Last summer I bought a Sears lawn tractor with a Kohler OHV engine. The speed control has a detent to set the engine speed for 'mowing'. The speed seems a little high for my needs. I was always told that one shouldn't run a 4-cycle gas engine faster than needed to get the job done, as it would just prematurely wear out the engine. Does anyone know the reason for a pre-set speed for the mower. It seems that there is no need to run it faster than needed depending upon how high the grass is and how much power is needed for cutting.
LAWN TRACTOR SPEED
- Thread starter thiggy
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MolaKule
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Aside from high engine loads and not enough cooling during lugging, the engine was designed to provide a specific RPM so that the cutting blades will spin at the most optimal rotational velocity for clean grass cutting.
If the RPM is too low, the blades of grass won't get "whacked," they will get pulled, and the top of the grass will look like someone went over it with a weed eater instead of a mower.
On my Sears mower, the engine pulley is about the same size as the mower deck pulleys, so the blade RPM needs to be about the same speed as the engine RPM.
Running the engine slower than the "detent" speed with a load is like lugging the engine
of a car with a manual transmission. This is not good because the internal engine loads will be higher than normal, the cooling will be inadequate, and the engine will simply not develop the horsepower needed for the RPM required by the mower deck.
In this case, slower RPM is not necessarily good. I believe you will see more wear from lugging the engine than running it at the goverened or "detented" speed.
[ May 20, 2003, 03:42 PM: Message edited by: MolaKule ]
If the RPM is too low, the blades of grass won't get "whacked," they will get pulled, and the top of the grass will look like someone went over it with a weed eater instead of a mower.
On my Sears mower, the engine pulley is about the same size as the mower deck pulleys, so the blade RPM needs to be about the same speed as the engine RPM.
Running the engine slower than the "detent" speed with a load is like lugging the engine
of a car with a manual transmission. This is not good because the internal engine loads will be higher than normal, the cooling will be inadequate, and the engine will simply not develop the horsepower needed for the RPM required by the mower deck.
In this case, slower RPM is not necessarily good. I believe you will see more wear from lugging the engine than running it at the goverened or "detented" speed.
[ May 20, 2003, 03:42 PM: Message edited by: MolaKule ]
MolaKule
Staff member
Thiggy,
The speed setting is most likely the rpm at which the engine develops the needed horsepower for the mowing. I prefer the highest speed setting possible for required power and engine cooling. Lugging the engine with a mower deck load is an engine killer.
Lower the ground speed by placing in a lower gear, but keep those rpms up the for best blade speed.
BTW, try Redline 10W40 or Schaeffer's 15W40 #700. Those moly oils seem to run cooler during those hot summer days.
[ May 20, 2003, 12:13 PM: Message edited by: MolaKule ]
The speed setting is most likely the rpm at which the engine develops the needed horsepower for the mowing. I prefer the highest speed setting possible for required power and engine cooling. Lugging the engine with a mower deck load is an engine killer.
Lower the ground speed by placing in a lower gear, but keep those rpms up the for best blade speed.
BTW, try Redline 10W40 or Schaeffer's 15W40 #700. Those moly oils seem to run cooler during those hot summer days.
[ May 20, 2003, 12:13 PM: Message edited by: MolaKule ]
MolaKule
Staff member
I believe any 0W40 to 15W40 protects better and smooths the engine out during those hot days of summer better than do straight 30 weights.
And straight 30 weights are an old mechanics tale, IMHO. Multigrades provide better oil control and longer running time than do straight weights.
I would never run those " water weights " in air-coolded, outdoor power equipment.
Looking at it another way, have you ever seen a motorocycle oil manufacturer spec an oil for their air-colded engines with less than 10W40?
BTW, in my experience, a 50 weight is much too thick for outdoor, air-coolded power equipment engines.
[ May 22, 2003, 05:30 PM: Message edited by: MolaKule ]
And straight 30 weights are an old mechanics tale, IMHO. Multigrades provide better oil control and longer running time than do straight weights.
I would never run those " water weights " in air-coolded, outdoor power equipment.
Looking at it another way, have you ever seen a motorocycle oil manufacturer spec an oil for their air-colded engines with less than 10W40?
BTW, in my experience, a 50 weight is much too thick for outdoor, air-coolded power equipment engines.
[ May 22, 2003, 05:30 PM: Message edited by: MolaKule ]
Molakule, so you'd recommend Red Line 10w40 where the mfr recommends SAE30? Seems kinda thick?
I was actually considering trying 0w20 Mobil 1 if it ever comes out. Since my motor bogs slightly on some thick sections. Running Mobil 1 10w30 now.
I figure since mower engines last forever with reasonable maintence on petro oil... a 20wt syn won't be much worse. I can live with 15yrs of life vs 30yrs. Especially on this cheapo mower.
I was actually considering trying 0w20 Mobil 1 if it ever comes out. Since my motor bogs slightly on some thick sections. Running Mobil 1 10w30 now.
I figure since mower engines last forever with reasonable maintence on petro oil... a 20wt syn won't be much worse. I can live with 15yrs of life vs 30yrs. Especially on this cheapo mower.
I'm another fan of 15W40 as a great choice for most outdoor lawn & garden equipment. I have to qualify this, however, that I am not concerned with low-temp starting. Anything I have to run during the winter months is in a heated garage (50F at worst).
And since I run such a good oil, I've been considering running even higher RPMs are 'Kule suggests. I usually fire up the tractor (mine's a 18hp twin-cylinder, liquid cooled OHC Honda), let it warm up for 30 seconds and then go wide open with the throttle. Engage the auger (42" 3-blade deck) and then back off the throttle about 5% or so by pulling it back 1/8" from the WOT position. Just enough to hear a change in engine note.
But now, I'm thinking of just leaving it at WOT. Using Schaeffer 15W40 synthetic blend, I shouldn't be worried about top end wear from RPMs but instead lugging going up hills with the auger engaged.
Running less than 60-70 hours in a typical year, I'm pretty sure I won't be shearing this stuff down.
--- Bror Jace
And since I run such a good oil, I've been considering running even higher RPMs are 'Kule suggests. I usually fire up the tractor (mine's a 18hp twin-cylinder, liquid cooled OHC Honda), let it warm up for 30 seconds and then go wide open with the throttle. Engage the auger (42" 3-blade deck) and then back off the throttle about 5% or so by pulling it back 1/8" from the WOT position. Just enough to hear a change in engine note.
But now, I'm thinking of just leaving it at WOT. Using Schaeffer 15W40 synthetic blend, I shouldn't be worried about top end wear from RPMs but instead lugging going up hills with the auger engaged.
Running less than 60-70 hours in a typical year, I'm pretty sure I won't be shearing this stuff down.
--- Bror Jace
molakule, my friend did commercal yard cutting for 20 years with an old cub cadet riding mower, he ran the engine at idle the entire time, and that engine still runs great today
this is in south florida heat mind you.
the trick to avoid pulling grass is to keep your blades sharp.
this is in south florida heat mind you.
the trick to avoid pulling grass is to keep your blades sharp.
MolaKule
Staff member
Keeping the blades sharp AND running at max governed RPM is the way to keep grass cut like the golf courses do. I assumed keeping a sharp blade is one of those things any person with a mower is going to do as part of preventative maintenance.
All I can say Crypto, is that this guy must not have mowed at the speeds modern riding momers are capable of moving. AT idle, most modern decks will kill the engine RPM, pronto.
[ May 26, 2003, 11:35 PM: Message edited by: MolaKule ]
All I can say Crypto, is that this guy must not have mowed at the speeds modern riding momers are capable of moving. AT idle, most modern decks will kill the engine RPM, pronto.
[ May 26, 2003, 11:35 PM: Message edited by: MolaKule ]
i have been mowing my 1 acre yard for the last 4 years at idle with a 4 year old riding mower.
she still has factory spec compression.
i think perhaps, if your cutting through high grass or somthing and the engine starts to lug then damage could be done. but i dont let my grass get out of hand.
you can tell when it lugs because you can "feel" each power stroke. like its workin hard.
as to my friends mower top speed, maybe ur right and its slower than modern ones. well see how mine is in 16 years i guess.
she still has factory spec compression.
i think perhaps, if your cutting through high grass or somthing and the engine starts to lug then damage could be done. but i dont let my grass get out of hand.
you can tell when it lugs because you can "feel" each power stroke. like its workin hard.
as to my friends mower top speed, maybe ur right and its slower than modern ones. well see how mine is in 16 years i guess.
MolaKule
Staff member
None of my Sears or MTD mowers, with 16 HP B&S and 20HP Kohler engines respectively, will keep running at idle RPM with the deck engaged, much less move forward. The idle RPM on both mowers is about 500 RPM. On both mowers, the engine drive pulley diameter is the same diameter as the deck pulleys, so these mowers were designed for max engine RPM and blade RPM. The detented RPM is 2,550-2,800 RPM. On a hot day in mid-summer, the 10W40 weight Redline or 15W40 Schaeffer's are as smooth as silk, not watery like the other synthetics or blends I have tried.
The Sears unit has a 42" deck, the MTD has a 44" deck. The Sears will outrun and outmow the MTD any day, which is why I let HER use the MTD.
[ May 27, 2003, 03:40 PM: Message edited by: MolaKule ]
The Sears unit has a 42" deck, the MTD has a 44" deck. The Sears will outrun and outmow the MTD any day, which is why I let HER use the MTD.
[ May 27, 2003, 03:40 PM: Message edited by: MolaKule ]
its totaly overkill to use redline oil is a lawnmower. probably schaffers as well.
oh that reminds me, my friend with the 20 year cub kadet, he used generic oil that whole time! 20w50 mind you.
oh that reminds me, my friend with the 20 year cub kadet, he used generic oil that whole time! 20w50 mind you.
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