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Tech Tip #106: ZF/Hurth Gears: A Dollar an Hour Gear

How to get the most out of your ZF/Hurth transmission

This Tech Tip is one of a series that we publish on the selection, care, and maintenance of ZF/Hurth mechanical transmissions found in marine applications, especially sail boats. For an overview of our thoughts on this important topic take a look at

This new Tech Tip came about accidentally. It came after the financial meltdown of Fall, 2008 when boat owners became more cost conscious. A Foley customer casually remarked one day to our Dr Diesel that he considered a ZF/Hurth gear to be a “dollar an hour gear.” Dr. Diesel™ looked up from his work bench and asked him what he meant. The customer explained that typically small Hurth gears, specifically the ZF/HBW50 to ZF/HBW250 gears in sailboat applications, last about 1000 hours on average. Since the cost of a rebuilding small ZF/Hurth mechanical transmission is roughly $1000, the fellow continued. this indicates that the cost of running a little 20 pound Hurth transmission attached to an auxiliary engine is about $1 per hour. Dr Diesel didn’t really like hearing this, but the fellow’s logic was impressive.

Now our Dr Diesel is a thoughtful guy and he chewed on it overnight. As much as he didn’t want to admit it, the fellow pretty much had it nailed. Oh, sure, a guy who sails in the Caribbean may be luckier. But a guy who moors in a harbor littered with lobster traps like Round Pond, ME has a good chance of getting his prop tangled in pot warp and ruining his ZF/Hurth in only a season or two. That must be why we ship a lot of gears to Maine, maybe 3 or more per week in-season. However, generally speaking, the average sailor whose boat is used recreationally and not in charter duty, usually gets about 1000 hours out of his Hurth marine gear. At least that seems to be the case with our customer base which is essentially limited to North America, the Caribbean, and Mexico.

Now our Dr. Diesel™ is a New Englander; He buys things and doesn’t rent them. He figures that paying $1 an hour for anything is too much money. So, he sat down and came up with a couple of recommendations that we think will cut that dollar an hour figure in half. They are all very inexpensive and easily installed by the average Hurth marine transmission owner. While one of our field service crews could install these for you, this is a true do-it-yourself project.

Use an oil cooler

Cool oil is happy oil. An oil cooler will increase the capacity of your ZF/Hurth gear to handle torque and will significantly extend its life. If you are running a HBW100 and add a cooler, your Hurth now has the same torque capacity of a HBW150. This should be of particular interest to Perkins and Westerbeke owners running the Perkins 4108/Westerbeke 40 marine engine with an under-specced HBW100, yacht clubs with inexperienced launch operators, and anyone who would like to get longer life out of their Hurth. Installing an oil cooler on your Hurth marine gear has a very quick payback. The modest cost is more than made up in longevity. Kind of like the old AAMCO transmission ad, pay a little now or a lot later.

For people who already have an old-style aluminum cooler, consider stepping up to our new stainless steel oil coolers. We are now making stainless steel coolers for the Hurth marine gear that will not rust, rot or corrode. Ever. They are so good, you can take the cooler with you when you change boats! (Yes, one cooler fits all the small Hurths.) Our new stainless oil cooler for the Hurth is significantly larger than the one Westerbeke uses and because of this cools better. Installation is simple. You just bolt the cooler to the four drilled and tapped 8 mm holes that already exist in your Hurth’s case and run a water line to the cooler and back out again. The cold sea water cools the surface of the case. Our stainless steel cooler kit even includes a container of our Hytork Fluid and the four bolts you will need.

Flex Coupling

One of the best things you can do to protect your engine/transmission is to install a flex coupling between the output flange on your Hurth and the propeller shaft flange. The idea is that if you hit rocks, a sandbar or other underwater obstacle flex coupling will break the connection between the prop shaft and your drive train. It serves in other words as a sacrificial link, protecting a very expensive engine and transmission. Take a look at Tech Tip #54, Marine Coolers and Couplings for more info on flex couplings.

There you have it Dr Diesel’s three tips on how to reduce the operating costs on your ZF/Hurth transmission and maybe cut them in half.