Correct Engine RPM, set? - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
Walk Behind Mowers We all use them from time to time... no seats on them.. but they get the job done!!!

 
Thread Tools Display Modes
post #1 of 6 Old 07-19-2006, 10:31 AM Thread Starter
2000 Posts and climbing!!!

 
jerry_nj's Avatar
 
Join Date: Dec 2005
Location: NJ
Posts: 2,104
Images: 1
Correct Engine RPM, set?

I have a Sears 6.5 B&S 22" push mower that I run in the mulch mode most of the time.

It came with an OEM mulch blade, single blade with extra cutting surface and curves. It works ok, but I think it may work better if the engine were at a higher RPM, engine sound is the usual loud, but not very high RPM. These come factory set and I don't think one can change the RPM without making up some kind of a kludge. As noted on another thread, I replaced the OEM blade with a Viper blade and the mulching is improved. I still wonder about the RPM, is there an inexpensive ignition pick-up tachometer good for lawn equipment anyone can recommend? Then if one has a tach, what is the correct RPM, I suppose it depends on the size of the blade, higher for a 20" than for a 22".http://www.mytractorforum.com/newthr...wthread&f=155#
Biglaugh
jerry_nj is offline  
Sponsored Links
Advertisement
 
post #2 of 6 Old 07-19-2006, 11:11 AM
2000 Posts and climbing!!!

 
slipshod's Avatar
 
Join Date: Mar 2005
Location: New York
Posts: 2,468
Images: 4
Re: Correct Engine RPM, set?

If it is mulching OK why do you want to run at higher RPM's?

slipshod is offline  
post #3 of 6 Old 07-19-2006, 11:45 AM Thread Starter
2000 Posts and climbing!!!

 
jerry_nj's Avatar
 
Join Date: Dec 2005
Location: NJ
Posts: 2,104
Images: 1
Re: Correct Engine RPM, set?

Good point, low RPM, better gas mileage I suppose. Still, I'd like the mower to run at the "design" RPM. My ear says it isn't, so a tach and spec would answer the question unambiguously. I suppose larger engines may run at lower RPM. 6.5 HP is the largest walkbehind (not power driven) engine I've ever had. Then too, I wear ear protection, to protect my already damaged hearing (horse it out of the barn) and that says I hear only part of the sound the engine makes. But, I think I do hear the "tempo" of the RPM.
jerry_nj is offline  
post #4 of 6 Old 07-19-2006, 02:09 PM
2000 Posts and climbing!!!
 
Join Date: Apr 2006
Location: Whitley Co. Indiana
Posts: 2,399
Re: Correct Engine RPM, set?

Jerry,
All push mowers have the engine speed set by the blade tip speed, not the top goverend speed . Somewhere, I have a chart that shows the maximum tip speed for all blades up to 30" . I got it from a Briggs field tech about 10 years ago. You can get a small tach called a Vibra Tach at most small engine shops.
Dave
DLF_IN is offline  
post #5 of 6 Old 07-19-2006, 08:14 PM
Lawn Mower Fan
 
Jason's Avatar
 
Join Date: Jun 2006
Location: Fayetteville, NC
Posts: 681
Re: Correct Engine RPM, set?

Blade tip speeds are federally-regulated to 19,000 feet per minute.

Cheers,
Jason

'87 Lawn-Boy Supreme 8157 (L-B F)
'94 Craftsman 3-n-1 (Honda GCV160)
'95 Lawn-Boy Silver 10301 (engineless)
'99 Lawn-Boy Silver 10330 (Tec LEV100)

'01 Honda Masters HR215SXA (GXV140)
Jason is offline  
post #6 of 6 Old 07-19-2006, 10:53 PM Thread Starter
2000 Posts and climbing!!!

 
jerry_nj's Avatar
 
Join Date: Dec 2005
Location: NJ
Posts: 2,104
Images: 1
Re: Correct Engine RPM, set?

Yes, I have understood that manufacturers have to limit blade tip speed, and it is lower for residential than for commercial machines. As residential lawn mowers are all direct drive, that is the blade is directly attached to the crankshaft there is a simple relationship between the RPM and tip speed. Let's see I if I can do the math:

2"pi"R (R = Radius, is 11" for a 22" mower) is the Circumference, is 69 Inches. and if limited to 19K feet per minute, or 209K inches per minute, I get RPM(max)=209,000/69 = about 3,000 RPM, hum if I didn't make a mistake, this sound a bit high. Well, as I compute it I'd not want the engine to run higher than 3K RPM, still need a tach to find the RPM.
jerry_nj is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome