Wobbling Up To 540 RPM?

[Jackrabbit_Slim]

I have a 5 foot rotary cutter made by World International Machinery(?)... the outfit out of Bethel, Ohio.

I drop my RPM's down to engage the PTO and as I'm powering up to the rated (2,600) engine RPM's I get a distinct wobble from the cutter. It stops at about 2,000 RPM.

I've only used this implement a couple of times, bought it new, and it's been happening from day one.

Thoughts, suggestions, advice etc. would be appreciated.

Thanks,

Slim

 

[RoyJackson]

Those heavy blades have to extend (they pivot on the mounting bolts...pivoting saves the blade when you strike a stump or rock). That extending will make a thump....

Then, it's a fair amount of inertia when those blades spin up.

My Land Pride vibrates quite a bit too, until those blades come up to speed.

Try this... Engage the PTO, but don't up the RPM (unless you have to "blip" the throttle to prevent stalling) for about 8 to 10 seconds, then smoothly raise the RPM until you get to PTO speed.

Without seeing your unit, I can't say the vibration you feel is normal or excessive. My guess is that it is normal.

 

[Charolais]

I have a 7 ft. KK that did the same thing. What I found was the nut that holds the stump jumper on the output shaft was never tightened properly from the factory. The stump jumper fits on a tapered splined shaft and has a nut and cotter pin. I raised the unit with the lift arms and blocked both sides, removed the cotter pin and got 5 rounds on the nut. Problem solved. You may want to check in that area of your unit.

 

[RalphVa]

My LX4 is this way. There's a SLAM, as the blades start and extend a bit. Then there's a tad of vibration as I rev it up. It smooths out nicely near the 540 rpm spot (2900 rpm on my JD 4010).

I have to rev my JD 4010 to around 1800-2000 rpm to avoid an engine stall when the PTO starts up, too. Not supposed to start at full rpm because of the shear pins. I'm used to all this because my Gravely PTO won't engage (all mechanical) unless the engine is at idle. It's completely smooth at all speeds though, as it has just a simple blade (well, 2 crossed blades).

Ralph

 

[timb]

I had an interesting experience with my MX6 on the first cutting this year. Normally it starts up just as Ralph mentions on his LX4. I keep trying to find the best starting engine RPM. Once running at speed it's smooth. So this year I check everthing over, greased all the fittings and it all looks good. Get out to the field - set the 4710 at 1500 rpm and hit the PTO switch. No slam, no vibration, barely pulls the rpms down. The mower spins up smooth as silk. I congratulate myself on finally finding the sweet spot RPM to use to start the deck. A little while later I have to shut the deck down for a few minutes for some reason or other and then restart it. Back to the same old commotion. I realized that the last time I used the deck last year - the blades must have remained perfectly straight out as it spun down - and there was just enough rust formed over the winter to hold them in place on the first start up this year. Once they loosened up though - back to the same old shake.

Makes you wonder if anyone ever put any spring-loaded setup on a rotary to start the blades out at some common angle (and in-balance!).

 

[Soundguy]

Take a look under the mower next time before you fire it or the tractor up.. see if the blade carrier has any play on the gearbox shaft.. or if the blades have free-play onthe stump jumper.. the blades need to be able to rotate out.. but not much more play than that.. I usually oil mine once a year..e tc.

My 5' KK does the same thing till the blades spread out..

Soundguy

 

[BB_TX]

The blades on my Howse 6' bind up pretty tight each year due to rust, grass, twine, etc. around the bolt between the stump jumper and the blade. At least once a year, I raise the cutter up on its side so I have easy access to the bottom. I chain it very securely to my FEL and raise it up until it is standing vertical with one side on the ground and then back the tractor up a little to let the cutter lean back against the FEL. That way there is no danger of it falling over on me. Then I can easily free up the blades and oil them so that they swing freely. I also can easily sharpen them with an angle grinder at the same time without having to crawl under it.

 

[RalphVa]

Had an interesting time starting my LX4. This was when it was still at 1500 rpm for idle (from the dealer). I could start the LX4 with throttle all the way back then. I pulled the PTO button. HUGH amount of vibration. Pushed button in. Tried it again. Tried revving it up. LOTS of vibration.

Got off and looked underneath. The blades were bent over and crossed. I ended up taking it back up to the garage, jacking up the rear end of the LX4 (I have a chain for the top link; so rear won't raise with it) and getting under there with a pry bar to get the blades uncrossed. Think I must have shut it down at speed, and one or both of the blades hit something while slowing down.

Ralph

 

[Pooh_Bear]

My rotary mower makes a racket when running with no load.
If I drop it down in the grass it is real quiet.
The ORC is worn on the internal splines and it wobbles.
It may be that with the driveshaft at a steep angle it stresses it and it makes racket then.
And when the RM is down the driveshaft is almost straight.
But I know I should get a new ORC for it.

Could the wobble and noise be coming from your driveline?

Pooh Bear