How do you guys measure RPMs? - Snowblower Forum : Snow Blower Forums
 
LinkBack Thread Tools
post #1 of 8 Old 12-13-2016, 09:36 AM Thread Starter
Senior Member
 
Join Date: Mar 2015
Location: NY
Posts: 173
Post Thanks / Like
Thanks (Given): 16
Thanks (Received): 3
Likes (Given): 9
Likes (Received): 10
How do you guys measure RPMs?

Having re-assembled some linkages on my old Tecumseh HM80, I wanted to check that I'm getting a proper 3600 rpm at full throttle. Is there any backyard mechanic way of measuring rpms on an engine with the old magneto ignition?

I don't have a timing light, but I do have a good multimeter.

My machine:
1979 Ariens 924039 (24", 8hp w/ differential)
Stang is offline  
Sponsored Links
Advertisement
 
post #2 of 8 Old 12-13-2016, 09:42 AM
Senior Member
 
bad69cat's Avatar
 
Join Date: Nov 2015
Location: Cedar Rapids, Iowa
Posts: 1,237
Post Thanks / Like
Thanks (Given): 0
Thanks (Received): 88
Likes (Given): 127
Likes (Received): 277






I am deathly allergic to shovels!


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
bad69cat is offline  
post #3 of 8 Old 12-13-2016, 12:26 PM
Senior Member
 
Join Date: Jan 2016
Location: Central NH
Posts: 352
Post Thanks / Like
Thanks (Given): 17
Thanks (Received): 20
Likes (Given): 103
Likes (Received): 73
Remove sparkplug. Remove belt cover.Lock down the lever that engages the impeller/auger.

Note/mark the starting position of the auger and the engine pulley and count how many times the engine turns over for one full revolution of the auger.Note this ratio.

Note/mark starting position of auger.Safely start blower-get it up to full throttle.Engage auger for 1 minute(timed) and count revolutions.Do the math.

This would be much easier with two people.

A cheap digital tach would be even easier.
Mike C. is offline  
Post Thanks / Like - 0 Thanks, 1 Likes, 0 Dislikes
Likes Toro-8-2-4 liked this post
post #4 of 8 Old 12-13-2016, 12:45 PM
Senior Member
 
Join Date: Jan 2016
Location: Central NH
Posts: 352
Post Thanks / Like
Thanks (Given): 17
Thanks (Received): 20
Likes (Given): 103
Likes (Received): 73
Quote:
Originally Posted by Stang View Post
......

I don't have a timing light, but I do have a good multimeter.
I was able to check the accuracy of my analog(needle type) tachometer recently by using my Fluke digital multimeter and a portable generator.

My generator is governed to run at 3600 RPMs so that the frequency of the ac produced will be 60 cycles-like house current.

The Fluke can measure ac frequency very accurately(.1%).So I started the generator and tweaked the governor to get the frequency exactly on 60 Hz.Then I measured the engine RPMs with the analog tachometer and found that it reads under by about 150 RPMs .I'll bet even a cheaper digital tach is more accurate.
Mike C. is offline  
post #5 of 8 Old 12-13-2016, 12:54 PM
Senior Member
 
db130's Avatar
 
Join Date: Feb 2013
Location: MA
Posts: 722
Post Thanks / Like
Thanks (Given): 15
Thanks (Received): 64
Likes (Given): 204
Likes (Received): 139
You can buy a Treysit sirometer on ebay... or there are several Android and Apple tachometer apps

Here's one:

https://play.google.com/store/apps/d...rpmgauge&hl=en


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by db130; 12-13-2016 at 12:58 PM.
db130 is offline  
post #6 of 8 Old 12-13-2016, 07:12 PM
Banned
 
Join Date: Nov 2016
Location: Glastonbury, CT
Posts: 474
Post Thanks / Like
Thanks (Given): 5
Thanks (Received): 33
Likes (Given): 28
Likes (Received): 68
I use a hand held mechanical tachometer which reads RPM of any rotating shaft.
DriverRider is offline  
post #7 of 8 Old 12-13-2016, 10:07 PM
Senior Member
 
Motor City's Avatar
 
Join Date: Jan 2014
Location: SE Michigan
Posts: 637
Post Thanks / Like
Thanks (Given): 0
Thanks (Received): 44
Likes (Given): 0
Likes (Received): 50
Their are some cheap Inductive Tachs on Amazon.




Ariens ST11528LE
Honda HS720
Motor City is offline  
post #8 of 8 Old 12-15-2016, 08:25 PM Thread Starter
Senior Member
 
Join Date: Mar 2015
Location: NY
Posts: 173
Post Thanks / Like
Thanks (Given): 16
Thanks (Received): 3
Likes (Given): 9
Likes (Received): 10
Great suggestions, guys. Thanks!

My machine:
1979 Ariens 924039 (24", 8hp w/ differential)
Stang is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Snowblower Forum : Snow Blower Forums 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










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may 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