Small Engines (Lawn Mowers, etc.): gearbox rocking, single speed, portal server

Question
I have a Toro model 20016 (yr 2004) self-propelled front drive single speed lawn mower. Mower stopped after lowering wheels to cut at 1-1/4". Pulled off front wheel and checked grease and gears in gear box. Appears ok. However, box does rock back and forth when manually handled. I cannot find a tightening screw although I must admit I do not know where it can be found. I considered replacing the belt but hesitated since it may not be my only problem. Should the gearbox rock? If so, how do I correctly replace and tighten the belt? If not, what do you think is the problem and how do I trouble  and repair same? Thank you.

Answer
The link below will take you to Toro's website.  Enter you model number and select "Manuals" and you will find the service manual for you mower.

https://homeownersolutions.toro.com/portal/server.pt/community/product_center/225#manualsResultPage


Your gear box will rock back and fourth.  When you squeeze the drive engage lever the cable puts tension on the belt by moving the gear box forward.

Will the engine start?

Eric