Correct Engine RPM, set? - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
Register Home FAQ Garage MTF Gallery Search Today's Posts Mark Forums Read Store Chat Room

Walk Behind Mowers We all use them from time to time... no seats on them.. but they get the job done!!!

Reply
 
Thread Tools Display Modes
Old 07-19-2006, 09:31 AM   post #1 of 6
jerry_nj
2000 Posts and climbing!!!
 
jerry_nj's Avatar
 
Join Date: Dec 2005
Location: NJ
Posts: 2,060
MTF Member # 1077
Images: 1
Default 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   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 07-19-2006, 10:11 AM   post #2 of 6
slipshod
2000 Posts and climbing!!!
 
slipshod's Avatar
 
Join Date: Mar 2005
Location: New York
Posts: 2,468
MTF Member # 17
Images: 4
Default Re: Correct Engine RPM, set?

If it is mulching OK why do you want to run at higher RPM's?
__________________
slipshod is offline   Reply With Quote Quick reply to this message
Old 07-19-2006, 10:45 AM   post #3 of 6
jerry_nj
2000 Posts and climbing!!!
 
jerry_nj's Avatar
 
Join Date: Dec 2005
Location: NJ
Posts: 2,060
MTF Member # 1077
Images: 1
Default 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   Reply With Quote Quick reply to this message
Old 07-19-2006, 01:09 PM   post #4 of 6
DLF_IN
2000 Posts and climbing!!!
 
Join Date: Apr 2006
Location: Whitley Co. Indiana
Posts: 2,242
MTF Member # 1844
Default 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   Reply With Quote Quick reply to this message
Old 07-19-2006, 07:14 PM   post #5 of 6
Jason
Lawn Mower Fan
 
Jason's Avatar
 
Join Date: Jun 2006
Location: Fayetteville, NC
Posts: 664
MTF Member # 2433
Default Re: Correct Engine RPM, set?

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

'87 Lawn-Boy Supreme 8157
'95 Lawn-Boy Silver 10301
'96 Lawn-Boy Gold 10523
'99 Lawn-Boy Silver 10330

'01 Honda Masters HR215SXA
Jason is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 07-19-2006, 09:53 PM   post #6 of 6
jerry_nj
2000 Posts and climbing!!!
 
jerry_nj's Avatar
 
Join Date: Dec 2005
Location: NJ
Posts: 2,060
MTF Member # 1077
Images: 1
Default 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   Reply With Quote Quick reply to this message
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:

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
Display Modes

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

Forum Jump


All times are GMT -4. The time now is 12:46 PM.



Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.
Compact Tractor Reviews Tractor Reviews Snowblowers Lawn Mower Forum
My Tractor Forum Snow Thrower Power Equipment Forum
Combine Forum Snowblower Forum ATV and UTV Reviews