RPM for a 22" residential push mower

[jekjr]

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 see this discussion in numerous places. I am retired now but ran a lawn service for years. We ran Scag Tiger Cat mowers with Kawasaki engines on them primarily. When I stared cutting back on my business a few years before I completely retired I had four. I always had them set up to run 3600 RPM. I have seen them run 3500 hours plus and still be going strong running at that RPM. Set up correctly they would cut 14 day Bahia Grass all day long week in and week out. Over the years I noticed a few RPM drop would change the cut quality severely. I understand there is much debate on it but 99% of those who say differently never cut 14 day Bahia Grass.

 

[GearHead36]

I thought I'd follow up on this. I did a little more troubleshooting with my cheap cone balancer, and found that it has too much play, and can't be relied on for accurate balancing. So that leaves the Oregon and its clones, or taking my blades to a shop. Years ago, I took some blades to a "shop", which was someone's house that always had 10 or so mowers out front. He sharpened the blades, but didn't balance them. When I asked, he said that he took the same amount off each side, so they would still be balanced. Ok, Einstein... how do you know that they started out balanced? So I can't depend on someone like that for well balanced blades. And given discussions here like "My Friend got ripped off by the Dealer", I don't feel I can trust a dealer either. So if I want well balanced blades, it's up to me. The clones are hit and miss, even within the same mfr. I figured that if I balanced my blade with a clone, and the mower still vibrated, I'd suspect the balancer, and would wind up buying an Oregon anyway. So I bought the Oregon. I balanced my 22" blade, set the RPMs to 3200, and it's perfectly smooth. Well, as smooth as you'd expect from a mower engine. No excessive vibrations.

 

[ILENGINE]

I thought I'd follow up on this. I did a little more troubleshooting with my cheap cone balancer, and found that it has too much play, and can't be relied on for accurate balancing. So that leaves the Oregon and its clones, or taking my blades to a shop. Years ago, I took some blades to a "shop", which was someone's house that always had 10 or so mowers out front. He sharpened the blades, but didn't balance them. When I asked, he said that he took the same amount off each side, so they would still be balanced. Ok, Einstein... how do you know that they started out balanced? So I can't depend on someone like that for well balanced blades. And given discussions here like "My Friend got ripped off by the Dealer", I don't feel I can trust a dealer either. So if I want well balanced blades, it's up to me. The clones are hit and miss, even within the same mfr. I figured that if I balanced my blade with a clone, and the mower still vibrated, I'd suspect the balancer, and would wind up buying an Oregon anyway. So I bought the Oregon. I balanced my 22" blade, set the RPMs to 3200, and it's perfectly smooth. Well, as smooth as you'd expect from a mower engine. No excessive vibrations.

You would be surprised by the number of repair shops that don't clean blades prior to sharpening or even own a blade balancer.

 

[GearHead36]

You would be surprised by the number of repair shops that don't clean blades prior to sharpening or even own a blade balancer.

After what I've read here... I'm not sure I'd be surprised.

 

[bertsmobile1]

I see this discussion in numerous places. I am retired now but ran a lawn service for years. We ran Scag Tiger Cat mowers with Kawasaki engines on them primarily. When I stared cutting back on my business a few years before I completely retired I had four. I always had them set up to run 3600 RPM. I have seen them run 3500 hours plus and still be going strong running at that RPM. Set up correctly they would cut 14 day Bahia Grass all day long week in and week out. Over the years I noticed a few RPM drop would change the cut quality severely. I understand there is much debate on it but 99% of those who say differently never cut 14 day Bahia Grass.

When an engine is made it has a balance rpm range designed into it .
So an engine designed to run at 2750 will be balanced at 2750
But when it gets to 3600 the tiny bit out of balance at 2750 can become so chronic that the mower moves sideways
There is no such thing as an engine that is dynamically balance over the entire rev range unless it has a countershaft with a variable revolution rate .
I play with vintage motorcycles and when they were made, balance was very much trial & error off slide rule calculations .
Now days it is calculated to a very precise range and manufacturing tolerances are tight enough to keep vibrations to a minimum

 

[GearHead36]

When an engine is made it has a balance rpm range designed into it .
So an engine designed to run at 2750 will be balanced at 2750

Where is that in the spec sheet? I've never seen such a spec. The ANSI blade tip speed limit for a 22" blade puts the engine RPMs at 3299, so the optimum RPMs IMO should be near that.