SERVICE Velocettte 350 & 500

discs (93) should not show evidence ofoverheating and should be perfectlyflat. When assembling, use soap to as-sist installation of rubber cushions(90).

GEAR BOX. The transmissiongears and shafts can be disassembledafter the engine is removed and thegenerator assembly, primary drive

gear and clutch assembly are removed.The intermediate (gear) cover, shiftcam, input shaft, countershaft and as-sociated parts can then be withdrawnfrom crankcase (Fig. TM3-31).

Late transmissions use differentparts (66, 67, 73 & 79—Fig. TM3-30),Later parts can be installed in earlymodels, but only if all of these parts are

the late type. The early shift cam (66)can be identified by "T** stamped oncam. The late cam is marked "69"stamped as shown in Fig. TM3-32. Thelate shift fork (67—Fig. TM3-30) has7/16-inch diameter boss. The latesecond gear (73) and third gear (79) arestamped "57". Jumping out of gear canbe caused by weak spring (110).

YELOCETfE350 AND 500CC MODELS

350MODEL ViperDisplacement—cc 349Bore—mm 72Stroke—mm 86Number of cylinders 1Plug gap—inch 0.018-0.023Point gap—inch 0.012-0.015Ignition timingDegrees BTDC—Full advance 38Valve Clearance—cold

Inlet—inch 0.005Exhaust—inch 0.006

Electrical System Voltage 6Battery terminal grounded PositiveTire size—front 3.25 x 19

Rear 3.25x19Tire pressure—front 16

Rear 18Rear chain free play—inch See TextNumber of speeds 4Weight^lbs. (Approx.) 380

350Clubman &Scrambler

34972861

0.018-0.0230.012-0.015

38

0.0060.008

6Positive3.00x214.00x21

See Text4

385

500MSS49986861

0.018-0.0230.012-0.015

36

0.0050.005

6Positive3.25x193.25x19

1618

See Text4

385

500Venom

49986861

0.018-0.0230.012-0,015

38

0.0050.005

6Positive3.25x193.25x19

1618

See Text4

404

500Clubman &Scrambler

49986861

0.018-0.0230.012-0.015

38

0.0060.008

6Positive3.00x214.00x21

See Text4

385

500Thruxtron

49986861

0.018-0.0230.012-0.015

38

0.0060.008

6Positive3.00x193.50x19

22-2424-29

See Text4

365

Fig. VL1-1-Expioded view of Amai Monobioccarburetor typicai of that used on some modeis.1. Pilot air screw2. Jet block screw3. Throttle slide4. Clip5. Valve needle6. Pilotjet7. Idle stop screw

10. Jet holder11. Needle jet13. Main jet15. Jetblock16. Float17. Inlet valve19. Primer

MAINTENANCESPARK PLUG. Spark plug elec-

trode gap should be 0.018-0.023 inch.The following plugs are recommended.KLG type FE80 or FEIOO, Lodge HLNor 3HLN, Champion N3 or N4.

CARBURETOR. Amal carburetorsare used on all models. The main jetsize listed in the following specifica-tions is considered minimum andshould be one or two sizes larger forprolonged full throttle operation.

ViperRefer to Fig. VLl-1Carburetor model 376/56Mainjet(13) 230Needlejet(ll) 106Pilotjet(6) 25Clip (4) in second groove from top ofneedle (5).

ViperRefer to Fig. VLl-1Carburetor model 376/61Mainjet(13) 270Needlejet(ll) 106Pilotjet(6) 30

Clip (4) in third groove from top ofneedle (5).

VenomRefer to Fig. VLl-1Carburetor model 389/14Main jet (13) 260Needlejet(ll) 106Pilotjet{6) 30Clip (4) in second groove from top ofneedle (5).

VenomRefer to Fig. VLl-1Carburetor model 389/15Main jet (13) 330Needlejet(ll) 106Pilotjet(6) 30Clip (4) in fourth |p"oove from top ofneedle (5).

MSSRefer to Fig. VLl-1Carburetor model 376/49Mainjet(13) 240Needle jet (11) 105Pilotjet (6) 25Clip (4) in third groove from top ofneedle (5).

129

Velocette 350 & 500 MOTORCYCLE

17

Fig. VL1-2-Exptoded view of Amal carburetor oftype used on Clubman and Scrambler models.

Refer to Fig. VL1-1 for legend.

Clubman (500cc)Refer to Fig. VLl-2Carburetor model 10TT9Choke bore 1 3/16 inchMainjet (13) 370Needle jet (11) 109Throttle slide (3) No.4Clip (4) should be in third groove fromtop of needle (5).Pilot adjusting screw (1) initial

setting lV̂ turns open

Scrambler (500cc)Refer to Fig. VLl-2Carburetor model 10TT9Choke bore 13/16 inchMainjet(13) 390Needlejet(ll) 109Throttle slide (3) No. 7Clip (4) should be in third groove fromtop of needle (5).Pilot adjusting screw (1) initial

setting lV^ turns openClubman (350cc)Refer to Fig. VLl-2Carburetor model TT9Choke bore 11/16 inchMainjet (13) 360Needlejet(ll) 109Throttle slide (3) No. 7Cl̂ p (4) should be in fourth groove fromtop of needle (5).Pilot adjusting screw (1) initial

setting lVfe turns openScrambler (350cc)Refer to Fig. VLl-2Carburetor model TT9Choke bore 11/16Mainjet (13) 340Needle jet (11) 109Throttle slide (3) No. 4Clip (4) in third groove from top ofneedle (5).Pilot adjusting screw (1) initial

setting i ^ turns open

130

ThruxtonRefer to Fig. VLl-3Carburetor model 5GP2Mainjet (13) 280Needlejet(ll) 109Throttle slide (3) No. 4Pilot jet (6) 25Starting jet (8) 125Clip (4) should be in fourth groove fromtop of needle (5).

Idle mixture is adjusted by turningpilot air adjusting screw (1—Fig. VLl-1, VLl-2 or VLl-3), idle speed is ad-justed at stop screw (7).

On models with GP carburetors (Fig.VLl-3), the fuel level should be atmark (line—Fig. VLl-4) on side of floatbowl 0.640 inch below gasket surface offloat bowl. When mounting the floatchamber, turn the mounting sjtud nuts(N) until the line on float chamber (fuellevel) is exactly in line with bottom ofcircle on the air jet plug as shown inFig. VLl-4.

IGNITION AND ELECTRICAL,Ignition point gap should be 0.012-0.015 inch. Full advanced ignitiontiming should occur 38 degrees BTDC

Fig. VL1-4-The fuel level line marked on floatchamber should be exactly in line with bottom ofcircle on the air jet plug as shown. Adjustment Isaccomplished at nuts (N). If float chamber Is toohigh or too low, the fuel-air ratio will be affected.

-24

Fig. VL1-3-Explod0d view of Amal QP carburetor and float boiW usBd on Thruxton models.

N. Nuts1. Pilot air screw3. Throttle slide4. Clip5. Valve needle6. Pilotjet

8. Startine air valve10. Jet holder11. Needle jet12. Airjet13. Mainjet14. Airjet plug

15. Jet block16. Float17. Inlet valve19. Primer20. Float bowl gasket

surface

21. Float pivot22. Flexible mount23. Mounting stud24. Fuel inlet baiuo bolt25. Washer

SERVICE Velocette 350 & 500

on compression stroke for all modelsexcept MSS. On MSS models, the igni-tion breaker points should just openthen the crankshaft is 36 degreesBTDC on compression stroke. Makecertain that ignition timing is checkedat full advanced position. On modelswith automatic (centrifugal) advance,weights can be wedged out whenchecking timing. Ignition timing canbe checked after removing the timinggear cover. A degree wheel can be at-tached to the crankshaft. To change thetiming, turn the crankshaft to correcttiming position and loosen the re-taining nut in the middle of the igni-tion drive gear. NOTE: Loosening thenut will pull gear from the tapered endof magneto shaft. Turn the ignitionbreaker points assembly until thepoints just open, then retighten gearretaining nut and recheck timing.

VALVE SYSTEM. Inlet and ex-haust valves are actuated by a cam-shaft located on the right side of thecrankcase, via rocker type cam follers,push rods and rocker arms. Valveclearance should he adjusted with en-gine cold. To check valve clearance,remove the cover from right side ofrocker box. Turn the crankshaft untilthe inlet push rod (IN—Fig. VLl-6)moves up then back down. When theinlet valve just closes, the exhaustvalve clearance can be checked asshown. To check inlet valve clearance,turn the crankshaft 240 degrees untilthe exhaust valve just begins to open(push rod EX—Fig. VL1-6* starts tomove up) then measure clearance be-tween top end and push rod. Valveclearance should be 0.005 inch for hothvalves on Viper, Venom and MSSmodels. Clearance for Clubman,Scrambler and Thruxton should be0.006 inch for inlet, 0.008 inch for ex-haust.

LUBRICATION. The engine is lu-bricated hy approximately 2 quarts ofSAE 40 oil above 60°F. or SAE 30 oilbelow 60°F. Engine oil should hechanged at least every 2000 miles.When the oil is drained from the reser-voir, the suction filter at bottom (rightcrankcase half) of engine should heremoved and cleaned. Oil should be

Fig. VL1-6-Refer to textwhen adjusting vaive dear-ance (C) between end (4)and push rod (S). Inlet pushrod (IN) Is toward cyiinderand exhaust (EX) is toward

outside.

1. A4ju8ting screw2. Locknut3. Rocker arm4. End5. Push rod6. Cam follower7. Camshaft

5 4 2 1

Fig. VL1-8-Expioded view of the oil tank and res-ervoir assembly. Make certain that oil suctiontube (6) is full of olt before starting engine after

servicing.1. Drain plug

nd cp g

2. Screen and checkvalve seat

3. Check valve ball4. Check valve spring5. Adaptor6. Suction tube7. Return tube

8. Stud9. Center tube

10. Lower plate11. Lower gasket12. Oil tank13. Filter14. Top gasket15. Top plate

maintained at iy2 inches from the topof the oil tank filler neck. The oil tankfilter (13—Fig. VLl-8) should be re-newed every 10,000 miles. If oil drainsfrom the reservoir (tank) into thecrankcase, the check valve (3) isleaking and should be reseated or re-newed.

Oil circulation can be checked afterremoving the oil tank filler cap. If oil isnot circulating back to the tank, makecertain that suction tube (6) is full of

2 1 3

Fig. VL1-9-The transmission ott shoutd be main-tained at ievei of piug (L). Refer~to text for ad-

justing the primary chain.

D. Drain plug F. Filler plug L. Level plug

oil. If the oil tube (6) is allowed todrain, make certain that tube is filledbefore starting engine. The primarychain case and gear box are lubricatedhy SAE 40 engine oil. Capacity of thechain case is approximately Vs pint.Capacity of the gear box is 1.2 pintsand oil should be maintained at level ofplug (L—Fig. VLl-9). Oil is filledthrough hole for plug (F).

CLUTCH CONTROLS. The clutchis provided with two adjustment points.The clutch cahle should have 1/8-3/16inch free play and can be adjusted atthe cable adjuster (1—Fig. VLl-11) inthe middle of the cable. If the clutchslips or does not disengage, proceed asfollows: Turn the clutch cable adjuster(1) all the way in and disconnect cablefrom the hand levijr. Open the throttleand starting air ccmtrols completely,shift transmission to neutral and presskick starter pedal against engine com-pression.

If the clutch slips, remove the frontsection of the rear chain guard. Insertspecial tool (part number KA62/2)through one of the holes in the outputsprocket and into a notch in clutchspring holder (C—Fig. VLl-11). Turnthe rear wheel in normal (forward)direction which will move the sprocketand clutch spring holder in direction(T—Fig. VLl-12) until all slippage isremoved. Connect the clutch cable andturn adjuster (1—Fig. VLl-11) untilcable has V8-3/16 inch free play.

If the clutch will not disengage, in-sert special tool as shown in Fig. VLl-12 and turn rear wheel, sprocket andclutch spring holder in direction (L).

DRIVE CHAINS. The primarychain should have l^ inch free play atinspection hole in primary chain coverat the tightest point. To adjust loosen

131

Velocette 350 & 500 MOTORCYCLE

2

C. Clutch spring holder1. Cable a((juster2. Cam lever3. Rod4. Thrust cup5. Thrust bearing and

races6. Thrust pins7. Back plate8. Front plate 8

Fig. VL1-11 "Drawing of the dutch operating linkage. Refer to text for adjustment

mounting screws (1 & 2—Fig. VLl-9)and the third screw under the trans-mission. Turn the adjusting nuts (4 &5) to move the transmission as requiredto set the correct chain free play, thentighten the three mounting screws. Ifthe primary chain tension is adjusted,the rear chain should also be adjusted.The rear chain free play should be ^inch when the rear shock absorbers arecompressed until the mounting screwsare IVA inches between centers. Therear chain free play can be adjustedwith the rear wheel off of the ground.With motorcycle on the center standand rear wheel free, rear chain shouldhave lVi inch free play.

SUSPENSION. Each front suspen-sion unit on Viper, Venom and MSSmodels should contain 7Ice of SAE 20engine oil. On Scrambler, Clubmanand Thruxton models, each front sus-pension unit should contain 120cc ofSAE 20 oil. The front suspensionshould be drained at plug (1—Fig.yLl-14) and filled at plug (2) with newoil every 10,000 miles.

The rear suspension units are adjust-able for varying load and riding condi-tion. With top mount in the forward

Fig. VL1-12-Clutch adjustment Is accomplishedusing special tool as shown. Sprocket is shownpartially cut away. The clutch spring holder is

shown at (C).

position (S—Fig. VLl-15), suspensionis soft. The top mount can be located atany position in the slot and the rearmost position (F) is firm. NOTE: Makecertain that both suspension units arein exactly the same position.

REPAIRSCYLINDER HEAD AND VALVES.

Remove the carburetor, fuel tank,spark plug, rocker arm oil tube andcover from right side of rocker box.Turn the crankshaft with kick starteruntil the inlet push rod (IN—Fig. VLl-6) opens (moves up), then closes (movesdown). Remove the rocker box re-taining screws and stud nuts. Lift therocker box slightly and turn around thepush rods until it can be lifted straightoff of push rods. NOTE: The rocker boxmay be warped if all retaining screwsand stud nuts are not loosened evenly.Remove the exhaust pipe. Remove therocker drain tube from the cylinderhead and push rod tube, then slide thetop of push rod tube down into lowerpart. Lift the push rods out and removethe cylinder head retaining stud nuts.The cylinder head studs are slotted onthe end and studs should be removed.The cylinder can now be removed.

Face and seat angle for both valves is45 degrees. Clearance between inletvalve stem and guide should be0.00125-0.0025 inch. Clearance be-tween exhaust valve stem and guideshould be 0.00225-0,0035 inch. Ifguides are renewed, the cylinder headshould be heated in water to 212°F.(100°C) before pressing old guides outor new guides in. New guides should bepressed in from top until valve guideprotrudes 11/32 inch above the ma-chined surface as shown at (A—Fig.VLl-16).

When assembling, the valve springs(32 & 33—Fig. VLl-17) overlap.

1. Drain plug2. Filler plug3. Oil seal4. Bushing5. Snap ring6. Damper bushing7. Bushing8. Snap ring9. Damper valve

10. Damper piston11. Washer12. Lockwasher13. Nut14. Damper retaining

screw

Fig. VL1-14-When assembling the front suspen-sion unit the chamfered side of bushing (6)

should be toward top.

Fig. VL1-15-Rear suspension Is adjustable. Atfront of slot (S) suspension Is soft and at rear (F)

Is firm.

132

SERVICE Velocette 350 & 500

27

VL1-16~Vatve guides shoutd protrude 11132 Inchabove machined surface as shown at (A).

Tighten screws and stud nuts retainingthe cylinder head and rocker boxevenly to prevent distortion. Make cer-tain that push rods are correctly posi-tioned as shown in Fig. VLl-6. Refer toVALVE SYSTEM paragraphs in theMaintenance section for adjustingvalve clearance.

PISTON, RINGS AND CYL-INDER. The cylinder can be removedwithout removing engine after re-moving the cylinder head and posi-tioning piston at bottom of stroke. Ringclearance in groove should be 0.001-0.003 inch for compression rings;0.0027-0.0047 inch for the oil controlring. Refer to the following specifica-tions:Ring end gap—

Compression rings—350cc 0.010 inch

Oil control—350cc 0.012 inchVenom—all rings 0.010 inchMSS—all rings 0.015 inchAll other 500cc models . . . 0.020 inch

Standard cylinder bore diameter—350cc models 2.8347 inches500cc models 3.385 inches

Cylinder bore taper or out ofround limit 0.008 inchPistons and rings are available in

standard size and oversizes of 0.020and 0.040 inch. The piston pin shouldhave 0.0007-0,0016 inch clearance inthe rod bushing. The oil hole in the topof piston pin bushing should be alignedwith hole in top of connecting rod. Ifbushing is worn or loose in connectingrod, renew bushing. Connecting rodalignment must be checked after in-stalling the bushing.

When assembling, the split in pistonskirt must be toward front. Compres-sion ratio is changed by installingcompression plates (11—Fig. VLl-18)of different thicknesses.

CAMSHAFTS AND TIMINGGEARS. The timing cover (2—Fig.VLl-18) is attached to the right side ofengine with 10 screws. When remov-ing, be careful not to warp or burr thecover or sealing surfaces. The timinggear steady plate (6) is attached with

3 2

VL1-17-Exploded view of thecrankshaft, camshaft andassociated parts. Beiieviitewasher (W) Is Instatted be-tween crankcase and cam

fottowers.1. Spring collar2. Washer3. Generator pulleyt. Shock absorber spring3. Shock absorber cfrive clutchi3. Primary drive sprocket7. Shims3. Roller bearing9. Roller bearing

10. Shims11. Crankshaft timing gear12. Idler gear13. BushingU. Idler shaft15. Camshaft spindle16. Camshaft17. Bushing13. Magneto drive gear and

advance assembly19. Oil pump worm gear20. Oil pump drive gear21. Oil pump pressure gears22. Oil pump return geare23. Cam followers24. Push rods25. End caps26. Exhaust rocker arm27. Inlet rocker arm28. Valve guide29. Keepers30. Cap31. Retainer32. Valve spring (large loop)33. Valve spring (small loop)34. Spring lower adaptor

four screws. It is necessary to removethe oil pump assembly and worm gear(19—Fig. VLl-17) before removing thecrankshaft timing gear (11). The nutretaining the oil pump worm gear andtiming gear to the crankshaft is lefthand thread.

Camshaft bushing (17) should have0.001 inch clearance on spindle (15).

Fig. VL1-18-Expioded view ofthe crankcase, cyttnderhead and rocker box. Refer

atso to Ftg. VLl-17.

1. Timing cover oil jet2. Timing cover3. Rocker arm pressure line4. Rocker box drain tube5. Suction oil filter6. Timing plate7. Camshaft oil jet8. Push rod tube (lower)9. Push rod tube (upper)

10. Push rod guide plate11. Cylinder spacer12. Decompression lever13. Rocker box

1 2133

Velocette 350 & 500 MOTORCYCLE SERVICE

Fig. VL1-19-ViBW of the camshaft timing gearswith marks (A & B) aligned.

Idler gear bushing (13) should have0.0015 inch clearance on spindle (14).End play of idler gear (12) and cam-shaft (16) should not exceed 0.0015inch.

When assembling, align timingmarks as shown at (A & B—Fig. VLl-19). Backlash of timing gears can beadjusted by loosening the three screwsattaching spindle (14—Fig. VLl-17) tothe crankcase, then moving spindleand idler gear (12) toward rear. Referto preceding paragraphs in Mainte-nance section for adjusting the ignitiontiming. When installing cover (2—Fig.VLl-18, leave oil tube (3) loose untilengine is started. Tighten the connec-tion to cover after oil begins flowingfrom the loose connection.

CONNECTING ROD ANDCRANKSHAFT. To remove the con-necting rod and crankshaft, the engineand gear box must be removed from theframe and crankcase halves must beseparated.

Remove the air cleaner, oil tank,generator and front section of the rearchain guard. Disconnect clutch anddecompression control cables. Removethe cylinder head steady strap, car-buretor and exhaust pipe. Remove thefinal drive sprocket from the transmis-sion output shaft, support the engineand remove bolts from the engine frontand rear mounting plates. Tilt the en-gine and gear box forward and lift outof frame. Remove the clutch assembly,primary drive shock absorber and theprimary drive chain. The gear box cannow be unbolted from the rear of crank-case. Remove the engine oil pump,timing gears, cylinder head, cylinderand piston.

The connecting rod and crankpin areremoved by pressing the crankshaftapart. When assembling, crankshafteccentricity must not exceed 0.001 inchwhen measured at main bearing sur-faces with crankshaft between lathecenters. Connecting rod side playshould be 0.008 inch.

Fig. VL1-20-Exploded view of the clutch and gear box. Most service can be accompiished without removing the engine and gear box from the fram:

134