TIMING CHARTS
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These charts can be used to measure the timings of an engine much more easily and just as accurately as any other method. To measure the exhaust, transfer and boost port timings it is only necessary to take the cylinder head off the engine and push the piston to the bottom of the stroke (BDC).
Use a vernier caliper (digital if possible) or it is possible to use an accurate small steel rule also. With digital vernier calipers, measure down from the top of the liner to the piston using the depth gauge, then reset to zero. Take the liner out, measure from the top of the liner to the top of the port and compare that measurement to the chart, this will give the port timing duration(total open period).
To measure the induction timing, measure again to BDC and reset to zero, turn the crank until the port starts to open or close, take the measurement, compare to the chart to show the before and after TDC timing measurement ( TDC = top dead centre ) A LOT EASIER THAN USING A TIMING DEGREE WHEEL!
If these charts are not comprehensive enough or do not cover the engines that you use then we sell  the ETP range of engine tuning kits. ETP2 is for all nitro marine engines. This contains software which displays port timings, blowdown, trapped and geometric compression ratios and  tuned pipe lengths. The text and pictures accompanying the software describe all aspects of modifying an engine and include step by step instructions.  ETP5 is for Zenoah engines only and this program is unique in that it shows how to measure the port timings from the base of the cylinder.   click here for ETP2     click here for
ETP5

PLEASE NOTE .  The terms referred to on these tech tips pages:
Induction refers to the disc/rotor/drum timing.  Transfers are the side ports in the liner ,normally either 1 or 2 ports each side. The boost is the  port/ports in the liner opposite the exhaust port. Bypass ports are the small ports through the side of the piston and liner. Sub exhaust ports are the extra small exhaust ports found on a few engines (CMB21TT) ( RB)
CMB21 LONGSTROKE
Transfer duration Exhaust duration

Induction opening BTDC

Induction closing ATDC
Degrees Height mm

120

3.29

121

3.34

122

3.40

123

3.45

124

3.51

125

3.57

126

3.62

127

3.68

128

3.74

129

3.79

130

3.85

131

3.91

132

3.97

133

4.03

134

4.09

135

4.15

136

4.21

Degrees Height mm

175

6.80

176

6.87

177

6.95

178

7.02

179

7.16

180

7.24

181

7.31

182

7.31

183

7.38

184

7.46

185

7.53

186

7.60

187

7.68

188

7.75

189

7.83

190

7.90

191

7.98

192

8.05

193

8.13

194

8.20

195

8.28

196

8.35

197

8.43

 

Degrees Height mm

150

0.83

151

0.77

152

0.72

153

0.67

154

0.62

155

0.57

156

0.53

157

0.49

158

0.44

159

0.40

160

0.37

 

Degrees Height mm

52

12.76

53

12.62

54

12.49

55

12.35

56

12.21

57

12.07

58

11.93

59

11.78

60

11.64

61

11.50

62

11.35

63

11.20

64

11.06

65

10.91

66

10.76

67

10.61

68

10.46

69

10.31

70

10.16

71

10.01

72

9.86

73

9.71

74

9.56

75

9.41

 

 

 
CMB21 Short Stroke
Exhaust, Transfer & Boost Timings(duration)
Degrees Height (mm) Degrees Height (mm)
171 6.42
172 6.49
173 6.56
120 3.25 174 6.63
121 3.30 175 6.70
122 3.35 176 6.77
123 3.41 177 6.84
124 3.46 178 6.91
125 3.52 179 6.99
126 3.57 180 7.06
127 3.63 181 7.13
128 3.69 182 7.20
129 3.74 183 7.27
130 3.80 184 7.35
131 3.86 185 7.42
132 3.91 186 7.49
133 3.97 187 7.56
134 4.03 188 7.64
189 7.70
XXXXXX XXX 190 7.78
166 6.08 191 7.85
167 6.14 192 7.93
168 6.21 193 8.00
169 6.28 194 8.07
170 6.38 195 8.15
 
CMB21 Short stroke 

Induction Timings before & after TDC

Before TDC After TDC
Degrees Height (mm) Degrees Height (mm)
138 1.61 50 12.8
139 1.53 51 12.68
140 1.45 52 12.54
141 1.38 53 12.41
142 1.31 54 12.28
143 1.24 55 12.14
144 1.18 56 12.00
145 1.11 57 11.87
146 1.05 58 11.73
147 .99 59 11.59
148 .93 60 11.48
149 .87 61 11.31
150 .82 62 11.16
151 .76 63 11.02
152 .71 64 10.88
153 .66 65 10.73
154 .61 66 10.58
155 .57 67 10.44
156 .52 68 10.29
69 10.15
70 10.00
71 9.85
72 9.7
CMB90 Timings
Exhaust, Transfer & Boost Timings(duration)
Degrees Height (mm) Degrees Height (mm)
125 5.18 178 10.16
126 5.26 179 10.27
127 5.35 180 10.37
128 5.43 181 10.48
129 5.51 182 10.58
130 5.59 183 10.69
131 5.68 184 10.79
132 5.76 185 10.90
133 5.85 186 11.00
134 5.93 187 11.11
135 6.02 188 11.22
136 6.11 189 11.32
137 6.19 190 11.43
138 6.28 191 11.54
139 6.37 192 11.64
140 6.46 193 11.75
141 6.55 194 11.86
142 6.64 195 11.96
143 6.73 196 12.07
144 6.82 197 12.18
145 6.91 198 12.29
146 7.00 199 12.39
147 7.10 200 12.50
148 NA 201 12.61
149 NA 202 12.72
150 NA 203 12.83
151 NA 204 12.94
152 NA 205 13.04
153 NA 206 13.15
154 NA 207 13.26
CMB90 Timings
Induction Timings before & after TDC
Before TDC After TDC
Degrees Height (mm) Degrees Height (mm)
133 2.95 50 18.76
134 2.83 51 18.57
135 2.71 52 18.38
136 2.59 53 18.19
137 2.47 54 17.99
138 2.36 55 17.80
139 2.24 56 17.60
140 2.14 57 17.40
141 2.04 58 17.19
142 1.93 59 16.99
143 1.83 60 16.78
144 1.74 61 16.58
145 1.64 62 16.37
146 1.55 63 16.16
147 1.46 64 15.95
148 1.37 65 15.74
149 1.29 66 15.53
150 1.21 67 15.31
151 1.13 68 15.10
152 1.05 69 14.88
153 0.98 70 14.66
154 0.91 71 14.45
155 0.84 72 14.24
156 0.77 73 14.02
 
CMB45H(CAM) / EVO Timings
Exhaust, Transfer & Boost Timings(duration)
Degrees Height (mm) Degrees Height (mm)
125 4.27 175 8.15
126 4.34 176 8.24
127 4.41 177 8.32
128 4.48 178 8.41
129 4.55 179 8.5
130 4.61 180 8.58
131 4.68 181 8.67
132 4.75 182 8.76
133 4.82 183 8.84
134 4.9 184 8.93
135 4.96 185 9.02
136 5.03 186 9.11
137 5.11 187 9.2
138 5.18 188 9.28
139 5.26 189 9.37
140 5.33 190 9.47
141 5.41 191 9.55
142 5.48 192 9.64
143 5.55 193 9.73
144 5.63 194 9.82
145 5.71 195 9.91
146 NA 196 10
147 NA 197 10.09
148 NA 198 10.18
149 NA 199 10.27
150 NA 200 10.36
151 NA 201 10.45
152 NA 202 10.54
153 NA 203 10.63
154 NA 204 10.73
 
CMB45H(CAM) / Timings
Induction Timings before & after TDC
Before TDC After TDC
Degrees Height (mm) Degrees Height (mm)
133 2.43 55 14.79
134 2.33 56 14.62
135 2.23 57 14.46
136 2.13 58 14.29
137 2.03 59 14.12
138 1.94 60 13.94
139 1.85 61 13.77
140 1.76 62 13.6
141 1.67 63 13.42
142 1.59 64 13.24
143 1.51 65 13.07
144 1.43 66 12.89
145 1.35 67 12.71
146 1.27 68 12.53
147 1.2 69 12.35
148 1.13 70 12.17
149 1.06 71 11.99
150 0.99 72 11.81
152 0.86 73 11.63
153 0.8 74 11.45
154 0.74 75 NA
155 0.69 76 NA

 

NOVAROSSI 21LONGSTROKE
Exhaust, Transfer & Boost Timings(duration)
Degrees Height (mm) Degrees Height (mm)
125 3.56
126 3.62 179 7.11
127 3.68 180 7.18
128 3.74 181 7.25
129 3.79 182 7.33
130 3.85 183 7.40
131 3.91 184 7.47
132 3.97 185 7.55
133 4.03 186 7.62
134 4.09 187 7.70
135 4.14 188 7.77
136 4.21 189 7.85
137 4.27 190 7.92
138 4.33 191 7.99
139 6.37 192 8.07
XXXX XXXX 193 8.15
165 6.1 194 8.22
166 6.17 195 8.30
167 6.24 196 8.37
168 6.31 197 8.45
169 6.39 198 8.52
170 6..46 199 8.60
171 6.53 200 8.68
172 6.60
173 6.67
174 6.74
175 6.81
176 6.89
177 6.99
178 7.03
NOVAROSSI 21 LONG STROKE

Induction Timings before & after TDC

Before TDC   After TDC
Degrees Height (mm)   Degrees Height (mm)
      50 13.09
      51 12.95
135 1.89   52 12.82
136 1.77   53 12.68
137 1.70   54 12.54
138 1.62   55 12.40
139 1.54   56 12.26
140 1.47   57 12.12
141 1.39   58 11.98
142 1.33   59 11.83
143 1.26   60 11.69
144 1.19   61 11.54
145 1.12   62 11.40
146 1.06   63 11.25
147 1.00   64 11.10
148 .94   65 10.95
149 .88   66 10.80
150 .82   67 10.65
151 .77   68 10.50
152 .72   69 10.35
153 .67   70 10.20
154 .62   71 10.05
155 .57      
156 .52      

 

CMB 67 / 80 H (CAM)
Exhaust, Transfer & Boost Timings(duration)
Degrees Height (mm) Height
(inches)
Degrees Height (mm) Height
(inches)
121 4.6 .181 174 9.24 .364
122 4.67 .184 175 9.34 .368
123 4.75 .187 176 9.44 .372
124 4.82 .190 177 9.54 .376
125 4.90 .193 178 9.64 .380
126 4.98 .196 179 9.74 .383
127 5.06 .199 180 9.84 .387
128 5.13 .202 181 9.94 .391
129 5.21 .205 182 10.04 .395
130 5.29 .208 183 10.14 .399
131 5.37 .211 184 10.24 .403
132 5.45 .215 185 10.34 .407
133 5.53 .218 186 10.44 .411
134 5.62 .221 187 10.54 .415
135 5.70 .224 188 10.65 .419
136 5.78 .228 189 10.75 .423
137 5.86 .231 190 10.85 .427
138 5.95 .234 191 10.95 .431
139 6.03 .237 192 11.05 .435
140 6.12 .241 193 11.16 .439
165 8.37 .330 194 11.26 .443
166 8.47 .333 195 11.36 .447
167 8.56 .337 196 11.46 .451
168 8.65 .341 197 11.56 .455
169 8.75 .344 198 11.67 .459
170 8.85 .348 199 11.77 .463
171 8.95 .352 200 11.87 .467
172 9.05 .356
173 9.15 .360
CMB67 / 80H (CAM)

Induction Timings before & after TDC

Opening Before TDC Closing  After TDC
Degrees Height (mm) Height
(inches)
Degrees Height (mm) Height
(inches)
138 2.23 50 17.87
139 2.12 51 17.69
140 2.02 52 17.51
141 1.92 53 17.32
142 1.82 54 17.13
143 1.73 55 16.94
144 1.64 56 16.75
145 1.55 57 16.56
146 1.46 58 16.37
147 1.38 59 16.17
148 1.29 60 15.97
149 1.21 61 15.77
150 1.14 62 15.52
151 1.06 63 15.37
152 .99 64 15.17
153 .92 65 14.97
154 .85 66 14.77
155 .79 67 14.56
156 .73 68 14.36
69 14.15
70 13.95

 

TECHNICAL INFORMATION
MOTOR CC BORE STROKE ROD LENGTH
CMB21SS 3.48 16.45 16.4 30mm
CMB21 LS  3.48 16.3 16.7 30mm
CMB45 EVO 7.46 21.8 20 36mm
CMB45 H(CAM) 7.46 21.8 20 36mm
CMB67EVO 10.9 25 22.2 41.5mm
CMB80EVO 13.1 27 22.9 41.5mm
CMB67H(CAM) 10.95 25.3 21.8 41.5mm
CMB80H(CAM) 12.5 27 21.8 41.5
CMB90 GP/EVO 14.9 28 24.2 45.5
         
         
         
         
         
         
 
   

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ęDave Marles, Prestwich Model Centre, 1 Mill St., Golborne, Nr Warrington, England.

 

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