ZF BW250 Gear No Oil Pressure--Resolution

[racclarkson@gmail.com]

Well, I've been through the mill on this one. It looks like my first impression was the correct one--loss of prime. (See original post below).

The gear has two ide​ntical oil pumps. One is input (engine) driven and the other output (shaft) driven. After getting no pressure from input driven pump, I ran the boat to windmill the prop and see if the output driven oil pump would supply pressure; it did. I concluded I had a bad input pump and planned to swap it with the output pump to prove it out. I accomplished this Saturday. Still no oil pressure!

I manually primed the pump with no result. I primed it a second time and got about 25psi. When I shut down, the pressure held for several minutes; it's never done that before. I'm thinking air bubble.

I primed for a third time and cranked the motor. Pressure came up to over 50psi--not enough to go into gear. After hunting for air leaks and trying to figure out where else to bleed the system, I cranked again. Same result, so I ran the rpm up to about 1,000 and noted the pressure approached 90psi. When back at idle the pressure again dropped. So, I ran the power up again, pulled it back, and quickly shifted it into forward. It went into gear and the pressure steadily built to the normal 175psi. I took it out of gear expecting the pressure to hold, but it dropped back. Repeated the process for reverse and got the same result.

What I've got is an airlock somewhere in the system. I noticed oil around the poppet valve on the control unit when I shutdown indicating air pressure was being relieved. I ran out of time and had to leave it, but I am certain that I've worked enough air out of the system to pickup were I left off. Most likely, swapping pumps was a waste of time; we'll see next time out when I can windmill on that pump. Time for a little research as well. Unfortunately, ZF treats their stuff as classified Top Secret. Chime in if you can shine some light my way.

A few concluding points:

1. The ZF gear has a common oil system supplied by either or both oil pumps. I still can't figure out how making pressure on the one pump wouldn't purge the system.

2. There is nothing in the ZF book about installation or service that speaks to purging air from the system. Just says run it two minutes and check the oil.

3. The filter screen reservoir holds oil normally when the plant in off. When I've drained the reservoir in the past, it has refilled on it's own displacing about a quart of air volume and making pressure. What's different?

4. MOST IMPORTANT: If you take a line off a ZF gear you must cap it PDQ. Even if it's Easter Sunday and everything's closed tighter than Dick's hatband and you have to steal a Bridgeport milling machine and learn to run it to make a flair cap, do it!

IMG_8761.jpg
Input pump removed. Output pump can be seen in background. Arrow indicates drive gear rotation.
IMG_8763.JPG
Pump 1 of 2. Your looking at $7,859 list plus tax and shipping (or $10,601 plus, plus if purchased from Rhode Island Engine).
IMG_8766.JPG
Pressure up. Electric gauge reads a tad low. Mechanical gauge shows 175psi in gear.

Anyway, I'm no longer seeing dollar signs. That's what I call a happy ending.

Last month, I posted as follows:

I'm stumped. Please help if you can.

Portside ZF BW250 marine gear (behind 12V71tic) has operated normally throughout ownership. Three weeks ago, the oil line from the gear to the mechanical ER gauge sprang a leak. I shut it down and removed the hose. There was some oil flowing freely from the top of the gear out the open flair fitting. Not having a cap, I cut the hose and reattached a foot or so of hose standing straight up to contain the oil; I wrapped the end of the hose, but not air tight.



I had two new lines made up, one for each engine, and installed. Cranked both motors today. Starboard warmed up as per normal. The port gear will not make pressure. The oil level is to the top mark. I loosened the flair on the mechanical ER gauge at the gauge; no oil was reaching the gauge. The electric oil pressure gauge on the bridge checks out OK.

My scientific wild-ass guess is I've lost prime to the oil pump while the hose was off for about a week. As I said, I changed the starboard oil pressure gauge line, but that was on and off in a very few minutes. A brief shot of port side RPM had no effect. The ER temp is around 60 degrees and the oil is 40 wt. I've run the shifter through the gears with no effect. I've manually turned the prop shaft and it's free.

Anyone have any suggestions?

[krush]

I think I'll stick with TwinDisc..........I think my whole transmission new is less than the cost of one of your pumps (of course it's a little bit smaller).

Positive displacement pumps don't loose prime. Sounds like a clog or a crack (air leak) on the suction. Hook the suction up to a hose and dunk it in 5gallon bucket and see if pressure jumps instantly upon startup.

[racclarkson@gmail.com]

I think I'll stick with TwinDisc..........I think my whole transmission new is less than the cost of one of your pumps (of course it's a little bit smaller).

Positive displacement pumps don't loose prime. Sounds like a clog or a crack (air leak) on the suction. Hook the suction up to a hose and dunk it in 5gallon bucket and see if pressure jumps instantly upon startup.

Oh, it's a massive gear. I've seen identical models spec'd for 120' boats and HP more than twice what I can give it. It's real impressive looking at the insides, and I'm sway-back from toting oil to it.

That's a good idea, though. I've already checked pump output. Its putting out pressure on startup. I also hand spun the pumps on the bench and saw they pumped. Kinda hard to hook stuff up to buckets on that thing. But I did loosen a plug on a manifold and it's making pressure alright--I finally found that plug. Nothing blocking the suction lines; I checked. The fact that it's making more pressure, now going into gear and exercising the poppet valve tells me the air is gradually being pushed through. Again, everything was A-OK until I took that oil pressure gauge line off for a week. When I removed the foot of hose I had left attached, no oil came out which means air was able to get in at that point. From that point a 1" pipe supplies oil to the control module where there's lot's of little need valves and cavities to hold air.

That's my story and I'm sticking to it. It's going to be real cold again this week, so I'm going to leave it alone and head to Las Vegas and deal with it when it heats up next week.

[SEVEN]

Great looking CLEAN motors Robert Congratulations

[racclarkson@gmail.com]

Great looking CLEAN motors Robert Congratulations

Well you know I’m from the Bible Belt and cleanliness is next to godliness.

[racclarkson@gmail.com]

Finally reached full resolution. I noticed a very slight film of oil on the suction side after sitting for several days. This would translate into a decent operational air leak. So, I decided to agin pull the input driven pump that was making less than full pressure and do a thorough strip and clean as well as go back with new copper crush washers. The washers (22 & 26 mm) were hard to locate from one source, but worth it.

IMG_8791.jpg

The pictured pump was originally the trailing pump. As such, it sat low and away in the engine bilge and accumulated a good bit of corrosion. Some of the parts actually took chipping before wire brushing the scale. They were treated to 24 hours of phosphoric acid, washed, primed and painted. The sum of the parts above (best price) is about $9,000.

After the reinstallation, I filled the gear to the mark, primed the pumps and let sit overnight. Next morning revealed no leaks. About 40 seconds after cranking the gear made and held full oil pressure (175psi) with no leaks on the pressure side. The initial shifts were slow until the clutch oil passages filled which took my oil level down below the add mark. After bringing it up to the full 37 liters of 40 wt., the gear operated normally.

Got about a day of touching up surrounding paint work and reinstalling wiring. This could have been a very expensive repair without some good advice and some luck. Still don't know the initial cause, but it was likely priming related. I surmise that I had a tiny air leak that finally did me in when I had the oil pressure sender line off for more than a week.

So I celebrated by cleaning the carpets. Ten minutes into that my carpet cleaner burned up its motor. Murphy is alive and well onboard ASLAN!

[krush]

The sum of the parts above (best price) is about $9,000.

Don't buy ZF is the take away? That's beyond insane. CAT doesn't even get that for their golden cast iron.

[sixty]

Glad you got it all figured out. I bet the satisfaction of saving $9k is euphoric! Those prices are crazy but is what it is. I would imagine you coukd get it all rebuilt for far less. Would probably require some machining to get it to use off the shelf seals, bushing and bearings but that would make rebuilding easier.

[racclarkson@gmail.com]

Glad you got it all figured out. I bet the satisfaction of saving $9k is euphoric! Those prices are crazy but is what it is. I would imagine you coukd get it all rebuilt for far less. Would probably require some machining to get it to use off the shelf seals, bushing and bearings but that would make rebuilding easier.

Looked into rebuild. The go to hydraulic shop in Charleston was pretty non-committal. But if I had to, I'd have had nothing to loose by trying. Just glad I didn't.

Regarding your and Krush's comments on pricing, I can't find any fault in what you say; you're both right. At least the ZF product seems outrageously strong and has given good service. Lately I've read on this forum about MTU water pumps and 1,000 hour services on Cats, MTUs and Mans. So the pricing is not exclusive to ZF. It points to what we all find out sooner or later. You have to be resourceful in life or pay, pay, pay.

And yes, I am pleased with the end result. I feel like I sort of beat ZF at their own game. They keep such a tight grip on their proprietary information that you just about need a 4-rotor enigma machine to make any sense of it.

I'm also pleased with the knowledge I picked up and passed along that may help someone else down the road.