Hydro-gear ZT-2800 input RPM.

[Low Flyer]

Folks,

My mower is a Cub Cadet RZT Z-Force 60". It has Hydro-gear ZT-2800 trans axles and a Kohler KT740 25hp engine. Kohler says that the engine should be 3,600 RPM at WOT. But the Hydro-gear manual says that the ZT-2800 maximum high idle is 3,000 RPM non-charged, and 3,600 RPM charged.

Of course my mower is non-charged. And I know that some of you must have mowers with the same trans axles. What is your high idle RPM? Do your engines run at 3,600?

My mower was set at 3,200 RPM high idle from the factory, and about 3,000 under load. I adjusted the high idle to 3,600 last night, but haven't mowed with it yet.

I guess I'm concerned of damaging the trans axles. Or could the lower RPM be to prevent the oil from getting too hot, and thus damaging the trans axle?

Should I readjust it to where it was, or just let it go?

Gil

 

[Johnbt]

"Kohler says that the engine should be 3,600 RPM at WOT."

I have a 2015 Toro MX-5050 with a 24 hp Kohler 7000-series and non-charged 2800s. According to Toro...

"24 hp, High Idle: 3300 + 100 RPM"

The 3600 rpm number only appears in the Kohler horsepower rating. I've never seen anything saying to run it at 3600.
Fwiw, I think the hp rating is also done without an air filter and muffler. The larger number makes better advertising.

 

[dfbroxy]

I am not an expert so take this only as food for thought. The RPM for the engine and the transaxle could be different due to pulley size. If you have a RPM reader use it to read rpms at the trans pulley. If you dont exceed maximum.....and keep it clean and cool it should be ok. May also require changing to a better grade of oil and more oil changes.

 

[Low Flyer]

"Kohler says that the engine should be 3,600 RPM at WOT."

I have a 2015 Toro MX-5050 with a 24 hp Kohler 7000-series and non-charged 2800s. According to Toro...

"24 hp, High Idle: 3300 + 100 RPM"

The 3600 rpm number only appears in the Kohler horsepower rating. I've never seen anything saying to run it at 3600.
Fwiw, I think the hp rating is also done without an air filter and muffler. The larger number makes better advertising.

The Kohler manual for this engine states:

1. Voltage tests should be made with engine running at 3600 RPM with no load.

2. Adjust idle speed screw and high-speed stop as necessary. Make sure maximum engine speed does not exceed 3750 RPM (no load).

On the top of the engine, the Kohler label states WOT 3600 RPM.

So, obviously Kohler intended for this engine to run at 3600 rpm.

Gil

 

[Johnbt]

The service manual for my KT-735 says the same thing. But Kohler doesn't know how the mower manufacturer will use the engine - which transmission, gearing, etc. - so I go by what the mower maker says. Maybe the other mower components will take 3600, and maybe they won't.

 

[bertsmobile1]

The Kohler manual for this engine states:

1. Voltage tests should be made with engine running at 3600 RPM with no load.

2. Adjust idle speed screw and high-speed stop as necessary. Make sure maximum engine speed does not exceed 3750 RPM (no load).

On the top of the engine, the Kohler label states WOT 3600 RPM.

So, obviously Kohler intended for this engine to run at 3600 rpm.

Gil

OK, Here is how it goes.
1) Kohler make a basic design engine and produce 1 and 1 only manual for it.
2) Toro design a mower then specify to Kohler how they want the engine to work and how many engines they want made like this.
3) Kohler then modify their standard engine to meet Toro's required specifications and then give the engine it's unique specification number. That is the bit after the family no on a Kohler or Code number on a Briggs.
4) Toro fit the engine to the mower with say a 4" engine pulley and then the tranny with a pulley bigger than 4.125" to prevent RUNNING overspeed ( this has been previously mentioned )
5) in both the Toro & Kohler manual you will find words like "suitably qualified persons " or "authorised technician"
These people actually know that they can run the engine up to 4000 rpm for brief periods for the purpose of testing.
In fact people who have gone to trade school will know how to make the engine spin at 3600 rpm to check the alternator output if needed however the same technically educated people should be able to test the output of the alternator at a lower RPM if needed because they went to trade school for a few years or served an apprenticeship under a tradesperson who knew the theory behind how these engine work and hopefully imparted that upon said same apprentice.

Because this is a very imperfect world, the actual engine specification is 3600rpm +/- xyz rpm.

Now as for the actual running speed of the engine.
This is generally just past the PEAK TORQUE point which on this engine is 3200 which is why Toro had the governed speed set there.
Running at faster speeds usually does little more than use near double the amount of fuel.
Generally the faster blade tip speed will give a cleaner cut but it will also change the air flow under the deck which might throw the clipping further, or cause them to build up on the underside of the deck.

There is a massive difference between the fastest allowable speed and the best performing speed and the latter should be how your mower arrived from Toro.
If you own a manual car, do you only change gears when the engine hits redline ( max Hp ) or when it stops accelerating rapidly ( peak torque)
Similarly you do not drive your car with the engine redlineing ( maximum Hp) all the time so why the hell do you think the mower should be run in the same mannar ?

 

[Darryl G]

Very informative Bert. Thanks. I knew most of what you said but had never managed to put it all together. You need a different analogy than a manual car transmission though. We don't have those here, lol.

 

[Johnbt]

www.jackssmallengines.com/jacks-parts-lookup/manufacturer/kohler/7000-series/kt740

Here's a list of 60+ models of the KT740.

28 of them are MTD versions.

 

[Low Flyer]

OK, Here is how it goes.
1) Kohler make a basic design engine and produce 1 and 1 only manual for it.
2) Toro design a mower then specify to Kohler how they want the engine to work and how many engines they want made like this.
3) Kohler then modify their standard engine to meet Toro's required specifications and then give the engine it's unique specification number. That is the bit after the family no on a Kohler or Code number on a Briggs.
4) Toro fit the engine to the mower with say a 4" engine pulley and then the tranny with a pulley bigger than 4.125" to prevent RUNNING overspeed ( this has been previously mentioned )
5) in both the Toro & Kohler manual you will find words like "suitably qualified persons " or "authorised technician"
These people actually know that they can run the engine up to 4000 rpm for brief periods for the purpose of testing.
In fact people who have gone to trade school will know how to make the engine spin at 3600 rpm to check the alternator output if needed however the same technically educated people should be able to test the output of the alternator at a lower RPM if needed because they went to trade school for a few years or served an apprenticeship under a tradesperson who knew the theory behind how these engine work and hopefully imparted that upon said same apprentice.

Because this is a very imperfect world, the actual engine specification is 3600rpm +/- xyz rpm.

Now as for the actual running speed of the engine.
This is generally just past the PEAK TORQUE point which on this engine is 3200 which is why Toro had the governed speed set there.
Running at faster speeds usually does little more than use near double the amount of fuel.
Generally the faster blade tip speed will give a cleaner cut but it will also change the air flow under the deck which might throw the clipping further, or cause them to build up on the underside of the deck.

There is a massive difference between the fastest allowable speed and the best performing speed and the latter should be how your mower arrived from Toro.
If you own a manual car, do you only change gears when the engine hits redline ( max Hp ) or when it stops accelerating rapidly ( peak torque)
Similarly you do not drive your car with the engine redlineing ( maximum Hp) all the time so why the hell do you think the mower should be run in the same mannar ?

You've answered your own question.

A car does not require the motor's maximum horsepower output to move it along the road. It requires only a fraction of what the engine can potentially produce. The cars' manuals do not say to run them at near maximum RPM. There is not a sticker on the car that states 3,600 RPM WOT. Also, the car's engine doesn't depend on the air flowing over the engine to cool it.

And comparing the operation of a lawn mower to a car is just silly. There is no comparison. They are two totally different machines with different designs and different purposes.

A more relative comparison would be the lawn mower to a tractor's PTO. Regardless of the implement attached to the tractor's PTO, the PTO speed is always the same, either 540RPM or 1000RPM, whether gas or diesel. These engines are designed to run near to maximum RPM to achieve the desired PTO RPM, as are these lawn mower engines. The ground speed is constant and the operator doesn't change gears. For instance, when I am bush hogging with my 82HP diesel tractor I put the tractor in 5th gear and that is where it stays. My ground speed is constant probably 95% of the time except on uneven ground, slopes, etc but the PTO speed remains the same, I do not slow the engine. It is generally the same with a lawn mower, except a person may slow his ground speed to change directions, maneuver around an obstacle. The there is no changing of gears, the PTO speed stays constant.

I'll run my KT740 at 3,600 RPM, it cuts much better at this speed than at 3,200 RPM.

And I don't know why you are talking about Toro. My question was referencing my Cub Cadet. I don't own a Toro, so I cannot speak about how a Toro operates or how it is built.

 

[Johnbt]

Here's an excerpt from Cub Cadet's spec sheet on a KT740 25 hp on a 2014 ZForce 60"...

As you can see from the Google entry below, the Kohler model is KT740-3027.

From the spec sheet:

"Max. Speed (No Load) 3350 R.P.M."
"Max. Speed (Full Load) 3300 R.P.M"

Maybe this isn't your mower. But it clearly shows that Cub Cadet has done the same thing that I was saying about the Kohler KT735 on my Toro. They've lowered the max revs to well under 3600.
___________________________________________________________________
"[PDF]Z-FORCE L and LZ SPECIFICATION SHEETS 2014 - Cub Cadet Parts
https://www.cubcadetpartsnmore.com/.../specs/CubCadet-Z-Force-L-LZ-Series-2014-S...
2014. 2014. Specification Sheets. CC ... MODEL: Z-Force L48 ... Reverse Speed. 0-3.0 mph. ENGINE SPECS: ENGINE SPECS: Make. Kohler ... KT740-3027."
___________________________________________________________________

MODEL: Z-Force L60 YEAR: 2014
Factory Model Number: 17ASDALD010 25 H.P. Hydro Drive
Electric P.T.O. / 60" Fabricated Deck

ENGINE SPECS: ENGINE SPECS:
Make Kohler Idle Speed 1600 R.P.M.
Model Series 7000 Series Pro (Vertical) Max. Speed (No Load) 3350 R.P.M.
Model/Type/Spec KT740-3027 Max. Speed (Full Load) 3300 R.P.M
No. Of Cylinders 2 Valve Lash (Intake) 0.006" (0.152 mm)
Horse Power Rated By Manufacturer 25 HP (18.6 kW) Valve Lash (Exhaust) 0.006" (0.152 mm)
Peak Torque Not Available Ignition Type Electronic
Displacement 44.2 cu in. (725cc) Spark Plug Gap 0.030"
Bore 3.27" Mag Air Gap 0.008"-0.012"