DIY Transmission Installation

[waterman46]

Just found out I have a significant leak in the rear seal of my Hurth HBW20.
My schedule makes it difficult to get the boat to a boatyard and returned to the marina when they are done. Thinking I could remove the tranny, take it to mechanic for rebuild then installing the rebuilt unit myself.

How hard is this to do by one person? I have fairly good mechanical skills but it would be a complete first-time thing. I worry about the weight of the unit and supporting it in the right position for installation. And of course the final alignment. Does alignment change because of removal and re-installation of the rebuilt unit?

This leak could have been cause by my neglecting to change the fluid. Ever. For the 20 years I've owned this boat.

[molo0928]

I just had this done this past week, although by a mechanic not by myself.

For a rebuilt KBW-10 Transmission, the quote was $2,900.00 + labor. A new one was $3,800.00. This all started by a small leak as well. I realize prices vary based on the model of the transmission. I have a 1985 boat and motor so as they age, the harder it is to come by parts.

Once the transmission was pulled, it looked like a rust factory so to my surprise, the boat was under water at some point for some time before me. Due to being almost 1/3rd of the way to a total repower, I had the mechanic take it to his shop, put it in a tank to clean it, replace the main seal and a couple bearings and then slap it back on.

To answer your question about pulling the tranny off, you have to disconnect the propeller shaft first and move it aft to create enough room to take it off. Going back on, the tranny goes back on the engine, the shaft gets reconnected. The shaft has to be realigned within .003" for mine. That took a couple hours of twisting and turning the engine/transmission to line up correctly. I also had new motor mounts put on during this time as well so the alignment was necessary regardless.

Hope this helps some.

[Jim Cate]

Molo has described the installation procedure pretty well, at least that's what it entailed on our boat.

However, do be aware that if the ATF has not been changed EVER, there is quite likely to be considerable internal damage to the tranny. Hurth gearboxes are known to enjoy frequent changes, and get unhappy with neglect. Be warned!

Jim

[JPA Cate]

Just a little addition to what Jim wrote. When we replaced ours, we did it with like; only afterwards, we discovered we could have put in a stronger, same sized one for the same price. So, armed with the knowledge that the atf has not been changed routinely, it will be prudent to expect the worst for the internal condition of the tranny.

Ann

[Jsta_Rebel]

I removed my velvet drive gearbox by myself. I was fortunate enough to have a hatch directly over the gear. I covered my floor first, sat two concrete blocks on end with a 4x4 going across. Made a sling that circled around the gear and hooked it up to a 2" ratchet strap hooked to the 4x4. Unhooked the shaft coupler, slid it back? removed the linkage and the 11mm bolts. I put a small amount of tension on the strap, and slid it right out. It was easy. I ratcheted it up as high as I could, slipped out of the engine room and pulled it up into the salon.

I would agree that if your motor mounts are in rough shape, that you should replace them at the same time because you will need to re-align the gear box after installing. I found out the hard way and had to replace my mounts after the fact when I couldn't realign the shaft to the gear. I had two engine mounts that could not be adjusted. Probably what caused my gear problem in the first place.

BTW, check or replace the heat exchanger if equipped.. Remember the Forrest Gump Syndrome. "Went this far, might as well go a little further"
Good luck with your project

[UNCIVILIZED]

Probably the most difficult part on boats is the poor access, combined with the weight of the thing. So that it's challenging getting things in & out, plus bolted back together.
Once you have things back together, setting the alignment shouldn't be too tough, assuming that none of the nuts & bolts you need to turn are frozen with rust. Start soaking everything in penetrating oil now.
Also, witness marks, as well as lots of pictures taken before un-bolting things, & in stages along the way, definitely help later on. So that you know what goes where, & how to get it there during the re-assembly.

[charliehows]

I did mine. Drilled a hole in the cockpit floor, put a wire through and set a steel lifting frame across the cockpit - did a bit of timber underpinning to be safer. Lifted the engine and box - spent a couple of days for the penetrol to unsieze the propshaft bolts - turned it sideways, took off the gearbox and dismantled it on the main cabin floor. Took out the clutch cluster and took it off to a mechanic who had the special tools to swap the clutches - his bit cost $800 plus i bought new rear seal and a waterpump kit - $300ish more. It can be done but not if you havent spent a few decades keeping old harleys going on the side of the road (would you believe the main gearbox rear bearing nut is the same size as a shovelhead clutchside main shaft nut - didnt even have to buy a socket...)

[Schooner Chandlery]

The access is the painful part. We have an oversized/overstrong Hurth HSW800 (same as the ZF80 now I think) on our Cummins engine. The engine and all were in a crate for many years before install (the previous owner bought a new engine but never installed) so we (my husband and I) replaced all the seals while the thing was not in the boat. That gave us an opportunity to see how hard it would be to deal with it in the boat.

The experience prompted us to mount the engine about 6" forward of where one might have done so. We would have gone even further forward but that was as high up under the sole as we could reasonably have the engine -- and it was close to a bulkhead so could go no further forward. In our case, one could probably actually replace all the seals, do proper measurements as you go along and do the rebuild in-boat as there's good room from both sides and above the Hurth. In most boats that wouldn't be the case and you'd pull it, of course.

Anyway, I think you can do it yourself, yes, but just do it when you've got plenty of time and be patient with yourself as you go about it. Each Hurth can be a little different -- by serial number -- so make sure you've got the right seals including output shaft seal for yours. In our case, the seal kit from ZF didn't include the correct output shaft seal and I ended up purchasing an appropriate seal from an industrial supply shop.

Best of luck!

[Uncle Bob]

Hi, the hurth gearbox on my boat started slipping and I discovered that the rebuild price was about two hundred bucks shy of a new, stronger, PRM.
Out with the Hurth and in with the PRM.
Really easy DIY. But I do have good room around the engine.

[CHM]

Agree with much of what's been said. I replaced mine this year with a ZF15. Cost new was not much more than having the old one rebuilt. You could rebuild yourself for around $300 in parts but getting the case shimmed properly apparently takes some experience. The transmission only weighs about 25 lbs or so and wasn't difficult to lift out of the engine space. The challenge is in access as has been mentioned.


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[Schooner Chandlery]

Originally Posted by CHM

Agree with much of what's been said. I replaced mine this year with a ZF15. Cost new was not much more than having the old one rebuilt. You could rebuild yourself for around $300 in parts but getting the case shimmed properly apparently takes some experience. The transmission only weighs about 25 lbs or so and wasn't difficult to lift out of the engine space. The challenge is in access as has been mentioned.


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If you have a lot of wear, measurements are critical but not impossible to deal with the shims. Experience is always helpful but if someone is on a budget, the DIY rebuild is easy enough. When we did ours (HSW800 equiv of the ZF80) a much larger one than the ZF15, our parts cost wasn't very high as I recall. This is a good site for parts ZF and Hurth Marine Equipment Sales, ZF and Hurth Marine Transmission Parts and the full clutch and seal kit shows something like $315 for clutch and seals for the ZF15m. Ours, the seal kit from them is like $143 but the full clutch and seal kit is $767. Seems higher than I recall. Of course the ZF80 (now replaced with ZF85...) looks like $4400 online prices or a rebuilt Hurth for maybe $2600...I'd still rather keep my extra $2K-3.5K for other projects.

So online the remanufactured ZF15 looks like maybe $1700. Was it much less than that where you are to get one? I'm always curious if the online pricing on this sort of thing is even close to what a local shop will do it for.

[phorvati]

I did the hurth HBW35 by myself. It seized because i ran it without oil. i have the PSS shaft seal, boat was in the water. Its not that difficult to go behind and loosen the prop shaft coupling bolts, and all the transmission mating bolts. At least not for me as a week prior to incident, I had just installed a rebuilt westebeake 4-108. I ended up ordering the bearings online. Very reasonable. Replaced the seized ones myself. Boy were they seized. Few nights later I put the tranny back and never looked back. Now I regularly check transmission fluid. That was a lesson learned. Now I carry a complete set of spare bearings.

[CHM]

The new one ran me around $1500 as I recall. I bought it from the ZF distributor in Cocoa. I probably could've rebuilt it for around $300 but the pain and time to replace it wasn't worth it for me if the rebuild failed for whatever reason. I still have my old one to sell as a core if anyone is interested.


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[roverhi]

R&R'd the Kanzaki transmission on my Yanmar 3GM30 by myself. On that size engine/transmission it's just a matter of unbolting the shaft coupling, unbolting the transmission, sliding it a little way aft and lifting it out. The transmission was surprisingly light and easy to lift out. Did have to remove the exhaust to get to the transmission.

On a boat your size, weight could be more of an issue.

[Bill Seal]

Jeez!!!
I guess I'm from the wrong generation. Back in the '50s we used to do things like pull the engine out of my roadster, stick it into my buddy's rail job, run Pomona, then stick it back into my roadster so I could get to school the next day. If you can change a faucet washer, you can change your tranny. Just be slow and methodical (and take lots of pictures so you can get things back in the right order)