Learning to Launch: universal joints

‘The universal joints are just showing a little bit of clearance. They are not in need of replacing at this stage but might need attention further down the track. This is not a particularly expensive repair.’

That’s a direct quote from the engine survey which I commissioned from engineer Graeme Fineran of Picton when I bought my boat, a Franklin 925. Back then I was happy that replacing the universal joints (UV joints) was a long way off and even happier that they were not ‘particularly expensive’.

Three years on, I felt that my boat was running with more engine noise and vibration than when I first owned her, and there was a definite ting-ting-ting creeping in. I phoned Graeme. ‘It’s time to check the universals,’ he said.

He disappeared headfirst beneath my saloon sole, emerged with a hefty section of drive train for dissection and eventually declared that two of the five universal joints were absolutely buggered. ‘I’ve kept the worst one to show you,’ he said triumphantly and indicated a series of light, parallel grooves in the metal. To my untrained eye, they didn’t look too serious. But then he showed me how the needle bearings fitted over the groovy sections, and I could see it would be like a car bumping over corrugations on a gravel road, at about 2000 bumps per minute.

Meanwhile, I was learning about universal joints. It turns out they feature throughout the mechanical world, including in the power take-off (PTO) of my Massey Ferguson 135 tractor. Basically, where two spinning shafts meet at an angle, the universal joint acts as the middle man, accommodating misalignment between the two, while allowing the drive train to continue spinning as required.

Not only do universal joints handle misalignment; they insist on it. Misalignment is deliberately introduced to the universal joints during installation so that wear occurs evenly in all parts. They should never be perfectly aligned, because then the bearings don’t turn or pivot, and will run constantly in the same spot.

Such near-perfect alignment may have caused the unwanted grooves in my universal joints. Or, it could have been insufficient lubrication through the grease nipple or just age. But worn universal joints can cause further damage to the drive train and I did hear one story from Greg Teece, Marine and General, Nelson. ‘The driveline gave a huge vibration out of nowhere,’ he says. Then, silence of the non-peaceful kind.Top of Form

In vee drive installations, universal joints are pretty much a certainty. On my boat, the engine sits back-to-front under the cockpit and sends power, ie, rotational force, forward in the boat to the gear box, then forward to the vee drive which then directs it aft, back to the propeller shaft beneath the engine. The vee drive allows the heavy guys – ie, the engine and gearbox – to be positioned for optimum weight distribution in the boat and optimum propeller shaft angle. However, the engine, gearbox and vee drive are securely bedded to the hull, and the driveline between them needs to absorb the constant thrusts and bumps generated by a diesel engine. The universal joints absorb the shocks and accommodate the angles between the big components. They also protect the engine and gearbox from the propeller’s thrust, which allows for softer engine mounts – especially handy if running a four-cylinder engine as they tend to be lumpy. Universal joints also feature on boats with sterndrives.

The star player in a universal joint is a steel component shaped like a ‘+’ sign, called a cross-shaft. Each axis of the cross-shaft is held within a bracket; there are bearings involved so the cross-shaft can move relative to the brackets, which sit at right angles to each other. All of the above comprises the universal joint.

Although Graeme had correctly attributed the increased engine noise to the universals, he says they are not easy to diagnose. ‘They’re not easy to get at and tend to get forgotten about,’ he says. In servicing universal joints, it’s best to remove the entire drive shaft, and he recommends the following:

·      check the angle of misalignment, which should ideally be between three and seven degrees, and the orientation between the universal joints;

·      check the splined connection is correctly assembled: the crosses on the universal joints need to be in line;

·      check that the universal joints move smoothly through their travel range. If they feel notchy or there is any end float, they need replacement.

Universal joints are available from automotive stores and come in different sizes and types; eg, internal circlip, external circlip, bolt-on retainers, so take a sample joint. In replacing them, a perfect fit is essential and the circlips may need shimming to take up slack or a tiny sliver removed, so it requires a reasonable level of DIY or an engineer.

So, with new universal joints fitted, it was time for a sea trial. We talked a lot about universal joints at a normal level of conversation, even with the door open to the cockpit –  proof that the old, groovy universal joints had been responsible for the noisy vibe.

Reprinted with permission from Powerboat magazine

The grooves in the cross-shaft were giving the bearing, right, a rough ride.

© Rebecca Hayter

www.rebeccahayter.co.nz

Wild Seas to Greenland by Rebecca Hayter

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