RPM for a 22" residential push mower

[rachel11]

Good tach should have a place to select how many cylinders it is timing.

On inside of tach , it has settings for 4,6,8. I don't think they intended it for mowers . I just thought there might be a way to use it on 1 ot 2 cylinders.

 

[rhkraft]

High rpm's are hard on your engine. I have a 22inch push mower that runs slowly, maybe 2200 rpm, guessing. It cuts good, but the big plus is that I bought it new in 1990 and it is still running as good as it did 30 years ago. Of course I keep it in a shed and do annual maintenance. Keeping them out of the weather prevents most problems. I change the oil and air filter, but I never had to remove and clean the carburetor or gas tank. I did replace the rear wheels because I just wore them out. No engines are designed to run full boar all the time. As an example, my airplane has a 150 HP engine with a 7653 propeller, 76 is the diameter in inches and the 53 is inches of pitch. This means in level flight in standard conditions at 2500 rpm, the airplane moves forward 53 inches for each revolution of the prop, or 125 mph. You can do the math. The point I am making is that we firewall the engine for take-off and initial climb to clear obstacles, about 2600-2700 rpm, but as soon as the airplane clears the trees or buildings, we throttle back to 2500 rpm, normal cruise, as described by the manufacturer. Excess speed increases engine wear.

 

[7394]

I did replace the rear wheels because I just wore them out.

Cool, my 18 year old B&S Flathead 22" pusher still runs fine as well. I keep the blade sharp & it cuts beautifully.

As to the wheels, of course all 4 of mine wore out. But I bored them plastic rims out to take bushings I made & installed.. No more cheap wheels situation.

 

[GearHead36]

High rpm's are hard on your engine. <snip> Excess speed increases engine wear.

True, but... these engines are typically rated at 3600 RPMs. I used to race go-karts. We ran horizontal shaft 5HP Briggs flatheads. The governors were removed, and the stock class engines ran considerably more than 3600 RPMs. If I had to guess, I'd say around 4500RPM. But I WILL admit, running an engine like that probably wouldn't allow it to last for decades. Point is, 3200 RPM is not overstressing the engine. Will it last longer at 2200 RPM? Probably. But then again, how many of these engines die from wearing out? Almost none. They usually die from abuse and/or lack of maintenance. I watch small engine repair videos, and when a dead engine is encountered, if it's a residential engine that had been used in a residential application, it almost always died from abuse/lack of maintenance. If it's a commercial engine that had been used commercially, it could go either way. It COULD have died from wear, but it's just as likely to have died from abuse/lack of maintenance. My main riding mower is commercial that had been subjected to abuse and lack of maintenance. It had 360 hrs on it when I got it, and I'm surprised it lasted that long. I found that the cooling fins were completely blocked. I don't see how the engine didn't self destruct. There were also several broken items on it as well.

 

[Earthquake Landscaping]

This is Rumour Control...
These are the facts..
Some great posts, especially from "Toby U"..
To me, the worst thing is that a lot of newer mowers are running at reduced R.P.M., due to trying to meet emission standards. Bluntly, they don't cut well.. at all. I've had a few in where all I've done is set the governor to a higher R.P.M., and suddenly, they were cutting well, throwing the clippings properly ( either out the side chute, or into the collecting bag). Only downside to that, was that if they were self propelled ( one speed ), was that they now went significantly faster ..
As far as blade tip speed is concerned, a touch over isn't the end of the world. It's not like the blade will self destruct at a couple of hundred FPS over ANSI rating. It's like a ratchet strap tie down.. There's a difference between working load and bursting load.
Realistically, there really shouldn't be a significant increase in vibration between 2,500 R.P.M., and 3,600 R.P.M. A significant difference in vibration, points to a separate issue.. out of balance blade, bent output shaft, etc. It's like having an out of balance tire.. It may shake the car at 50 M.P.H., but not at 60 M.P.H., and then shake again at 70. It's called (IIRC), sympathetic, or harmonic vibration.
If you can't find the reason for the vibration, then just tune for the sweet spot, and be done with it.
Is it smooth.. does it cut and bag well? Walk away from the nuclear device.

 

[BWH]

Ditto here.
You can even check them for straight before wasting any time sharpening with the MM.
As far as the tachometer you bought, is it a quality piece or a Scamazon cheapie?
I would have trust issues on some knock offs.
When it comes to tools, get the best quality you can afford.
Buy once, cry once. The proven good stuff gives a lifetime of use/reliability imo.

I've used the Magna-Matic balancer for over 10 years, looking back at the price it seems like a very reasonable piece of equipment today. I also have the Magna-Matic sharpener it's great and just doing a couple dozen blades around the neighborhood eventually pays me back.

 

[bertsmobile1]

This is Rumour Control...
These are the facts..
Some great posts, especially from "Toby U"..
To me, the worst thing is that a lot of newer mowers are running at reduced R.P.M., due to trying to meet emission standards. Bluntly, they don't cut well.. at all. I've had a few in where all I've done is set the governor to a higher R.P.M., and suddenly, they were cutting well, throwing the clippings properly ( either out the side chute, or into the collecting bag). Only downside to that, was that if they were self propelled ( one speed ), was that they now went significantly faster ..
As far as blade tip speed is concerned, a touch over isn't the end of the world. It's not like the blade will self destruct at a couple of hundred FPS over ANSI rating. It's like a ratchet strap tie down.. There's a difference between working load and bursting load.
Realistically, there really shouldn't be a significant increase in vibration between 2,500 R.P.M., and 3,600 R.P.M. A significant difference in vibration, points to a separate issue.. out of balance blade, bent output shaft, etc. It's like having an out of balance tire.. It may shake the car at 50 M.P.H., but not at 60 M.P.H., and then shake again at 70. It's called (IIRC), sympathetic, or harmonic vibration.
If you can't find the reason for the vibration, then just tune for the sweet spot, and be done with it.
Is it smooth.. does it cut and bag well? Walk away from the nuclear device.

The one thing you re missing is engine balance factor
Now I have zero idea if mower engines are actually balanced at all being that modern production tollerances are such that they probably can run without dynamic balancing.
I ride single cylinder motorcycles and we go to great lengths to get a nicely balanced engine around maximum torque then we gear the bike to have it running at those revs when riding at the usual road speeds .

 

[sessman55]

I know that the blade tip speed is limited by ANSI to 19000 FPM. Which, on a 22" blade, equates to 3299RPM according to my calculator. I recently bought a tachometer, and found that my residential push mower, with a 22" blade, is running at 2750 RPM. So I started increasing it. When I got to 2950, it seemed like it was running really fast, and had a lot of vibration. So I backed it down to 2900, and the vibrations seem to get better. So my question is, of course, what speed should I set my engine to?

Engine: Briggs 128T05-5123-B.
Mower: 2011 Toro Recycler w/Personal Pace.

I still have the owner's manual and the engine manual. Neither mention engine RPM settings.

Not sure if this is the right forum, but the only other blade tip speed discussion I could find was in this forum.

I’ve set 22” blades at 3080 and 21” at 3140. Good torque and stays under the sound barrier.

 

[Sue sharpener]

I know that the blade tip speed is limited by ANSI to 19000 FPM. Which, on a 22" blade, equates to 3299RPM according to my calculator. I recently bought a tachometer, and found that my residential push mower, with a 22" blade, is running at 2750 RPM. So I started increasing it. When I got to 2950, it seemed like it was running really fast, and had a lot of vibration. So I backed it down to 2900, and the vibrations seem to get better. So my question is, of course, what speed should I set my engine to?

Engine: Briggs 128T05-5123-B.
Mower: 2011 Toro Recycler w/Personal Pace.

I still have the owner's manual and the engine manual. Neither mention engine RPM settings.

Not sure if this is the right forum, but the only other blade tip speed discussion I could find was in this forum.

You can check the engine manufacturer website. Briggs & Stratton or Techumseh has that information.

 

[ybor]

I know that the blade tip speed is limited by ANSI to 19000 FPM. Which, on a 22" blade, equates to 3299RPM according to my calculator. I recently bought a tachometer, and found that my residential push mower, with a 22" blade, is running at 2750 RPM. So I started increasing it. When I got to 2950, it seemed like it was running really fast, and had a lot of vibration. So I backed it down to 2900, and the vibrations seem to get better. So my question is, of course, what speed should I set my engine to?

Engine: Briggs 128T05-5123-B.
Mower: 2011 Toro Recycler w/Personal Pace.

I still have the owner's manual and the engine manual. Neither mention engine RPM settings.

Not sure if this is the right forum, but the only other blade tip speed discussion I could find was in this forum.

I did a lot of work in the 80's on how to cut grass efficiently. I was working on corded and cordless mowers for a large power tool and electric outdoor products company. You are correct on the 19000 FPM for max speed. We also found that dropping below 14000 FPM resulted in very poor cutting, more knocking the grass down rather than actually cutting it. As many have stated, blade sharpness and lift (suction) is also critical. Adding a little rake angle into the design also resulted in less power consumption on cordless units. Rake angle ensures the blade is slightly lower in the front of the deck versus the rear of the deck. On a push unit, this might mean setting the rear deck wheels for a slightly higher cut than the front wheels.