how to check true rpms
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=111168
Printed Date: 01 Sep 2025 at 5:41pm
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Topic: how to check true rpms
Posted By: screwloose
Subject: how to check true rpms
Date Posted: 29 Aug 2015 at 1:31pm
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New tach, new cable, original gears and original pulley and at idle it read 1,100 rpms, at about 3/4 throttle it read pegged. Mack told me the original pulley was worn out. He was correct. Bought a new pulley and you wouldn't believe the amount of wear on the old one now that I can compare the two. But, I still think the rpm reading is a tweak off. Idle read 800, when I rev it up to what the tach says is 1,900 rpms, 540 pto speed, the engine sounds to me like its only about half throttle lol. How can I check what the true rpms are so I can compare that to what thd tach is reading? |
Replies:
Posted By: screwloose
Date Posted: 29 Aug 2015 at 1:34pm
| Hold on a minute, I forgot something. It's a 190xtd |
Posted By: Fred in Pa
Date Posted: 29 Aug 2015 at 1:37pm
If I have a guys tractor here at my shop .I Hook the tractor to my Dyno and go by where tractor tact is reading to the PTO RPM's  ------------- He who dies with the most toys is, nonetheless ,still dead. If all else fails ,Read all that is PRINTED. |
Posted By: Brian-KS
Date Posted: 29 Aug 2015 at 1:46pm
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I have one of these I use. http://www.ebay.com/itm/like/291537322220?ul_noapp=true&chn=ps&lpid=82" rel="nofollow - http://www.ebay.com/itm/like/291537322220?ul_noapp=true&chn=ps&lpid=82 ------------- EAT BEEF! |
Posted By: screwloose
Date Posted: 29 Aug 2015 at 1:57pm
| So a dyno tells you the pto speed? |
Posted By: SHAMELESS
Date Posted: 29 Aug 2015 at 3:58pm
| hold a RPM gauge on the end of the PTO shaft....Napa sells them |
Posted By: SHAMELESS
Date Posted: 29 Aug 2015 at 4:00pm
| or with the radiator off, hold the gauge on the center of the crank pulley! |
Posted By: DrAllis
Date Posted: 29 Aug 2015 at 4:29pm
| Dynomometers all have a tachometer on them and it should be a good one, because HP rating are at a given PTO speed. Tractor tachs are generally NOT that accurate. Go by the specs in the Dyno Operation manual to have correct engine/PTO speeds. |
Posted By: 427435
Date Posted: 29 Aug 2015 at 6:14pm
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http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html" rel="nofollow - http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html ------------- Mark B10 Allis, 917 Allis, 7116 Simplicity, 7790 Simplicity Diesel, GTH-L Simplicity Ignorance is curable-----stupidity is not. |
Posted By: CALEBnOK
Date Posted: 29 Aug 2015 at 8:50pm
I use my laser tach all the time. Has a center attachment and a wheel if you put in the diameter of whatever your driving it with. I also have a caterpillar tach that uses a clip on a fuel line so you read the pulse of the injection line. Can use it the set three engines side by side at one time all by look at the gages in the box |
427435 wrote:Posted By: MACK
Date Posted: 29 Aug 2015 at 9:40pm
| 427435 has the best way to check RPMs. Can be used on any thing that turns that you can put a piece of tape on. MACK |
Posted By: wayneIA
Date Posted: 29 Aug 2015 at 9:52pm
| My M&W dyno tach is off about 40 rpm at 540, I checked it using a photo tach. Just a word of warning that you still need to know if the dyno tach is correct if you are going to use it to check your tractor rpm. |
Posted By: Lonn
Date Posted: 30 Aug 2015 at 12:45pm
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20 years ago I bought a photo tach but back then I think I paid over $100. If you get one, take the batteries out when you're not using it. Ruins your tach if you leave it too long without use and the batteries start leaking. I found out the hard way. It's on my list of things to take apart for a looksee. ------------- -- --- .... .- -- -- .- -.. / .-- .- ... / .- / -- ..- .-. -.. . .-. .. -. --. / -.-. .... .. .-.. -.. / .-. .- .--. .. ... - Wink I am a Russian Bot |