I've never been really happy with my 857 and mowing. I think it has an RL-367 deck. But the motor/deck belt has been a been a problem. The belt was shot. So, I went to get a new belt. I got a 4L belt which fits on the engine pulley and the idler pulley. But it looks like the triple pulley is a 3L. And it will throw a new 4L belt. So when all else fails I look at the part diagram and the drawing looks like the outside pulley is a different size. Do I have a similar but different model deck? Or over the years did someone put the wrong pulley on?