A Lefty Hurth box

[Chris M]

I've inherited a pile of bits that was once a Hurth 100 2.0 L.

It's all there and with new bearings should be as good as new but my engine needs the righthanded version.

 

I've never had the clutch assembly apart on one of these and I don't pretend to understand it but as far as I can tell (apart from the selector being on the other side of the box) the only difference is the direction of slip on the clutch.

 

Is it just a matter of fitting the clutch assembly the other way round on the shaft ??? I'm guessing not but if you don't ask you'll never know.

 

Any gearbox gurus here ?

[Tony Brooks]

I've inherited a pile of bits that was once a Hurth 100 2.0 L.

It's all there and with new bearings should be as good as new but my engine needs the righthanded version.

 

I've never had the clutch assembly apart on one of these and I don't pretend to understand it but as far as I can tell (apart from the selector being on the other side of the box) the only difference is the direction of slip on the clutch.

 

Is it just a matter of fitting the clutch assembly the other way round on the shaft ??? I'm guessing not but if you don't ask you'll never know.

 

Any gearbox gurus here ?

 

 

I have been trying to find a Hurth parts list so I can see exactly whatn is inside your box, without sucess, and as no--one has replied you I will throw in my theortical sixpennuth. It might prompt some more responses.

 

I think the Hurth box is a three shaft box with the three shafts organised much like an "inline" car's gearbox. Inputshaft with a fixed gear on it and a spigot bearing to support the front of the output shaft which has a free to rotate gear mounted on it.

 

In the bottom of the box is another shaft that migght be thought of as a reverse gear idler shaft. This oen has two gears fixed to it and meshing with the gears on the input and output shaft.

 

This shaft rotates all the time the engien is runninmg and is also in the bottom of the box, almost certainly it is running on half decent bearings (I would expect needle rollers) with loads of oil all around it.

 

Ahead gear is selected by a cone clutch (a bit like a simple synchromesh unit) that locks the input and output shaft together and this causes the lower shaft to rotate the reverse ghear on the output shaft, but in the opposit direction to the shaft rotation.

 

Reverse is selected by another clutch locking the reverse gear to the output shaft. Thus the fixed gear on the input shaft and the lower shaft drives the output shaft backwards rotating in the spigot bearing.

 

I believe that these boxes will run in reverse for far longer periods than the traditional sun/planet gear type boxes and the only item that would give me any concern is the spigot bearing.

 

As far as I can see the only way to reverse the output of this type of box relative to the input is to fit a three gear reversing train eiother at the front or back of the actual box mechanism.

 

I will now stick my neck out. If the spigot bearing is a needle rollet, ball or roller type then I think (as the box is a freeby) you simply reverse the gear lever in the single lever control. This will cause the box to go into reverse when ahead is selected and ahead when reverse is selected and thus convert a l/h box to a r/h one. You may get a shorter life, but I bet it will be measured in years, rather than the months when you tried this with sun/planet gear boxes.

 

I hope this is of some help, but the decision to follow my belief or not must be down to you. Otherwise you need the opposit handed prop.

 

Tony Brooks

[Chris M]

It has a multi plate wet clutch.

The gears on the output shaft are free to rotate on the shaft. The clutch locks one or the other of the gears to the shaft.

When in gear the clutch allows power to be inputed in one direction only. If you input power in the other direction the clutch slips.

This is presumably designed in to allow slip when quickly changing direction as the prop has significant inertia.

 

The rotation direction of the engine is significant. My engine with the left version of this box will just slip the clutch continuously.

My question is can the box me modified / reconstructed to reverse the action of the clutch?

I''ve uploaded a couple of photos to show the design.

 

[Tony Brooks]

It has a multi plate wet clutch.

The gears on the output shaft are free to rotate on the shaft. The clutch locks one or the other of the gears to the shaft.

When in gear the clutch allows power to be inputed in one direction only. If you input power in the other direction the clutch slips.

This is presumably designed in to allow slip when quickly changing direction as the prop has significant inertia.

 

The rotation direction of the engine is significant. My engine with the left version of this box will just slip the clutch continuously.

My question is can the box me modified / reconstructed to reverse the action of the clutch?

I''ve uploaded a couple of photos to show the design.

 

Snip images

 

 

Thanks for the pics.

 

Right. At least its a comfort to know that you have decent clutches and not the horrid cones some of the smaller boxes use.

 

I am now not sure what you mean by a "lefty" box. Traditionally twin screw boats had engines that actually rotated in opposit directions, but for years all the engiens go the same way and the direction of prop movement is obtaind in the gearbox. So left and right handed gearboxes tend to refer to the direction of the output shaft, not the input shaft.

 

I think I dimley recall that Listers may have offered a reverse rotating engine, but it was years ago, so as far as I can see, unless you have a marinised Honda petrol engine your engine is most likley to rotate the same way as normal. If this is not the case then I fear you need to talk to a dealer, also if the box is suppose dto accept a reverse rotating engine.

 

I have not seen a reverse rotating engine built since the war, but I expect there were a few, but its 60 years ago, therefore I would not expect someone to come up a reverse rotating gaerbox some 60 years later.

 

If your gearbox has been built for a "wrong" handed engien, then my first call, would be to a major dealer and if that failed to get me the info I needed I would inspect all the clutch parts to see if they have common identifiaction numbers. If a significant number of them do, then it is likely that you could rebuild them for opposit engine rotation. Taking everything into account I wonder if you got the box because it had been missassembled in the past.

 

 

My suggestion was based on the belief that your engine rotated teh normal way and that your box reversed that rotation.

 

 

I would add to my last post that there may be a wear issue with the reverse gear idler if teh box is run in reverse, but the boat is going ahead, but I rather doubt if it will ne a major issue unless its on a bushed bearing.

 

Hope thsi claers things up & good luck.

 

Tony Brooks

 

It has a multi plate wet clutch.

The gears on the output shaft are free to rotate on the shaft. The clutch locks one or the other of the gears to the shaft.

When in gear the clutch allows power to be inputed in one direction only. If you input power in the other direction the clutch slips.

This is presumably designed in to allow slip when quickly changing direction as the prop has significant inertia.

 

The rotation direction of the engine is significant. My engine with the left version of this box will just slip the clutch continuously.

My question is can the box me modified / reconstructed to reverse the action of the clutch?

I''ve uploaded a couple of photos to show the design.

 

 

PS this type is known as a drop shaft box because the input and ouput shafts are in a different line.

 

TB

[Chris M]

I believe it may have been fitted to a lister ST2. Is this the engine you refer to?

 

I'm going to strip it down and take a look later. There's nothing to lose and if nothing else it'll be interesting to do.

 

I'll try and get some pics of the clutch assembly in bits.

Edited January 11, 2007 by Chris M

[IanS]

I've inherited a pile of bits that was once a Hurth 100 2.0 L.

It's all there and with new bearings should be as good as new but my engine needs the righthanded version.

 

I've never had the clutch assembly apart on one of these and I don't pretend to understand it but as far as I can tell (apart from the selector being on the other side of the box) the only difference is the direction of slip on the clutch.

 

Is it just a matter of fitting the clutch assembly the other way round on the shaft ??? I'm guessing not but if you don't ask you'll never know.

 

Any gearbox gurus here ?

 

 

I've been looking at this myself as my Hurth gearbox is also on it's last legs. According to the info I have the gearbox in reverse has a lower duty rating than in forward, although I should add that it's not much.

I would be surprised if the majority of parts are not interchangable between left & right handed boxes, looking at spares lists for them there is no mention of parts being specific to either.

 

Regards

Ian

[John Orentas]

It is not normally a good idea to run continuously in reverse which is probably what you have in mind, when in reverse the drive is transmitted through a lay-shaft, the idividuall gear that can be seen bottom right. I must say though and I haven't seen this type of box before it does look the 'part' I can see it would work very well in reverse. On ballance though I would buy a new prop.

[Chris M]

Yes these boxes can be run in reverse continuously as long as you fit the optional oil cooler.

However the handing of the prop and the option of running the box in reverse are irrelevant here.

The key point is the rotation direction of the engine. This box is built for an unconventional rotation engine.

If this box was fitted to most engines it would simply slip the clutch when a gear is selected.

 

I took all of the parts off of the output shaft today to replace the bearings and examine the clutch plates.

The photo below shows the centre pieces of the double clutch assembly.

When rotated in one direction these plates are forced apart by the ball bearings riding up the channels, this in turn squashes the clutch plates and gives drive.

If the engine or prop is rotating in the wrong direction (as mine would be) these plates are not forced apart so there is no drive.

This is designed in so when switching from one gear to another the prop must stop before the clutch plates are pressed therefore reducing wear.

 

 

So in conclusion, no I can't just fit the clutch assembly the other way over. However I could source and fit an alternative clutch assembly.

 

One thing I did consider was swapping the gears over and building the gearbox the other way up but as the forward and reverse ratios are slightly different this was also not an option.

 

Anybody got a dead Hurth box they want to sell me ??