From RROCA-info
The Silencing of 'Henry R'
By Peter Heuzenroeder, 1995
In 1975 I purchased SDB 114, a very original black 1951 Silver Dawn with beige upholstery. After the initial flush of enthusiasm wore off and I became more and more familiar with the car and its particular foibles I became acutely aware of a habit it had of emitting a most un-Rolls-Royceish roar as soon as the engine reached about 2,000 rpm (i.e. about 40 mph in top gear).
The previous owner, who had only had the car for a short time, claimed that one of his reasons for wanting to sell it was that it was not as quiet as he had imagined Rolls-Royces should be - it was his first, and as far as I know his only venture into the realm of Rolls-Royce. (I later heard that he regretted selling it - a common complaint of people who sell their Silver Dawns!)
Originally I thought, as I still do, that the 'silence' of a Rolls-Royce has to be judged by its era; i.e. a Silver Dawn should be compared to say a '48 series' Holden, Mk V Jaguar, Morris Oxford or to a Standard Vanguard. By those standards it is very quiet if not so much by today's standards (although not bad even so).
However, all that aside, I began to realise a little of what the previous owner meant, and the more I became aware of the noise the more it got to me, particularly when driving other Silver Dawns which didn't do it!
Some years ago I had the engine removed and reconditioned. I thought that this would incidentally cure the roar as well, and you can imagine my disappointment when I got the car back and nothing had changed in that regard.
I conducted various tests and determined that it was definitely related to engine speed, and not road speed, and that it was something to do with the engine rather than the gearbox, differential, tailshaft or wheel bearings etc., (the list of possibilities that went through my mind was endless). I thought perhaps there was a hole in the firewall which shouldn't be there or some trim missing, but comparison with other cars revealed that such was not the case; it was all intact and original. I thought there might be some peculiar quirk with the early post-war six cylinder engine, for which someone else had by now found a cure, and I wrote to the technical people in the Rolls-Royce Enthusiasts' Club. Whilst they were very prompt and solicitous they could offer no solution ... obviously not an inherent problem.
I finally began to suspect the fan. It sounded like a fan noise. So I had the fan removed and balanced and the pitch fined a little by an engineer who balances aircraft propellers. There seemed to be a very slight improvement. Disappointed. I went on putting up with it. I thought perhaps it was something to do with the way the air was drawn through the radiator matrix. That was recorded recently to overcome overheating and leakage problems, but still the roar persisted. It really took the edge off the pleasure of the car.
I was told that a previous owner but one, a Mr Sullivan who owned the car for many years, having bought it from the original owner, had tried different fans and all sorts of things to cure the problem. People helpfully just shook their heads and said it was "always a problem with that car". But why, damn it?!
When the engine was reconditioned and again when the radiator came out it was said that the car seemed to have been in a front end collision at some stage of its life. Perhaps the fan had been damaged. Perhaps someone put the wrong type of fan on the engine when the car was repaired.
In desperation I checked through what mechanical literature I have and discovered that at chassis number LSCA9 the fan size was changed from 16" rotating at 1. 1 engine speed to 17� rotating at .850 engine speed. Was this part of the answer? I removed the fan and measured it. It was exactly 17� i.e. what it was supposed to be. Gloom ... but wait. To rotate at a lower speed must have meant a bigger pulley! Just at that time I needed a new fan belt and was told there were two sizes. Did I want the large or small?
Ahha!
Having fitted the large one I found that there was no adjustment left to tighten it on the dynamo. Obviously too big for my car! Anyway, having taken the fan off I took the car for a drive without it in the cool of the evening. Suddenly there was silence at any speed!! Bliss! A quick check with my cousin's Silver Dawn (a renownedly silent car) revealed that its fan pulley was enormous compared to mine. At last, the answer! God knows why but my car had the small pulley rotating the big fan much faster than it was supposed to go. A 'phone call to a dealer elicited that they indeed had a large pulley. A deal was struck, the pulley fitted and now 'Henry R' is as silent as it should be at last.
Why 'Henry R'? When my father was a child the family car was a much loved Model T Ford which was affectionately called 'Henry F' - the choice was obvious.
Editorial note: Though a Silver Dawn is the subject of this article, the lesson contained therein applies equally to all the early post-war six cylinder cars. The high-speed fan pulley (for use only with the 16" fan) is part number RE11270, and the low-speed pulley (for use with the 17� fan) is part number RE4736. As Peter's experience shows, mixing and matching doesn't work! - M.I.B.