The Boatist

Sailboat Ownership, Translation Work and Tales of Minor Adventure

Retire early, be passionate, don't worry, die poor

Wednesday, June 12, 2013

Replacing a Hurth gearbox with a ZF 12M

I'm pooped. Every muscle in my body is aching. Please do not try this at home under any circumstances!

I spent nearly the whole morning removing small screws with stripped heads from the pressure ring of the Duramax stuffing box. I tried every trick in the book. I even went out and bought a set of special allen keys - the ones with blades for more traction. What an idiot, all the time I had what I needed in a tool kit I bought long ago at Lidl.

Once I got the pesky little screws out, I got into mission mode and nothing was going to stop me - not even blood!
tetanus vaccination
Looks like fake blood. Good thing my tetanus shots are up to date. 
Duramax stuffing box
Got the screws off the stuffing box collar, which enabled me to pull the propeller shaft back.
Universal 5444
Since I was working solo, I enlisted a couple of lines for support when I removed the bellhousing. You have to remove the bellhousing and then loosen the bolts from the inside. There's no other way.
Kubota bellhousing
Shot showing the bolt heads on the inside.
Hurth HW 10
After 13 years in operation, it's history. Very tight fit getting it out of the engine compartment - another 2 or 3 cm and I would have had to slide the engine forward. What luck!
kubota damping plate
All the springs on the damping plate are intact, otherwise...don't even want to think of "otherwise". Gave it a few shots of WD40, also known as holy water.
ZF 12 M
And there it is. If it lasts another 13 years I'll be happy.
Now I need to align the engine, change the anodes, paint the bottom with two coats, scrub the topsides and a few other minor details. Easy, right? Non-boat owners must think we're completely nuts.

Oh yeah, one last thing: when I was trying to bolt on the new gearbox (holding the bellhousing with my teeth and right foot, thus leaving my hands free to hold the wrench and bolts), the silly thing refused to mate with the gearbox. I glanced over my shoulder at the old gearbox and my whole body, mind, soul and any hope of a fulfilling life crumbled into total despair...they weren't identical!!!!! But they were, it was an optical illusion. What a day.


  1. Ouuuuuuu! I can relate so much, it scares me. Great post... blood, holy water, optical illusions! I'm thoroughly impressed you did all this alone. Bravo!
    What a day indeed

    1. Thanks Pete. From what you've been doing on your boat, I'll say you can relate, and all too well. But like they say, what doesn't kill you makes you stronger...strong boat slaves!!

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  5. This replacement transmission is factory-made by ZF as a replacement for the Hurth transmissions originally put in on most Universal Diesel engines. simply just in case you're unacquainted with the name, ZF provides transmissions to Mercedes and BMW similarly as drive systems for super tankers. Rental Mobil Jakarta 

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