Radio and an M.G.
John Norfolk gives some useful hints about installing car radio in a sports car.
I have an “L”-type M.G. Magna, fast but noisy. The other day I acquired a very impressive-looking American Bosch car radio, complete with illuminated remote controls. Rather sheepishly I showed it to my wife.
“What on earth is that cake tin with all the wires coming out of it? ” was her opening and rather damping remark. I explained to her what it was. I told her it was going to be installed in our car. I extolled wistfully the joys of driving through leafy lanes while listening to “I’ve got you under my skin.” I told her how much nicer the “news in Gaelic” sounded at 70 m.p.h. She was not impressed. “Don’t be silly,” she said, “as it is, one can’t hear oneself talk above 20 miles per hour and over 50 miles an hour one couldn’t hear a bomb drop.” In a highly chastened mood I retired to the garage to brood upon the wire-infested cake tin. You see, as usual, my wife was perfectly right; amongst all the other noises that my car makes, music from a car radio would be absolutely wasted. It would be a mere drop in the ocean. But I had set my heart on hearing Stuart Hibberd’s well-modulated tones drifting out from underneath the dashboard, and so I started on the job of noise elimination.
The biggest item, of course, was the exhaust. At that time the pipe from the exhaust manifold entered a small expansion chamber about 2 ft. long, from the other end of which protruded another pipe, terminating in a fishtail; all very nice and efficient, no back pressure and a healthy roar. The healthy roar now had to be subdued to a soft whisper without loss of performance. The breaker’s yard was visited, and I returned triumphantly with a huge silencer about 6 ft long and 1 ft, in diameter. I fitted this in place of the expansion chamber and fishtail. The result was excellent, with no falling off in performance.
Having effectively quietened the exhaust, all the other noises became much more apparent and, therefore, more easily diagnosed. By far the worst offender was the valve gear, calling for the comparatively simple job of rocker adjustment. I say comparatively simple because, with an overhead camshaft, adjusting the rockers to their correct clearance of .003 in. can, when the engine becomes old, be a rather deceptive job, inasmuch as hollows get worn in the undersides of the rockers, so that, although the feeler gauge may show a clearance of 3 thou., the actual clearance may be as much as 6 thou. After the valve gear, I turned my attention to all those things which rattle and squeak on an elderly car, such as the doors and hood. In effect, installing radio galvanised me into doing all those maddening little jobs which normally do not get done until a door falls off or the hood becomes airborne at high speed.
The car now being relatively quiet, I got down to installing the radio. To start with, I drilled two holes through the side of the tool box, which is under the bonnet directly behind the facia board. Through these holes I inserted the two long bolts protruding from the back of the set. A couple of large washers and nuts tightened up from the inside of the tool box rendered the set fairly secure. As an extra support I passed a metal strap underneath the set, anchoring both ends of it to the underside of the scuttle. Between the top of the set and the scuttle I inserted a strip of Sorbo rubber to damp out vibration.
So far so good. Now for an aerial. I rather fancied a telescopic one, so with this end in view I straightened out a 3-ft. length of copper petrol piping, into which I inserted a 6-ft,. length of heavy gauge steel wire. It was a perfect fit, loose enough to be pulled in and out, tight enough to stay put in any position desired. The lower half of the copper piping I enclosed in a short piece of small bore rubber hose as an insulator. By means of two small “U” bolts the whole assembly was then secured to the outside of the scuttle on the same side as the set. From the bottom of the aerial a short, heavily-insulated wire passed to the set. The body of the set I earthed to the car chassis. The positive connection from the set was plugged into the inspection lamp socket on the dashboard via a 15-amp. fuse.
I switched on. The dial on the dash lit up cheerfully and a heartening hum emanated from the set. After about 30 sec. the valves warmed up and music poured forth. The volume was terrific, the tone good; I had a fair choice of stations and good selectivity. Then I turned on the ignition and the first snag became apparent. A loud “tick-tick-tick” broke in on the programme; it was the S.U. petrol pump. Worse was in store, for as soon as the engine started the interference became absolutely deafening. I stopped the engine and began, by methods of trial and error, to suppress the interference.
First of all I fitted 5,000-ohm suppressors to all the plugs. The result was not entirely satisfactory. The interference, though lessened in volume, was still present and engine performance suffered considerably; starting from cold became very difficult and running at all speeds very sluggish. The suppressors were removed and a single 10,000-ohm resistance inserted in the circuit from the H.T. terminal on the coil to the centre electrode in the distributor head. As well as this I connected a .5-mfd. condenser between the battery side of the primary coil and earth. At a tick-over the result was perfect, no interference at all, except for an occasional click from the petrol pump. Upon accelerating, however, a sort of whirring noise became apparent, always coming in at the same speed and increasing in volume. It was the dynamo, which only interfered when the cut-out points closed. To combat this I connected a .025-mfd. condenser between the armature terminal and earth. At the same time I connected a similar condenser between the petrol pump and earth.
I can now listen to the radio with ease and without interference at any speed, and none of the modifications carried out affect the engine performance.