|Posted on Sunday, 18 March, 2001 - 14:49: |
My Mark VI is fitted with a Lucas Special Equipment dynamo. The service handbook talks at length about earthing the dynamo is as to stop rusting out of the block. The picture shows a dynamo with a third post to attach the earth strap,to which a capacitor is also attached.
My Dynamo does not have this third post for the earth strap, and I have incorrectly attached the earth strap to the motor during reassembly of the motor car 5000 miles ago. If the dynamo was replaced with a later type with no earth strap post, is this a problem? Any thoughts welcome.
|Posted on Sunday, 18 March, 2001 - 14:51: |
I have just been through the areas you mention as a part of a rebuild, and might be able to help.
First, can you give me the chassis no. of your MkVI?
The voltage regulator problem might be solvable without having to do the transplant you suggest. We achieved the desired result by removing some shims in order to restore the nominated clearance; but I'll give you more explicit detail later.
As to earthing: there was a lot of trouble experienced in finding a satisfactory generator/radiator/engine block electrical connection that would minimise voltage differences and thereby reduce corrosion. The problem you had with locating the third terminal was one we also experenced.
In both of these matters I want to consult with my electrical mechanic friend, to make sure that I get it right.
In any case, we'll need chassis no. in order to be sure which set of electrics you have.
|Posted on Sunday, 18 March, 2001 - 14:52: |
Thanks for your reply. My chassis number is B256MD. It is a 4.5 litre engine, and has a Freestone & Webb body on it.
I fitted the spare regulator I had, and have just completed a test run to the petrol station, which showed the amp meter moving as I would expect. I have earthed the generator by bolting the earth strap to the adjusting bracket, which is as close as I can get it to bolting it to the actual body of the generator.
Would like to know what your friend thinks of this.
|Posted on Sunday, 18 March, 2001 - 14:54: |
Some more comments on the earthing situation. Might be simplest if I just quote from James Taylor's book, "Original Rolls-Royce & Bentley 1946-65", p30, which I have found to be accurate in other respects. (of course, you may well have it, and I'm teaching you how to suck eggs - sorry!) The things he says are also consistent with the service bulletins I have.
"Rolls-Royce was well aware of the problem of silt gathering in the car's cooling system, and attempted to inhibit its formation by electrolytic methods. These involved bonding the dynamo to the radiator and using the current to reverse the natural polarity of the differences existing between radiator and engine. Various methods of bonding were tried as service schemes, and not all of them - as the company admitted in service literature - were successful.
A further modification designed to achieve the same end was introduced during 1951, when the dynamo was insulated from the engine, from 4 1/2-litre chassis B313MB.
On cars where the bonding was applied during production, a bolt for the bonding strip was added to the right-hand frame member behind the radiator. A first scheme was used on: B330MD, B334MD to B340MD, B390MD to B400MD, B15MB, B131MB to B137MB, and B233MB onwards.
This scheme had the bonding strip running from dynamo to chassis bolt and then to radiator. It was found to be unsatisfactory, and in May 1954 a service bulletin announced the definitive scheme, with the bonding running from dynamo to radiator to chassis. Rolls-Royce also recommended that the bonding on earlier cars was altered to conform to the new pattern, and many cars in the list above were probably modified."
So there you have it. I agree that modern inhibitors for radiators go a long way to avoiding the problem. Let's admit that the engines of that period were very multi-metal devices, and consequently any electrolyte in the radiator encourages the establishment of voltaic cells which have lots of nasty outcomes ... And Australia has the hardest water in the world and SA (where I am) has the hardest water in Australia ...
Two other comments. The suppliers of "Tectalloy" radiator inhibitors (for which I have considerable respect) sell a meter which enables potential differences between different points to be measured. I haven't seen it, but I suspect that a modern digital voltmeter with a high impedance input and capable of measuring in the millivolt region might do the same thing, I intend to test the theory later this year.
Secondly, has anyone tried to insert a sacrificial anode into the system? I would imagine using a magnesium plug in an appropriate carrier so that the nagnesium is in contact with the coolant. It works well in yachts.
Re your voltage control regulator: Excellent that you're on the road! But don't throw the old one away. I'm still trying to get the maintenance instructions which details set-up: my friend kept it from when he was at SA Automotive Trades School. It worked for us!
|Posted on Sunday, 18 March, 2001 - 14:55: |
Thaks very much for your detailed reply. I don't have the book you mentioned, so may order a copy. I have a photocopied version of the service manual, which was lent by a friend to copy.
I run inhibitors in the system, but will modify my earthing strap to join to the radiator as well.
My car was exported to Singapore after a few years in England, from where it made its way to Sydney. I expect it missed out on being modified whilst in Signapore. The original radiator was rusted out! The car has a new core, and I am hoping to keep it in good condition.
Thanks again for your help.
|Posted on Sunday, 18 March, 2001 - 14:56: |
On some Mk V1s the Dynamo was insulated from the mounting bracket and the adjustment bracket. These Dynamos had a terminal which let you earth to the radiator matrix and then from there to the chassis. Remember the radiator is also insulated by its mounting too.
Alan ( my first visit to this 'site )