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coggonobrien 
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Joined: 14 Nov 2010
Location: Eastern Iowa
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 Topic: 7040 Alternator
Posted: 12 Feb 2024 at 12:38pm |
Can somebody point me in the direction of the correct 10si alternator with the right pulley to have the tach work on my 7040?
Thanks David
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steve(ill)
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Location: illinois
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Posted: 12 Feb 2024 at 4:03pm |
this should be it... I would call them and verify the pulley and tack terminal before i ordered..
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Like them all, but love the "B"s.
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Steve in NJ
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Posted: 12 Feb 2024 at 6:52pm |
You have to watch with some of these Alternators for accuracy. The pulley has a lot to do with the accuracy of the signal for certain tachs. I just custom built two 100 amp SI's for a customer's 180 and his 200 Tractors.
Steve@B&B
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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Lynn Marshall
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Location: Dana, Iowa
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Posted: 13 Feb 2024 at 8:40am |
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Early 7040,7060,7080s used a Delco alternator. Later tractors used a Niehoff alternator. The Niehoff tractors used a different tachometer head because of a difference in the wave signal to operate the tach. I don't know if the supplier change was because of a reliability issue with the Delco or something else. I can't believe that it was a cost savings. Some of the early tractors were changed over to the Niehoff if the customer wanted. The kits included the alternator, pulley, wiring harness, and new tachometer head. When the Niehoffs failed, they were very expensive to repair or replace. Many were switched back to a Delco,but then the tach would read high. A larger (tach correcting) pulley can be used to compensate for this. Pulley wear and belt stretch also affect tachometer accuracy. Your tachometer head may be bad or the wiring could have a problem, but it's usually the alternator itself. I keep a new 105 Amp Delco and the larger pulley on hand.
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coggonobrien
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Posted: 14 Feb 2024 at 11:44am |
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My tractor had a niehoff on it, assuming it was original looking at it. 1975 tractor
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coggonobrien
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Posted: 14 Feb 2024 at 11:46am |
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serial # 3168
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Lynn Marshall
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Posted: 14 Feb 2024 at 6:06pm |
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The Niehoff started at serial # 3501. Like I said, many of those tractors were converted to the Niehoff system , especially if the Delco had been troublesome on particular tractors.
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coggonobrien
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Posted: 15 Feb 2024 at 7:28am |
 Lynn Marshall wrote:
The Niehoff started at serial # 3501. Like I said, many of those tractors were converted to the Niehoff system , especially if the Delco had been troublesome on particular tractors. |
Lynn, so if mine has a Niehoff now, and should not of originally, does that mean my tach will be off? If so by how much? As far as I know the tach is original (working status unknown), engine is from a later L2 combine. The alternator came with the tractor. Thanks
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Lynn Marshall
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Posted: 15 Feb 2024 at 8:14am |
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That's hard to tell. Given that the tractor is almost 50 years old, who knows the history of what was done. There may be a part number on the tach that an experienced parts person at a dealership could identify. Otherwise, if the tach is for a Delco, it will read 2 or 3 hundred RPM higher than actual speed. I don't think that it will bury the tach with some wild reading so it should be somewhat accurate. If the operator knows this and doesn't lug the engine down, it will at least give a fair idea of engine speed.
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Alvin M
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Posted: 15 Feb 2024 at 8:50am |
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If you go from a Niehoff to Delco just change the pulley to 3-7/8 I did that it was the right rpm did about 6
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