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I have about 6000 miles on mine.
Kimberlite Amel Super Maramu #376
From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Tuesday, December 19, 2017 10:54 AM
Subject: Re: [Amel Yacht Owners] Hurth Transmissions freewheeling folding prop
That is amazing, you must be taking exceptional care of your transmission. Do you have a cooler on your transmission? Foley seems to be saying that 1000 hours is about all that we should expect. It would be nice to know which factors seem to lead to a longer service life.
I can confirm you that the Hurth 250 transmission can work much more than 4,000 hours. Mine passed 10,000 hours and , still now, never gave me a problem.
Thanks for this information. At least I now know that at least some of the Hurth 250 transmissions installed on Maramu’s are lasting longer than the 4,000 hours that mine has. So far my transmission seems to be working fine but the failure mode that you experienced does not sound like a pleasant to experience so maybe I will do something preemptive before long.
I have heard of others having a problem with their aluminum coolers corroding quickly as well.. Without being bonded, I would think that the aluminum parts immersed in seawater would become the sacrificial items on the engine so maybe that could be part of your problem as you suspect. I am wondering however if there is more than one manufacturer of these coolers with some being made of a more corrosion resistant alloy? The original cooler on my transmission had a plate on it that in large letters had the name Hurth, Monchen, Made in West Germany. The old rusty hose clamps, hoses and the apparent age of the ID plate and mounting bolts suggests to me that this cooler had been on the transmission for a very long time. The one that I ordered as a replacement and installed this year with all new hoses was sold by “Mr Cool” 3306107001 ZF Transmission/Gear Cooler. The replacement cooler cost $165.00 USD. The Cooler being sold by Foley is much more expensive, $395.00 which comes with a quart of their special synthetic fluid. I think I will inquire and see what they say about the large cost differential. Can you tell me where you have been buying your coolers?
In part over corrosion concerns for my cooler, I have been flushing the engine with fresh water whenever the engine will sit for more than a couple of days which I think should help to reduce the corrosion some. I think that I will open the cooler at least every couple of seasons to see how much corrosion is present.
Our Hurth 250 started acting up in 2002 with about 6000 hours on the engine. Intermittently it would not go into forward, first discovered when backing out of a slip which made for an interesting evolution. We had it rebuilt with no issue.
Maybe I have a grounding problem on the 4.154 but the aluminum cooler only seems to last a year or two. I now have several, and try to catch the corrosion before it gets to bad. Then I clean up the cooler and rebuild it with aluminum epoxy that I buy from Cotronics. Works really well.
My Maramu has a plate mounted just in front of the shift lever warning to never leave the transmission in Fwd. gear while sailing. My boat has a fixed 20” (?) 3 blade prop which can produce a large amount of torque when sailing at higher speeds. I am guessing that since your prop feathers(so produces little torque if any when feathered) that it may not matter as much which gear you use but apparently due to the design the Reverse gear is stronger and therefore safer to use when locking the prop shaft. Perhaps others can verify if this would be correct.
I also read in Foley the these gears seem to last about 1000 hours on average. The gear on my boat has the same paint as the engine and I don’t see any evidence of it having been replaced. The engine now has just over 4,000 hours. Could others comment on the life expectancy the have experienced with the Hurth gears? My boat appears to have had an aluminum cooler for a very long time, it may in fact have been original based on the installation. I replaced the old cooler with a new aluminum one. The old one was not leaking but when cleaning out the inside I found several pin holes that were only plugged with corrosion so it was overdue. I just got an email back from Foley saying that they have discontinued selling the stainless coolers and now only sell the aluminum. I wonder if there were corrosion concerns betwee the aluminum gear case and the stainless coolers. I will try to find out.
Who’d of thought there was so much to know about transmissions and their lubrication! Foley website full of interesting information. On a related topic..
Dr. Diesel Tip #101 at Foley says DO NOT put Hurth trans into forward to stop freewheeling, only reverse.
We have always put the trans in forward to stop the freewheeling and fold the Autoprop when under sail. Given Amels have a “C” drive, does Dr. Diesels Tip apply? Have to pose the question just in case there are opinions among our ranks.