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OLYMPIAN TECHNICALITIES

22nd November 1935
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Page 39, 22nd November 1935 — OLYMPIAN TECHNICALITIES
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The Second and Concluding Series of Interesting Points Selected from the Editor's Note-book After a Tour of the Commercial Motor

Exhibition

SCORING in clutches has been traced to rivet pockets collecting dust. Now, the clutch facings on the Bristol are fully floating. They fit into a register on the flywheel, and both this and the floating plate have renewable surfacings. A further advantage of the floating facing, which is # in. thick, 3s that in creeping it evenly distributes both the wear and the heat.

An unusual feature is that the dynamo is now driven off the gearbox instead of the engine. The fairly long shaft has rubber-tube flexible joints with centring devices, ami the ample room available permits any. size of dynamo to be employed.

We were surprised to learn that the gearbox is actually electrically insulated from the chassis, not necessarily by intent, but because the propeller-shaft joints are of the Durid rubber type and the box is mounted on long, thick rubber slabs at each side, thus damping out both noise and vibration. .

.An inquiry brought to light the difficulty which makers are experiencing owing to the Variation in tyre sizes as between the products of different factories. This materially alters the speedometer readings, there being as

much as 5 per cent. variation, and as 3 per cent, is the maximum permitted, something had to be done regarding the matter. Altering the drive in the gearbox is sometimes a big job, so the Bristol concern fits a neat 1 to 1 gear in a case at the rear end of the geatbox, and at the upper end of this case is the bevel drive, the ratio of which can easily be changed.

Stop-lamp switches are often very tinny affairs, yet failure may easily be responsible for an accident through warning of a sudden stop not being given; we were therefore pleased to note on the Bristol a really substantial stoplight switch (incidentally, of C.A.V.-Bosch make) which may cost a little more but is worth the difference.

Point's on the Arran Oilers.

Many points of interest were found on the Arran chassis. For instance, we were assured that all the springs are made individually by hand, each leaf being separately bedded, whilst the groove on each spring-shackle pin is widened to permit taking up side play when fitting the cotter bolt.

The push-on form of hand-brake lever is used to give freer access to the cab when the vehicle is stationary.

The mounting of the Gardner engine is also worthy of note. Each arm of the crankcase is exceptionally long and is carried, on a highly compressed rubber cup resting on the top flange of the frame, but a bridge plate of V shape fitted inside the channel transfers part of the load to the bottom flange and over a much larger area. An unusually larrge rubber nosepiece provides the third point of suspension.

The radiator is mounted on a front cross-member and the removal of three bolts at each side permits the two te come away together. At the points where this crossmember is bolted to the side members, the latter are lined with short lengths of smaller channel reversed to give a box section for the bolts.

In several chassis the practice is followed of fitting the Clayton-llewandre vacuum servos for the front wheels over the stub-axle pivots—a simple method which reduces the length and number of connections. Good examples are the Bristol and Gilford.

We believe that the Gifford CF176 chassis is the only one in the Show employing a British.-built engine with overhead inlet valves and side exhaust valves. The unit employed is the Coventry-Climax, and the arrangement is so satisfactory that it is almost impossible to obtain detonation, with the result that a compression ratio of 6.75 to 1 is used. Ignition on this engine is by a Scintilla Vertex magneto, driven by a long vertical rod extending from the oil-pump drive and through the cylinder head, dogs being employed at each end. Although on one model fir:ward control is utilized, the change-speed-Operating shaft is commendably shOrt, thus being more rigid, whilst to bring the lever within easy s29 reach of the driver it is bent forward at a considerable angle, but the upward and backward movement of the lever is said to be preferable to a straight pull.

Amongst the suspension methods possessing special features is that on the Crane maximimi-load trailer. To meet the new regulations the only method that can be employed is to have twin axles at the front and rear, and these must pivot transversely to follow the ground contour. The Crane patented method is to use one underslung spring of small camber with its ends fitting into slots in steel trunnions which have phosphor-bronze bushes and Tecalernic lubricators. The pivoting centre is kept as low as possible, and the. resulting radius described by the tyres when oscillating gives ample vertical movement with small outward movement at the point of contact with the road surface, thus preventing undue scrubbing of the tyres.

The Yorkshire is 'rather unusual, in that, in respect of the side members of the frame, there is not one hole in the flanges except at the extreme. end, where no 'stresses have to be borne. All the cross-members are of welded construction with the ends turned over so that the fitted bolts all pass through the web.

The Maudslay Rolled-steel-channel Frame.

Another interesting frame is that of the Maudslay, because straight-rolled steel channels are employed. Some people may be inclined to look upon this procedure as somewhat old-fashioned. The feature is retained, because customers will not countenance a change. War experience, when vehicles were operating under most difficult conditions, showed that this type of frame stood up to its work without cracking better than any other. The dumbirons are finished in an unusual manner. A V-slot is cut in the web of each channel and the two flanges are pressed together to form a curved and tapered 'end. The parts are then welded and the usual casting fitted in. In each spring the master leaf is carried around the spring eye, the second leaf around this, the third three-quarters around, arid the fourth far enough for its end to come immediately under the centre of the pin, and thus take part of the direct load.

• The engine and gearbox on this vehicle are mounted on a perfectly straight channel-steel subframe slung from -cross-members by inverted V-bolts passing through steel housings, above and below the channel, which contain rubber blocks.

On the oil-engined Vulcan our eye was caught by the unusual but simple arrangement of the change-speed mechanism. The hand lever ends in a bell crank, the horizontal portion having a ball cup engaging with a second horizontal member pivoting in a ball housing bolted to the flywheel casing. At its farther end this second member engages, through a ball joint, with the lever on the selector shaft.

Reverting to the change-speed lever, this is carried in a member which can rock sideways, but is prevented from going to the reverse position by a stud; lifting the lever allows this stud to enter a hole in the rocker.

On the Morris-Commercial is a neat by-pass operating in conjunction with the thermostat and preventing the 'flow of the water from being altogether atrested.

An Anti-splaying Device for Springs.

The rear suspension of the International embodies an anti-splaying device for the spring leaves, the holding-down plate on the top of each spring having its sides extended and recessed to mesh with dogs on the spring pad. The scheme also permits slight vertical movement and reduces the stresses on the bolts.

The crown wheel on this vehicle has a brass-pad torquereaction device, which is adjustable. Between the twin wheels at the rear are spacing plates which permit individual wheels to be adjusted either close together Jor work in brickyards, etc., or apart where sand may be encountered; the sand is then allowed to drop between the wheels. On the Dorman Ajax oil engine is a neat duplex-chain drive. to the overhead camshaft. A feature of this is that by undoing four studs the sprocket wheel can be drawn -back and on to a special stud, so that the timing is not disturbed.

Itat

Notable in the Sunbeam trolleybus braking system is the maker's special Sunbeam-Lockheed compensating and sealing device. This has triple cylinders, and if one of the connections leaks the oil is cut off by a valve, the other two giving full braking. The driving of the Reavell rotary exhauster direct from the driving motor of the vehicle dispenses with the need for an auxiliary •motor,' thus saving considerable weight and being very silent. CABLE TO REAR DRAKES

At the rear of the clutch on the Scammell light multiwheeler is a simple but effective form of rubber-cushion drive.

In the Reo any tendency for the brake cross-shaft to whip is overcome by connecting this shaft to a frame cross member by an adjustable stay. . On the G.E.C.-Leyland trolleybus there is a G.E.C. electrically operated brake with a 12-volt motor. At the end of the motor shaft is a brake drum in which are two shoes. These shoes are brought into use by a member shaped like a pulley but having projecting pieces to operate the shoes. Secured to this pulley and passing partly around it is a wire cable connected to the brake pedal. When the pedal is depressed it tends to turn the pulley, thus assisting in applying the brake, and, at the same time, passing current to the motor, which tends to turn in the same direction and can give any desired degree of braking up to the stalling point, which is high. The friction brake really acts as a servo motor for the Lockheed master piston within the casing. The ordinary brake can still be utilized if the current fails.

Torsion springing is employed in an interesting manner on certain Brockhouse trailers. That shown on a trailer , which was exhibited in conjunction with a Straussler tractor is illustrated.

The duralumin light-alloy undenframe eliminates the localized stressing set up by chassis movements. It is more flexible than steel, and the floorboards are bolted directly on to it. It is claimed that a saving of 60 per cent. is obtained in comparison with an oak underframe of similar strength.

We admired the simple hand or tommybar brake adjuster on the side rods of the Crossley.

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Locations: Coventry, Gilford, Bristol

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