rear engine rider? if so, all you do is loosen the pinch clamp under seat on the frame tube, then as i have found, use a heavy hammer on a wood block against inside of front end below handle bars, to knock the frame tube forward little by little.
Reason is the weight of all that rear end is pushing down on tube making it move hard to move it. You could jack it up to relieve the weight directly below the seat,under the machine, that may help/ just take the pressure off the tube.
what i don't quite understand is this, a "old" belt should be longer than a new one, when i replaced mine, i had to move tube backwards, not forwards. Something doesn't sound right.
Also be aware, if you move that front end from one position to another, it will throw your shifter out of place, notice shifter bracket has 2 bolts, slotted holes to readjust it.
May also make clutch/brake take hold in a different location too. Now i am not sure about this, but i "think" i read the idlers on deck should be no closer than 1 or 1 1/2" together when deck is engaged, i am sure someone will correct me if that isn't right, but.. that is about the distance on my 41" two blade deck.

shotzi, go the the Snapper website and download the 2 free PDF manuals that cover parts and service on your machine. Keep them in your computer and you can refer to them any time you want. The service manual does a good job explaining how to do all maintenance work on the machine. And.....moving the front end of the mower to adjust the blade belt tension does not affect the shifter settings. The shifter mechanism is part of the REAR section of the 2 frame halves and does not move when sliding the front section to tense the deck belt. The part about the clutch/brake pedal is right though. The manual will explain it all.

I should have given the model #421613BVE & serial #35501535. The mower has SR170 on front end. Does this thing come all the way out? The guy that sold me the belt & brg. said they were right, but he would say that anyway. I got on the Snapper web site but got an error message when I asked for a parts or service manual. Is there another site to look at for parts and service manuals? I really think I've got the wrong belt, but that doesn't explain why my frame won't move. I'll go back and try again.

John, thanks for your quick response.

Mike

Mownie Sorry I missed your post till now I guess I was busy writing my own.Just left the snapper site I'm still getting error message.I may be going to the wrong site I'm going to www.snapper.com

Mike

sheesh, you are right about the shifter, i wasnt thinking, i put new belt on at same time i replaced drive disk and easy clutch, it was my drive disk that was not sitting in right spot for low gear when i had to adjust shifter, sorry for the missinfo

I have found, if you loosen the tube clamp, then go up front and using both hands, and brace your self well, you can jerk the front section forward to adjust the belt tension. The spacing between the belt sides under the cover, should be 3 fingers apart, when the handle is in the mowing position. To move it back, it may take a BFH to move it back!

I have a 28 inch Snapper rear engine rider that is not the tube frame how do I adjust the belt for the for the cutting deck