tachometer check

   / tachometer check #1  

winston1

Super Member
Joined
Dec 16, 2009
Messages
5,462
Location
gilmer tx
Tractor
Bobcat CT235
This may be a lot of blah blah blah to some but not forced reading. I've always wanted one of these digital tachometers so finally bought a $26 model at Harbor Freight. First thing I did was check it out on our 2009 RAV4 and also on my old 97 GMC. The digital reads in tenths but of course the auto tachs don't read that close. Anyway, as close as I could tell the digital tach was right on with the auto tachs. Now to the reason I actually bought it. The operation manual for my ym2002d states on specification page that my pto is 540rpm @ 2200rpm, 2nd range 1000 @ 2200 rpm, 3rd range appx engine speed. First off, my mechanical tach starts off being 37rpm fast at 700 rpm and ends up being 190rpm fast @2600 rpm. I guess a 30 year old tack deserves to be a little wrong. The big thing I found tho was 540 pto rpm @ 2360 rpm, 2nd range 756rpm @ 2360 rpm, 3rd range 1057 @ 2360 rpm. After having read thru some of these forums and other places I see other model Yanmars with speeds close to mine. I would like to think I could trust my owners manual but evidently not. My ym2002d is a vn polish job so it may be some of the pto gearing is not original. I'm more happy with the speeds I've discovered because I have been guilty of finish mowing in 2nd range @ 1800rpm on the mechanical tach which on the digital tach is only 1667 rpm which equals 540 pto rpm. Right on recommeded mower speed. :)
 
   / tachometer check #2  
Makes sense to me!
Part of my initial renovation when I bought my first used Yanmar was to get out my little 1970's Briggs & Stratton mechanical tach
19200-th.jpg
and verify the tractor's tachometer. This B&S tach has a wire that you extend out gradually until it resonates in harmony with the engine vibration. The Yanmar tach checked out fine. I didn't think to measure the PTO since it is a direct mechanical connection.

I need to do this on the little YM186D I bought last summer. It's tach shrieked and pegged, obviously rusted between the spinning magnet and the needle, so I had planned to replace it. But now with some hours on it it has calmed down so I'll keep it in service for a while. I really should go verify it with the B&S unit.
 
   / tachometer check #3  
This may be a lot of blah blah blah to some but not forced reading. I've always wanted one of these digital tachometers so finally bought a $26 model at Harbor Freight. First thing I did was check it out on our 2009 RAV4 and also on my old 97 GMC. The digital reads in tenths but of course the auto tachs don't read that close. Anyway, as close as I could tell the digital tach was right on with the auto tachs. Now to the reason I actually bought it. The operation manual for my ym2002d states on specification page that my pto is 540rpm @ 2200rpm, 2nd range 1000 @ 2200 rpm, 3rd range appx engine speed. First off, my mechanical tach starts off being 37rpm fast at 700 rpm and ends up being 190rpm fast @2600 rpm. I guess a 30 year old tack deserves to be a little wrong. The big thing I found tho was 540 pto rpm @ 2360 rpm, 2nd range 756rpm @ 2360 rpm, 3rd range 1057 @ 2360 rpm. After having read thru some of these forums and other places I see other model Yanmars with speeds close to mine. I would like to think I could trust my owners manual but evidently not. My ym2002d is a vn polish job so it may be some of the pto gearing is not original. I'm more happy with the speeds I've discovered because I have been guilty of finish mowing in 2nd range @ 1800rpm on the mechanical tach which on the digital tach is only 1667 rpm which equals 540 pto rpm. Right on recommeded mower speed. :)

YM2002D PTO
1st 550
2nd 784
3rd 1096

Danny
 
   / tachometer check
  • Thread Starter
#4  
Danny, is that at 2400 rpm? Thanks
 
   / tachometer check #5  
Is that a strobe type tachometer? You can check its accuracy by the shaft on a synchronous electric motor.
 
   / tachometer check
  • Thread Starter
#6  
Is that a strobe type tachometer? You can check its accuracy by the shaft on a synchronous electric motor.

Yes it is a strobe type. I confess my ignorance on synchronous motors. I read a little about them but can't think of any I have I could check against. I have all sorts of motors on table saws, grinders, blah blah. I read clock motors have them but a little to small for me to put a piece of reflecive tape. I did check it on some of my grinder and saw motors against the tag speed. Comes out close but not right on. Still thinking the tach probably closer than tag. Have you any suggestions about a snychrouous motor that is commonly used?
 
   / tachometer check #7  
Do these numbers actually come from Japanese, (Yanmar), operators manuals, or are they what American users have observed?
 
   / tachometer check #8  
industrial motors
Clocks
Audio turntables
ac powered tape drives
possibly vcr drives
 
   / tachometer check
  • Thread Starter
#9  
Do these numbers actually come from Japanese, (Yanmar), operators manuals, or are they what American users have observed?

Norm, I'm not sure which numbers you are talking about but the ones I posted came from the operators manual I bought when I purchased the tractor. There is no indication in the manual where it came from so therefore I don't know. I do know the pto speeds given are not correct. I think mine lines up with those given by Danny.
 
   / tachometer check #10  
Norm, I'm not sure which numbers you are talking about but the ones I posted came from the operators manual I bought when I purchased the tractor. There is no indication in the manual where it came from so therefore I don't know. I do know the pto speeds given are not correct. I think mine lines up with those given by Danny.

yep, pto rpm's. Your manual is either for a different tractor, or was probably written by Aaron, and who knows where he might have gotten the #'s from;).
 
 
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