Servicing a hydraulic steering helm on a boat

After finding a hydraulic oil leak in the steering of his Nauticat 331, Mike Corp services the yacht’s helm pump and steering ram

Seeing small amounts of hydraulic fluid below the steering wheel and having to top levels up hinted at a maintenance job for the winter.

However, it wasn’t until we were entering Lymington behind the Isle of Wight ferry that we realised the severity of the hydraulic oil leak.

We had to use the bow thruster to coax the Nauticat 331 out of the line-up so we could anchor and top up the fluid level.

I was sailing with John, a former work colleague, and we returned to our Brixham base.

The near-miss motivated us to change the seals on the upper Capilano helm pump and Capilano steering cylinder, which was also showing some seepage.

The Nauticat is a dual helm boat, and even though the lower helm was free from leaks, we decided to change the seals on the lower helm at the same time.

For someone with little mechanical experience, pulling apart a helm pump and the steering cylinder can seem like a daunting job.

However, if approached carefully, with the occasional image to aid recall, it’s doable and definitely cheaper than contracting the work out.

There are online videos that demonstrate similar jobs being carried out.

Disassembly, inspection, clean

This was probably the first time the pump had been pulled apart since the boat was launched in 2003.

There was a small amount of sludge inside the pump housing and the seven pistons. The ball bearing race and pivot plate were in good condition.

All the parts were cleaned in white spirit, dried, and reassembled with hydraulic fluid.

The recommended fluid is either Dextron 2 or Dextron 3.

Although not shown in the step by step, the rear plate was removed, and the flat bearings were cleaned and replaced with a new gasket.

We never succeeded in removing the two pressure relief valve screws.

The valves worked, there was no leakage and we risked damaging their heads if we persisted with their removal.

Reassembly issues

The seal kit includes seals and O-rings for several models, so it’s important to match your old seals against those in the new kit.

Care is required when fitting the front plate to avoid trapping the new O-ring against the pump housing.

It’s made more difficult because the seven piston springs were resisting our attempts to evenly refit the plate.

After various attempts, we saturated the area in hydraulic fluid and slowly screwed the plate down using longer bolts, which bridged the gap between the plate and housing.

The correct bolts were then inserted and tightened in a criss-cross pattern.

The final job is fitting the seal plate over the seal. It’s a tight press fit and requires a tag to be inserted into a recess.

A simple tap with a hammer and block didn’t work, and we eventually chamfered the leading edge of the plate to facilitate the fit.

A small amount of fluid was found below the steering cylinder (at C, above), and we decided to press ahead to bring all the hydraulics up to spec.

There is a little more work involved when disassembling and replacing cylinder seals – the cylinder seal pack includes four pages of diagrams and instructions.

Disassemble

The two supply pipes are disconnected and covered to prevent contamination. Before we can access the seals, two hose fittings, the mounting foot (B, above), and the rod end ball joint (A, above) were removed.

The threads on the hose fittings and cylinder access holes were clogged with sealant and needed particular attention.

Carefully placing the cylinder in a vice, we removed the two end glands.

A couple of C-spanners were obtained via ebay, though the guidelines recommend using a pin wrench.

As the C-spanner tip was slightly larger than the gland access hole, we ground it down to the correct size. Rotating the gland anticlockwise, the retaining ring appears.

We bent the leading edge with a screwdriver so that it protruded above the cylinder and could be extracted with pliers while continuing to turn the C-spanner.

It is the same procedure at the other end of the cylinder. Both glands were removed and the cylinder shaft pulled out.

Inspect, clean, and reassemble

For a piece of equipment that is working continuously, the cylinder internals were in very good condition.

If we’d experienced difficulty removing the glands, and especially the cylinder shaft, it may have hinted at damage within the cylinder requiring a major purchase.

Fortunately, the cylinder was free of scratches and dents, so we moved on.

Old seals were removed; everything was cleaned and lightly covered in hydraulic fluid.