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Bob Reynolds
Yet to post message
Username: bobreynolds

Post Number: 1
Registered: 8-2012
Posted on Sunday, 12 August, 2012 - 11:40 pm:   Edit PostDelete PostView Post/Check IP

Does anybody know what the static voltage across the ignition coil is supposed to be (with the points closed)?

I always thought that ignition coils with ballast resistors were designed to work on about 7 to 8 volts. But when I measure the voltage across my ignition coil (with the ballast resistor in circuit and the points closed) I am getting 10 volts. This seems a bit high to me. I am trying to figure out whether I have the right coil and ballast resistor fitted to the car.
(1975 Silver Shadow with conventional ignition)
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John Kilkenny
Prolific User
Username: john_kilkenny

Post Number: 127
Registered: 6-2005
Posted on Monday, 13 August, 2012 - 12:03 pm:   Edit PostDelete PostView Post/Check IP

Bob,unless you have recently changed the coil or ballast resistor I wouldn't worry about seeing 10 volts at the coil the way you are measuring it.

When the engine is running the inductance of the coil provides an initial high impedance when the points are closed.

The combination of ballast resistance and coil are designed to ensure that current buildup in the coil is sufficient to provide an adequate spark across the whole engine RPM range.
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Bob Reynolds
New User
Username: bobreynolds

Post Number: 2
Registered: 8-2012
Posted on Tuesday, 14 August, 2012 - 07:04 am:   Edit PostDelete PostView Post/Check IP

Thank you for your reply. The ignition components are of unknown pedigree at the moment. The coil looks like it has been changed fairly recently as it is bright and shiny and the wiring has been (badly) replaced. With the suspicious voltage, I am concerned that the wrong one might have been fitted as a quick replacement.

I think I will change it, and the ballast resistor, as a matter of course.

Does anybody have any tips on changing these two components without taking the engine out? They are buried underneath the heater actuator box, and blocked in by the distributor and fuel reciever cylinder. The fixing bolts seem completely inaccessible from where I'm standing!
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Jan Forrest
Grand Master
Username: got_one

Post Number: 378
Registered: 1-2008
Posted on Tuesday, 14 August, 2012 - 12:25 pm:   Edit PostDelete PostView Post/Check IP

The secret to accessing components in that (and other shielded areas) is the ability to hang from the garage rafters by your heels while bending your arms in 3 or 4 places. Failing that a wide range of combination spanners, sockets and rachet handle extensions in 5mm steps is essential - even if they aren't officially available.

I've lost numerous bolt, nuts, washers and even spanners doing jobs like this and come to the conclusion that the only way of retaining the latter is to tie a length of twine between the spanner and your wrist.
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Geoff Wootton
Frequent User
Username: dounraey

Post Number: 64
Registered: 5-2012
Posted on Wednesday, 23 January, 2013 - 03:23 am:   Edit PostDelete PostView Post/Check IP

I tried Jan's method but everything appeared upside down. So, came up with this solution.

bench

The bench rests on the front spring suspension pillars. The air intake pipe (elephant's trunk) has to be removed first. Definitely an "at your own risk" device, however I found it very stable to sit on and made accessing the coil components an absolute doddle. In winter, if you run the engine before starting work, it keeps you nice and warm.
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Bob Reynolds
Experienced User
Username: bobreynolds

Post Number: 24
Registered: 8-2012
Posted on Wednesday, 23 January, 2013 - 01:47 pm:   Edit PostDelete PostView Post/Check IP

Very clever, but how on Earth do you get up on it?
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Geoff Wootton
Frequent User
Username: dounraey

Post Number: 65
Registered: 5-2012
Posted on Wednesday, 23 January, 2013 - 03:45 pm:   Edit PostDelete PostView Post/Check IP

The technique is to place a chair by the front wing and stand on it. Then place your knee on the edge of the bench, grasp the middle of the bench and pull yourself onto it. This way you avoid putting any weight on the front wing. The position I found most comfortable was to kneel on the bench and steady my weight with one hand whilst using the spanners etc with the other.

I should note that the bench is screwed solidly together and there are two 1" holes that locate on the damper nuts at the top of the suspension pillars.

A bit eccentric I agree, but after one has spent three hours trying to bolt the hydraulic pipe clip to the rear of the engine, as I did, it doesn't seem so crazy.
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Bill Coburn
Moderator
Username: bill_coburn

Post Number: 1473
Registered: 4-2003
Posted on Wednesday, 23 January, 2013 - 04:15 pm:   Edit PostDelete PostView Post/Check IP

Very resourceful. Can I add two other access approaches for the record.

Remove the bonnet with two of you working put a thick covering on the roof of the car disconnect the earth wire and lamp connector four bolts either side to ratchet off and carry the thing over the top of the car and leave it on the roof.

If you have to get a neighbour or a passing postman in to help make sure he is not a short arse as a 'normal height' person needs to lift the bonnet to face level.

You can undo all the main bolts on your own except the lower outer ones. Give your helper and yourself a ratchet 1/2" A/F spanner. You both hold the panel like a lover, one hand tucked under the lower leading edge and your face cheek pressed against the underside at face height. Best you have some cloth in the gutters either side of the radiator in case there is a slip up.

I realise the bonnet off would not be much help with Geoff's access problem. Another approach I have is to remove the front wheels and sit the car on the bottom swivels of the suspension. With something the size of a PVI this is almost essential to get at the engine unless you want to make up a long platform for both sides of the car!
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Jan Forrest
Grand Master
Username: got_one

Post Number: 432
Registered: 1-2008
Posted on Wednesday, 23 January, 2013 - 09:56 pm:   Edit PostDelete PostView Post/Check IP

Frankly gentlemen, apart from the decidedly ungainly and indecorous attitude I have to take when sprawling across the wing and whole width of the engine, I still find it to be a most effective way of accessing some of the more awkward to reach nuts, bolts, components, etc. In my case this is the easiest approach due to the pain that is caused by excessive (or even any) bending of my spine as all my weight is taken up across my chest. The lower rear exhaust manifold bolts on the A bank side are a case in point. The only thing to remember there is that you're tightening them up backwards (counter clockwise) compared to your point of view!

I must admit that the 'painters trestle' idea could be better when working on the more exposed areas of the engine towards the center and/or rear. I've got some spare lumber kicking around in the garage and will explore the possibility of making something along those lines once the snow has evaporated and air temperatures are more conducive to a shirt sleeve environment. You would think that 6+ decades of living in The North I would be inured to such petty considerations. Sadly nothing could be farther from the truth as I don't do well in the cold or wet - which pretty much describes the average Summer here in Blighty

Regarding climbing over the front wings: I was rather timid the first time I attempted that approach. However I very soon ascertained that the wings are more than stiff enough to take my sylph-like 14+ stone (200+ Lbs) frame. Don't forget that The Old Girl took on a new Audi with one wing and eliminated its driver's front door and wing with just a little crazing of the paint at the leading edge and a few mm of rearward movement!
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Geoff Wootton
Frequent User
Username: dounraey

Post Number: 66
Registered: 5-2012
Posted on Thursday, 24 January, 2013 - 03:11 am:   Edit PostDelete PostView Post/Check IP

I had originally thought of the 'painters trestle' method, but this would have required the making of two robust trestles, 3.5 ft high. These would have been time consuming to make. In addition, I do not like storing bulky pieces of equipment that are used once in a blue moon. How much easier to just lay the 'bench' across the two suspension pillars on the odd occassion I need access to centre/rear area of the engine.
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Jan Forrest
Grand Master
Username: got_one

Post Number: 433
Registered: 1-2008
Posted on Thursday, 24 January, 2013 - 04:02 am:   Edit PostDelete PostView Post/Check IP

Fortunately I already have a pair of folding steel and wood 'workmate' type benches collapsed and hanging from screws on the garage wall. I bought them several years ago as a cheaper and more flexible alternative to a pair of plastic sawhorses. I also have some lumber that was originally purchased for a project that was eventually shelved. Between the lot I can knock up something in a few minutes and tear it down again for storage when not in use.
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Bob Reynolds
Experienced User
Username: bobreynolds

Post Number: 25
Registered: 8-2012
Posted on Thursday, 24 January, 2013 - 12:57 pm:   Edit PostDelete PostView Post/Check IP

That bench is a brilliant idea -until somebody comes along and moves the chair! HELP!
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Randy Roberson
Prolific User
Username: wascator

Post Number: 122
Registered: 5-2009
Posted on Thursday, 02 May, 2013 - 01:51 am:   Edit PostDelete PostView Post/Check IP

Excellent Idea! Somehow I missed this when posted.
Thanks for sharing!