Converting to an Alternator

[cass3958]

I have considered this for a long time but as I have power steering I needed the pickup off the back of the alternator. There was a company that supply alternators wrapped up in the original generator body so they not only look the same but also fit on the same brackets, and use the same fan belts. Problem was the ones that had the power steering pickup on the back were over £600 plus tax so way out of my price range. Then I came across this site http://www.bbclassics.co.uk/home.html who sell the same item but for just £160 both in positive and positive earth with the power steering pickup as per the original.
Question is what benefit would I get out of an alternator over the old generator? I don't tend to drive at night and do not have a fancy stereo system in the car, don't use a SatNav system and the battery charges fine with the generator.
If I was to change to an alternator should I go negative earth as I am still running positive earth as original at the moment, or should I stay with positive earth system. I did change to an electronic distributor a couple of years ago and this was positive earth specific so to change to negative earth I would have to change this unit back which is about £60?
Any suggestions or advice would be welcome.

[cass3958]

OK some good news if I did decide to change to negative earth the company who supplied me with the dizzy (worth keeping the invoices) can supply me with a replacement module so I can change the dizzy from positive to negative for £35. Means I don't have to buy a whole new unit and its a simple two screw and two wire change over.

[johngosnell]

Hi Rob
I had a look at some pictures of my power steering set up, and the power steering pump power is taken off is from a duel grooved pulley on the crankshaft. This of course would mean that either a different pump is used or the original modified to take a pulley. when I acquired my car the original pump had been modified but it now has a pump used from an early Range rover that I bought off ebay. If you you don't mind me saying it seems like an awful lot of work and cost particularly if you don't have any issues. I suppose you could change the pump for a pump/motor and attach it to the inner wing. Some of the small cars use this in the past

jag restoration 005.JPG (1.64 MiB) Viewed 3793 times

. As you can see this picture shows an oil leak and that is why the pump was replaced after three attempts to cue the problem.

Regards John
1B1257BW
1972 Rover P6

[cass3958]

Interesting set up you have there John. I have the original PAS pump set up which runs off the back of the generator. I had wanted to change to an alternator previously during my rebuild but I could not find one with a drive on the back for the PAS pump. These alternators by Dynalite have the same housing as the original generator and the same drive off the back so I would not need to change the original PAS pump. They have come down in price since I first saw them at over £600 so at £160 they are now in my price range. Just wanted to know from others experience if running an alternator and negative earth gives you any benefits over the original generator and positive earth. My system is working fine as it is so there is not a need to change. Just curious.

[NigelW]

Hi Rob, I did this change way back in the 70's. The problem I had was the Kenlow fan was draining the battery especially at night with the lights on sitting in London traffic, the old dynamo couldn't keep up and once left me stranded in Chelsea late one night in the rain. I fitted a 18ACR alternator and an XJ6 battery in the boot - never had any more problems after that including crawling through the Los Angeles traffic at rush hour down to Long Beach.

As far as the - or + earth, it gave me the opportunity to fit an updated stereo system and could later on use any - earth gadgets as required. For me it was well worth doing but in your circumstances I'd keep my money in my pocket.

[johngosnell]

If you convert to negative earth would you need to change other electric items, such the clock , rev counter, coil ?. I did read along time ago that the direction of flow of the spark plugs is reversed, not sure how that works or if it is correct. Just as an add on I think that the power steering to my car was a retro fit going by the chassis number

Regards John

1B1257BW

[cass3958]

Actually John the change over to negative earth is very simple and has been discussed on the old forum at length. This is the link http://www.jagstyperegister.com/forum/v ... f=15&t=144
Most Jaguar clocks no longer work and mine is one of those so no problem with that. All the other dials do not need to be changed other than the Amp Meter which needs to be reversed. If you were running the generator that would have to be re polarized but the new alternator would already be running negative earth. The fuel pumps need swapping over and things like the radio but otherwise its a fairly straightforward operation. As for the plugs as the coil is swapped over the flow of electricity through the plugs should remain the same but would not really matter if it was reversed.
I just have to figure out if the swap over has enough benefits to justify the cost. At well over £600 three years ago it was not but now these units are getting cheaper £200 would allow my to change over to an alternator and have negative earth.

[cass3958]

Well I think my decision has been made for me.
Earlier this week I started to get a stutter/cut out on the ignition under load. Annoying but not at that point fatal.
Friday I had time so decided to do some tests on the electrical side, one thing at a time, to try and track down the fault.
Changed the plugs although I knew it was not them as all six would not cut out all at once. Ran fine but still with the stutter/cut out.
Changed the coil for a new one, took it for a drive and the problem remained. Two mins later at home on the drive and the car would not restart. No spark at High or low even though I had power going in to the distributor and the earth was fine.
Phoned up SimonBBC whom I bought the system off four years ago and gave them the symptoms. They basically confirmed that the electronic distributor had broken down but there was no way of testing it unless I sent it back.
So a replacement positive earth insert module is about £40. A complete negative earth distributor is £65. The alternator conversion which sits in the original dynamo housing and has the drive off the back for the power steering pump is £145 which then allows me to convert to Negative earth. £215 for the lot with postage but it will not be here until Tuesday.
Always happens on a Friday and this weekend is the big Powderham classic car rally over two days which I was going to attend. Still it gave me the opportunity to take the classic bike along instead and as the weather was great it made a change for a nice ride out. Full leathers made it bloody hot on the bike though.
Once the bits arrive I will get them fitted and write a thread about the conversion to this new alternator and converting from Positive to Negative earth.

[NigelW]

I'm chasing a similar fault on my XJ, it was going to go to Wroxall last week but only got 300yards from my drive when the engine cut out. Got it started and limped back home to change cars to the S Type. Previous day did a 25 mile run in it with no problems. So far changed fuel filter, coil, spark plugs and a host of other stuff checked but engine won't rev beyond 2k rpm.

[cass3958]

Electrical problems are easy when the thing does not work as you just keep changing things until it does but when its an intermittent fault as mine started out as they can be a real pain to track down. Fingers crossed mine will be solved on Tuesday.
Do you have an electronic distributor on your XJ6 Nigel?