RPM for a 22" residential push mower

GearHead36

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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.
 

GearHead36

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Ok. My balance is one of those cheap cone things. So if blade balance is the problem, I may be limited to 2900 until I get something better. However, 2950 still just seemed to be fast. I watch small engine repair videos every so often, and 2950 seems faster than any of the engines I hear on the videos.
 

7394

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Don't blow it up.
 

woodstover

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Why are you wanting to up the rpm? Do you think it's not mowing well enough?
 

GearHead36

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Why are you wanting to up the rpm? Do you think it's not mowing well enough?
I've only recently acquired a small engine tach, and I never trusted the dealer who sold the mower to me, so I wanted to adjust it "per spec". But I really couldn't find the spec. The only spec I could find is the 19000 FPM spec. Is it cutting well enough? Tough to say. I have a riding mower that cuts better. Is that because the RPMs on my push mower is too low? I don't know, but I'm interesting in finding out.
 

woodstover

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I've only recently acquired a small engine tach, and I never trusted the dealer who sold the mower to me, so I wanted to adjust it "per spec". But I really couldn't find the spec. The only spec I could find is the 19000 FPM spec. Is it cutting well enough? Tough to say. I have a riding mower that cuts better. Is that because the RPMs on my push mower is too low? I don't know, but I'm interesting in finding out.
It's 13yr old now, I would sharpen and balance the blade and not raise it more than 2900rpm. Sharp/balanced blades make all the difference. Running with an unbalanced blade just going to damage the engine. New blades are pretty cheap.
 

StarTech

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Ok. My balance is one of those cheap cone things. So if blade balance is the problem, I may be limited to 2900 until I get something better. However, 2950 still just seemed to be fast. I watch small engine repair videos every so often, and 2950 seems faster than any of the engines I hear on the videos.
Those cones usually has steps rings which poorly fit the blades so you could blade off center.

And hopefully the RPM meter is set to one count per revolution. But if the mower cuts well at 2900 rpm then just leave it at that. Usually you will have more Ft-Lb torque at the slower speed.

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bertsmobile1

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Governed engines usually run around 1000 rpm faster than peak torque
The reason for this is as the revs drop the torque increases to counter the load that is making the revs drop in the first place
So if that curve is the correct one for you engine then 2900 rpm is probably fine
What makes engine sound like they are running faster when they are not is a burned out muffler
 

kbowley

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The spec is 3100 to 3200 RPM's for a 21 or 22 walk behind. Those cone balancers are useless. Simply drive a large nail in the wall and wipe a bit of grease on it to balance. If it is a star hole, simply place a similar sized socket in the blade hole to balance. Balance is important on the long blades; even new blades are off many times. I simply grind a groove on the lift/back side of the blade to balance. I have a busy outdoor power equipment shop and use the this tool to balance. You simply can't beat one of these tachometers for small engines.
 
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