Finish Mower Blade Alignment Question

[Erik Graham]

Greetings;

I have just dusted off a finishing mower that came with my B7100. After lubing bearings, checking the belt and topping up the gearbox I hooked it up to the tractor. It seems to have a lot of vibration, which is worse at low PTO speeds and gradually gets a little better as RPM's increase. I've checked all the spindles and there is no perceivable play and the blades are tightened down. The blades appear to be pretty new with no visible chunks missing. I looked under the mower and can see that all 3 blades are in a different position. Are they supposed to be in any particular position relative to one another? For example should the two outside ones point at noon and six and the middle one at 9 and 3, or does that matter at all?I watched a couple of YouTube videos about changing blades and belts but couldn't see any reference to how the blades should be oriented after. Any insights greatly appreciated.

Cheers, Erik

 

[Daren Todd]

If it has belt driven spindles, then they don't need to be timed. If your getting lots of vibration, I would think either a bearing is going out, blades are out of balance, or something is loose or binding.

Another thing to check is the pto shaft. If you have the old square style shaft that isn't keyed, then your joints could be out of sink.

 

[rkidd]

The belt that drives the blades can cause that problem also if it does not have enough tension as I finally figured out when I first got mine.

 

[D2Cat]

You said, "The blades appear to be pretty new with no visible chunks missing." I would remove them and make sure they are the correct blades and the same length. Then check the balance of each blade.

You mentioned you checked the belt. Be sure a chunk isn't loose or missing.

If the spindles have no play, there's not much more that rotates except, as Daren mentioned, the drive shaft being out of time.

 

[rjcorazza]

All good suggestions... I would start by checking blade balance, remove the belt and check each spindle and the idler / tensioner. My bobcat was vibrating earlier this season and the belt was jumping all over the place. Turned out the idler pulley was partially broken. It was manufactured in 2 halves and pop rivited together- half of the rivet heads were missing on the underside, allowing the belt to bounce all over the place.

 

[Erik Graham]

Thanks for the replies, will check all to the components as suggested. Must admit didn't really look closely at belt although tension seemed okay. As far as PTO alignment goes, the shaft is the old school square type. Is the correct alignment for best balance to have the mower end and the tractor ends at 90 degrees to each other?

Cheers, Erik

 

[D2Cat]

Eric, if you check the PTO shaft closely it's probably not square. It's hexagon, so two sides are one dimension and the other two are a different dimension.

After you check out all the other components, if it still vibrates, then you can remove the PTO shaft from the tractor, and rotate the end that connects to your tractor 180 deg. This is what Daren was referring to as "out of sink (synchronized)".

 

[Daren Todd]

Thanks for the replies, will check all to the components as suggested. Must admit didn't really look closely at belt although tension seemed okay. As far as PTO alignment goes, the shaft is the old school square type. Is the correct alignment for best balance to have the mower end and the tractor ends at 90 degrees to each other?

Cheers, Erik

I will have to look at my rotary cutter tonight and get back to you. I got it out of sync when I shortened the shaft and put it back together. Boy did it bounce around pretty good I believe 90 degrees from each other is correct. When I realized what happened, I pulled the shaft off the tractor side, rotated 90 degrees and put back together and tried it. Ran smooth after that.

Looking at the joints, one end should be horizontal, the other verticle (opposite each other)

Edit: can't look at it tonight. Forgot the rotary cutter is still at my father in laws till I can get my trailer decked

 

[Erik Graham]

I only had a bit of time this evening to monkey around with the mower. I rechecked the belt, still couldn't see any chunks missing but tighten it a bit. While it was loose I checked the bearings in the idler wheel and they seemed fine. I did look at the PTO shaft and to my surprise it is indeed rectangular and not square. I took my calipers and measured and sure enough there is a few thou more than an 1/8" difference from height to width. As it will only fit in one way I'll will mark and rotate 180 degrees and see if that makes any difference. This week end I'll pull the blades and will measure and balance them. Thanks for all the tips.

Cheers, Erik

 

[Erik Graham]

Well, mystery solved! Decided to start with the easiest and just disconnected the PTO shaft, rotated it 180 degrees and reconnected. Now purrs like the proverbial kitten. In the process of doing that I noticed that the universal joint on the PTO shaft closest the tractor was missing a grease nipple, for years by the look of it, so will install and load with grease. Thanks again for various comments.

Cheers, Erik

 

[D2Cat]

Erik, a grease zert and grease in that PTO u-joint will make that joint last much longer, and my even quiet it down even more!