• Peter Frinchaboy

42 Degree and 90 Degree Sight Glasses


I have seen many 42 deg. and 90 deg. gearbox sight glasses that get stained and the oil very dark.

Many times this shows up after a coupling repack. Mechanics will repack the coupling before installing the retainer P/N’s 204-040-607-001, 204-040-607-003, 204-040-607-007 and packing.

The photo shows that coupling grease can be pushed into the gearbox. The packing is there to keep the oil in and the grease and oil separated.

Before assembling the inner and outer coupling, with the outer coupling seal

(red or brown ) installed grease the teeth at the seal end and assemble the inner and outer coupling taking care not to unseat the seal.

Pull the inner coupling into the outer coupling thus forcing the grease past the inner coupling teeth. The back half is packed.

Install the coupling with spacer and nut, assembly on the gearbox and torque.

Before installing the retainer leave the packing off and the lock ring off the retainer, on the head of the retainer use a felt tip pen and mark the location of the holes.

Insert the retainer and rotate it as necessary a quarter turn at a time until a hole lines up with a lock slot on the inner coupling.

Install the packing and the lock ring on the retainer make sure there is no grease on the inside of the inner coupling and install.

Now with the outer coupling pulled forward you can pack the rest of the coupling install the spring, cap and lock ring. This should help keep your gearbox oil looking good.

Peter Frinchaboy

Helicopter Maintenance Manager

Sacramento Metro Fire District

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