Metal Contamination in Hydraulic Systems

I’m currently working on a Yanmar ZT350 drive that stopped shifting reliably due to contaminated oil. Shifting is by means of two multi plate clutch packs, actuated by a piston located between the two, fed by a pair of solenoid valves. In other words, it’s pretty much like any other hydraulically shifted transmission of comparable power level.

The failure mode is several sintered metal pucks from the clutch pack breaking apart, whereupon the material has been ground to a very fine powder by the gear train, rendering the oil a deeply lustrous shade of metallic green. The fine metal particles have subsequently lodged themselves in the very tight clearances, bringing things to a halt.

I have been warned by several highly competent engineers with much equipment specific experience against having anything to do with this. Apparently, once things have gotten to this stage, the drive tends to never get reliable again, because it is practically impossible to fully get rid of the contamination. The Yanmar ZT drives have rapidly lost the workboat market because of this exact fault. However, the powers that be want me to forge ahead, so here I go.

My plan is to make things as clean as possible with chlorocarbon solvent, compressed air, lots of clean oil and a paint brush. I then intend to flush the drive several times with DFO once it’s on the boat. Any thoughts? Does someone know of a magic pill for this type of situation?

Unfortunate workshop fire?


I didn’t see anything . . . . .

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Use a multistage filtration unit to flush until oil sample analysis results are good prior to running. Obtain a side stream filtration unit for permanent installation once its running. Sample regularly and keep fingers crossed.


Well who knew there were so many pirates around, but the good news is they only ran off with one thing :wink:

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clean the housings in ultra sonic baths

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From what I can see the ZT350 stern drives do not have an oil filter (correct me if I am wrong) so when a contamination problem occurs it becomes a big problem fast. Like others have said flush until you get it as clean as possible. I agree with @tengineer1 with the idea of installing some sort of side stream (sometimes call kidney) oil filtration.

The problem is figuring out how install such a system with the limited space and power the boat may have. The drive transmission has drain and fill plugs. It may be possible to use those as connection points for a small pump and filter thereby adding a filter to a system that may not have one.



My money is on these guys.

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Yes, Seadog is probably right. I didn’t realize they are so small. Probably throw away units by design. Kinda like a 8 year old iPhone with a dead battery. Gotta buy another unit.

RE: that photo, That’s it? well, tengineer is right, you’d want to install a filter on the system but really? wouldn’t it be more expedient to just get another unit? but if the boss wants you to fix it, tell him you’ll need a inline filter “somewhere” or you’ll be facing more down time and it’d save money to get another unit.

@tengineer1, your comment made me miss the days of big boats and bigger budgets. Have a $3k solution to oil contamination that requires external logistics and attention while underway? Sure, have at it. Meanwhile, I intend to use an electric vane pump drawing through a 2 micron 2010 for flusing. Do you reckon DFO is a good choice? I’ve had great luck using it for purging mayonnaise, and it’s cheap.

@powerabout, our ultrasonic bath is sized for a set of outboard carbs, and I haven’t even seen one big enough for the lower housing on a ZT.

@Chief_Seadog, the drive does have two filters, one suction side and a finer one for the oil that passes through the control valves. The particles got down to the size that passed through the mesh of the former, while the latter caved under the differential pressure. According to the experts, neither really does the job when you have copper contamination throughout.

As for installing an external filtration system through the filler plugs, that has been done almost routinely by the guys who take the Bravo out of its comfort zone. It is the only way to keep them cool cool when pushing 600+ Hp.

The disposability of mass produced mechanical components is much too big a subject for this thread, but outdrives don’t really fall into the “no serviceable components inside” category. I have done a fair amount of work on Alphas and Bravos, not to mention outboard gearcases, which are all of cheaper construction than the ZT. The problem with working on Yanmar drives is partially their scarcity, which makes good knowledge hard to come by, and partially the utterly ludicrous array of special tools specified by the manual. We’re talking about 4-5 full pages in the EPC at a cumulative cost well north of 10k USD. That being said, the insurance companies tend to not sanction such work, but prefer paying for a complete drive.

I guess the answer I was hoping for was something along the lines of “Sure, just add 2% [carcinogenic substance known to cause long term harm to the aquatic environment] to the oil and let it sit for a week, that’ll take care of your copper contamination” :stuck_out_tongue:

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problem with most stern drives ( except Merc Dry sump race drives) is the oil is not being pumped around its just a bath or has a poor method to get some circulation.
They are made for pleasureboats not commerical
Cant speak for Konrad, maybe they are?

PS ultra sonic bath can be any size you like, Jay Leno has a vid of his its about 6’ long

Yanmar ZT and the latest Volvo Penta drives have oil pumps as well.

The problem with stern drives in general is that they are just so… inelegant. Taking the driving fore through two 90 degree bends like that is necessarily going to strike up an unpleasant balance between cost and reliability. If you look at the Bravo 2, which shares the fast commercial craft market with various VP offerings, you realize that it achieves reliability by being so chunky that it starts losing its performance advantage over shafts, pods and jets. The reason why stern drives exist in such numbers is largely historical, and their market share is rapidly being eaten up by large outboards.

DFO won’t hurt for sure. At this point it’s worth a try. Use DFO and then a slightly heavier oil as it’s “sticker” for lack of a better term, and may grab a few more of the particles out. Drain it all out, fill with the regular oil and tell the owner this is as good as it gets. The particles left in after a good rebuild and flushing probably won’t hurt for a 1000 hours or so if then or at all. Engines and transmissions coming from the factory are not pristine, oil analysis isn’t great on a new transmission or engine, they just have a warranty which accounts for a large percentage of the cost.