Choosing and Tuning a Riley Nine
The notes in the October issue on "Riley Nine Recognition" aroused so much interest among prospective purchasers of these still-popular cars that it is opportune to add a few further comments.
If you are contemplating the purchase of a Riley Nine it pays to check the oil pressure when the engine is properly warmed-up. If it is low and if you hear noises like piston slap, it is probable that the oil is being released straight back to the crankcase via cracked main bearings. These main bearings wear well for some 60,000 to 100,000 miles, but pieces of white metal tend to break away and to extend from the inside of the bearing to the oil-supply groove. Incidentally, as these bearings are sleeve-type, their replacement will entail dismantling of the engine and replacement or remetalling of the sleeves — you cannot, as a temporary expedient, merely "take-up" the wear. The Riley Nine has the merit of running astonishingly well even when the bores are appreciably worn, while even with slack big-ends oil-pressure is well maintained if the main bearings are sound. Nor does the engine indicate its need for a rebore by excessive smoking or loss of oil. In other words, apart from discovering the state of the main bearings, it is not easy to ascertain the wear in other parts merely by observing the oil-pressure and general symptoms. Incidentally, a dirty relief valve or a strained oil pump can also give low oil-pressure, but usually the main bearings will be at fault. The normal pressure is 40 to 50 lb./sq. in. and one turn of the release valve screw should cause an alteration of 10 lb./sq. in.
So far as engine noise is concerned, the timing gears may be worn, but they are actually seldom at fault. It is worth while checking that the springs which control camshaft end-float have not been omitted when assembling the two plates in the cage containing three balls, beneath the bronze housing in the timing cover. Other sources of noise are worn dynamo bearings, traceable by removing the dynamo to see if the noise will cease, a worn dynamo-driving dog, which should receive the attention of a welder if the dynamo bearings are found to be sound, or broken camshaft damper springs, discoverable by lifting the cylinder head. These springs should be proud of the block when the head is off; replace only by genuine Riley spares.
So far as increasing the power of a standard Riley Nine engine is concerned, a popular dodge is to replace the inlet camshaft with an exhaust camshaft, but if this is done use a camshaft from an engine of the same series, as the ends of Riley camshafts vary appreciably. Otherwise leave the camshaft settings alone. The standard timing should be: inlet opens at t.d.c., exhaust opens 55 degrees after b.d.c. With the dynamo dog slots vertical, the two "O"s on the crankshaft pinion should mesh with the tooth similarly marked on the idler wheel and the camshaft pinions mesh with the double-marked teeth on the idler. A Solex carburetter seems to give good torque at low speeds, but an S.U. gives better general performance. A pre-1936 engine with Solex carburetter will respond well if a 22-mm. choke is used, with jets 10 per cent. larger than those specified. Leave the compensator alone, and only use a larger one if the mixture is rich at high engine speeds. With standard camshafts, twin 26-mm. S.U.s give excellent results, starting tuning with D8 needles. When an exhaust camshaft has been substituted for an inlet one or if a genuine "Brooklands" engine is used, twin 30-mm. S.U.s give the best maximum speed. The 26-mm. S.U.s can sometimes be salvaged from the later Morris Minor or from 1935-38 Morris Eight engines, or those from an M.G. Midget can be used if a taper washer is fitted at the flange to bring the float-chamber level. If such carburetters are adapted, load their pistons with Plasticine until the pistons just give maximum choke-opening at full r.p.m., then cast a ring of the same weight as the Plasticine to fit on the tops of the pistons, when weaker needles can be used without causing spitting back.
Valves and valve gear, if set correctly, will stand up to normal tuning and the straight-through cotter is quite satisfactory even if stronger valve springs are employed. Increasing the compression-ratio results in slight roughness on pre-1933 engines, makes the exhaust more noisy, but improves the "urge." The maximum desirable is about 7.75 to 1 even with benzol in the fuel. Pistons, and proprietary replacements to raise the compression-ratio, interchange pretty freely between different models and years, but note that the 1936-37 "Monaco" and "Merlin" engines have different pistons, some 9 mm. greater from gudgeon-pin to crown than the others.