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Hurth hbw gearbox


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10 hours ago, AndrewIC said:

All the installation diagrams are available online (Hurth is now ZF). I swapped a HBW100 for a PRM120 a few years ago, and had to have the engine raised a bit.

Are you sure that was not because the mounts had sunk. If it was a hydraulic PRM then that may well be the case but the PRM mechanicals and the Hurths have the input shaft and output shaft running in the same plane so the output coupling and the flywheel should all be in the same relative position. The thing I am not so sure about is the length of the two boxes but as most shaft couplings are now clamp on it shoudl allow for minor adjustments for box length.

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Why do you want to do this change?

I ask because my boat had this done(before my ownership) to cure gear change problems.

Later investigation, showed the clamp holding the gear change lever was loose....

Much later I sold the "spare" Hurth box, the buyer put it onto a testing machine, which gave it a underload workout, and pronounced it all good.

 

Bod

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34 minutes ago, Tony Brooks said:

Are you sure that was not because the mounts had sunk. If it was a hydraulic PRM then that may well be the case but the PRM mechanicals and the Hurths have the input shaft and output shaft running in the same plane so the output coupling and the flywheel should all be in the same relative position. The thing I am not so sure about is the length of the two boxes but as most shaft couplings are now clamp on it shoudl allow for minor adjustments for box length.

Just checked the drawings :) . I went from an HBW100 (now ZF10M), which has a drop of 62mm, to a PRM120, which (like its current successor the PRM125) has a drop of 72mm. That could have been just about taken up on the mounts, but the engine would have been waggling about right at the top of the threads, so the mounts were packed up at the bottom on steel blocks.

 

However, the OP has an HBW125 (superseded by the ZF12M) which does indeed also have a drop of 72mm. However the lengths are different, the PRM120 is 26mm longer, mounting face to flange, so the OP would need room for that.

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34 minutes ago, Tony Brooks said:

Sorry about the previous post, obviously age is catching up with me - been doing it a lot recently.

 

Me too Tony.

I don't reckon owt to this getting old business.

Had a Hurth gearbox on my last boat coupled to a BMC 1500,and I heard the word on the street (cut) that they were non too reliable.Read on an American forum some time ago that Hurths were known as the "dollar an hour gearbox"because at that time they cost $1000 and were only reckoned to last 1000 hours.

There was no information as to what engine they were coupled to or the type of boat.

However in the time I owned the boat I did about 1000 hours and don't know how many hours it had done before I owned it,but it had been no trouble at all and the boat is still moored here,and chugs past still.

One tip I got from even older geezers than me who had probably been boating since Pontius got his pilot's licence,was to have a good slow tickover so that gears engaged without a crunch.This I was advised prolonged the life of the gearbox.

Edited by Mad Harold
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21 minutes ago, Mad Harold said:

Me too Tony.

I don't reckon owt to this getting old business.

Had a Hurth gearbox on my last boat coupled to a BMC 1500,and I heard the word on the street (cut) that they were non too reliable.Read on an American forum some time ago that Hurths were known as the "dollar an hour gearbox"because at that time they cost $1000 and were only reckoned to last 1000 hours.

There was no information as to what engine they were coupled to or the type of boat.

However in the time I owned the boat I did about 1000 hours and don't know how many hours it had done before I owned it,but it had been no trouble at all and the boat is still moored here,and chugs past still.

One tip I got from even older geezers than me who had probably been boating since Pontius got his pilot's licence,was to have a good slow tickover so that gears engaged without a crunch.This I was advised prolonged the life of the gearbox.

Also I expect you are normally gentle on your gearbox. There are too many reports of short life to ignore them. I believe that may Hurths have been fitted to engines that are too powerful for the box or the duty required is too onerous. I also suspect a lot of this arose from boat builders who often seem to lack basic engineering knowledge selecting a box on the basis of its light duty loading rather than looking at the full specification and giving it some thought. There is a world of difference between inland canal use and sea use in respect of gear operations.

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Having had a few to rebuild I still don't like them. Even with a slow tickover [ difficult on many modern engines ]  they engage with a nasty clunk.

But its the cost of spares that is really terrible, you can buy a new PRM125 for nearly the same price as 2 sets of Hurth clutches and a few hours bench labour.

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