4TR VOLTAGE REGULATOR

[ALAN COCHRANE]

Hi Everyone

I've been having a problem with my battery overcharging since I bought my 3.8 OTS back in October 2011. Firstly I replaced the battery which was having trouble holding it's charge overnight. Then the alternator with a new 11AC unit. The original was a strange hybrid of Lucas 11AC and braised on dynamo pulley wheel and fan. The ammeter still showed constant charging at all revs.
I measured the voltage at the regulator terminals with the engine at 1500rpm and it registered a steady 14.55V and remained at this level, even at much higher revs. This is obviously outwith the usual range of 13.9-14.3V. This is backed up by the fact that the battery terminals are showing grey powdery deposits which usually mean it's gassing up.
The problem I have is that the regulator does not have the usual wax sealed adjustment screw on the back. It looks identical to the 4TR unit from the front but is not actually marked as such. Has anyone else come across this before and if so is there any other way to adjust it?
I think I may be clutching at straws here since the unit's plastic cover is riveted rather than screwed to the metal back-plate.
But if someone can come up with a brilliant idea it may save me the ?30 or so for a new one.
I should have said at the start that my 3.8 has been converted to negative earth with a 4.2 wiring loom.
One useful thing I have learned is that all Lucas alternators appear to have the same shaft diameter, so any pulley and fan will fit any alternator. This is how I avoided returning to the braised "Frankenstein" hybrid.

Thanks in advance

Alan

[christopher storey]

One of the possibilities is that you still have the original front pulley and damper, which IIRC is larger than that for the 4.2 engine. If that is the case, then the alternator with its new and correct front pulley will be driven at a significantly greater speed than it should be . Secondly, I doubt very much that an overvoltage of about 0.25 volts would cause any trouble , and in any event such readings are very susceptible to temperature variations ( the gassing voltage of a lead acid battery varies from about 16.5 volts at 0 degs C and is 14.5 volts at 20C ). It is once you reach the realms of 15 to 16 volts that you start to get boiling off of the electrolyte . You need to be a little more cautious with a sealed for life lead acid battery . As far as your terminals are concerned, have you coated them with petroleum jelly ? This should eliminate any corrosion of the terminals

[ALAN COCHRANE]

Chris

I see your point about the pulley wheel although with a larger wheel the alternator would actually go more slowly than when fitted with the smaller double vee belt wheel a 4.2 would have. I sourced a 3"pulley wheel to match the size of the dynamo pulley. This shouldn't make any difference since the regulator should cut off the alternator output at a preset value.
I've swapped the ammeter for another I had and it's still showing constant charge when running at 1500rpm, so it's not that. In addition when you rev the engine both ammeters flicked off the scale and then fluctuated wildy until settling halfway between the centre mark and full charge.
Yes I always lather the battery terminals with lithium grease everytime I disconnect the leads. I'm using a Lincon battery which is less than a year old. The electrolyte levels are fine on all the cells and it holds it's charge for long periods.
I'm going to try a new regulator from SNG and see if that solves the problem. I suspect the regulator may be allowing brief bursts of overcharging when the engine speed picks up and then settles at 14.5V which is still on the high side of the recommended level.

I'll let you know how I get on.

Cheers

Alan

[christopher storey]

Alan, it was the crankshaft pulley I was referring to , which I think, but would not be categorical about it, is larger than that for a 4.2 . This will overspeed the alternator with a standard alt pulley, and may be the reason why you had a bodged pulley brazed onto the earlier alternator which would have corrected the "gear ratio"

PS without wishing to teach my grandmother etc. , the larger the driving pulley, the faster the driven pulley will travel, because the linear speed of the belt is higher

[ALAN COCHRANE]

Chris

Sorry I did misunderstand you.
We were both correct-the driving wheel increases the speed as it increases in diameter. The driven wheel does the opposite.
The 4.2l crankshaft pulley may well have been smaller because the standard alternator wheel was only 2" in diameter. This would mean that it must have been mated to a smaller crankshaft pulley in order to prevent the alternator overspeeding.
In the meantime I've ordered another regulator from Hutson's. I'm still concerned about the wild fluctuations registered by both ameters I've tried and the fact that the regulator output is outwith the recommended range.
If this fails to cure the problem then I'll have to look at increasing the size of the alternator pulley wheel. That means trying to work out fan belt lengths-a job I hate. If you have a magic solution to this or if anyone else has had to overcome this problem please let me know-I'd be eternally grateful.
For anyone who's interested or who may have encountered this, my set-up is as follows:-
1961 3.8 OTS converted to 4.2l negative earth spec.
6" Crankshaft pulley
Driving a Lucas 11AC alternator with a 3" pulley.
Fan belt appears to be standard length single V for an early 3.8l
Chris and I suspect the alternator is overspeeding.
What combination of fan belt length and alternator pulley wheel diameter do I need to cure this?

All answers greatly received.

Cheers

Alan

[ALAN COCHRANE]

Latest update.
I've fitted the new regulator from Hutson's and the Ammeter still does a bit of a dance on start-up. It then settles to indicate a slight charge, which is what should happen.
The regulator voltage is 14.5V at 1500rpm which although high is better than before. I think I'll leave things as they are and see what if anything happens-hopefully nothing.
I've now got a new problem-the radio set-up I bought from Tadpole Radios has decided to cut out every so often. A new wiring loom plug has been ordered to hopefully cure this latest annoyance.
This is quite a set-up. The Sony head unit is situated in the boot and is controlled remotely by a classic Radiomobile radio fitted in the cabin's central console. Great when it works!

Alan