Stern tube oil above 60 °C: what to do?

Cause: Bearing damage, cooler or thermometer fault. What to do: Check for white metal, slow down, repair cooler

Sudden drop of stern tube oil level: what to do?

Cause: Leak from aft or forward seal. What to do: Find leak; with double security type close spare-seal valves and use ring #3S

Emulsified oil or seawater in drain: what to do?

Cause: Damaged No.1/No.2 rings or trapped foreign matter. What to do: Raise oil pressure 0.3–0.5 kgf/cm², drain emulsion, contact maker

Fresh water in drain: what to do?

Cause: Leak from aft peak tank. What to do: Drain and inform the shipyard

Forward seal tank level changes: what to do?

Cause: No.4 or No.5 ring damage. What to do: Recover or refill oil, contact maker

Kobelco Compact Seal CX-500

Oil-lubricated stern tube seals (aft and forward)

The Kobelco Compact Seal CX-500 keeps sea water out of the oil-lubricated stern tube and keeps oil in. The aft seal has Viton lip sealing rings (No.1–No.3) running on a chrome steel liner fixed to the propeller boss; the forward seal has rings No.4 and No.5 with its own oil tank. The finished plan has assembly drawings with parts lists for both seals, the distance ring, tank arrangements, repair rules (liner skimming limits, alignment after refitting) and a daily/weekly inspection table linking each abnormal reading to its likely cause and the action at sea.

Click a part on the model to see its number and purpose.Open the 3D manual

Maintenance procedures

Seal renewal in dry dock

With propeller and shaft withdrawn, detach the seal housings from the hull. p. 29
Replace sealing rings; skim the chrome liners if worn, within the D − X limit, otherwise renew the liner. p. 29
Use stainless steel bolts for the aft seal when reassembling. p. 29
Refit and check alignment with dial indicators: eccentricity 0.2 mm, squareness 0.1 mm per diameter (670 types and below). p. 29

Maintenance intervals

Item	When	Action	Manual
Stern tube oil temperature	daily	Over 60 °C: check white metal in strainer, cooler, thermometer; slow down if bearing damage	p. 31
Stern tube oil pressure and tank level	daily	Sudden drop: look for leaks at forward seal or oil outside the ship	p. 31
Aft seal drain	weekly	Check for emulsified oil / seawater and drain it	p. 31
Forward seal tank level and temperature	daily	Sudden rise or drop indicates No.4/No.5 ring damage; refill or recover oil	p. 31
Aft seal tank level	daily	Sudden rise with emulsion means seawater past rings No.1/No.2	p. 31

Faults and what to do

Stern tube oil above 60 °CBearing damage, cooler or thermometer fault Sudden drop of stern tube oil levelLeak from aft or forward seal Emulsified oil or seawater in drainDamaged No.1/No.2 rings or trapped foreign matter Fresh water in drainLeak from aft peak tank Forward seal tank level changesNo.4 or No.5 ring damage

Technical specifications

Seal size	CX-500 (shaft liner 500 mm class)	p. 1
Sealing rings	Viton, aft and forward	p. 2
Liner skimming limit	D − X: X = 3.4 mm for size 500 (e.g. 600 type: 3.7 mm)	p. 29
Alignment after refitting (≤670 types)	eccentricity 0.2 mm/dia, squareness 0.1 mm/dia	p. 29
Stern tube oil temperature alarm	over 60 °C	p. 31
Oil pressure margin for seawater ingress	raise 0.3–0.5 kgf/cm² above normal	p. 31

Source: manufacturer's manual “EM-35 KOBELCO COMPACT SEAL-STERNTUBE SEALING”, 47 pages. Page numbers refer to the original. Check against the manual on board before work.