Download Manual - Tech Space

JRB Operating Procedures Outline
JET UNIT FAULT FINDING
Jet Unit
No.
Symptom
Possible Cause
1
2
3
4
Solution
The engine unloads (rpm increases).
There is some blockage in the jet unit.
Clear blockage.
Air is getting into the jet.
Check waterseal, inspection cover;
Consult Hamiltons.
A lack of jet thrust (boat speed drops while rpm is high).
There is some blockage in the jet.
Clear jet.
Air is getting into the jet.
Check waterseal, inspection cover, hull design; Consult Hamiltons.
Excessive noise and vibration comes from the Jet Unit.
Blockage of the Jet Unit.
Clear jet.
Blockage of the impeller or stator.
Clear impeller.
Water leaking from under front bearing.
Faulty water seal.
5
Replace water seal.
Excessive high pitched rattling, or rattling whine.
Blockage of the Jet Unit.
Clear jet.
Faulty thrust bearing.
Inspect and repair the thrust bearing.
Cavitation is occurring.
6
7
8
Bad vibrations.
Blockage of the Jet Unit.
The blockage must be removed.
Worn cutless bearing, or cutless bearing
water drain hole blocked.
Check water drain hole; inspect and repair the cutless bearing.
Something caught in the impeller.
Check through inspection hatch; clear obstruction.
Worn driveshaft universal joints.
Inspect and repair the driveshaft as per manufacturer’s
recommendations.
Engine revolutions gradually increasing over a period of time.
Worn or blunt impellers.
Inspect and repair the impeller as well as the wear ring.
Excessive impeller tip clearance.
Inspect and repair the impeller as well as the wear ring.
Sudden increase in engine revolutions with no noticeable decrease in thrust.
Air ingestion, or cavitation.
Faulty tachometer.
9
10
11
Repair tachometer.
Excessive engine revolutions, noisy jet unit with aerated water from nozzle.
Screen blocked with wood or debris or
rope through screen and wrapped around
shaft.
Remove blockage.
Object jammed in stators an/or impeller.
Remove object.
Low engine RPM.
Problem with engine.
Investigate operation of engine.
Incorrect impeller and nozzle selection.
Consult Hamiltons.
Thrust bearing housing too hot to keep your hand on.
Thrust bearing or seal failure.
Overhaul thrust bearing.
Table 1: Jet unit fault finding
D:\dvd\Copy of SA JRB Operating Procedures v0.4.doc
Page 21 of 139