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Tech Tip #153: Hurth HBW50/100/125/150 Transmissions: Two Common Problems Easily Avoided

This Tech Tip is one of an ongoing series that we write to help people maintain their ZF/Hurth mechanical transmissions in good working order.
Tech Tip # 22: Hurth Gears: Care and Maintenance, we helped you properly maintain your ZFHurth transmission. We visited the topic again in Tech Tip # 78: Hurth Marine Transmissions: The Ins and Outs of Basic Service. In Tech Tip # 96: ZF Hurth Marine Transmissions: A Six Step Program, Dr. Diesel™ released his Top Secret 6-step Program to help keep your ZF-Hurth transmission running in top condition.
Here are two more issues with ZF/Hurth transmissions. We want to thank Bob Gerwig at Brewer’s South Freeport in Maine for mentioning these additional thoughts to us.
Two Common Problems with Hurth Gears

It is important to maintain the 0.5mm distance between the shaft arm and the shaft housing point. Not doing so can be harmful and cause drivetrain blinding, potential overheating of the Hurth gear transmission and its eventual failure.
Losing the dipstick washer. This can cause two problems. The copper washer works as an anticorrosive insulator between the carbon steel dipstick and the aluminum case of the ZF/Hurth transmission. Without this washer, you could find yourself in a situation where the dipstick becomes stuck in the case. Secondly, the absence of the washer will result in an incorrect reading of the oil level and even allow fluid to leak out.

P.S. We strongly encourage that you use our Foley Hurth Hytork Fluid in your Hurth mechanical transmission. It will run cooler and last longer. Cool gears are happy gears.

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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

Tech Tip #22, Hurth Gears, There Care and Maintenance,
Tech Tip #78, Hurth Marine Transmissions, The Ins and Outs of Basic Service,
Tech Tip # 96, ZF/Hurth Marine Transmissions: A Six Step Program,
Tech Tip #104: ZF/ Hurth Transmission and Borg Warner Damper Plates: Shake, Rattle and Roll,
Tech Tip #101, ZF/Hurth Marine Gear Shift Position: A Warning,
Tech Tip #105, HurthZF/Hurth Marine Transmissions: Old Wine in New Bottles?

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.

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Tech Tip #105: Hurth and ZF/Hurth Marine Transmissions: Old Wine in New Bottles?

Helpful guide on identifying your Hurth and ZF/Hurth Marine Transmission
Most of our Tech Tips about Hurth mechanical marine transmissions have been about maintenance. See for example

Tech Tip #59, ZF/Hurth Marine Gear Damper Plate 101
Tech Tip #22, Hurth Marine Gears, Their Care and Maintenance
Tech Tip #78, Hurth Gears: the Ins and Outs of Basic Maintenance
Tech Tip #96, ZF/Hurth Marine Transmissions: a Six Step Program

and others on our web site. This one is different. It discusses how you can tell if you have a Hurth Company in Munich, Germany or a later model Hurth marine gear manufactured by ZF in Italy after ZF purchased the assets of the original Hurth Company.
Roughly 15 years ago, the Carl Hurth Company of Munich, Germany was purchased by the much larger ZF company, a world wide conglomerate. ZF continued to build the Hurth marine transmission but moved production to Italy. Once ZF Marine took over they instituted a major change in the Hurth marine gear model numbering system and implemented several subtle design changes. People frequently call us after seeing a used Hurth marine gear for sale at a their local boat yard. They often ask for help in unscrambling the model numbers as well as asking if the Hurth mechanical gear they are looking is an original Carl Hurth marine transmission or a Hurth gear manufactured by ZF. Here is how to tell.
Hurth Gear Model Numbers Made Easy

Old Hurth Marine Gear Model Number
New Style Hurth Number
Current ZF Model Number








Output Flange Change Change
In addition to changing model numbers, ZF/Hurth also changed several design features. The output flange at the rear of the transmission was strengthened. The original Carl Hurth marine transmission had a flange with four ears. The late style ZF/Hurth flange has two ears. The flanges are identical in bolt hole spacing and essential function but the later flange is stronger and preferable on the ZF/Hurth marine gear. We have not seen the same number of broken flanges on the late style flange as we have with the earlier one.
Shift Handle Change
Getting your shift linkage set up correctly is critical. Having good linkage alignment is very important. Shift linkage alignment is so important that it is the second thing , after checking the fluid level, that you should check in your Hurth if you are having any problems. We touched on it in Tech Tip #101, Hurth Marine Gear Shift Position: A Warning. ZF changed the shift handle design when they bought the company to a more rigid, stronger design. Both handles, the early Hurth as well as the late ZF design, slide on the shifting shaft and are interchangeable. The late style ZF designed handle is rectangular in shape, appears to have a brass colored finish, is held on with a better fastening system and appears to offer more attachment points for the linkage. This late style ZF/Hurth designed shift lever appears to have a brass finish because of the protective coating the ZF Factory now uses to add longevity to the former problematic part. We recommend that you use the late style shift handle. The early style Hurth shift lever is just casted “white metal” and will not hold up to the elements. We stock them for retrofitting to an older Hurth and could ship you one today.
This Tech Tip seeks to assist Hurth marine gear owners by unscrambling a confusing numbering system as well as outlining how they can tell if they have an early or a late Hurth gear.

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Tech Tip #104: ZF/Hurth and BorgWarner Damper Plates: Shake, Rattle and Roll

The hard life of Damper Plates
This Tech Tip, one in ongoing series we publish for Hurth and Borgwarner Velvet Drive marine transmission owners, is aimed at helping people understand their marine damper plates. This Tech Tip follows other Tech Tips that discuss Hurth marine transmissions:

Tech Tip #22: Hurth Gears: Care and Maintenance,
 Tech Tip #78: Hurth Marine Transmissions: The Ins and Outs of Basic Service,
Tech Tip #96: ZF/Hurth Marine Transmissions: A Six Step Program.

We also discuss Hurth and Borg warner marine gears in our

Tech Tip #2: Marine Transmission Fluid
 Tech Tip #47: Avoiding Idling Gears, An Interview in National Fisherman
Tech Tip #51: Souping Up the Series 72 Borg Warner Gear
Tech Tip #59: ZF/Hurth Marine Coupler or Damper Plate 101
Tech Tip #101: Hurth Gear Shift Position: A Warning
Tech Tip #105: Hurth and ZF/ Hurth Marine Transmissions: Old Wine in New Bottles?

Damper plates lead a tough life
They work in the dark, are often soaked in salt water, and are never checked, let alone maintained. They are the marine equivalent of a mushroom! The damper plate is bolted to the flywheel with a half dozen or so small metric allen bolts. Into this clutch like plate slides the splined input shaft of the Hurth or Borgwarner gear. The damper plate acts as coupler between the engine and the transmission and all torque is transmitted through it.
Noisy damper plate
Sometimes these hard working clutches rebel and their springs loosen up and even fall out. Or one or more of the allen bolts back out and the plate become loose and moves around. Symptoms of this will be a rattling sound from the bellhousing area when in neutral. Engaging gear is often difficult and the Hurth gear is hard to shift. Often loose or missing springs is the only problem. People often think that they need a new transmission when all they need is to replace the damper plate.
What to look for
If you suspect that your damper plate springs are loose and rattling around and that you have damper plate problems here is what to look for. First check your linkage to ensure that everything is tight and working properly. Then check that the bolts holding the damper plate in place are present and installed correctly. Verify that the Hurth or Borgwarner gear is not mis-aligned. Use a dial indicator to check for this. Finally, if the damper plate is worn and/or springs are missing, check to see that your Hurth or Borgwarner gear’s front bearing hasn’t failed. Worn damper plates can often cause the transmissions’ input shaft to wear and result in front bearing failure.
If your damper plate is worn, not to worry. We stock damper plates for most applications and have them ready for same day shipment anywhere in the world. We also have ZF/Hurth and Borgwarner Workshop Manuals and our Foley Hurth Hytork Fluid that we can send. As you can see, if you own a Hurth or a Borgwarner, we’ve got you covered!

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Tech Tip #101: Hurth Gear Shift Position: A Warning

Help keep from being stuck at sea by following this simple guide
In previous Tech Tips, we have written about the care and maintenance of ZF/Hurth transmissions. These Dr Diesel Tips have focused on the correct lube oil to use, our innovative stainless steel oil coolers, damper plates etc. See, for example:

Tech Tip #22, Hurth Gears: Their Care and Maintenance,
Tech Tip #54, Marine Coolers and Couplers,
Tech Tip #78, Hurth Marine Transmissions: The Ins and Outs of Basic Maintenance, and
Tech Tip #96, ZF/Hurth Transmissions: A Six Step Program.

We have also written about ZF marine gears in our more informal Tech Tip Series. See, for example,

Tech Tip #2, Marine Transmission Fluid,
Tech Tip #47, Avoiding Idle Gears, which originally appeared in National Fisherman, and
Tech Tip #59, ZF/Hurth Marine Gears: Coupler or Damper Plate 101.

But this Tech Tip is different. It offers a note of caution.
When sailing or when being towed never leave your Hurth mechanical transmission in the “Forward” position. This puts an unacceptable strain on your Hurth marine transmission. Transmission damage will result. To avoid this you can lock the propeller by putting the gear shift lever in the “Reverse” position or leave it in the “Neutral” position and it will free wheel.

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Tech Tip #96: ZF/Hurth Marine Transmissions: A Six Step Program

Helpful tips to keep your ZF/Hurth Transmission running.
Hurth gears have a bad reputation. We had a call last week from a customer in Woolwich, ME who owns a Hurth HBW 100 transmission. Seems he wanted to order another one. His third in 12 years. In the course of the conversation he complained that his ZF/Hurth marine gear was costing him somewhere around $1 an hour to operate. He said that ZF should have a consumer warning label on all small ZF/Hurth HBW mechanical gears: “Hurth the $1 An Hour Gear.”
This got me thinking. Sure to keep the weight down, ZF/Hurth uses lightweight aluminum cases. Like everything else in life, the Hurth aluminum case doesn’t like being submerged in salt water. Additionally, like the air cooled VW bug you drove in grad school, Hurth marine gears have a tiny oil sump, no oil filter, and, usually, no oil cooler. As a result, Hurth marine gears don’t last if run while even just pint low on lube oil. Yes, if abused the seals will leak and the clutches will slip. But having to reseal a Hurth every two years or to buy a new Hurth transmission every 4 years really shouldn’t be necessary with good care.
Here are some easy steps you can take to prolong the life of your Hurth marine transmission. You might want to call this the Foley Six Step Program for Hurth Transmissions! These steps build on earlier Tech Tips we have published. For more information, please read the following  Tech Tips:

Tech Tip #2, Marine Transmission Fluid
Tech Tip #23, Oil Filters: Capacity Counts
Tech Tip #33, Disposing of Used Oil
Tech Tip #59, ZF/Hurth Marine Gear Couplings and Damper Plates
Tech Tip #22, Hurth Gears: Care and Maintenance
Tech Tip #54, Marine Coolers and Couplings
Tech Tip #78, Hurth Transmissions, The Ins and Outs of Basic Service

1. A well lubricated Hurth transmission is a happy Hurth transmission
You should run the correct lube oil in a Hurth mechanical gear. Upgrade to our Foley Hurth Hytork fluid and your Hurth transmission will last longer. For more information regarding the fluid please read Tech Tip #2, Marine Transmission Fluid. Regardless of the fluid you use, change it frequently and dispose of the old oil properly. For help and ideas in taking care of your old oil please read our Tech Tip #33,Disposing of Used Oil.
2. A cool Hurth transmission is a happy Hurth transmission
Most Hurth gears don’t have oil coolers. You should install an oil cooler in your Hurthif you don’t have one. An oil cooler will increase the torque capacity of your Hurth by one model number because you will have cooler fluid. For example, if you are running a Hurth HBW 100 behind a 50 HP Perkins Model 4108 you are right on the ragged edge of the gear’s capability. Translation: you will be buying a new Hurth gear every few years. However, if you install an oil cooler on your Hurth you will effectively raise the capability of your Hurth HBW 100 to that of a HBW 150. (This is like a free lunch. Where else can you upgrade one model for simply the price of an accessory? Would your friendly BMW dealer give you a new 7 Series for the price of a 5 Series plus a option?)
We used to supply aluminum oil coolers from a German manufacturer for Hurth transmissions. Unfortunately, they wouldn’t hold up in the salt water environment that the Hurth marine transmission lives in. Foley now offers new stainless Hurth oil coolers that we custom build here in Worcester for the same price as an aluminum one. Our stainless steel Hurth oil cooler is a small investment that yields big savings. For more information regarding Hurth transmission coolers please read Tech Tip #54, Marine Coolers and Couplings.
3. Replace your Hurth’s damper plate/clutch
Every time you have your Hurth removed for inspection or new seals, change your damper plate. No matter how good it looks. If your damper plate fails, it will damage the input shaft on your Hurth without you realizing it until it is too late. This little clutch-like plate is inexpensive but does a big job and is time consuming to change if you are not already servicing the marine gear. To learn more about damper plates please take a look at  Tech Tip #59, Coupler or Damper Plate 101.
4. Install a flex coupling to protect your Hurth
No matter how good a sailor you are or how few sand bars and rocks there are where you sail, you should install a flex coupling between the Hurth output flange and the propeller shaft coupling. Flex couplings are often called drive savers and do two things. They protect your transmission from shocks in the event of a grounding or wrapping pot warp around your propeller. They also will help cover-up alignment problems.
We sell both the original red “drive saver” type coupling as well as a newer style coupling that we custom make. The newer style coupling protects your Hurth in two additional ways. First, it offers the same protection as the original red coupling, but because it doesn’t fully break the connection between the Hurth and the prop shaft it allows you to still motor home after an incident. Additionally, these new style couplings install within not between the Hurth output flange the prop shaft coupling so they don’t push your propeller shaft back the same 1.5+” as the red style couplings do. We’ve been able to keep the cost of this newer style flex coupling down to the same level as the style red coupling. The choice is yours.
5. Check and recheck your shaft alignment with a dial indicator
While a flex coupling will mitigate bad alignment, it can’t do the whole job. Check also your engine mounts. Worn mounts will cause the prop shaft to move around and can damage your Hurth.
6. Include your Hurth in your daily checks
When you do your dailies, include your Hurth gear. Check the level of the lube oil. Look for leaks. Look at the hoses going to the oil cooler. Is your Hurth happy?
There you have it. Our Six Step Program to avoid having your Hurth becoming a $1 an hour marine transmission.

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Tech Tip #78: Hurth Marine Transmissions: The Ins and Outs of Basic Service

Helpful tips on performing basic maintenance on your Hurth marine transmission
In this Tech Tip, one of an ongoing series that we publish for both our customers as well as the international marine audience, we present a few basic thoughts on how to maintain your Hurth marine mechanical gear. These small reduction gears are commonly found mounted on auxiliary engines. As Hurth mechanical transmissions, they have a model number prefix of HBW. The larger Hurth hydraulic marine gears have a HSW prefix; we will discuss these units in a later Foley Engine Tech Tip.
The information presented below is drawn from both our 88 years in the marine power train business as well as the Hurth Workshop Manual (call us toll free at 800-233-6539 if you would like us to send you a manual). Please call or email us with any thoughts or comments.

Fluid Change Cycle. People frequently ask us how often they should change their fluid. Fluid in Hurth marine gears should be changed at the start of each season and at 250 hour intervals. Change it more often, perhaps every 100 hours, if you are using the marine transmission in a severe duty cycle such as launch duty or the placement of moorings or towing. Change it immediately if you have tangled the prop in lobster pot wrap, overheated the gear, or if the fluid is discolored.
Which Fluid? The ZF/Hurth Workshop Manual indicates that automatic transmission fluid or ATF is to be used in these mechanical gears. ATF, commonly known as Dextron II or III, is far preferable to the thicker SAE 90 hydraulic gear oil. However, given that these small gears are essentially oil cooled and that they contain very little fluid, we strongly recommend that you upgrade to our Foley Hytork Fluid. Cool transmissions are happy transmissions because heat is the enemy of all marine gears.
How Much Fluid? Generally speaking, the smallest Hurth gears use about a half a quart of fluid. See the chart below for exact capacities.

Capacity in Quarts

HBW 40 4M

HBW 50 (5M), HBW 100 (10M) (nee 5)

HBW 125 (12M), HBW 150 (15M) (nee 10)

HBW 150A (15MA)

HBW 150V (15MIV)

HBW HBW 250 (25M) (nee 20)

HBW 360

HBW 360A

HBW 450

HBW 630

Smelly Fluid? Why does my fluid smell and look discolored? You may have burned the fiber clutches because of heating caused by severe duty, under-speccing of the gear, or getting tangled in a line. You should immediately change the fluid and carefully monitor the performance of the gear.
Transmission Coolers. Despite your best intentions for a variety of reasons some transmissions will run hot. In addition to the problems caused by severe use and getting tangled in a line, some gears are simply under-spec’d.  The Perkins 4108 is rated at 50 HP at 4000 RPM yet many boat builders equip them with the HBW 100 which is not rated for this. One could install a more appropriate transmission such as the HBW 150 with 37% more fluid (0.63 quarts versus 0.44 quarts), and shorten the shaft to accommodate the longer HBW 150. Or, recognizing that heat is the enemy of gears you can increase the torque capacity of the gear that you now have. The first step is to upgrade to a better transmission fluid which we discussed above. The next step is to install a transmission cooler. Hurth mechanical gears don’t have a provision for the long oil coolers composed of a “tube with a bundle inside” as seen on Borg Warner and Hurth hydraulic gears. To mount a cooler on a Hurth mechanical gear, Foley Engines can supply a small aluminum box that installs on four pre-drilled holes on the outside of the transmission’s case. Raw water is run to and through the small box (about the size of three stacked decks of playing cards) and it cools the fluid inside the transmission. This Foley Cooler Kit works so well that it effectively changes the torque capacity of the Hurth HBW 100 to that of the HBW 150. It is a very cost effective way to upgrade your drive train.
Damper Plates. All Hurth marine transmissions have damper plates. They are installed on the engine’s flywheel in front of the gear. They resemble a small, spring loaded clutch that you might see on a Ford 8N farm tractor.
It is visible when you remove the transmission. To function well all the damper plate springs should be in place, tight and not loose or rattling. We strongly recommend that you change the damper plate whenever you have the transmission removed for service for several reasons. The “Always Change the Damper Plate” rule is because the plate is normally inaccessible, probably is rusted and frozen on the flywheel, is a small dollar item, and has seen as much service as the transmission which you are now servicing. Use Nevr-Sieze when you install the new damper plate so you can easily service the small metric fasteners in the future.
Shifting Problems? First check and adjust your linkage. Linkage problems are very common on Hurth marine gears when mounted to auxiliary engines. If the problem is still there, see if there is a difference in the difficulty in engaging forward versus reverse. If it is significantly more difficult to engage the marine gear in forward as opposed to reverse, this indicates that the thrust washers are worn. The gear will require service or replacement.
Hurth Transmission Filters. Small mechanical Hurth gear boxes do not have filters. One could drill and tap the case to install a remote mount filter kit (costing probably $100 or so). The transmission would last significantly longer and definitely run cooler because you would have easily tripled the oil capacity with the addition of lines and a filter holding a quart of oil. We have this idea in queue but have yet to field test it.

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Tech Tip #59: ZF/Hurth Marine Coupler and Damper Plate 101

Useful guide for your ZF/Hurth Marine Coupler and Damper Plate
This Tech Tip is one in a series that we publish. We welcome your comments.
Check the Installation
For people who are experiencing abnormal coupling or damper plate wear we recommend that they check the installation of the plate to the flywheel, the splines on the plate, and the linkage on the marine transmission. These are always the first steps. Once you are confident the installation is okay and the damper plate is still serviceable, but you still have damper plate problems, consider balancing the damper plate or the damper plate/flywheel assembly.
Balancing Damper Plates
Using a Stewart Warner industrial balancing machine, we have developed a technique to dynamically balance the entire damper plate/flywheel assembly or just the coupler or damper plate for smoother operation and longer life. The couplings (for example the Centa coupling) used on a larger Hurth can be quite heavy and the damper plates used on smaller Hurths can be unbalanced. This has worked so well that we now offer balancing to all of our drive train customers. We now ship only couplings and damper plates that are balanced and within specs.
Installing a Damper Plate
Sometimes people ask if they should use Locktite on the threads of the bolts that mount the damper plate or coupling. The short answer is no. Indeed, we recommend that you use NevrSez on these bolts to facilitate later removal. It is a good idea to change the damper plate every time the transmission is serviced. In fact, ZF/Hurth will not warranty a replacement Hurth gear without a new damper plate being installed. NevrSez will make the removal of the plate an easy job.

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Tech Tip #22: Hurth Gears: Care and Maintenance

Helpful guide on maintaining your Hurth transmission
Maintaining a Hurth gear can be easy if you follow a few procedures. This Tech Tip, one of an ongoing series published by Foley Engines, discusses the care and maintenance of the Hurth marine gear.
Vital Fluids
The Hurth marine gear is quite forgiving of owners who use less than ideal lubrication fluids. Many owners use common automatic transmission fluid (ATF) while others rely on shop manuals that (incorrectly) recommend SAE 20 engine oil. In our experience neither is optional. We had a major oil company develop fluid that seems to work best. We market it as Foley Hytork Fluid and supply it in gallon and half gallon containers.
Damper Plates
Whenever the engine is removed for service it is a good idea to replace the spring loaded damper plate that mounts between the gear and the flywheel. These clutch-like discs are important to the operation of your flywheel. Our shop people have seen many a gear in for total overhaul whose damper plate was neglected and rusted on to the flywheel. For boats with high duty cycles and/or multiple users, like launch operators or those who just want absolute peace of mind, we have severe duty damper plates. These are marketed under the name of the Foley Diamond Damper for a slight premium.
Like a heavy duty damper plate, adding a cooler to a Hurth marine transmission will extend its life, particularly in situations where the gear is at the upper limit of its horsepower capacity. Hurth coolers are an easy add-on and we highly recommend them, especially in launch applications.
In summary, good synthetic lubrication changed twice a year, a decent damper plate, a Diamond Damper if in doubt, and a mid-career tune-up will keep your Hurth operating well for a number of years. We have Hurth Workshop manuals ready to Federal Express out to you and UPS standing by to pick up any gear needing work. Please call us toll free with any questions or if we could pick up your gear for a tune-up. Foley wants to help.

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