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Post by Clinton Cool on Dec 15, 2016 20:32:15 GMT
I have a vetus m2.04 with a Hurth gearbox.
All seems fine apart from one thing: In forward gear the engine is responsive, revs picking up as they should do when I move the control lever forward. However in reverse, when I move the control backwards the response is very slow. Revs will increase very slowly, maybe taking 5 or 6 seconds to get to where they should be.
Any ideas what might be causing this?
Just to add, prop is clear, the boat has done this since I bought it, over 3 years ago.
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Post by Mr Stabby on Dec 15, 2016 21:01:38 GMT
Not sure, but mine is exactly the same, also the exhaust smokes badly when it is revved in reverse gear even though it doesn't smoke at all in forward gear at the same revs.
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Post by Clinton Cool on Dec 15, 2016 21:07:33 GMT
Not sure, but mine is exactly the same, also the exhaust smokes badly when it is revved in reverse gear even though it doesn't smoke at all in forward gear at the same revs. Hopefully someone knowledgeable will be along shortly. What engine and gearbox do you have? I haven't noticed any difference in smoking but will look out for it. My best guess would be that it's a problem with the gearbox or possibly, slack on the control cable? |
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Post by Mr Stabby on Dec 15, 2016 21:14:40 GMT
BMC 1.5 engine and a Hurth 150 gearbox, so maybe the gearbox is the clue, although I don't know why that would be. Perhaps there is far more drag on it in reverse?
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Post by Clinton Cool on Dec 15, 2016 21:20:12 GMT
I don't know if mine is a 150 or not. I can't see it being drag. Mine does this even when the boat isn't moving. The hire boat I used to own was just as responsive in reverse as in forward.
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Post by Deleted on Dec 15, 2016 21:22:14 GMT
Depends on the box, the mechanical boxes have a slightly higher ratio in reverse thus...
On this transmission, RH rotation (ie opposed to engine rotation) is forward. In fwd you have ratio 2.05:1 or 2.72:1, and in reverse 1.86 for both. The reason is that in fwd all power is transmitted over one set of gear wheels, while in reverse it passes two gears and a layshaft.
Because of this, the max allowed power in reverse is reduced to 0.5 hp / 100 rpm (0.7 hp / 100 rpm in forward).
May be enough with a badly proped setup to make the difference?
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Post by Ditchcrawler on Dec 15, 2016 23:17:39 GMT
Depends on the box, the mechanical boxes have a slightly higher ratio in reverse thus... On this transmission, RH rotation (ie opposed to engine rotation) is forward. In fwd you have ratio 2.05:1 or 2.72:1, and in reverse 1.86 for both. The reason is that in fwd all power is transmitted over one set of gear wheels, while in reverse it passes two gears and a layshaft. Because of this, the max allowed power in reverse is reduced to 0.5 hp / 100 rpm (0.7 hp / 100 rpm in forward). May be enough with a badly proped setup to make the difference? The ratios are listed here www.iwabss-limited.co.uk/upload/hurth_manual.pdf |
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Post by naughtyfox on Dec 16, 2016 8:41:41 GMT
When did you last change the gearbox oil? Might help.
Exhaust smoking badly - what colour? Why would the exhaust be smoky in reverse, the gearbox has sod all to do with the engine (?).
Gear cables - how old? If nothing else, remove from sheaths and re-grease?
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Post by Deleted on Dec 16, 2016 8:54:08 GMT
When did you last change the gearbox oil? Might help. Exhaust smoking badly - what colour? Why would the exhaust be smoky in reverse, the gearbox has sod all to do with the engine (?). Gear cables - how old? If nothing else, remove from sheaths and re-grease? The ratio effects the load on the engine. A higher ratio on a badly propped set up may cause enough extra load. The Hurth mechanical boxes aren't bad little units. Not had to play with the hydraulic ones though. |
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Post by tonyb on Dec 16, 2016 9:01:03 GMT
When did you last change the gearbox oil? Might help. Exhaust smoking badly - what colour? Why would the exhaust be smoky in reverse, the gearbox has sod all to do with the engine (?). Gear cables - how old? If nothing else, remove from sheaths and re-grease? The different gear ratios for ahead and reverse quoted above give a clue. Look up "overloading diesels engines". I suspect the boat in question (not the one with the slipping clutch) is probably over propped but the owner is gentle when pulling away in ahead. When stopping they probably give it full power but with the gear ratio make sit even harder to bring the prop up to speed and overloads the engine. That is the speed is held down so the governor in the pump goes to maximum fuel in an attempt to speed the engine up. The lower engine speed and attendant lack of swirl in the combustion chamber causes incomplete combustion and thus smoke. However I woudl expect it to be less marked on indirect injected engines like most canal boats have. |
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Post by Deleted on Dec 16, 2016 9:05:18 GMT
Cheers Tony, I'm supposed to be working my fingers to the bone so wasn't going to expand on my previous until dinner.  |
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Post by discodave on Dec 24, 2016 0:50:19 GMT
Sounds like a slipping clutch, hurth boxes + BMC engines can be problematic, depending on the model of hurth gearbox. Apparently the problem stems from engaging reverse too quickly from neutral after disengaging forward drive, BMC engine tick over can be slightly higher than a purpose built marine set up, and as such creates a perfect situation where the reverse gear is selected when the input shaft rpm is higher than ideal. The result is rapid wear. If you can pause and let the engine speed drop before selecting reverse it is possible to minimise it - maybe check the idle speed is as low as possible without uneven running.
I wouldn't be surprised if a replacement box is the better long term solution, if its a HB 100 or similar (125 ? I can't remember exactly ) I wouldn't spend much time on it as even new / reconditioned they were prone to the same failure. I replaced mine with the newer version, if my brain is working correctly I remember hurth was bought out by a german (?) Company, the new improved boxsomeing the 'Z' series . direct replacement . I've heard of a few folks finding them second hand, the only thing I would add is ensure it is a 'z' series box. Anyways, even if it lasts some time in its current state, if its an early hurth box, get rid of it at your earliest possible convenience 😊
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