SPECIAL INSTRUCTIONS FOR SCRAMBLER MODEL

In most respects the methods of adjustment, and maintenance needed to certain parts of the Scrambler do not differ from those employed for the standard model. The standard instruction literature can be taken to apply therefore unless special reference is made, and other instructions given in this section.

ENGINE STARTING

Turn on the fuel at both taps, and if the engine is cold, flood the carburetter. (Some machines may need a little flooding even when hot to get a " first-kick " start).

Retard the ignition to approximately half the travel of the lever.

Depress the kick-start crank until compression is felt. Release the crank and allow it to return to the top. Using the exhaust valve lifter control, press down the kick-start crank slowly to the bottom—not further.

After bringing the kick-start crank back to the top again the engine is ready to start by using the kick-start without lifting the exhaust valve.

One kick should suffice if the throttle has been set correctly. The throttle valve should not be opened more than approximately 1/16 -in. when starting.

FRONT FORK.

Lubrication.

Each strut carries 120 c.c. of oil. Periodical draining and renewal of the oil is unnecessary. Refilling should be needed only after complete dismantling or in the case of leakage. Oil of S.A.E. 20 viscosity must be used. Grades recommended are :-

Maintenance.

External cleaning only is required.

Dismantling.

Before doing anything else remove the 3/8-in. dowel screw from the front of the top cross member. This dowel—not fitted to standard models—prevents movement between the cross member and the steering column. All other work is as described in the Service Manual, except that when the adaptors are taken out of the top ends of the fork tubes the damper rods must not be allowed to fall to the bottom of the sliders after the adaptors have been unscrewed from them, as they will bend the ball retaining pins making the ball valves inoperative.

Reassembling.

Assemble as described for standard fork as far as the struts are con-cerned, but do not fit these until the column and top cross member have been fitted to the steering head, and the dowel screw correctly fitted. Note also that a spring steel washer is fitted between the bearing dust cover and the top cross member. This spring washer takes up play in the head bearings, as adjustment in the normal way is impossible because of the screwed dowel.

After fitting the column and top cross member these must be lined up so that the dowel holes in them register exactly with each other to allow the dowel to be fitted.

If it is difficult to fit, line up the holes again until it will enter readily. Do not in any circumstances force the dowel or tap out the threads to make it fit.

When the column and cross member are correctly fitted and the dowel is in place and tightened up, fit the struts, pushing them up through the holes in the bottom cross member, setting them so that the vent holes at the top face to the rear.

Pour the correct quantity of oil into each strut and fit the adaptors to the damper rods, tightening the lock nuts. Screw in the adaptors, but tighten them later.

Fit the front wheel, and with the spindle clamp bolt, and bottom cross member clamp bolts just slack, bounce the wheel several times sharply to line up the sliders and to seat the sleeves in the bottom cross member. Finally tighten the three clamp bolts, and tighten adaptors in the fork tubes.

STEERING HEAD BEARINGS

No adjustment required—see above.

CLUTCH ADJUSTMENT

Adjust exactly as described on page 29. Note however that the clutch cable adjuster is placed accessibly near the carburetter to enable a quick change of cable assembly to be made if necessary. It is not provided for the adjustment of the clutch, which is by means of the clutch spring holder as on standard models.

CHAIN ADJUSTMENT

Primary.

See page 88.

Rear.

Adjust when the machine is normally loaded (suspension strut anchor pins at 11½-in. centres) see page 89, with the rider in the saddle. In this position of loading, and with the bottom run of the chain held taut, it must be possible to depress the top run of the chain to within ½-in. of the head of the swinging arm clamp bolt.

TYRES.

Standard Equipment.

Tyre Pressures.

For Scrambles (Moto-Cross) tyre pressures can be adjusted to suit in­dividual requirements and conditions.

GEAR RATIOS.

With standard sprockets (Gearbox, 16t. ; Rear wheel, 60t.) the overall ratios of the 500 c.c. model are :

• 1st, 16.65 to 1;
• 2nd, 11.41 to 1;
• 3rd, 8.85 to 1.
• Top, 7.2 to 1.

Ratios of 350 c.c. model are :

• 1st, 17.9 to 1,
• 2nd, 12.46 to 1,
• 3rd, 9.5 to 1,
• Top, 7.85 to 1.

These are the lowest available. Higher ratios are obtainable by using larger gearbox sprockets. These can be supplied in several sizes.

REAR SWINGING FORK.

The left and right hand torque tube assemblies are dowelled to the trunnion shaft, and the dowels have to be removed before the trunnion shaft can be taken out. Otherwise dismantling is as detailed on page 60.

When reassembling the procedure will be as for the standard models except that after having pushed the trunnion shaft through the torque tube end lugs and attached the torque tube clamp tool X2938 it will be necessary to line up the threaded holes in the tops of the lugs with the corresponding holes in the trunnion shaft and fit the dowels before tightening the torque clamp bolts. In no circumstances must the threads be tapped out in order to get the dowels to enter. Perfect alignment of the holes must be achieved.

ENGINE.

Maximum power is developed at 6,200 r.p.m. on 500 c.c. engines and at 7,000 r.p.m. on the 350. Any running at much in excess of these speeds will probably cause the valves to touch one another resulting in loss of compression and power. Over revving must be avoided.

LUBRICATION.

The system is the same as on standard models. Oil of S.A.E. 50 viscosity is recommended. Do not use Castor base oils or additives of any sort in the oil or fuel.

Recommended grades are:—

Shell X100. 50.                      Duckham's NOL Fifty                Castrol G.P.

B.P. Energol 50                                                                          Mobiloil D

SPARKING PLUGS.

The cylinder head is threaded for 14 mm. ¾-in. (extra long reach) type plug.

Recommended makes and types are :—

PISTON.

Gives a compression ratio of 8.75 to one on the 500 c.c. model and 9.3 to one on the 350 for Premium grade (80 Octane) fuel.

Piston Ring Gaps.

The end gaps of new rings (checked just inside the mouth of the cylinder at the bottom of the bore) must not be less than :—

IGNITION TIMING.

Contact points to be open to .0015-in. at 38 degrees before top dead centre on full advance. Always check, and if necessary adjust the point gap to .012-in. before checking or resetting the timing. Take all slack out of the timing gears when checking.

TAPPET CLEARANCES.

Tappet clearances cannot be set accurately unless the bottom rocker of the valve that is being adjusted is set midway along the neutral of the cam. See diagram, page 25.

Clearances for checking valve timing—.053-inlet .052 exhaust. Running clearances—Inlet, .006-in. ; Exhaust, .008-in.

It has beenfound that new cylinder base and rocker box gaskets compress during the first forty-eight hours after being fitted, and the shrinkage is enough to reduce the tappet clearances sufficiently to make readjustment necessary.

The shrinkage is due more to the time factor than to heat. In all cases therefore recheck and if necessary reset the clearances after time has been allowed for the gaskets to settle if new ones have been fitted to either or both of these joints.

VALVE TIMING.

Cam No. M17-8. Timing when checked with inlet tappet clearance at

.053-in. and exhaust tappet clearance at .052-in.

Inlet opens 45° before T.D.C. Closes 55° after B.D.C.

Exhaust opens 65° before B.D.C. Closes 35° after T.D.C.

Always have the exhaust push rod removed when checking inlet timing,

and the Inlet push rod removed when checking the exhaust timing.

The tappet clearances must be reset to the running clearances before starting engine.

CARBURETTERS.

• Amal type 10TT9. 1 1/8-in. choke bore.
  • Main jet, 420. Needle jet, 109. Needle position, 4th from top.
  • Throttle valve No. 7. Pilot adjusting screw 1½ turns open.
• Amal type 10TT9. 1 3/16-in. choke bore.
  • Main jet, 390. Needle jet, 109. Needle position, 3.
  • Throttle valve No. 7.
• Amal type TT9. 1 1/16-in. choke bore.
  • Main jet, 360. Needle jet, 109. Needle position, 4.
  • Throttle valve No. 7.

These settings are general and alterations may be necessary to suit different course, weather, or barometric conditions to get the best results.

DISMANTLING ENGINE.

See page 38 onwards.

REASSEMBLING ENGINE.

As described page 44 onwards, except that when refitting cylinder head the four cylinder studs must be screwed as far as they will go, without forcing them, into the crankcase studs. Use a screwdriver in the slots in the tops of the studs.

With the head in place and head nuts fitted the studs must not protrude more than 5/8-in. above the nut faces on any account. On the other hand, the Nylon oil seals in the tops of the special Nylock nuts must engage the top thread of the studs.