Ignition warning light issue with revving

[Fingolfin]

Here's a good one for you.

I've been trying to set up Mog's idle. I find the new tachometer quite useful for this job. Anyway, when I was in the car, I revved it moderately (for kicks), and noticed the ignition warning light was blinking a bit at the higher revs. Paying close attention, the blinking began around 2500 rpm and became persistent about 2700-2800. The blinks were accompanied by a strange electrical crackling sound, as if somewhere the current was having to arc across a gap. I dared not rev it up any further for fear of damaging something.

My suspicion is the voltage regulator box, which is type RB340, as I had the dynamo tested and it checked out fine (in addition to conducting my own visual inspection of brushes, etc.). Could the contacts be stuck open or closed? I know little about these boxes -- and in fact I'm not even sure how to take the cover off! It doesn't appear to be the clip-on type of cover.

[mike.perry]

First check the fan belt tension
What is an RB340 control box? The normal box is an RB 106/2 for a C40/1 dynamo, both with spade connecters.
According to the workshop manual sect. N48 they should not be mixed, maybe your control box and dynamo are not compatible.

[Fingolfin]

Mike, the consensus on this earlier thread (http://mmoc.org.uk/viewtopic.php?f=11&t=45432) was that the RB340 was okay for the C40. I believe the fan belt has the correct deflection across its longest run, though at the moment I can't recall what that deflection is supposed to be. Moreover I've not heard it slipping at all.

[mike.perry]

Check the dynamo brushes and springs

[Fingolfin]

I shall check the brushes and springs later today (waiting for rain to stop) but last night I took the control box off to have a look inside.
Here's the back, before opening it...[frame][/frame]
And here's the inside after opening it.[frame][/frame]
I took out the two unscrewable contacts (I believe the one furthest left is for the cut-out, but I don't know the other), and both of those screws had this sort of contamination. The cut-out screw had a raised metal part (a weld!), which you can see in this photo; the other screw had a slight depression instead, with a 'weld' on the unremovable contact.[frame][/frame]So I got out the trusty file and took care of the bits on the screws, and cleaned up the trouble on the cut-out unremovable contact, but it's nigh impossible to get to the other one (due to coils being in the way!), so I could only clean that up a little bit with a lady's nail file. While I was at it, I shined up the spades along the bottom of the box.

There's another 'contact' but it has no screw, between coils two and three (left to right). It looks wide open, and I thought I'd post a photo to make sure it's supposed to be that way.[frame][/frame]
So, the verdict is: the control box may not have created the problem (though I have no idea if the screws were adjusted correctly), but it needed servicing anyway! And now I can hopefully eliminate it as a difficulty, once I adjust the cut-out.

[Fingolfin]

Happily, there was a lull in the rain, and I got the dynamo off. I'm getting really quick at removing and disassembling it! The dynamo is in excellent shape, I found, and should by rights be producing electricity.
The brushes are quite meaty and clean, and the springs function well:[frame][/frame]I DID find that one of the springs wasn't quite tensioned enough, and the brush was moving only slowly toward the center. So I took the spring and brush out and cleaned the pathway, then put the brush in and wound the spring another turn -- and great success! It moved rapidly to the center.
The rotor is also quite clean and not cracked, and the end is oiled nicely:[frame][/frame]
Now I need to reassemble the dynamo and control box back on the car, retension the fanbelt, and see if the system works. Before doing so, I shall have to reset the mixture at the carburetor, as it's FAR too rich right now (due to a carb stripdown and rebuild), but that shouldn't be awfully difficult.

[bmcecosse]

Minors never had the 3 bobbin control box - not a problem - just means someone fitted it later in life. To test the dynamo - join both the terminals with a cable, earth the dynamo and then touch the cable to the non-earth terminal of the battery. Steady it with your foot if it's not bolted to the engine ! It will run as a motor if ok.

[autolycus]

Google for "lucas generator and control box tests" and download one of the free copies of this early 60s Lucas publication.

Good stuff.

Kevin

[Fingolfin]

Well, I did the 'motor' test this morning, and it worked! The dynamo ran nicely at something like five turns a second (though of course it's very hard to tell just by eye!). So that knocks the dynamo out as the cause of the malfunction -- and I think that means it can only be the control box.

Kevin, I've looked through that before, and it is excellent -- I haven't had time yet to get into doing the control box tests -- and won't have time for a while, as I'm going back to uni today.

[welshrat]

I'd go for swapping the control box, have a look at this link http://www.mmoc.org.uk/viewtopic.php?f=11&t=44025

[Fingolfin]

Thanks, Welshrat, that's likely what's going to happen -- I came home today and fiddling with it has only made the warning light stay on all the time. Should I stick with the RB340 model or should I get one of the earlier models?

[welshrat]

Thanks, Welshrat, that's likely what's going to happen -- I came home today and fiddling with it has only made the warning light stay on all the time. Should I stick with the RB340 model or should I get one of the earlier models?

Not sure what you have been fiddling with, guessing the controll box, not recommended I must say, pick up a second hand one that is the same as yours and swap it. As above they are rarely the problem but worth doing if you have a spare, saved me a lot of time and expense as sorted my problem out.

[Fingolfin]

Yeah, the control box -- fiddling as here: http://mgaguru.com/mgtech/books/pdf/Luc ... _Tests.pdf I'll go on and order one from eBay then. They're not too pricey.

[Fingolfin]

Well, I received a NOS RB340 control box, fitted it, and tried the system. Ignition warning light on all the time, as before. Not sure what to do. The three obvious answers are that both control boxes need fine adjustment, per the .pdfs, or both control boxes are bad (unlikely due to the new one being NOS), or the dynamo is bad despite running as a motor (highly unlikely).

[bmcecosse]

Or your wiring to the control box is wrong...... Test the dynamo as a generator - join both terminals and take a wire from it to the non-earth terminal of the battery - engine already running at a good fast idle of course! And now measure the battery volts - it should be charging flat out - probably as much as 14 volts.........certainly 13.5 volts. When you ran it 'as a motor' did you preserve the polarity at the connections ? If not - you will have reverse polarised it..........

[katy]

How old is that "NOS RB340 control box"? If it's been sitting around for a long time the contact points may need polishing up.
Easy to do, use clean brown paper as a burnishing tool.

[Fingolfin]

I unscrewed the two threaded contacts and both pairs of surfaces appeared shiny, but good thinking, Katy. BMC, my wiring is as it was when I received the car, and it all worked then! I will do that test. And yes, I made sure to keep the polarity correct when "motor" testing it.

[Fingolfin]

Well, I finally got home, and I conducted the first series of tests, as here: http://mgaguru.com/mgtech/books/pdf/Luc ... _Tests.pdf These tests are intended to ensure the dynamo is in good working order. Refer to the linked file (pp. 3 and 4) to see particulars of each test scenario.

Test 1: dynamo gave 2V at 3000rpm, meaning the armature and brush connections are good.

Test 2: dynamo gave rising voltage with rising speed, reaching a full reading (20V) at fast tickover (ca. 1500rpm), settling to 12V around 1200rpm. This is as expected for a good generator. Also, an ammeter was used to link terminals D and F, and the reading was about 2 amps, as expected.

Test 3: Results similar to Test 1, as expected. D lead to control box is good.

Test 4: Results similar to Test 2, as expected. Both cables are good.

Conclusion: dynamo is in good working order, per the listed tests.
Also, the battery gave an even 12V when isolated, so the battery is good.

Next up: tests on the control box! Results tomorrow...

[Fingolfin]

I decided to get a head start this evening, but it didn't go well, mostly because I have no idea what I'm doing. I sell myself short, but I do feel a bit lost.
Test 5 didn't make a lick of sense to me -- it says all the load connections have to run through the "battery side of the ammeter", connected in series between the D and F terminals on the control box (I think -- can't figure that part out either!) and the control box B blades, but which side of these is the battery side? I guessed the B blades, but that only gave me an off-the-dial reading (normally indicative of a short), so I didn't leave it connected THAT way! I tried connecting the B connectors to each other with a length of wire, and the car ran that way, but the ammeter needle didn't move, so clearly the test rig was incorrectly set up.
I decided to skip Test 5 and try Test 6. I was successful in testing it, but instead of getting a reading of 19-23 amps, got a reading of 2 amps! Adjusting the voltage cam (no matter how far) gave virtually no change.

So, in short, I'm up a creek without a paddle or a canoe (but with a nicely functional dynamo, apparently).

[Fingolfin]

I came upon a different instructional guide, here: http://www.vitessesteve.co.uk/PDF/Lucas ... Manual.pdf and I conducted the voltage regulator test, Test 1 in this guide (page 29). The essence of Test 1 is to connect a voltmeter between the D terminal on the box, leaving the cable to the dynamo connected, and earth; when the dynamo is run at 3000rpm, the voltmeter should give a reading of between 14 and 16 volts. The reading I got was -- wait for it -- 3 volts!
Test 1 goes on to read, "If the setting is more than 0.5V outside the limits (14.5V to 15.5V), the regulator can be considered faulty and should be replaced." Oh, sonofa... That just means I'll have to remount the old box and test it the same way.