Gravely sickle bar mower advice

I put this over on the Gravely Group in Yahoo, thought I'd put it here too and see what other advice I got.

I have an L walkbehind with the 42" sickle mower. I use it to mow mixed field grass (some clover, timothy, onions, a little bit of everything). The problem is, it will start out mowing perfectly for about five feet, and then it plugs up. It starts out with the mowed grass falling nicely back over the mower, and then after a few feet I've accumulated a big gob of cuttings around the gearbox and I'm pushing the grass over and going over the top of it, and I have to stop and back up and start again. I have the two-speed gearbox and I'm running in the lowest ground speed. I'm running the tractor in the lower range (lever forward); if I run it in high range (lever back) it sounds like its going to shake the mower to pieces, and it makes no difference in the plugging up. Sections are new, I use the serrated edge ones so they stay sharp. Holddowns are tight. Rock guards are new. I use plow bolts to fasten them on the bar, so that the bottom surface riding on the ground is smooth and not digging up the roots. I know these tractors pretty well, I used to work on them in a small engine shop back in the 70's, but I always worked on the engines, not the implements.


Any ideas? What am I missing?

You need more ground speed [high gear] while idling the engine slower so the sickle is running slowly so as to not shake so badly. Kind of like a snow thrower, you have to keep "feeding" it.
That's my guess.
Is your sickle mower attachment rusty? Surface rust could cause drag on the clippings and not allow them to slide on past. ???

If it's cutting the grass and not ripping it out, then you either need to find a "sweet spot" where the cut material falls over like you want or you can rig a sheet metal Vee shaped cover over the gear box as you call it, kind of like the Jari mowers had. I would start by checking to ensure it's actually cutting and not ripping the grass. All it takes is one bad section of guard to do it.

I'm not familiar with the Gravely but all sickle bars need to be properly timed. The cutting bar stroke must stop in each direction with the sections centered behind the stone guard. Other than that they will plug up. Also, they need to ride tight to the stationary edges of the stone guards like a pair of scissors. A gap will allow debris to plug up.