Hey guys.

Since I put the new engine in my Disco, and have begin to drive it more often, I am trying to hunt down the little gremlins

When we first installed my engine (which is out of a 1990 Range Rover) the alternator would not charge correctly. The tach was working, but the alternator was not charging at all. My friend obtained another alternator that charges correctly, but the tach doesn't work anymore.

Where should I begin to look to track this problem down?

Take into mind; When the new engine was installed, I opted to stay with the V-belt setup, rather than convert it to a serpentine belt (just to keep things simple).

Thanks for any help!
Aaron

 

Are you POSITIVE the alt is charging?

 

doesn't the alt turn opposite on the older V-belt RR?

Are you using a disco alt?

I'm not certain it matters, except for alt cooling.

luck,greg

 

Greg might be onto something...

 

I am 100% positive the alt is charging. The battery was the one that sat dead and frozen in my garage all winter. Gave it a jump, drove it for a couple of hours and it hasn't gone down since. My whole powertrain was swapped over from the range rover. If the alt spun backwards, why would the tachometer have worked with the non-charging alt?

 

An alternater can charge spinning in either direction the only problem is the cooling fins are only made to go one way...... I would get another alternater that from the 1995 and swap over your pulley on it

 

Really, your tach should not have been working with no alternator. Things are backwards of what they should be. My tach drops out when I wade through water and the belt slips.

 

2X with Long Haul
An alternator generates AC power, it is then rectified to DC with a bank od 6 Diodes. It is the diodes that determine the DC polarity, not the rotor rotation. The bank of diodes is cooled with air from the rotor fan and the rotation is important. So the difference between the alternators is the fan. Some generic alternators work both ways.
The tach pick up is linked to the AC frequency and it is not dependent on rotation. Take the "other" alternator and connect the tach wire to it. Run a wire to the ground. Hold the alternator with one hand and with the key on "Run" and engine off, spin the alternator pulley an have someone look at the tach gage, it should indicate RPM. If not, the wire is not good, I'd look at the connector first.

I am open to corrections.
SD

 

I fail to see how my alternator is spinning backwards. Everything was swapped over from the Range Rover, including the fan and alternator. The replacement alternator is from another Range Rover. Plus, I am still running the V-Belt setup, I did NOT convert to a serpentine belt.

 

I always notice this on the forum. The question was simple and about the tach, out of 7 people, only one addressed the question, the others all went about the back ground information. I love this forum, it is as helpful as it is entertaining.