Question(s) About Tractor Hours??

My David Brown has on the Tractormeter that hours are calculated @ 14** rpm per hour. I looked @ an MF135 today that had hours @ 18** rpm per hour. First question, why are hours figured @ different rpms? How do the manufacturers/engineers arrive @ these #'s. Lastly, wouldn't 1,000 hours @ 18** rpm mean that tractor has been run harder than one w/ 1,000 hours @ 14** rpms?
 
Generally with mechanical
tachs hours are at PTO rpms,
so the count up faster at full
throttle and slower at idle.
That is why modern tractors
with electrical tachs get more
hours, they count the same
regardless.
 
In addition to below info,Hour meters are only good for the original owner to keep track of oil changes. Hour meters break and get replaced all the time. New meters start off at 0 hours. You can't use them to compare wear and tear.
 
The engine hour equals a clock hour at the rated tach speed; hours accrue slower below rated speed and faster above rated speed. In reality it is a crank rpm totalizer. An engine hour is typically aligned at PTO speed which is aligned at the engine torque peak.

Engine life dependent on care and % load. As I think about it, holistically engine life is defined by the amount of total fuel burned. Running at full load, rated speed and 50% load rated speed should in theory yield a longer life. Hang a turbo on it and run at 1XX load, shorter life. Not all engine hours are equal.
 
A mechanical tach measures RPM hours where a modern electric tach measures clock hours. Are you more confused now? LOL
 
Most older tractors were that way, it gives the owner a good idea of how much work the tractor has done. If it was running an
auger with the PTO at idle for many hours it doesn't have the wear as if it was pulling a large tillage implement at full
throttle.
 
All depends on the mfr's "rated" engine RPM for accumulating hours. We had a Farmall 450 with a rated RPM of 1620 RPM. And an Oliver 1850 rated at 2300. And if memory serves the John Deere 830 is rated at something around 1,100 RPM

Also......we had a Brockway farm dump with a Cummins 855 diesel. Beneath the totalizer window on the tach face was printed "ENGINE REVOLUTIONS x 100,000" - no mention of hours whatsoever.
 
the 1412 rpm figure on DBs is the speed that engineers in England figured as an average engine speed for a multi purpose tractor 60 plus years ago...

PTO speed has nothing to do with it.
 
Ford calculated the "hours" based on 540
pto speed. Like say if your 540 pto
speed is 1800 rpms the tach would accrue
1 hour for each hour it ran at 1800.
If you ran it at 900 rpms it would take
2 hours of run time to put one hour on
the tach.
The "clock" really has nothing to do
with time. It has to do with total rpms.
You could compute the total Rpms on the
tractor. But not the number of hours it
ran.
 
Can't help with your DB, but my F-2000 Kubota came with a tach driven hour meter. I bought it used with about 600
hours on it. I change the oil every 50 hours and I wasn't sure how accurate the meter was so I added a digital meter
that runs off the ignition switch. Most of my work with the machine is either cutting grass or blowing snow, so, at
full throttle. After 1000 hours, the difference between the 2 meters is about 12 hours (digital higher).
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