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Ford 4000 motor 3 cylinder rpms crazy

mikewood869

mikewood869

Well-known Member
Just wondering how high does the rpms go on that motor? The stick shows that the motor will go past 26 rpms which maxs the gauge.
 
What kind of tach drive? If it was a generator driven tach and changed to an alternator it might be pulley size.
 

4000 3 cyl's max rpm is 2450-2500, it's common for a tach to be off a hundred rpm or so.
If it has a alternator conversion it'll be way off, by as much as 500 rpm fast, a bigger pulley will help but won't completely fix it.
I had the gen pulley bored to fit a Delco alt, tach is still off about 300 rpm.
Used my digital tack to find 540 pto speed, tractor with swapped pulley shows 2100 rpm, tractor with Delco pulley shows 2300.
 
I might just swap the gas one that we bought last year. Right now it has the one from the diesel motor.
 

I'm not sure what your saying, but....


If someone messed with the adjustments, it can run way faster... But that would greatly shorten the life of the engine.
 
(quoted from post at 23:47:37 05/21/19) So far this was probably caused by a loose belt, smaller belt or the generator.
Click to expand...

The belt size shouldn't matter unless it's so narrow that it slips, in which case the results would be similar to a loose belt, which would slip as well and wouldn't spin the pulley on the generator as fast as it would if it wasn't slipping so the tach should read slower than the engine is actually turning, not faster.

The generator itself wouldn't cause the tach to be off. The size of the pulley on the front of the generator or an incorrect tach drive mechanism on the back of the generator might, but not the generator itself.
 

A very narrow belt that rides deep into the pulley would show higher revolutions than the correct belt that rode further out and had to travel further per revolution.
 
(quoted from post at 09:20:25 05/22/19)
A very narrow belt that rides deep into the pulley would show higher revolutions than the correct belt that rode further out and had to travel further per revolution.
Click to expand...

But it would ride lower in both pulleys (crank and generator pulley) so the rotational speed of the 2 pulleys relative to each other wouldn't change.
 

Is this the original generator or has it been converted to a alternator.
The alternator conversion kits I've gotten have caused the tach readings to be high by 3-400 rpm's
 

We ended up using the generator from the 3000 gas motor (which had a alternator). The belt that is on the tractor right now is 2 inches smaller (the bracket that mounts near the valve cover doesn t even attach). The rpm gauge isn t as far off as before.
 
We ended up using the generator from the 3000 gas motor (which had a alternator).
Click to expand...

I'm sorry, but I just re-read the sentence above and I am confused. If it had an alternator, then how could you use the generator from it?
 
(quoted from post at 00:50:37 05/23/19)
We ended up using the generator from the 3000 gas motor (which had a alternator).
Click to expand...

I'm sorry, but I just re-read the sentence above and I am confused. If it had an alternator, then how could you use the generator from it?
Click to expand...
Sorry. back in the late 1980's, a guy my grand father knew rewired the tractor, then in the summer of 2017, we bought a wiring harness and generator and rewired the tractor. We ended up pulling the pulley and that part that goes on for the tach cable from a generator from a parts gas 3000 )https://www.amazon.com/gp/product/B008XBBVLA/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

The old alternator for the tractor

mvphoto36534.jpg
 
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