Testing 7000 series tachometer
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=193560
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Topic: Testing 7000 series tachometer
Posted By: CrestonM
Subject: Testing 7000 series tachometer
Date Posted: 16 Feb 2023 at 10:39pm
| Is there a good way to test a tachometer? I fixed some incorrect splicing in my wiring harness, and got the tachometer to work again on my 7080, it looks like it has the correct double pulley on the Delco alternator, and it was originally a Delco system from what I was told. Currently the tachometer reads my low idle rpm is 600, and high idle is 2,200. It is my understanding high idle should be more like 2,800. Is there a way to check and see if the fault is in the tachometer or if something is keeping the engine from reaching the proper high idle? |
Replies:
Posted By: 8070nc
Date Posted: 17 Feb 2023 at 3:42am
|
You can get an optical tachometer and put white reflective tape on the dampner on the front of the crankshaft and check it. I cut a piece off the white part of DOT tape like is on trucks. Works great ------------- 1984 80780 1957 D14 DES 300 with 25000 engine 616 tractor |
Posted By: Stan R
Date Posted: 17 Feb 2023 at 7:40am
| Never used it or have it, but i-phone's have an app to measure rpm's. |
Posted By: SteveM C/IL
Date Posted: 17 Feb 2023 at 7:53am
| get the optical tach.....they are cheap....ebay or amazon 2 yrs ago was $12...used it recently for first time on "new" tractor to check rpm |
Posted By: CrestonM
Date Posted: 17 Feb 2023 at 8:56am
| That sounds like a good plan! I just checked them out, got one on the way. |
Posted By: ryan(IN)
Date Posted: 17 Feb 2023 at 11:43am
|
If the pulley is the wrong diameter it will read wrong ------------- ryan 1984 8070 FWA,1979 7060,1975 7040,1971 190,1960 D-17D,1957 D-14, 196? D-19G, 1975 5040,1971? 160,1994 R62 |
Posted By: HudCo
Date Posted: 17 Feb 2023 at 8:19pm
| all the grooves in the rest of the pulleys are all worn in after all these years belts all wore in a little has to change the ratio a littlle bit |
Posted By: CrestonM
Date Posted: 21 Feb 2023 at 4:31am
You make a point. That’s one reason I don’t care for these kinds of tachometer drive systems. |
HudCo wrote:Posted By: SteveM C/IL
Date Posted: 21 Feb 2023 at 9:14am
| I wonder what kind of a nightmare it would be to try to drill,thread,mount an 8000 series pickup and wire an 8000 tach? I don't have the knowledge to do it. |
Posted By: Les Kerf
Date Posted: 21 Feb 2023 at 12:16pm
Yup. When you get your optical tach, just mark the gauge at a couple of the most important speeds. Re-check it every year or so. |
Posted By: 8070nc
Date Posted: 21 Feb 2023 at 1:30pm
|
I dont see how you could drill the plate on the ttractor. I changed the piickup on my 8070 and it was plenty tight. Im guessing theb 7 and 8000 series plates are the same execpt for the pickup hole but im not sure If you could find an 8000 series plate and change it?????????? ------------- 1984 80780 1957 D14 DES 300 with 25000 engine 616 tractor |
Posted By: SteveM C/IL
Date Posted: 21 Feb 2023 at 2:51pm
| I figured you could change location (lower?) so long as you "hit" the teeth. Yes it would be a trick to drill/tap same spot. Rt angle drill? I suppose there are some situations (pto) where you need a given rpm but most times you just gas and go!! Dad used to use the shaft tach on the WD to note position on throttle quadrant before using the all crop. Apparently wide open is more than 540? I was very young. Les has good advice. |
Posted By: AC720Man
Date Posted: 21 Feb 2023 at 9:05pm
|
Creston I can understand why you want to be correct. If we run our 390 mower/conditioner at 540 it does a much better job cutting and conditioning. A 100 or 200 rpm off and it makes a big difference on that machine. ------------- 1968 B-208, 1976 720 (2 of them)Danco brush hog, single bottom plow,52" snow thrower, belly mower,rear tine tiller, rear blade, front blade, 57"sickle bar,1983 917 hydro, 1968 7hp sno-bee, 1968 190XTD |
Posted By: CrestonM
Date Posted: 21 Feb 2023 at 10:07pm
| My main concern is keeping loaded RPMs when plowing around 2,300. Being as it's a 7080 with a lot of hours, I don't want to let the RPMs climb up around their top rated RPM. That, and I just like everything to work the way it should or it bugs me. |
Posted By: SteveM C/IL
Date Posted: 22 Feb 2023 at 1:53pm
Doesn't that have a Roosa? The one on my 220 has stop screws you can set low and high idle with. If so I'd turn it back to 2600 max.
|
Posted By: 8070nc
Date Posted: 22 Feb 2023 at 2:22pm
|
After thinking about it the pickup has extra threads. I dont see any reason not to drill a larger holo than the pickup. Tap a plate for the pickup and put oversized mounting holes in the plate. Drill snd tap the engine engine plate for the mounting holes. That way if the hole for the pickup isnt in the right place it could be moved until it worked ------------- 1984 80780 1957 D14 DES 300 with 25000 engine 616 tractor |
Posted By: 8070nc
Date Posted: 22 Feb 2023 at 2:25pm
|
To clarify thats to put a 8000 pickup on a 7000 series tractor ------------- 1984 80780 1957 D14 DES 300 with 25000 engine 616 tractor |
Posted By: CrestonM
Date Posted: 22 Feb 2023 at 7:07pm
Yes it does, that’s something I’ll look into. |
Posted By: CrestonM
Date Posted: 22 Feb 2023 at 7:08pm
If this doesn’t work for me, I’ll look into this. |
Posted By: SteveM C/IL
Date Posted: 22 Feb 2023 at 9:27pm
| You say it's high hours. I don't know what that means but if over 5000 and you don't have a history,I'd be putting brgs in the bottom end. You are capable. Just follow directions on the rod bolts. They ran at 2800 and they didn't stay together. The 8070 was turned down to 2600. I set mine to 2500. |
Posted By: Lynn Marshall
Date Posted: 23 Feb 2023 at 8:44am
| I'm not so sure that the 8000 series flywheel sensor will work in a 7000 series. I was thinking that the flywheels were different. I don't think that it reads off of the teeth of the ring gear. Doesn't the 8000 series flywheel have a series of bumps or slots on the front face to give the sensor a reading?? The parts book shows the flywheels to be a common number now, but that maybe just a parts supersession . |
Posted By: Kevin in WA
Date Posted: 23 Feb 2023 at 10:11am
| I put an 8000 series tach in my 7050, the pickup reads off the ring gear, I had mine split for PD work so it was easy to drill with the adapter plate off the machine. I located the pickup on the RH side where there is more room, no fuel filter there like on the 8000s. |
Posted By: 8070nc
Date Posted: 23 Feb 2023 at 10:22am
|
Dakota Digital make a tach and speedometer interface that you can scale the input so the tach reads what its supposed to. Might be the simplest solution.for you Creston ------------- 1984 80780 1957 D14 DES 300 with 25000 engine 616 tractor |
Posted By: Lynn Marshall
Date Posted: 23 Feb 2023 at 12:34pm
| Kevin, good information. Did the rpm read correctly with the original 7050 tach or did you need to get an 8000 series tachometer head? |
Posted By: CrestonM
Date Posted: 24 Feb 2023 at 8:10am
Hour meter stopped at just over 8,900. Previous owner said it was that way when he bought it from the original owner, so I’m not sure how many hours are on it. The PO said he only put maybe 100 hrs on it the several years he had it. Someone wrote on the valve cover the valves were set at 9,800 hrs, but I don’t know how they would’ve known that without a working hour meter. This will be a topic for another thread, but is rolling in bearings really that simple? Will the crank journals being worn out of round not effect that? I just worry a little more on a high horsepower, fast turning engine like this. I do plan to replace the fluid dampener. |
Posted By: CrestonM
Date Posted: 11 Apr 2023 at 8:11pm
|
Finally got a hand held laser tach and tried it tonight. At low idle the dash tachometer reads 600. Hand held laser tachometer read about 740. Book says spec is 750. When the dash tach read 1,800 the hand held was reading 2,300. So since it’s not a linear correlation, I’m not sure what the issue would be. Alternator belts are good and tight. Any ideas? Thanks |
Posted By: Tim NH
Date Posted: 11 Apr 2023 at 8:17pm
|
Creston, see if you can find a smaller diameter pulley. Tim ------------- 1950 WD 1959 D14 1955 WD45 1976 7000 B 207 |
Posted By: CrestonM
Date Posted: 11 Apr 2023 at 8:25pm
|
If it was a linear correlation that might work, but since the difference starts with 150 RPM at idle and increases to a difference of 500 RPM between the dash tachometer and handheld tachometer at 2,300 engine RPM, I’m not sure a pulley would solve it. This is assuming the hand held tachometer is reading correctly, but based on throttle positions, I believe it is correct. |
Posted By: Stan R
Date Posted: 12 Apr 2023 at 5:44am
|
It is linear: 740/600: 23% off, 2300/1800: 28% off. Close enough to say a pulley that increases the ratio by about 25% would correct the problem, if you opt to go that way. |
Posted By: Tbone95
Date Posted: 12 Apr 2023 at 6:50am
| I'm with Stan, it's pretty close to linear (probably is linear within reason) I did 740/600 = 1.233. 1.233 x 1800 = 2220. Give or take the width of the needle on the dial on the dash, and the math would probably work out perfectly. |
Posted By: CrestonM
Date Posted: 12 Apr 2023 at 6:54am
Well then I owe Tim an apology! I didn’t think of it that way. It’s no secret math wasn’t my best subject  So how do I go about figuring what size pulley to get?
|
Posted By: Tbone95
Date Posted: 12 Apr 2023 at 6:59am
| Divide the diameter of your current pulley by 1.25. I don't know if that's realistic, but that's how you'd change the ratio. |
Posted By: CrestonM
Date Posted: 12 Apr 2023 at 7:13am
| Thank you, I’ll see what I can find. What would be nice is if there was an adjustment on the tachometer to compensate for slightly incorrect readings. |
Posted By: Les Kerf
Date Posted: 12 Apr 2023 at 9:40am
|
Most of the aftermarket automotive tachometers do have a way to adjust between 4-6-8 cylinder engines. I have no idea if yours has any provision for this, but I suspect that there was some way of calibrating this at the factory. |
Posted By: SteveM C/IL
Date Posted: 12 Apr 2023 at 1:09pm
Those would be for electronic ignition systems not fuel injection.
|
Posted By: Les Kerf
Date Posted: 12 Apr 2023 at 9:09pm
Correct. But I was under the impression that the tach in question here receives its signal from the alternator, which sounds like it might be kinda sorta electronic. I could be wrong though ;-) |
Posted By: CrestonM
Date Posted: 12 Apr 2023 at 10:44pm
|
Correct, it does run off a pulse signal. A lot of aftermarket gauges get their signal via induction from a spark plug wire, right? |
Posted By: Les Kerf
Date Posted: 13 Apr 2023 at 6:17am
All of the tachometers I have used get their signal from the low-voltage side of the coil. The alternator style tachs are just a simple frequency counter that turns this signal into an analog signal to drive the indicator needle. I'm going to hazard a guess that whoever designed the tach also put some means of calibrating it into the circuitry (it would be pretty dumb not to) to allow it to be used on various applications. This calibration adjustment may not be readily accessible to the end user though. |
Posted By: Ron(AB)
Date Posted: 13 Apr 2023 at 8:10am
We need a picture(s). There is a lot of 7000 series with non functioning tachs. ------------- 405, 7000, 7050, 8050, 8070, L3, 2300 & 2600 disk |
Posted By: Tim NH
Date Posted: 13 Apr 2023 at 5:57pm
|
I'll let you slide Creston, lol. Use a impact wrench to take the pulley off. Then go see what NAPA can get you. Tim ------------- 1950 WD 1959 D14 1955 WD45 1976 7000 B 207 |
Posted By: CrestonM
Date Posted: 14 Apr 2023 at 8:18am
| That’s probably what I’ll do. I may also check with McMaster Carr if Napa doesn’t have it. |