My 1964 Mk2 3.8 passed its MOT today with a few advisories (mostly oil leaks).



The garage indicated that the dynamo was operating normally except when the engine was hot - not charging.
They did not know why this was the case - belt tension checked.
I am thinking of buying a replacement dynamo (if necessary). I do not at this stage want to go down the alternator route.

Does anyone have any suggestions about the dynamo issue?

Thanks

 

Certainly check the belts first. Check any connections along the line also. Could also be the dynamo internals breaking down when hot.

 

Check the connections on the regulator, look for corrosion.
Remove the regulator, turn it over and you'll find two big resistors there, check the ends where the metal tangs are crimped onto them.
Consider inspecting and cleaning the points in the regulator.

Use a point file and don't over do it, do not use emery cloth or any type of sand paper.
Clean them afterwards with acetone or lacquer thinner with a lint free rag, don't use paper towels.
Keep the points file square to the contact surface.

EDIT:
When you say "not charging" is the red ignition light coming on ?
OR is the light OFF and the gauge is showing a discharge ?

 

Jeff,

Thanks for the advice on checking connections etc. I'll let you know what the outcome is.

Regarding what I see when I'm driving:
While warming up in the drive, car comes off choke nicely, then IGN light glows dimly.
When car is being driven initially, the meter indicates good charging, IGN light off.
BTW - it is surprising how much the meter swings back when the double speed fan switch is turned on.
Anyway, with fan off and after driving for a bit, the meter stays at zero (charge in = charge out I guess), IGN light off.
After a longer period of driving, the meter drops a bit into the discharge zone, but only slightly. Revving or more driving does not bring it back to zero condition.

So I guess the meter is indicating that the battery is not receiving enough charge (but only slightly) when the engine is running at normal temperature.

 

If the red ignition light is not coming on, then I don't believe you have a generator or charging problem.
It's normal for the light to glow red when it's at a very slow idle _ at any temp. This is the only time the red light should come on when the car is running.
If the needle is way far into the discharge area, then the battery is fully charged.

Sounds like the regulator is simply out of adjustment or the points need cleaning or both.

An old battery can cause this situation.
To test this, remove the earth side of the battery, that would be the positive side of the battery if positive ground (the cable that is bolted to to the firewall).
test with a volt meter and you should have a round 12 volts. (give or take _ note the voltage)

Connect the battery and start the car and take another voltage reading across the terminals and it should read above battery voltage at high idle. (not more then around 14 volts, any more then then 14.5 volts and you will ruin the battery).
If it's more then 14.5 volts, then the cut out relay in the regulator isn't working and the points need cleaning and or adjusting.

Allow the car to warm up to where the perceived problem is and take another voltage reading, it should be at least be at battery voltage or a little better.
Turn on the lights or anything with a big voltage drain and watch the meter, does the gauge still show a big discharge _ what is the voltage reading at this point.

 

Thanks for the detailed instructions.
I will try and look at this over the weekend and let you know.
BTW - the battery is a few years old but I did a full charge with it using a C-TEK charger a few days before the dynamo issue was suggested.
I also ran a diagnostic test on the battery with a handheld tester which showed Statement of Charge to be 100% and Statement of Health to be 73%. Its Cold Cranking Amps value is 570.

 

I have no suggestion to make regarding the issue, but I must comment on the car: it is simply beautiful, both in the paint/trim combination and in overall condition.

 

Thanks Gregory, she is a thing of beauty, but like all classics, they have their problems which keep me busy.....
It's done 48k miles and probably only about 200 of those have been since the family obtained the car in 1988.
I want to drive it more now, so it does not just become a museum piece.
It's just come back from the garage (where it turned a few heads) and has an MOT pass - although it is probably exempt.

It dropped a valve onto a piston last year so the engine had to be completely removed, stripped down and rebuilt with new parts. This was done by a local company who specialize in building racing engines - they did an excellent job.

 

Well, my 3.8 (now 26,200 original miles) has only given me one problem - twice: the locating peg on two ignition rotors has sheared, bringing the car to a halt as the timing changed. The first time was not a good experience - the second time I was prepared - I had a spare rotor in the glovebox!

 

Beautiful car and lovely colour.
Only one problem - how long have you had it?

 

I have owned this car for 18 years (is this a problem?). I bought it when it had just 16,000 (documented) on the odometer. The colour (but not the paint) is the original Pale Primrose.

 

Sorry, I should have chosen my words more carefully. What I meant was - I presumed you have had the car for a long time (18 years indeed) and to only have had one problem in that time is quite fortunate and envious!

 

And that problem wasn't the cars fault, but crappy aftermarket parts _ probably made in China...

Jaguars are not unreliable, but when things go wrong I can always trace it down to poor quality or ill fitting parts.

Or in some cases (unfortunately) the error of a mechanic.

 

No, this shearing of the locating tab was not on a reproduction rotor in either case. The rotors were the correct rotors - look carefully at the inside of the mounting cavity of the rotor on the left - difficult to see but if seen from the side (instead of head on as in the photo) it no longer has the block shape it should have to prevent movement:








I have remembered one more item that has needed replacement, although it was not responsible for any aspect of the performance. The tachometer stopped working - the cause was that the protruding metal shaft that engages at the rear of the right-hand camshaft had slipped back into the generator unit. No engagement, no signal. It was replaced with the NOS unit pictured below with the help of a friend with a more supple body and longer arms (!).

 

So, returning to the original question.......
I followed your instructions and decided to make a note of everything I saw. First of all, a few notes…..

1. The regulator is a Lucas RB340 – please see the photos at end of this post.

2. The drive belt is not incredibly tight, but has movement of about ± 0.5 inches when engine is warm.

3. I recorded various readings of indicators over a period of about 45 minutes.

4. A digital volt meter measured the voltage directly across the battery (Vbatt).

5. IGN lamp only comes on at low revs.

The table shows the values recorded and the status of things at the time. The ammeter reads Charge on the left and Discharge on the right of the gauge. The middle position I take to read zero. I take full scale deflection to be ± 30 in each case.

The engine was started from cold. The ammeter needle is never rock solid, it kind of twitches around an average point.





A few initial observations …….

The water temperature reading appears too low?

Tick over speed of 450rpm seems too low?

After start up, Vbatt gradually drops from about 14.50 volts to when choke kicks out (did you say this was a dangerous level?)

Initial operation of fan or headlights results in ammeter displaying a charge status of about +5 at high revs.

However at 550rpm, this results in the ammeter displaying negative values (discharge).

The interesting readings are at 34 and 41 minutes. The engine is warming up nicely and engine speed is increased to 1500rpm, BUT the system reads a discharge under load. This seems to confirm what the garage said, the system is not charging when the engine is hot.

I have taken various photos of the regulator and related circuitry. I would appear to need a good clean. I also have the Mark 2 3.8 Service Manual, which explains about regulator adjustments on page Ps3 etc. Looks pretty detailed.

BTW - next to the regulator, there is a black rubber connector block with wires in and wires out. The third photo below shows this block. There has always been a loose disconnected wire (in the photo) which I presume should connect into the block somewhere. I cannot tell the wire colour. Does anyone know what this wire is for. I cannot find the rubber connector in the wiring diagram?

Hope the information in this message is useful and hopefully someone can tell me what the next step is.
Many Thanks.

 

You have quite some work ahead of you, you need to clean up your wiring, it's in pretty bad shape and in my opinion is a fire hazard.
Carry a 10 or 15lb fire extinguisher in the car and keep it handy _ when the car is in the garage, disconnect the battery until all that wiring is cleaned up.
You can see in your screen shots the rusted and oxidized connections, some wires are even exposed from being too hot and the insulation has burned away.
I would get a new regulator too.
All the bad connections are the problem, there is too much resistance in the circuits and when the heads light come on, the battery voltage and generator can't over come the load and the voltage drops below the battery voltage.

I would also look at the switch panel in the car as well, I'm sure it looks almost the same, the temp gauge only showing 60 degrees indicates that the voltage regulator in the switch panel is faulty and or has bad connection with it as well.
Not to alarm you, but if this was my car, I wouldn't drive it until all this was cleaned up.
All the connections in the car should be checked and dealt with accordingly, tail lights, interior lights, door switches etc....

Once all is cleaned up, I'm pretty sure that would solve your discharge problem.
My screen shots only show the severe problems, all the female spade terminals on the regulator need cleaning as well as the fuse junction box terminals, that's where to start as well as that large junction where the burned wire is.

Also, the disconnected wire in that junction box looks as if it's been that way for years and probably does not need to be connected.
Wiring looms are made up to suit different countries and to connect up different accessories as ordered, I would say that is what that wire is for, but it simply isn't used.
My car was never fitted with fog lamps and the wires for them are included in the harness _ they are just there with nothing connected too them.
I also have spare un-used wires in the wiper wiring loom, after doing some digging, they were used for the park brake light on the right side of the car, but because my car is left hand drive, they are not used.
At this point, I wouldn't worry about it.

The 14.5 volt spike should settle down once all this is dealt with.
The idle speed is low at 450rpm, should be at 600 when the engine is all warmed up, however this has nothing to do with the wiring/charging problem.

 

Thanks Jeff (I think). I agree the wiring and connections are not in a good state. I have disconnected the battery. I will take things methodically and get a new regulator and fuse box. I have seen the Lucas RB340 for about £25 on the web. I presume it will need adjusting (voltage, current and cut-out) before correct use. However, it may be hard to get reliable readings if the wiring is high resistance as you say.

The fuse box seems to be about £30 as well.

The next question might be a bit dumb.....In the photos there is a large Lucas relay with 5 wires going to it. This looks a bit ropey as well so I will replace it. I presume it is not part of the charging circuit - I can't easily spot it in the wiring diagram. The labelling states 6RA Lucas 33209D. Do you know what it is for?

 

The new regulator box will not need adjusting, it's done at the factory _ plug and play.
The fuse box doesn't necessarily need replacing, it just needs to be taken apart and cleaned.
If you have access to a brass wire wheel, that's what I used to clean the screw lugs.
I also cut back the wires and solder new ones in place using crimp type connectors that require solder with heat shrink.
The problem that one faces is that the old wiring is so hard and brittle it breaks as soon as it's disturbed, so going back into the wiring harness where the casing is still good may be necessary.
What does need replacing is the oval shaped rubber grommet on the fuse block mounting plate, yours looks rotten and sticky.
Take lots of photos and mark things if you can't keep track using the manuals wiring diagram.

As for the mystery junction box, I can't help you much there, the only thing I can tell you is to do some continuity tests and start tracing back wires to find what circuits are involved.
Start with the wires where the colour codes can be seen, the blue wires with the white and red tracers.
Those are the colours that are used for the head lights, that would also explain why one of the feed wires for the one is so hot.

Looking again at your photo, the ones go into the fender well _ probably to the park lights and maybe the blinker and possible the horn circuit.
Also not the single screw that holds that junction box to the fender-well, that's also acting as a ground, clean that up as well even though it may look like it's OK

 

The connector blocks are still available new.

 

For £9.64, it's not worth the time to clean the old one.
May as well get some new bullet connectors too.