Yeah, I wrote a thesis trying to put to text what you just showed by video lol. Great job. I cut professionally for many years. I had one deck get tweaked up in service from an employee blunder and that I have no idea how it cut because it got trailered because the blades were hitting intermittently. But I also had two brand new ones with tweaked decks right off the showroom floor. The first one cut exactly like his is doing. Two strips were it was just missing the grass, kinda just beating it over. What I call mowhawking. The blades were not even on the cutting plane when aligned with each other. Mans brain says well that should just cause uneven gapped cut the same amount the blades are uneven like it does when you bend a blade a little. But it doesn't. Depending on how the deck is tweaked, what it causes is insane turbulence under the deck that causes the grass to get pulled, blown down and laid over instead of cut and it kind of leaves that mowhawk look. Mans brain also says well you should be able to hear this too. But you can't because the mower is new to you. You can't realize you did hear it until it's fixed or replaced. Only way you can hear it is if you ran that mower a while, then bought a new one... or mowed with that one for a week before you hit a cast iron sewer cleanout and warped it up lol. Anyways, it's the air disturbance caused by the tweaked deck and uneven blades that causes the mowhawking in my experience. The other brand new one, rolled it off the showroom floor, took it to the shop, did my setup on it, checked at the right and left blade for right to left level, then rotated the blades front to back and set the pitch to 1/4". Double checked at right and left blade after locking it down. Took it out on the first job, made one pass, turned around and was like WTH? Long story short it cut fairly even, but the deck was so tweaked the center blade striped the grass opposite of the direction of travel. It looked like someone walked down the middle of every pass with a 16" push broom brushing the grass back the other way. At first I was sure an adjustment I made came loose. So back to the shop I went. Checked left to right level and then front to back pitch at the right and left blade. Was dead on. I scratched my head a bit, then checked pitch at the center blade and it was pitched the opposite direction. Spun the blade around, same thing. Took the deck off, flipped it over and started measuring with a steel ruler from the blade to the deck as I turned the blade. I dont remember the measurement now but it was closest at 1:00 and farthest at 7:00. It was way tweaked but you couldn't see a thing wrong just eyeballing it. MFG rep said this happened on rare occasion during manufacturing from welding stresses. Basically if it got too hot during welding, removed from the jig too soon, or cooled too quickly after welding or too much after removed from the jig this would occur. Said it was like jar lid effect for dimpling down in the middle and sheet cake pan effect if it tweak twisted corner to corner. He also explained it happened rarely and so it was far more cost effective just to remedy with the buyer than set up a station to tediously inspect every deck for trueness between welding and the pre-powder coat prep cleaning bath. Back then everything was 10 guage with doublers or triplers, and had the bar stock welded around where the belts run to encase them and stiffen the deck and to have something to mount the covers on. These days are better, but I still look for simply constructed decks that don't need all that stuff welded on the tops.
