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Problem: Vibrations
Possible Cause Solution
Poor alignment to shaft: The alignment must be accurate even if a flexible
coupling is used (please refer to ‘Alignment’ on page 10).
Flexible mounts not adjusted correctly to take even weight: Check relative compression of each mount.
Flexible mount rubber perished: Replace. (Diesel or oil will eventually perish rubbers).
Loose securing nut on flexible mount: Check alignment and then tighten the nuts.
Insufficient clearance between the propeller There must be at least 10% of the propeller diameter
tip and the bottom of the boat: as tip clearance between the propeller and the bottom
of the boat. Reduce propeller diameter/increase pitch
Loose zinc anode on the shaft: Tighten or replace.
Worn cutless bearing or shaft: Replace.
Weak engine support/bearers: Check for cracked or broken feet.
Problem: Knocking noise
Possible Cause Solution
Propshaft touching gearbox output coupling Adjust, giving correct clearance give 5mm - 10mm
through split boss or Type 16 coupling: between gearbox and propeller shaft.
Flexible mount stud touching engine bed: Adjust stud to clear.
Drive plate broken: Replace/repair.
Engine touching engine bed: Re-align engine/modify bed.
Injectors blocked through excess carbon Remove and check injector nozzles, replace if required.
caused by water in the fuel:
Problem: Transmission noise
Possible Cause Solution
Check gearbox oil level: Top up.
“Singing” propeller: Check with propeller supplier about ‘harmonics’.
Drive plate rattle at tickover: Check engine rpm (must be 850rpm min. in gear).
Worn drive plate: Change.
Propeller shaft hitting the Gearbox half coupling: Move shaft back to give 5mm - 10mm clearance
(Type 12/16 couplings only).
Propeller torsionals causing gears to rattle at low rpm: Fit a torsional flexible coupling such as Centaflex
type 16 or equivalent.
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