mott 72HD flail mower idler

[jonsstihl]

Just tried out my newly fixed up Mott 72 HD flail mower.

I have a funny issue when I get into tall grass. the idler starts flapping around. I have 22 pto hp and this may be at the low end of what is possible but the engine doesn't seem to bog down. the RPM stays right up in the proper range (drops maybe 50 RPM) but when I get going a little too fast the idler starts to flop around. This is in medium to thick grass about 24" high (no brush)

The knives are dull except for the 42 odd knives I replaced. the cutter shaft pulley is about 1/4 inch off from the extension shaft pulley but the belt did not shred at all in one hour of mowing. There was a little rust on the pulley sheaves but I clean it off with a file.

anyone have any ideas.

 

[Fallon]

If all your pulleys aren't in a perfectly flat plane, you'll have issues. If I read that as your idler is 1/4" proud from the other pulleys, that's your issue.

 

[jonsstihl]

the idler is roughly in the middle where it should be. I wish it were the idler, it would be easier to move. the 1/4 inch difference is when I put a straight edge on one pulley and extend it to the other pulley. the only problem is that I can't move the cuttershaft pulley any closer to the mower and I don't seem to be able to shim the extension shaft pulley out since I'm not exactly sure how it all goes together. And they went and put twelve point socket head screws on the extension shaft housing so I can't just take it all off and see how it fits together.

 

[jimmysisson]

I would not think 1/4" out of line would hurt, if the pulleys are a foot apart or more. The idler on my SHD88 "flops around" a bit all the time. By which I mean it not only turns but moves a bit sideways at the same time, maybe 1/4-3/8"?. If the belt is not wearing funny I'd just keep an eye on it. And keep a spare belt on hand!
Jim

 

[jonsstihl]

by flopping around I mean putting more or less tension on the belt. but it only does it under load. At idle it spins up fine, and at pto rated speed it spins fine with no vibration but when I get a load on it it will begin a jig up and down on the belt. I just measured a little more accurately and it is 3/16" off. the cuttershaft pulley is farther out than extension shaft pulley.

 

[leonz]

View attachment mott utility 60 & 72.pdf

Just tried out my newly fixed up Mott 72 HD flail mower.

I have a funny issue when I get into tall grass. the idler starts flapping around. I have 22 pto hp and this may be at the low end of what is possible but the engine doesn't seem to bog down. the RPM stays right up in the proper range (drops maybe 50 RPM) but when I get going a little too fast the idler starts to flop around. This is in medium to thick grass about 24" high (no brush)

The knives are dull except for the 42 odd knives I replaced. the cutter shaft pulley is about 1/4 inch off from the extension shaft pulley but the belt did not shred at all in one hour of mowing. There was a little rust on the pulley sheaves but I clean it off with a file.

anyone have any ideas.

If all your pulleys aren't in a perfectly flat plane, you'll have issues. If I read that as your idler is 1/4" proud from the other pulleys, that's your issue.

by flopping around I mean putting more or less tension on the belt. but it only does it under load. At idle it spins up fine, and at pto rated speed it spins fine with no vibration but when I get a load on it it will begin a jig up and down on the belt. I just measured a little more accurately and it is 3/16" off. the cuttershaft pulley is farther out than extension shaft pulley.

I would not think 1/4" out of line would hurt, if the pulleys are a foot apart or more. The idler on my SHD88 "flops around" a bit all the time. By which I mean it not only turns but moves a bit sideways at the same time, maybe 1/4-3/8"?. If the belt is not wearing funny I'd just keep an eye on it. And keep a spare belt on hand!
Jim

the idler is roughly in the middle where it should be. I wish it were the idler, it would be easier to move. the 1/4 inch difference is when I put a straight edge on one pulley and extend it to the other pulley. the only problem is that I can't move the cuttershaft pulley any closer to the mower and I don't seem to be able to shim the extension shaft pulley out since I'm not exactly sure how it all goes together. And they went and put twelve point socket head screws on the extension shaft housing so I can't just take it all off and see how it fits together.

=====================================================================



Hello Johnstihl,


When you encounter tall grass you will have impact resistance from the load created by the tall brush/grass that you encounter. This happens with any mower or "UGH" rotary cutter.


You may need a new idler arm for your beautiful flail mower. The pulleys have to be aligned to operate properly to save on belts and bearings.


I have attached a copy of the 60 and 72 inch Mott Flail Mower manual that I have.

I would order a new pulley and arm assembly from Flail MAster or other supplier as you may need a new pulley bearing.


IF your Flail Mower Rotor Bearings were loose they would make a lot of noise to make themselves known to the operator and you would have to stop to check them and be sure the bearing hub set screws are tight.

 

[jonsstihl]

Thanks for the manual, It is the same one I found in a google search. I think the idler arm is fine, although a new spring probably wouldn't hurt. Looking at the parts list I realized that the cutter shaft pulley and the extension shaft pulley are supposed to be the same but mine seem every so slightly different. I will have to take them off and compare the offset. I think they are not the same offset. The extension shaft pulley seems to have been replaced by the previous owner at some point

My problem is that I can't seem to get the extension shaft pulley off. I need a gear puller that will push on the shaft as its pulling on the pulley. or a twelve point socket to pull the extension housing off the gearbox. Hitting it with a rubber mallet isn't helping and I think I may have damaged the snap ring because the shaft and pulley now moves in and out about 1/8 of an inch.

the parts lists mentions that the idler pulley can be shimmed in or out with washers as required. so I'm not worried about the idlers position.

cutter shaft bearings are good, pulley side I just replaced and the other side was fine when I had the cuttershaft out, I have no set screws on my cuttershaft bearings.

I will have to get the extension shaft off and see if I can shim the pulley out rather than replace it.

 

[jonsstihl]

Just took another look at it and the pulley is definitely not original it has been sleeved to fit the extension shaft. and I fell like an idiot, If anyone is looking for a twelve point socket look no further than your box end wrenches.

 

[jonsstihl]

Got it up and running this weekend. I used two 1" spacers and ground out the center to fit the 1 1/8" shaft. I got lucky with the thickness. Two .150" spacers was just right so I didn't need to have any machining done to them.

It is much better with the pulleys in alignment. I still can't go very fast in tall grass but it is definitely better than before.

 

[2458n]

22 hp and your going to mow 24 inch grass. Give the mower a chance -you either have to much mower,by about a foot. Or too small on the horse power. Mow slow and do not tear up what you have.

 

[jonsstihl]

It is much better than before when the pulleys weren't aligned. I realise I don't have 100hp to run it but it is on a 30hp tractor with 22 pto hp. By slow I mean in low range I move forward about a foot and I have to stop and let the mower catch up them I repeat. move one foot and stop.

Now with the pulleys aligned I can actually keep moving slowly without stopping every foot. I think a new belt will improve it even more because the mower has sat for a long time so the belt that is on it has developed a certain memory of how it has been for the last few years.

 

[jonsstihl]

Just tried out the mower with a new belt and a new tension spring and the difference is night and day. I can go full speed in low in fairly tall grass now taking a full width of cut and there is no flopping around of the idler anymore. I think the belt was probably worn out and it may have been bottoming out on the bottom of the pulley grooves instead of on the sides. also like I mentioned before the belt had a kink in it from sitting so long with the pulleys out of alignment.

now all i need to do is put on the fresh set of blades I bought and it will be ready to go even though it seems to work fine with the old rounded off blades that are on it.