TM 10-3950-672-24-2
Blowby Limits
The following table gives the values of blow-by that should be seen on the B Series engines. These blow-by values have
been calculated on amount of displacement of the engine, volumetric efficiency, and cylinder pressure.
Engine
Speed
New Limit
Worn Limit
Model
RPM
(Litres/Minute)
(Litres/Minute)
4B
2200
18
36
4B
2500
20
40
4B
2800
23
46
Note: The blow-by values are for 100 percent load at the given speed. The B Series engines are measured using a
5.613 mm [0.221 in] diameter orifice.
Blowby Measurement
Blowby is generally recorded in Liters/Minute, but a water manometer may be used to measure blowby from the breather
tube after fabricating the following adaptation:
1. Plug the end of the straight portion of a pipe tee.
2. Drill a 5.613 mm [0.221 in] orifice in the plug.
3. Connect the open straight portion of the pipe tee
to the breather tube.
4. Connect a water manometer to the 90 degree
outlet.
5. Use the Blowby Conversion Chart to convert the
manometer reading to litres/minute.
Blowby Conversion Chart (5.613 mm [0.221 in] Orifice)
Inches of Water
Litres/Minute
Inches of Water
Litres/Minute
1
27
19
121
2
40
20
124
3
49
21
128
4
58
22
131
5
64
23
135
6
71
24
137
7
76
25
140
8
81
26
144
9
86
27
147
10
90
28
150
11
94
29
154
12
98
30
157
13
102
31
160
14
105
32
163
15
109
33
166
16
112
34
169
17
115
35
172
18
118
5-313