Prolonging the life of your marine transmission is fairly easy if you follow the basics. These include using an oil cooler, proper lubricant, a good damper plate, and a flex coupling. This Tech Tip, one of a series we publish, discusses marine coolers and flex couplings. An earlier Tech Tip (Number 11) discussed gearbox lubricant and damper plates.

Coolers

Most hydraulic gears (all Borg Warner Velvet Drive and the large Hurth gears) are installed with a gear oil cooler. These can be single tube or a pair of tubes to also cool engine lube oil. Maintenance of these coolers is straightforward: reverse flush the tube stacks to clear out debris, check your hydraulic hoses for leaks and chaffing.

When in doubt, replace. Hoses and coolers are cheaper than a blown gear. Mechanical Hurth gears (the smaller HBW 100-150-250 series) usually don't come with coolers. We now have Hurth cooler kits for under $100. The factory thinks so much of these coolers that they significantly uprate the capacity rating of a gear when coolers are equipped. This is especially important if the gear is already at the upper limits of its capacity (say a Hurth HBW 100 behind a Perkins 4108 or if the boat is used in a difficult application such as yacht club launch duty.

Flex Couplings

Now that we've gotten the gear cooled, mated to a good damper plate, with the proper lubrication, we suggest that you use a flex coupling to protect your power train. A good flex coupling absorbs vibration, thrust and torque, as well as reduced noise.

Acting as a sacrificial link or circuit breaker, a coupling can absorb the impact of a rock or log, saving the engine and transmission. Flex couplings also prevent electrolysis and resulting corrosion.

Recently we began stocking a superior coupling. This flex coupling has all the advantages of the familiar red units plus they can be installed without disturbing shaft alignment. Additionally they have space between the polyurethane flanges to dissipate heat; this prolongs their service life. Finally, under severe impact, when the new style couple distorts, its opposing metal compression plates retain the connection, making the unit fail-safe and insuring drive line integrity. This, unlike the older red-style couplings, allows you to motor home safely. Surprisingly enough, these new advanced couplings are no more expensive than the older style.

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