a smooth and quiet rotation, if no spindle bearings require attention.
Replace the deck belt
It is very important that the drive belt is on the deck as it will pull against the spindles and shift them if they are loose.
Turn the balde again.
Check that they are in alignment. Mark where one side passes the deck then check he other side against the mark.
Check that the bades ar the same height where they pass each other.
Check the ends of the blades , if they have been hitting there will be a spot where the paint has been scrapped off.
If a blade is striking the deck, hammer the deck out a bit they tend to close in a bit around the discharge hole and along the front where the deck strikes rocks & roots.
If a pair of blades are striking take a little off both ends of one blade only, and just enough to allow clearence .
You will have to take the same amount of each end to keep the bades in balance.