I realize that this post is a bit off topic but still perhaps it can still be lubrication related. I have a Craftsman lawn tractor with a 17 (I think)hp Kohler engine which I purchased last spring. The owners' manual says that the speed control should be placed at a specific detent when mowing. Well it seems to me to have the RPMs unnecessarily high when running at this pre-set speed. I have always been of the opinion that a 4-cycle engine will last longer and give better service if it is not run faster than necessary to perform the task at hand. Does anyone know any specific reason that I should not bring down the speed as long as the mower does not bog down and the quality of cut is satisfactory?
Mower Engine Speed
- Thread starter thiggy
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1 People are free to ignore stuff they don't think should be here.
2 My first thought was to somehow keep the EPA happy. Could it be there is a specific RPM where the vibrations cancel our and it rune smoother? If so, how accurate is the detent? Maybe on your specific mower, the detent is on the high side. Unless somebody comes up with a good reason why, I would run it where it seems to do a good job.
2 My first thought was to somehow keep the EPA happy. Could it be there is a specific RPM where the vibrations cancel our and it rune smoother? If so, how accurate is the detent? Maybe on your specific mower, the detent is on the high side. Unless somebody comes up with a good reason why, I would run it where it seems to do a good job.
thiggy, I think they are weighing higher-RPMs (usually associated with accelerated wear ... for good reason) with the bottom-end wear associated with over-burdening an engine at lower speeds.
If you use a good oil changed regularly, you are better off running the engine a little on the fast side. If you poke around and explore tractor/mowing related topics here, you'll find that most of us feel these 4-stroke engines will long outlast the rest of the typical lawn & garden machine its installed in ... even when somewhat abused.
Do a search using the word "mowing" and/or "mower speed" and you'll pull up a few relevant threads.
--- Bror Jace
If you use a good oil changed regularly, you are better off running the engine a little on the fast side. If you poke around and explore tractor/mowing related topics here, you'll find that most of us feel these 4-stroke engines will long outlast the rest of the typical lawn & garden machine its installed in ... even when somewhat abused.
Do a search using the word "mowing" and/or "mower speed" and you'll pull up a few relevant threads.
--- Bror Jace
Well, I disagree. I believe that if the engine load is low, such as cutting thin grass, lower RPM will result in less engine wear. There are 2 factors to consider. The first is that piston rings have a limited life in terms of distance traveled. The higher the RPM the more distance the rings travel for a given time period.
The second is the bearing load. The bearing load due to the reciprocating action of the piston is far greater than the combustion loads. This is especially true at higher RPM's. Remember, the piston is moving at a high rate of speed and must come to a full stop at TDC and BDC. The bearing loads required to decelerate the piston to a stop are very high indeed at high RPM.
If your engine has pressure lubrication and you use quality oil of the proper viscosity, I see no reason to run the engine at a higher RPM than necessary. Doing so can only reduce engine life.
Chris
The second is the bearing load. The bearing load due to the reciprocating action of the piston is far greater than the combustion loads. This is especially true at higher RPM's. Remember, the piston is moving at a high rate of speed and must come to a full stop at TDC and BDC. The bearing loads required to decelerate the piston to a stop are very high indeed at high RPM.
If your engine has pressure lubrication and you use quality oil of the proper viscosity, I see no reason to run the engine at a higher RPM than necessary. Doing so can only reduce engine life.
Chris
I'm w/MolaKule on this one. I have a riding mower, Husq w/15hp Kawasaki v-twin and I think the manual states that the detent is 3600 rpm. This may not be as important with push mowers but my engine not only has to spin 2 blades (42 inch cut) but it also has to run the hydrostat trans. You can tell that it works hard if you move the speed control too low. I think my brother's toro push mower came w/o a speed control. When he asked the shop why, they stated that warranty issues arise because people aren't running them at high enough throttle. The lugging will hurt an engine way before running them at full speed will. They are designed to run a certain rpm and that's where they should run. IMO. YMMV.
MolaKule
Staff member
Cujet,
Your engine load will actually be higher at low rpms. Running an engine at lower than required rpms is very similar to lugging an engine, and is detrimental.
1. Let's say the detent is for 2,800 rpm. This is most likely the most efficient rpm point at which the engine produces the best Hp and Torque.
2. Engine cooling is better at higher rpms.
3. The manufacturer has designed the deck pulleys (we've discussed this before) to have a 1:1 or almost 1:1 ratio of the engine pulley to deck pulleys. They want the blades to also spin at 2,800 rpm in order to cut the grass sharply and not leave the grass looking like it was eaten by goats.
In this case, higher rpms is better and there is no advantage to lugging a single cylinder or twin; in fact, low rpms can cause overheating and higher loads resulting in greater wear.
[ October 03, 2003, 12:35 PM: Message edited by: MolaKule ]
Your engine load will actually be higher at low rpms. Running an engine at lower than required rpms is very similar to lugging an engine, and is detrimental.
1. Let's say the detent is for 2,800 rpm. This is most likely the most efficient rpm point at which the engine produces the best Hp and Torque.
2. Engine cooling is better at higher rpms.
3. The manufacturer has designed the deck pulleys (we've discussed this before) to have a 1:1 or almost 1:1 ratio of the engine pulley to deck pulleys. They want the blades to also spin at 2,800 rpm in order to cut the grass sharply and not leave the grass looking like it was eaten by goats.
In this case, higher rpms is better and there is no advantage to lugging a single cylinder or twin; in fact, low rpms can cause overheating and higher loads resulting in greater wear.
[ October 03, 2003, 12:35 PM: Message edited by: MolaKule ]
Yes, 3600 RPM is the common standard speed. However if you look in most engine manufacturers data, The dyno chart generally has a window that shows maximum continuous operation. You will notice that the window extends well down into low RPM and high load conditions. However that window often does not extend up to 3600 RPM for non generator engines.
In addition, I was conditional in my lower RPM statement. The conditions were that the load on the engine must be low. As such, no lugging would occur. I still suggest running lawn equipment engines at the RPM necessary to get the job done smoothly, 2800 comes to mind. No lugging there! To suggest that the engine would be lugging at low load and slightly lower than 3600RPM is absurd. Stop making people worry for nothing.
To run an engine at a higher than necessary RPM is a waste.
Do you drive your car in a lower gear and the resulting higher RPM than necessary? What is the difference between the car engine internals and the lawn equipment engine?
Chris
In addition, I was conditional in my lower RPM statement. The conditions were that the load on the engine must be low. As such, no lugging would occur. I still suggest running lawn equipment engines at the RPM necessary to get the job done smoothly, 2800 comes to mind. No lugging there! To suggest that the engine would be lugging at low load and slightly lower than 3600RPM is absurd. Stop making people worry for nothing.
To run an engine at a higher than necessary RPM is a waste.
Do you drive your car in a lower gear and the resulting higher RPM than necessary? What is the difference between the car engine internals and the lawn equipment engine?
Chris
I have never really known but I have figured it would be better to run at full RPM so the engine will be makeing full horsepower while mowing. It is interesting to read the cooling is best at full rpm also.
I usually cool my riding mower for a minute or so before shutting it off. I have been using a idle speed with the blades disengaged and wondering if it would be better cooled by using a faster speed or maybe full speed? With water cooled engines it seems idle would be best but I have wondered about air cooled engines.
I hope this is still on topic.
[ October 04, 2003, 11:28 PM: Message edited by: White 03 ]
I usually cool my riding mower for a minute or so before shutting it off. I have been using a idle speed with the blades disengaged and wondering if it would be better cooled by using a faster speed or maybe full speed? With water cooled engines it seems idle would be best but I have wondered about air cooled engines.
I hope this is still on topic.
[ October 04, 2003, 11:28 PM: Message edited by: White 03 ]
I was once cruising back to the storage shed on
a riding mower, and I had the governor turned way
down to cut back on the vibrations. I started
to smell burning rubber. I shut off the machine,
and smoke began coming from under my seat. There
was no electrical fire (battery under seat), and
I was puzzled. Then I checked the belts, and
touched the pulley, which was scorching hot.
I suspect the flywheel was not heavy enough to
smooth out the engine at low RPM's, and the belt
started slipping from the speed variations that
happen during each cycle.
a riding mower, and I had the governor turned way
down to cut back on the vibrations. I started
to smell burning rubber. I shut off the machine,
and smoke began coming from under my seat. There
was no electrical fire (battery under seat), and
I was puzzled. Then I checked the belts, and
touched the pulley, which was scorching hot.
I suspect the flywheel was not heavy enough to
smooth out the engine at low RPM's, and the belt
started slipping from the speed variations that
happen during each cycle.
Propflux01
$100 Site Donor 2026
Air Cooled Vs. Water Cooled. If you run an Air-cooled moter that depends on cooling air from a flywheel, running at lower RPM under load both lugs the engine ( they are almost all designed for peak power at 3600PRM), and starves it of cooling air. The result? I think we all already know that. Plus remember the generator is also designed to charge at this speed.
MolaKule
Staff member
"To run an engine at a higher than necessary RPM is a waste."
We're not talking about jerryrigging the governor or running max wot, were talking about running the engine where it was designed to run for maxiumum cutting efficiency. If peak torque and hp is where the detent setting is calibrated, it is not a waste of anything. You get max battery charge as some pointed out, max cooling versus heat generation, best lubrication, best blade inertia, and best blade rpm for clean cutting.
"Do you drive your car in a lower gear and the resulting higher RPM than necessary? What is the difference between the car engine internals and the lawn equipment engine?"
Not a proper analogy.
Cujet,
Would you run a chainsaw engine at 3,000 rpm or 14,000 rpm while cutting a 12" log with an 18" chainsaw?
[ October 05, 2003, 05:56 PM: Message edited by: MolaKule ]
We're not talking about jerryrigging the governor or running max wot, were talking about running the engine where it was designed to run for maxiumum cutting efficiency. If peak torque and hp is where the detent setting is calibrated, it is not a waste of anything. You get max battery charge as some pointed out, max cooling versus heat generation, best lubrication, best blade inertia, and best blade rpm for clean cutting.
"Do you drive your car in a lower gear and the resulting higher RPM than necessary? What is the difference between the car engine internals and the lawn equipment engine?"
Not a proper analogy.
Cujet,
Would you run a chainsaw engine at 3,000 rpm or 14,000 rpm while cutting a 12" log with an 18" chainsaw?
[ October 05, 2003, 05:56 PM: Message edited by: MolaKule ]
Has any one else noticed that todays 20 hp motors dont compare favorably with older 20 hp motors. We had a simplicity growing up with a 12 hp briggs that will cut circles around the craftsman 20 hp briggs I just sold. BTW the new sears stuff is junk IMO. I had nothing but problems with this mower.
MolaKule
Staff member
I do know the older Kohlers had more torque and reserve Hp compared to the more modern engines.
I think a lot has to do with governing and pollutant output restrictions.
I think a lot has to do with governing and pollutant output restrictions.
Propflux01
$100 Site Donor 2026
there actually is some truth to this. It appears that when companies 'upped' the HP of popular engines, what they in fact did was design the camshaft to produce a higher horsepower number, but sacrificed torque in the process. this, of course, in turn lowered the actual 'power' from an engine. I do know i have a Crapsman 6HP push mower, with a Tecumseh engine and an old beater 4hp Tecumseh engine. the 4hp engine will not bog down in thicker grass anything like the 6hp will, and they are both side-valve engines. and the 4hp is 6 years older than the Crapsman. Gotta remember..HP numbers sell.
The deck and blade design can also make a big difference in the cutting power of the mower. I took a 3 hp. B&S motor off a $90 Lowe's special when the deck rotted away and put it on an old Toro deck. FYI, you can get adapters to mount just about any engine on any deck. Made a big difference in how the mower cut. The Toro had a baffled deck and a big side discharge area and cut a lot better than the cheapie deck. That old Briggs engine was tough. Ran it for over 10 years with lots of abuse and infrequent oil changes. Sold it when it was still running strong and have been running Lawnboys ever since.
You don't see professional gardeners running 6.75 HP push mowers. In my area, they are running 5.0-5.5 Hondas.
Cooling is an issue in air cooled engines run at low RPM. The belt slippage issue is valid and may also be a factor with some engines.
However, if you read the engine manufacturers instructions (they probably know best) on certain laen engines, there is a maximum output and a maximum continuous output. Often they are quite different.
So, rather than make general statements that will be untrue for certain situations, I would like to talk about specific engines. give me a specific engine and I will research the data.
Chris
However, if you read the engine manufacturers instructions (they probably know best) on certain laen engines, there is a maximum output and a maximum continuous output. Often they are quite different.
So, rather than make general statements that will be untrue for certain situations, I would like to talk about specific engines. give me a specific engine and I will research the data.
Chris
Well, I looked up the Kawasaki 17HP FH500V, a popular tractor and commercial mower engine. Kawasaki allows maximum operational output from 3600 to 2000 RPM at a high load, however, as I mentioned before, the recommended continous load (which is also 2000-3600) is at less than full throttle. The only speed that prolonged operation is prohibited is at idle due to cooling issues.
You be the judge.
Chris
You be the judge.
Chris
Likely you won't find any professionals using engines that don't say "Made in Japan" on them. They'd be replacing them every month...
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