TC45D tach calibration

[Jerry/MT]

PM,

What are the numbers you got, such as Engine rpm vs PTO rpm. For example at about 2500 rpm for the engine I should expect to get 450 rpm at the pto. Do you get numbers like that? What PTO rpm do you get or expect to get. The relationship between engine rpm and PTO might not be linear or in straight line. What that means is if the relationship was linear the following could be expected. Let's say @ 1000 engine rpm you got 300 pto rpm and at 2000 engine rpm you got 500 pto rpm then you should expect for sure to get 400 rpm right at engine 1500 rpm. You need to look at your Owner's Manual and if it says for example 540 pto rpm at 2600 engine rpm then that's where you need to run your tractor at.

You can monitor your pto with your optical tach, keep increasing or decreasing your engine till you reach 540 and that's where you need to run the engine at. If that does not appear to be severely overramping the engine, then I stick to it for pto driven operation.

JC,

"The relationship between engine rpm and PTO might not be linear or in straight line."


I'm curious as to why you say that the the relationship between engine speed and pto ispeed would be non-linear. To my way of thinking they just different by a fixed gear ratio?

The tach itself maybe behaving in a non-linear fashion but if there is a fixed ratio between pto speed and engine speed it wil be linear.

 

[Jerry/MT]

PM,

What are the numbers you got, such as Engine rpm vs PTO rpm. For example at about 2500 rpm for the engine I should expect to get 450 rpm at the pto. Do you get numbers like that? What PTO rpm do you get or expect to get. The relationship between engine rpm and PTO might not be linear or in straight line. What that means is if the relationship was linear the following could be expected. Let's say @ 1000 engine rpm you got 300 pto rpm and at 2000 engine rpm you got 500 pto rpm then you should expect for sure to get 400 rpm right at engine 1500 rpm. You need to look at your Owner's Manual and if it says for example 540 pto rpm at 2600 engine rpm then that's where you need to run your tractor at.

You can monitor your pto with your optical tach, keep increasing or decreasing your engine till you reach 540 and that's where you need to run the engine at. If that does not appear to be severely overramping the engine, then I stick to it for pto driven operation.

JC,

"The relationship between engine rpm and PTO might not be linear or in straight line."


I'm curious as to why you say that the the relationship between engine speed and pto ispeed would be non-linear. To my way of thinking they just different by a fixed gear ratio?

The tach itself maybe behaving in a non-linear fashion but if there is a fixed ratio between pto speed and engine speed it wil be linear if you independently measure those speeds. The only possibility that I could for non-linear speed realtionship between engine speed and pto speed is if it were an independent pto and the clutch were slipping. If that were the case the clutch would soon wear and fail to tranmit much torque.

 

[JC-jetro]

"The relationship between engine rpm and PTO might not be linear or in straight line."


I'm curious as to why you say that the the relationship between engine speed and pto ispeed would be non-linear. To my way of thinking they just different by a fixed gear ratio?

The tach itself maybe behaving in a non-linear fashion but if there is a fixed ratio between pto speed and engine speed it wil be linear.

Jerry,

The only reason I said it was because I was not sure. Now if I had some time and were very curious then I would have taken my strobe light, started engine , raised rpm 100 at a time and recorded PTO rpm accordingly. I could have then plotted the engine rpm vs pto rpm to see if it were linear or not. I might not have shared the data as I would be branded as a nerdy engineer with his calculator at work The gearing ratio will change the slope of the curve.

JC,

Your idea of clutch slippage to make it non linear is perfectly plausible.

 

[JC-jetro]

JC, I just looked at the needle in one of my photos and it seems to have a wide area around the pin that could help pull it off. The proper way to get it right would be to remove the needle and then power up the tach with the ignition key. While the tach is powered, place the needle on the pin with it pointing toward zero. Let it stay powered until the glue dries if glue is needed. If it feels firm without glue, turn the power off and the needle will move down to the lower stop peg. Power the tach on/off a few times to make sure the needle is going to stay put and then try it with the engine running to see if it has not improved. It won't be 100% accurate, but it won't have a 500 rpm offset either.

Jim,

I have seen some meter with a small calibration screw to move the needle while in operation to calibrate it against a known standard value. Do yo have any calibration screw on your tractor's tach?

JC,

 

[Professor Marvel]

Thanks guys. I will try to take the tach out of the cluster and check further. My shop manual tells me to ohm out the 4 terminals to see if it is bad. If it is I would rather not buy a whole new cluster.
I will do further investigation as you suggest with the needle as well and get back to you.

 

[Professor Marvel]

I might need to adjust my throttle stops so it can rev up more and see if the pto light comes on. It does not right now but the tach only goes to 3k which if 500 off would still not be high enough if pto speed is 2600 rpm. I just did not feel comfortable running the engine speed up past what appears to be red line.

 

[Professor Marvel]

Is the pto light looking at the tach or is it using something else to make its decision?

 

[Jerry/MT]

Jerry,

The only reason I said it was because I was not sure. Now if I had some time and were very curious then I would have taken my strobe light, started engine , raised rpm 100 at a time and recorded PTO rpm accordingly. I could have then plotted the engine rpm vs pto rpm to see if it were linear or not. I might not have shared the data as I would be branded as a nerdy engineer with his calculator at work The gearing ratio will change the slope of the curve.

JC,

Your idea of clutch slippage to make it non linear is perfectly plausible.

Usually the pto/engine speed ratio ratio is either given in the owners manual or can be deduced from info in the owners manual ie "540 pto rpm occurs at 1800 engine rpm " implies the speed ratio of 0.3 Npto/N engine. Often times the tach is marked and you can figure out the ratio.
My point was I've never heard of a non linear variation in pto speed being designed into a pto drive system on an ag tractor. Not saying I heard it all. Just saying I've never seen anything other than a linear relationship.

Another nerdy engineer !

 

[JC-jetro]

. Not saying I heard it all. Just saying I've never seen anything other than a linear relationship.

Another nerdy engineer !

Same here Jerry. I can imagine a CVT that has variable pto design .. can't imagine why.

JC,

 

[jinman]

Jim,

I have seen some meter with a small calibration screw to move the needle while in operation to calibrate it against a known standard value. Do yo have any calibration screw on your tractor's tach?

JC,

Gotta bust your chops a bit here, JC. If that tach had an adjustment and I knew about it, do you think I'd have waited until you asked to tell PF about it?:laughing: No sir! No tach adjustment that I know of.:confused3:

Professor Marvel: If you look on the back of the instrument panel, it has a tiny adjustment screw. That's for the 540 RPM light. Your Repair Manual should cover its adjustment.