Engine

Cylinder capacity

Model

MAC (Alloy)

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Capacity

349 cc

349 cc

349 cc

499 cc

499 cc

499 cc

499 cc

Bore

68 mm

72 mm

72 mm

86 mm

86 mm

86 mm

86 mm

Stroke

96 mm

86 mm

86 mm

86 mm

86 mm

86 mm

86 mm

Bore (in.)

2.677

2.8347

2.8347

3.3858

3.3858

3.3858

3.3858

Stroke (in.)

3.780

3.3858

3.3858

3.3858

3.3858

3.3858

3.3858

Capacity (in.)

21.29

21.29

21.29

30.45

30.45

30.45

30.45

Allowable bore wear

0.008

0.008

0.008

0.008

0.008

0.008

0.008

Comp ratio

6.75:1

9.3:1

8.5:1

6.8:1

8:1

8.75: 1

9: 1

Comp ratio vol.

 

42 to 43 c.c.

47 to 48 c.c.

86 to 88 c.c.

68 to 69 c.c.

64 to 65 c.c.

 

.010 Comp plate =

 

1.04 c.c.

1.04 c.c.

1.48 c.c.

1.48 c.c.

1.48 c.c.

1.48 c.c.

.031 Comp plate =

 

3.24 c.c.

3.24 c.c.

4.6 c.c.

4.6 c.c.

4.6 c.c.

4.6 c.c.

   

Piston rings: end gap

Model

MAC (Alloy)

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Compression  (in.) Max wear + 50%

0.0085-0.0115

0.010

0.010

0.015

0.010

0.020

0.020

Compression ring depth (in) 0.062 (-0.001") 0.078 (-0.001") 0.062 (-0.001") 0.078 (-0.001") 0.078 (-0.001") 0.078 (-0.001") 0.078 (-0.001")

Oil control (in.) Max wear + 50%

0.0105-0.0135

0.012

0.012

0.015

0.010

0.020

0.020

Side clearance Compression (in.). Permissible vertical play 0.005"

0.0005 - 0.0025

0.001 - 0.003

0.001 - 0.003

0.001 - 0.003

0.001 - 0.003

0.001 - 0.003

0.001 - 0.003

Side clearance oil control (in.)

0.0025 - 0.0045

0.0027 - 0.0047

0.0027 - 0.0047

0.0027 - 0.0047

0.0027 - 0.0047

0.0027 - 0.0047

0.0027 - 0.0047

 Pistons 

Model

Std. Bore Diameter

Bottom Skirt Clearance

Top Skirt Clearance

Top Land Clearance

Note

VM/TX/MSS solid skirt Hepolite /  Wellworthy / AE

3.3858

0.006

0.008

-

Reduce by0.001 for alloy barrels

VM/TX/MSS solid skirt Omega

3.3858

0.0060 - 0.0065

-

-

Reduce by0.002 for alloy barrels

VM/MSS split skirt Hepolite / Wellworthy

3.3858

0.004

0.005

-

Reduce by0.001 for alloy barrels

VR solid skirt Hepolite / Wellworthy / AE

2.8347

0.005

0.007

-

Reduce by0.001 for alloy barrels

VR solid skirt Omega

2.8347

0.005 - 0.0055

-

-

Reduce by0.0015 for alloy barrels

VR split skirt Hepolite / Wellworthy / AE

2.8347

0.0035

0.0045

-

Reduce by0.001 for alloy barrels

MAC Alloy

0.00

0.00

0.00

0.00

0.00

Iron MSS

3.189 (-0.0003)

0.0052 - 0.0065

0.0092 - 0.0105

0.0178 - 0.0185

Use lower limit for quieter running if carefully running  in
Iron MOV / MAC Hepolite / Wellworthy 2.677 (+/- 0.0005) 0.0045 - 0.006 0.007 - 0.0085 0.0125 - 0.0140 Use lower limit for quieter running if carefully running  in
Iron MOV / MAC Omega 2.677 (+/- 0.0005) 0.0045 - 0.005 - - Reduce by 0.0015 for alloy barrels
MKII KSS Omega  

0.005 - 0.0055

-

-

Reduce by 0.0015 for alloy barrels

 

For piston clearances click here

Cylinder Barrel Lengths

Venom 4.448" (in addition these are normally fitted with one 0.031" and one 0.010" thick compression plates)

Thruxton 4.334"

Tappet clearances (running, set cold)

Model

MAC (Alloy)

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Inlet (in) ...

0.005

0.006

0.006

0.006

0.006

0.006

0.006

Exhaust (in)

0.005

0.008

0.008

0.008

0.008

0.008

0.008

 

Valve Timing (and tappet clearances for checking valve timing) 

Model

MAC (Alloy)

Viper C/man#

Viper#

MSS

Venom

Venom C/man

Thruxton

Cam No.

M17/5

M17/8

M17/8

M17/7

M17/8

M17/8

M17/8

Inlet (in) ...

0.030

0.053

0.053

0.030

0.053

0.053

0.053

Exhaust (in)

0.035

0.052

0.052

0.030

0.052

0.052

0.052

Valve timing:

 

 

 

 

 

 

 

Inlet opens BTDC

30

45

45

19

45

45

45

Inlet closes ABDC

60

55

55

49

55

55

55

Exhaust opens BBDC

60

65

65

49

65

65

65

Exhaust closes ATDC

30

35

35

19

35

35

35

Cam follower radius

0.375

1.000

1.000

1.000

1.000

1.000

1.250

 #Engines prior to VR1262 have M17/7 cam

 

M Series Cam and Cam Timings 

 

 

 

 

 

Clearances 

 

 

 

 

 

 

 

Checking 

Running 

 

 

Cam No.

IO B
TDC

IC A
BDC

EO B
BDC

EC A
TDC

Inlet

Ex

Inlet

Ex

Timing

 

M17

50

60

70

40

.010"

.015"

.003"

.006"

4

MOV & MAC Iron Head

M17- 2

50

60

70

40

.015

.020

.003"

.006"

4

MSS Early rigid

M17-3

30

60

60

30

.025"

.025

.005"

.010

4

MAC Rigid Frame

M17-4

50

60

70

40

.030

.030

.005

.005"

4

MAC Spring Frame

M17-5

30

60

60

30

.030"

.030"

.005"

005"

38

MAC Spring Frame

M17-6

55

65

75

45

.030"

.030"

.006

.006

38

"Competition" cam - Alloy Head MAC

M17-6

55

65

75

45

.030

.030

.012

.012

38

"Competition" cam - Iron and Bronze Head

M17-7

19

49

49'

19'

.030

.030

.005

.005"

36

MSS S/F & Early Viper to eng no 1261

M17-8 

55

65

75

45

.030" 

.030"

.006

.008"

38

Scrambler, Endurance, Venom, Viper from eng no 1262

  

Rockers 

Model

MAC

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Rocker box bore diameter

 

0.750

0.750

0.750

0.750

0.750

0.750

Rocker shaft diameter

 

0.749

0.749

0.749

0.749

0.749

0.749

Max axial wear

 

0.010

0.010

0.010

0.010

0.010

0.010

Max radial wear on either bore or shaft

 

0.005

0.005

0.005

0.005

0.005

0.005

Oil metering hole diameter

 

0.046

0.046

0.046

0.046

0.046

0.046

  

 Valves

Model

MAC

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Valve Head Size In 

1.437 (1952-55)
1.687 (1956-60)

 1.687

 1.687

1.812

1.812

1.812

2.000

Stem Dia - In

 0.310 +0.0005

0.310 +0.0005

0.310 +0.0005

0.310 +0.0005

0.310 +0.0005

0.310 +0.0005

0.310 +0.0005

Valve Guide Bore

 0.312 +0.0005 0.0002

0.312 +0.0005 0.0002

0.312 +0.0005 0.0002

0.312 +0.0005 0.0002

0.312 +0.0005 0.0002

0.312 +0.0005 0.0002

0.312 +0.0005 0.0002

Working Clearance

 .00125 - .0025

.00125 - .0025

.00125 - .0025

.00125 - .0025

.00125 - .0025

.00125 - .0025

.00125 - .0025

Allowable Wear

 .006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

Valve Size Ex

 1.437

 1.560

 1.560

1.687

1.687

1.687

1.687

Stem Dia Ex

0.310 +0.0005 (1952-55)
0.372 +0.0005 (1956-60)

0.372 +0.0005

0.372 +0.0005

0.372 +0.0005

0.372 +0.0005

0.372 +0.0005

0.372 +0.0005

Valve Guide Bore

0.312 +0.0005 0.0002 (1952-55)
0.375 +0.0005 0.0002 (1956-60)

0.375 +0.0005 0.0002

0.375 +0.0005 0.0002

0.375 +0.0005 0.0002

0.375 +0.0005 0.0002

0.375 +0.0005 0.0002

0.375 +0.0005 0.0002

Working clearance

0.0025 - 0.0035

0.0025 - 0.0035

0.0025 - 0.0035

0.0025 - 0.0035

0.0025 - 0.0035

0.0025 - 0.0035

0.0025 - 0.0035

Allowable Wear

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

.006 total, max .003 on each component

Included angle

 

67.5

67.5

67.5

67.5

67.5

70

Valve seat angle

45

45

45

45

45

45

45

Valve seat width Inlet

3/32

3/32

3/32

3/32

3/32

3/32

3/32

Valve seat width - exhaust

1/10

1/10

1/10

1/10

1/10

1/10

1/10

Valve guide protrusion

0.625

0.343

0.343

0.343

0.343

0.343

0.343

Valve spring shim

Installed length of outer 1.500"

0.542 0.562

0.542 0.562

0.542 0.562

10.542 0.562

10.542 0.562

0.542 0.562

Seat pressure at installed length

 102 - 106 lb

108 - 112 lb

108 - 112 lb

108 - 112 lb

108 - 112 lb

108 - 112 lb

108 - 112 lb

Free coil valve spring length 
- Outer
- Inner


2.1875"
2.000"
           

Inlet tract bore

 

1.000 later 1 1/16

1.000 later 1 1/16

1 1/16

1 1/8 later 1 3/16

1 1/8 later 1 3/16

1 3/8

Downdraft angle

 

8

8

8

8

8

10

Exhaust spigot interference fit

 

0.002 0.003

0.002 0.003

0.002 0.003

0.002 0.003

0.002 0.003

0.002 0.003

 

 Hairpin Valve Spring, Wear on Top Coil 

Spring diameters 0.125 Allowable wear 0.025

  Small End and Gudgeon Pin 

Model

MAC (Alloy)

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Gudgeon pin diameter (in.)

0.624

(+.0001)

(-.0001)

0.8235

(+.0001)

(-.0001)

0.8235

(+.0001)

(-.0001)

0.8235

(+.0001)

(-.0001)

0.8235

(+.0001)

(-.0001)

0.8235

(+.0001)

(-.0001)

0.8235

(+.0001)

(-.0001)

Small end bush diameter (in.)

0.625

(+.0003)

(-.0002)

0.8245

(+.0003)

(-.0002)

0.8245

(+.0003)

(-.0002)

0.8245

(+.0003)

(-.0002)

0.8245

(+.0003)

(-.0002)

0.8245

(+.0003)

(-.0002)

0.8245

(+.0003)

(-.0002)

Running clearance

.001

.001

.001

.001

.001

.001

.001

Allowable Wear, pin to bush

.004 - .005

.004 - .005

.004 - .005

.004 - .005

.004 - .005

.004 - .005

.004 - .005

Interference fit

.001 - .0015

.001 - .0015

.001 - .0015

.001 - .0015

.001 - .0015

.001 - .0015

.001 - .0015

Big end to small end centers

 

6.875

6.875

6.875

6.875

6.875

6.875

 

Big end

Model

MAC (Alloy)

Viper  C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Crankpin roller,

track diameter (in.)

1.374 +0.0004

1.499 +0.0004

1.499 +0.0004

1.499 +0.0004

1.499 +0.0004

1.499 +0.0004

1.499 +0.0004

Crankpin rollers, (size, in.)

3/16 x 9/16

3/16 x 9/16

3/16 x 9/16

3/16 x 9/16

3/16 x 9/16

3/16 x 9/16

3/16 x 9/16

Number

16

18

18

18

18

18

18

Oversize available

+0.0002 & 0.0004

+0.0002 & 0.0004

+0.0002 & 0.0004

+0.0002 & 0.0004

+0.0002 & 0.0004

+0.0002 & 0.0004

+0.0002 & 0.0004

Running clearance

0.001

0.001

0.001

0.001

0.001

0.001

0.001

Conrod eye diameter

 1.750 +0.0002 0.0002

1.875 +0.0002 0.0002

1.875 +0.0002 0.0002

1.875 +0.0002 0.0002

1.875 +0.0002 0.0002

1.875 +0.0002 0.0002

1.875 +0.0002 0.0002

Max wear

0.004

0.004

0.004

0.004

0.004

0.004

0.004

Max side play

0.008

0.008

0.008

0.008

0.008

0.008

0.008

Connecting Rod Length

6.875"

6.875" 6.875" 6.875" 6.875" 6.875" 6.875"

  

Timing Gears 

Intermediate Timing Bush bore

0.5625 
+ 0.00025
- 0.0005


Intermediate Gear End Float

0.0015

Camwheel bush bore

0.500
+/- 0.00025

Camwheel spindle diameter

0.499
+0.001

Cam follower bore

0.437
+/- 0.00025 

Rocker bearing bore

0.750

Rocker spindle diameter

0.749

  

Main Bearings

Model

MAC (Alloy)

MSS, VM, VR etc.

Bearing Size

 

 

Interference fit on shaft

 

0.001

Crankcase to chain case o ring dimensions

2.5 x 3/16

To MSS 12078

2.5 x 3/16

MSS 12078, VM etc

3.0 x 7/32

  

Oil Pump 

Model

MAC (Alloy)

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Diameter of gear bore 0.800 +0.001" 0.800 +0.001" 0.800 +0.001" 0.800 +0.001" 0.800 +0.001" 0.800 +0.001" 0.800 +0.001"

Max end float

0.001

0.001

0.001

0.001

0.001

0.001

0.001

Max radial clearance

0.002

0.002

0.002

0.002

0.002

0.002

0.002

Max backlash in gears

0.005

0.005

0.005

0.005

0.005

0.005

0.005

Diameter of pump 1.689" - 0.0005" 1.689" - 0.0005" 1.689" - 0.0005" 1.689" - 0.0005" 1.689" - 0.0005" 1.689" - 0.0005" 1.689" - 0.0005"

Optimum oil temperature after "hard use" 82 degrees C

Maximum Temperature for Removing Oil Pump, Bearings, Valve Guides etc. 160 Degrees C

 

Wet sumping Ball valve diameter 

Ball seat width max 0.020"

Filler - Tecalemite FG 2368

 

Sparking Plug   (14 m.m. dia. 18 m.m. (extra long) reach.) 

Model

MAC (Alloy)

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton
(Hard Ridden)

KLG

FE70

FE100

FE100

FE80

FE100

FE100

FE220

Champion

N5

N3

N3

N5

N3

N3

 

NGK

B5ES

B8ES

B8ES

B6ES

B8ES

B8ES

B9ES

Lodge

HBLN

3HLN

3HLN

HLN

3HLN

3HLN

 

Plug gap (Smallest gap for magneto, largest for coil ignition)

0.018 0.023

0.018 0.023

0.018 0.023

0.018 0.023

0.018 0.023

0.018 0.023

0.018   0.023

 

Torque Settings 

Model

MAC (Alloy)

Viper C/man

Viper

MSS

Venom

Venom C/man

Thruxton

Head 5/16 in studs

15 lb ft

-

18 lb ft

18 lb ft

18 lb ft

-

-

Head 3/8 studs

 

20 lb ft

20 lb ft

20 lb ft

20 lb ft

20 lb ft

20 lb ft

Rocker box cover

3 lb ft

14.5 lb ft

14.5 lb ft

14.5 lb ft

14.5 lb ft

14.5 lb ft

14.5 lb ft

Rocker block

13 lb ft

-

-

-

-

-

-

Oil bolts

10 lb ft

10 lb ft

10 lb ft

10 lb ft

10 lb ft

10 lb ft

10 lb ft

Gearbox main shaft

50 lb ft

50 lb ft

50 lb ft

50 lb ft

50 lb ft

50 lb ft

50 lb ft