Outer Limits 4x4 Board

Hi all,

Has anyone tried using another brand of alternator in their Disco's / Rangies? Someone put in a Bosch unit from XE/XF carbie Fords into my 91 Disco. Worked good until some Murrundindi mud wrecked it. Replaced it with a brand spanking new unit, exactly the same model, and now the tacho is way off. eg. off the scale when the engine's at about 2000rpm.
The tacho was fine with the old Bosch alternator, so I'm at a loss as to why the new one has affected the tacho!
Anyone had similar situation's when changing alternators?

Tacho takes a pulse from back of alt.

Pully size could be different.
Or the pulse.

Regards
Michael.

Your tacho goes off a couple of things in your alternator.... firstly being the ammount of poles on the rotor, if this is different itll change your tacho and plus what HSV rangie said to about pulley size etc... is the alternator the same current rating as your old one? and is the pulley the same size? without dismantling your alt you wont know the ammount of poles on the rotor but if you did you could always get your tacho recalibrated to suit your new alternator...

You were spot on guys! The new one came with a bigger pulley than the old one. Someone had actually put in a custom spacer with the original alternator as well. I've changed over the pulleys and will try it out tonight.
Makes perfect sense to me now though. My auto-elec. had no idea!

Thanks guys!

Bugger!

Sorry guys but changing the pulley didn't make a difference.
Tacho is still way out.
I'll leave it disconnected for the meantime, but I sure would like to know why this has happened when the alternators are exactly the same models, but one is brand new!
I might chuck the old one on for a laugh on the weekend and see if all works ok and I might see what sort of voltage is coming out of the tacho connection on the alternator. I measured the new one last night, so I can compare and see if there is indeed a difference.

Anyone else out there with a different alternator than a genuine Rover?

I have a bosch on mine not sure what model will check this arvo and have a look if you want, though I don't think I have a factory tacho so it may not run off the alternater.

Clean out and fix the old one.

Bazzle

I run a bosche on mine, BUT I have recalibrated tacho to run from coil pulses.

Michael.

Bazzle, can't fix the old one. The bearings in the rear of the casing overheated and seized, stripping out the casing. It's truly F.U.B.A.R.
I'll still try to put it on tomorrow to see if the tacho still works with it and measure the tacho output terminal to see if it's different to the new unit.
It will run, just makes a hell of a lot of noise and if it heats up, it'll probably seize again.
Otherwise, i'll have to get the tacho re-calibrated, as Michael suggested.
Pity, you'd think you wouldn't have to do anything when you replace the part with an exact match!

Again you have to check how many poles on the rotor inside the alt. This will change the frequency of the output for the tacho.....