The turbo-compressor (ie. turbo-charger) depicted, on this page, was
selected for it's wide range of application and specifications do change
from one engine to the next.
In the event of excessive exhaust smoke or loss of engine power, faulty action of the turbo-compressor is to be suspected. The supercharging pressure should then be checked. When speed slowly decreases the bottom of the boat should also be examined and, if necessary, cleaned.
CHECKING THE SUPERCHARGING PRESSURE
A. Connect a pressure gauge to the measuring connection on the intake manifold.
B. Measure the supercharging pressure
under full load and at full throttle whilst the engine speed passes relatively slowly through a suitable speed, e.g. 56.7 r/s (3.400 r/m) for B-power engines or 46.6 r/s (2.800 r/m) for C-power engines, see the Supercharging Pressure Diagram
below. The supercharging pressure should not be less than the specified minimum value. Check the engine speed with a hand tachometer.
NOTE: It is important to maintain full loading long enough to enable the pressure to
stabilize if results are to be correct. Also note that the pressure
varies with the temperature of the intake air, as shown in the diagram below. The supercharging pressure is given at +200 (680F). which implies that the measured pressure must be corrected as shown in the diagram if the intake air is not at this temperature when the measurement is made.
Example: A measured pressure of 80 kPa (0.8 kp/cm2 = 1 1.3 Ibf/in2) measured at -100C (140F) corresponds to 70 kPa (0.7 kp/cm2 = 9.9 Ibf/in2) at +200C (680F), i.e. the pressure decreases as the temperature rises, due to reduced air density.
MEASURES TO BE CARRIED OUT WHEN THE SUPERCHARGING PRESSURE IS TOO LOW
A. Air intake. air cleaner
Check that the air intake is not blocked. Check the air cleaner and replace it if
Check for leakage between the turbo housing and bearing housing or between the compressor housing and the bearing housing. Also check the joint between the turbo compressor and the inlet manifold.
Remove the air cleaner. Check that the compressor rotor is at rest and then see whether the rotor is stiff when turned by hand. If the rotor is difficult to turn, the compressor should be replaced or reconditioned.
Measure the axial and radial clearances of the rotor unit. The radial clearance is measured on the turbine side (at the outer edge of the hub, see illustration).
Max. allowable axial clearance: 0.16 mm (0.00630 in). Max. allowable radial clearance: 0.42 mm (0.01654 in). If the wear limits are reached, the turbo-compressor should be replaced or reconditioned.
If no faults are found:
Check whether the compressor section requires cleaning, see point D. Deposits of soot and oil can cause low supercharging pressure.
The compressor section can be cleaned with the unit still on the engine, as follows:
Remove the compressor housing. Clean the compressor housing, the compressor rotor and the bearing shield with an agent such as white spirit. Fit the compressor housing and
re-measure the supercharging pressure.
If the supercharging pressure is still too low the following checks should be made:
E. Throttle Control
Check that the throttle control can move the injection pump throttle arm to the maximum position.
F. Injection Pump
Check the injection angle and the high idle speed.
If necessary, check the entire pump on a pump test bench.
G. Feed Pressure
If necessary. replace the fuel fine filter and clean the pre-filter. There must be no fuel leakage.
Check the opening pressure and the spray pattern.
I. Condition of engine
Check the valve clearances and the compression pressure. If the supercharging pressure is still
unsatisfactory, the compressor must be reconditioned or replaced.
See basic internal diagram.