Hurth HBW50-3R Gearbox problem

[conor54]

Towards the end of the season I had some problems with the gearbox. The engine is running well but there seemed to be no drive when the revs go up. The propellor is turning but it seems that only a fraction of the usual power is actually being delivered at the prop. Not sure the age of the gearbox but definitely more than 20years!

I did some experiments one evening while it was very calm. Turned the boat around on the mooring so she was moored by the stern and tried going ahead. Not much push. Disconnected the gear cable from the lever on the gearbox and put it into forward - much more drive. So maybe the lever wasn't being thrown far enough. I adjusted the cable position on the throttle/gear selector so it should travel further and on the gearbox level so that for a given travel it should rotate through more angle.(See diagram). This seemed to work. I cast off and motored around the moorings at 5 knots and did some backing up and going forward etc. Not sure if this is a proper long term fix or does it just postpone things. However on the day we craned out I thought again that there seemed to be less than full thrust.

Is this a known type of failure mode for these gearboxes?

 

[earlybird]

Could well be wear, either in the shifting device itself, which moves the central clutch cone or the cones themselves. Your fix might buy a little time, but I'd get it repaired, which means dismantling the 'box.
The shifter component shouldn't be too expensive, (I'd hope!)
When I had need of a Hurth repair, I found canal boat yards were good.

 

[peteK]

When did you last change the gearbox oil?

 

[conor54]

Hi, thanks for the replies. Gear box oil was last changed 3 seasons ago when I got the engine serviced professionally. Most years I’ve just done the engine oil and filters and changed the coolant. I haven’t checked the oil level yet, I suppose that I should have started there.

 

[Gallant Spirit]

sounds like your clutch is slipping, i had similar and fitted new discs

 

[Dutch01527]

I have the same gearbox and a similar problem. My gearbox is ok in forward gear but slips in reverse three times out of four which makes mooring / lock manoeuvres a bit exciting!!!

I would initially change the oil (ATF fluid) and revisit the cable shift to ensure that lever has full throw. That did not work for me.

My prop shaft turns in reverse but when I tested the rpm using a laser device bought cheaply on eBay it was only turning at about 280rpm. Conclusion was slipping clutch.

Options for me were:
1) Proffesional gearbox rebuild £300 to £500 plus removal/refit. I was not confident that my mechanical skills were up to doing the job myself.
2) Replace gearbox with new. No longer produced but compatible alternatives available from PRM and others - c.£500 to £700 plus removal/refit and need to shorten prop shaft by about 25mm
3) Buy 2nd hand

It took 2 months to find one (that I was confident was working ok and a low use/newish model) but I eventually bought a second hand unit for £75 and will fit it next week hopefully. My new one was bought on eBay and came from a canal house boat following a prop upgrade by a new owner. Most units advertised had no or dubious provenance and were about £150. I did not want to buy one with faults obviously so waited for the right one(hopefully).

PM me if anyone wants more info on option 1 or 2 above, I did a fair bit of research.

 

[Flica]

I have the same gearbox and a similar problem. My gearbox is ok in forward gear but slips in reverse three times out of four which makes mooring / lock manoeuvres a bit exciting!!!

I would initially change the oil (ATF fluid) and revisit the cable shift to ensure that lever has full throw. That did not work for me.

My prop shaft turns in reverse but when I tested the rpm using a laser device bought cheaply on eBay it was only turning at about 280rpm. Conclusion was slipping clutch.

Options for me were:
1) Proffesional gearbox rebuild £300 to £500 plus removal/refit. I was not confident that my mechanical skills were up to doing the job myself.
2) Replace gearbox with new. No longer produced but compatible alternatives available from PRM and others - c.£500 to £700 plus removal/refit and need to shorten prop shaft by about 25mm
3) Buy 2nd hand

It took 2 months to find one (that I was confident was working ok and a low use/newish model) but I eventually bought a second hand unit for £75 and will fit it next week hopefully. My new one was bought on eBay and came from a canal house boat following a prop upgrade by a new owner. Most units advertised had no or dubious provenance and were about £150. I did not want to buy one with faults obviously so waited for the right one(hopefully).

PM me if anyone wants more info on option 1 or 2 above, I did a fair bit of research.

My similar problems, turned out to be worn selector forks on the forward gear face.
As I was investigating my lack of forward gear, between tides @ Castletownberehead, I reversed the selector which cured the problem.
5 years later I junked engine and gearbox for a new unit. But, the problem never occured again in about 4000 hrs running.

 

[Dutch01527]

My similar problems, turned out to be worn selector forks on the forward gear face.
As I was investigating my lack of forward gear, between tides @ Castletownberehead, I reversed the selector which cured the problem.
5 years later I junked engine and gearbox for a new unit. But, the problem never occured again in about 4000 hrs running.

Interesting - by forward gear face do you mean the external gear selection lever on the gearbox?


I have tried manually changing gear and problem persists.

 

[peteK]

I had the fault that it would go in to reverse ok but when put into forward the propeller would only turn slowly as if it was slipping in the gearbox.Didn't think it could be worn as engine nearly new when bought boat.
Had this problem for a few years and find it I change the gearbox oil the problem virtually goes,so it it is if something is sticking inside the gearbox.

 

[Flica]

Interesting - by forward gear face do you mean the external gear selection lever on the gearbox?


I have tried manually changing gear and problem persists.

No, I mean the gear selector forks on the sliding shaft inside the box. My box was not a Hurth box, and had twin cone-clutches, one for forward and one for reverse. Instead of cone-clutches (which are self energising) the Hurth uses multiple plate clutches.
To get at it you have to dis-assemble the box.

Look here http://www.wbryant.com/temp/hurth_manual.pdf

@ 1.5 where it actually refers to the item,

Good luck

 

[Caer Urfa]

I had to replace my Hurth 100 gearbox a few years ago and when speaking to ZF (who took over Hurth) they recommended changing the oil every year or max 100 hrs, not had any issues in 4 years
Also looked into buying second hand BUT do you really know what you are getting?? I paid the extra for a new one and have no regrets.

Not sure just how many hours you have done but if you have had your gearbox for 20 years me thinks you are on borrowed time.

One tip: IF YOU replace the gearbox I would change the drive/damper plate at the same time which I expect will be from R & D, otherwise if you change the gearbox only and still have problems
then you will have to take it all out again to replace the drive plate.

 

[Brent Swain]

How many horsepower you running?A Hurth 50 is pretty tiny.

 

[westhinder]

Oil is pretty critical in a Hurth 50, I think you should start there.
The first time I changed the oil in mine, I put engine oil into it, instead of ATF, and it slipped and made clunking noises. Removed the oil, put ATF in and changed that after a couple of hours. Problem solved and never returned.

 

[Hydrozoan]

Oil is pretty critical in a Hurth 50, I think you should start there.
The first time I changed the oil in mine, I put engine oil into it, instead of ATF, and it slipped and made clunking noises. Removed the oil, put ATF in and changed that after a couple of hours. Problem solved and never returned.

I change mine every year - all 300ml of it (I think, not having the manual to hand) or as much of it as drains out!

 

[conor54]

Thanks for all the replies, plenty to ponder over. The engine is an 18hp Perkins Perama.

 

[Dutch01527]

One tip: IF YOU replace the gearbox I would change the drive/damper plate at the same time which I expect will be from R & D, otherwise if you change the gearbox only and still have problems
then you will have to take it all out again to replace the drive plate.[/QUOTE]

I have no experience of damper plates - are there many different versions for the same gearbox or does a gearbox have a single specific compatibile damper plate? I would like to do the job in one go if possible, which would mean buying one in advance before I have seen the old one.

 

[Brent Swain]

Several friends here were sold 30 HP engines with Hurth 50 trannys on them, by Detroit Diesel Allison, the local dealer. They crapped out in as little as 60 hours. When I talked to the dealers ,they said the boats must have been used for commercial use, as a pleasure craft will never motor more than 12 hours in a stretch. The pleasure boat rating is based on that assumption.
A size or two bigger, rated for full time use would be good choice. A friend, who once rebuilt them for a living, said the Hurth 150 is a huge jump in capacity and reliability from a 100.
An oversize pitch and diameter prop will screw them up, go undersize and they will last a long time.
I have had the dipstick come loose , unscrew, and go thru the gears, twice . A friend had the same experience.Now I stick one strand from 5/16th stainless rigging wire in the vent hole on the cap, to stop that from happening,
However, a Twin Disc is a far better tranny than a Hurth, for less money. They are made to fit the same bolt holes as the Hurth.
If your tranny is slow to kick into gear, the oil needs changing. It may look clean on the dip stick ,yet look like mud in a jar.
I have been told that synthetic oil will let the discs slip, and wear them out quicker, as it is just too slippery. Best avoid synthetic tranny fluid.

 

[Dutch01527]

I think that my Hurth HBW50 has lasted 30+ years with a 20 hp engine. A bigger gearbox would undoubtedly be better but would need modifications to the prop shaft and engine mountings. I am happy to replace like for like and see how it goes.

 

[Brent Swain]

As it is impossible to change the oil seal or rear bearing on a Hurth without taking it apart, after aligning it within .002 inch, is is well worth while using a drive saver on it to compensate for any remaining misalignment. I have built several spares out of 3/4 inch poly sheet, altho the original one has lasted for decades.

 

[conor54]

Hi,

After talking to lots of people the advice I got was to replace the gearbox with a TMC40. The Hurth HBW50 stopped being made about 10 or 15 years ago and while various companies can supply new or reconditioned Hurth's they generally only recommend that where there is no space to fit the TMC40 which is about 4cm longer and has 5mm more offset between the input shaft and output shaft.

Having explored the darker recesses of the engine compartment I will also replace the engine mounts and the drive plate too. And add a RND flexible coupling. (Are any boat jobs ever limited in scope or do they always add more extra steps?)

Thanks for all the replies,

Conor