Tall grass Doesn't cut all the tall grass

jk3700 · May 20, 2019

I have a RZT-50 Zero Turn.

When I cut taller grass, the deck leaves a strip of uncut grass about a foot from the left side of the deck.

The uncut grass is about 4" in width.

Anyone have any idea why this is happening?

My blades are brand new.

My blades are not bent.

Just replaced the belt.

I do run a power bagger behind the mower and pickup grass as I go.

mechanic mark · May 20, 2019

are your blades perpendicular to each other, 3 blade setup? are you blades OEM Cub Cadet blades?

Darryl G · May 20, 2019

That's not uncommon when cutting tall grass. Does the strip fall in line with the left front caster wheel? It's probably laying the grass down as it rolls over and the grass doesn't stand up enough to get cut properly.

Same question as above - what blades are you using? I'd recommend high lift blades for those conditions. Also is your deck pitched properly? Do you keep your deck clean underneath? Are you going too fast and causing the engine rpms to drop? That's pretty easy to do when running a powered bagger in tall grass. Are your rpms up to spec to begin with?

jk3700 · May 21, 2019

mechanic mark said:
are your blades perpendicular to each other, 3 blade setup? are you blades OEM Cub Cadet blades?

I do have the 3 blade setup. Didn't think the blade position was critical as they do not overlap.

Can you tell me why this would be critical?

I do not have cub OEM blades.

Can you tell me why the OEM blades would make a difference?

jk3700 · May 21, 2019

Darryl G said:
That's not uncommon when cutting tall grass. Does the strip fall in line with the left front caster wheel? It's probably laying the grass down as it rolls over and the grass doesn't stand up enough to get cut properly.

Same question as above - what blades are you using? I'd recommend high lift blades for those conditions. Also is your deck pitched properly? Do you keep your deck clean underneath? Are you going too fast and causing the engine rpms to drop? That's pretty easy to do when running a powered bagger in tall grass. Are your rpms up to spec to begin with?

I do have high lift blades.

I'll need to check that front wheel laying the grass down.

Engine running at full throttle.

There is no drop in rpms as far as I can tell.

Can you tell me how the deck pitch would have an effect on the grass cutting?

7394 · May 21, 2019

The blades do overlap, but in different locations, since blades are staggered with center being farthest forward on 3 blade.

So there is an imaginary line where overlap occurs. They just can never hit each other.

bertsmobile1 · May 22, 2019

When grass gets really tall quite a few things are working against you.
Firstly as already mentioned, the grass gets laid down flat and if long enough does not stand up again till the cutting section of the blade has passed so the blade just lays it down again.
Then their is the draught created by the blades.
It is strongest on the discharge side and weakest on the left side.
Also the higher the deck the weaker the draught.
Then there is the circulating mass of the cut grass itself that can push the uncut grass flat.
Three ways to overcome it.
1) heel the deck so the back is a lot lower than the front.
When you do this the blades cut better but all 3 cut at quite a different height so you end up with a wave type of level.
If this is only being done to cut catch up on really tall lawn it won;t matter because you can relevel the deck latter on

2) mow a lot slower

3) mow backwards

Darryl G · May 22, 2019

jk3700 said:
I do have high lift blades.

I'll need to check that front wheel laying the grass down.

Engine running at full throttle.

There is no drop in rpms as far as I can tell.

Can you tell me how the deck pitch would have an effect on the grass cutting?

The deck pitch effects the approach angle of the blades to the grass and how the grass moves into/around/out of the deck.

I just double cut tall grass to both cut any missed blades of grass and to disperse the clippings better. The 2nd pass can be done at speed and you'll get the best results going in a different direction, but I'll often go in the same direction to enhance the stripes.

jk3700 · May 23, 2019

7394 said:
The blades do overlap, but in different locations, since blades are staggered with center being farthest forward on 3 blade.

So there is an imaginary line where overlap occurs. They just can never hit each other.

The blades are on a pulley that can slip. So I assume they could not hit because of their position.

I guess they could be mounted with the middle blade being higher or lower that the end blades.

I'll have to look at that.

jk3700 · May 23, 2019

bertsmobile1 said:
When grass gets really tall quite a few things are working against you.
Firstly as already mentioned, the grass gets laid down flat and if long enough does not stand up again till the cutting section of the blade has passed so the blade just lays it down again.
Then their is the draught created by the blades.
It is strongest on the discharge side and weakest on the left side.
Also the higher the deck the weaker the draught.
Then there is the circulating mass of the cut grass itself that can push the uncut grass flat.
Three ways to overcome it.
1) heel the deck so the back is a lot lower than the front.
When you do this the blades cut better but all 3 cut at quite a different height so you end up with a wave type of level.
If this is only being done to cut catch up on really tall lawn it won;t matter because you can relevel the deck latter on

2) mow a lot slower

3) mow backwards

I have noticed in the past that if I cut at a lower height setting that there is less grass missed across the deck.

I am just puzzled by the fact that any grass could be missed by the blades under the deck.

I do slow to a crawl in higher grass to let the cut grass be sucked up into the power blower hose.

If I cut too fast, the cut grass packs in the discharge pickup and then eventually plugs up.

Tall grass Doesn't cut all the tall grass

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