How does it work?

[Chertsey]

I wonder if this has the potential to become a new sub-forum, where people with furrowed brows (like me) can get a simple explanation, with pictures, of how some bit of equipment or technology works. Not when it goes wrong, but just how it works normally.

 

One thing that has mystified me forever is how reversing boxes work. This began with Warrior's occasionally temperamental Bruntons box which I am told has a sliding shaft, but I think I will leave that for the advanced class.

 

For now I will be happy if I can understand how Chertsey's Parsons box works (I think it's a type F but I have left the manual on the boat. Yes, I have the manual but it doesn't help me!). We had the cover off it the other week to adjust the brake band and I was able to look inside. I was even able to follow the instructions in the manual to make the adjustment (well, PB did the adjusting but I was reading the instructions). I gazed in wonderment at the contents looking as clean and new as when they were made in 1960-ish, isn't oil wonderful.

But I still do not understand how it actually works. Over to you, CWF teachers.

[RLWP]

 

Perhaps there should be a gearboxes section in the Engines part of the forum

 

Richard

[Timleech]

I wonder if this has the potential to become a new sub-forum, where people with furrowed brows (like me) can get a simple explanation, with pictures, of how some bit of equipment or technology works. Not when it goes wrong, but just how it works normally.

 

One thing that has mystified me forever is how reversing boxes work. This began with Warrior's occasionally temperamental Bruntons box which I am told has a sliding shaft, but I think I will leave that for the advanced class.

 

For now I will be happy if I can understand how Chertsey's Parsons box works (I think it's a type F but I have left the manual on the boat. Yes, I have the manual but it doesn't help me!). We had the cover off it the other week to adjust the brake band and I was able to look inside. I was even able to follow the instructions in the manual to make the adjustment (well, PB did the adjusting but I was reading the instructions). I gazed in wonderment at the contents looking as clean and new as when they were made in 1960-ish, isn't oil wonderful.

But I still do not understand how it actually works. Over to you, CWF teachers.

 

The Parsons manuals are not very good.

 

No time now, but if nobody else comes up with an explanation beforehand I'll try to do one when I have a few minutes spare.

 

Tim

[Sir Nibble]

Google "Epicyclic".

[Chertsey]

Google "Epicyclic".

I am almost certain that is not how my reversing box works.

The reduction box I do understand, in theory at least.

[alan_fincher]

If it works the way I recall it does, the first thing to know is that it really only does anything more than the very basic when it's in reverse.....

 

In ahead gear, if all is as it should be, all the moving parts are locked together, so it is effectively just a (very lumpy!) "shaft" between the engine and the reversing box.

 

The "reverse" bit is the clever bit, but I'm sat in a car dealership on a dying battery, so I'll leave that to someone else.

 

From our own disastrous experiences with a Type F box many, many years ago, the most important thing is that the gears are fully selected by the rodding, but once they are, the rodding doesn't rest on the lever, or try to push it further than its natural selection position.

 

We had one fail grand style, because it was effectively trying to support a lot of heavy rodding used to operate it.

 

Your will almost certainly be the "Type F", I think.

[RLWP]

I am almost certain that is not how my reversing box works.

The reduction box I do understand, in theory at least.

 

Are you sure? I think the Lister one works that way

 

Richard

[Chertsey]

Here is a picture:

 

Alan, you've frightened me now... I was told they were bombproof!

Edited October 10, 2011 by Chertsey

[alan_fincher]

I am almost certain that is not how my reversing box works.

The reduction box I do understand, in theory at least.

I'm fairly certain, from memory, that in reverse it works broadly like a rear wheel drive car differential, if you were to have the back wheels jacked up, but the prop-shaft locked out. If you rotate one wheel in one direction, then the other one rotates the other way.

 

I seem to remember that internally these boxes have 4 bevel gears in the same format broadly as a car diff.

 

I may be remembering quite wrongly, though!

[Timleech]

Are you sure? I think the Lister one works that way

 

Richard

 

Not epicyclic, bevels as has been stated.

 

Tim

[Chertsey]

I'm fairly certain, from memory, that in reverse it works broadly like a rear wheel drive car differential, if you were to have the back wheels jacked up, but the prop-shaft locked out. If you rotate one wheel in one direction, then the other one rotates the other way.

 

I seem to remember that internally these boxes have 4 bevel gears in the same format broadly as a car diff.

 

I may be remembering quite wrongly, though!

Oh my god, this isn't helping!!

[alan_fincher]

Alan, you've frightened me now... I was told they were bombproof!

A very big bill that my parents paid at Union Canal Carriers in the 1970s said otherwise!

 

Can't recall the detail, but basically if the actual casing gets damaged by misuse, (holes enlarged, I think), you were into having "aluminium welding" of some kind done, (sorry don't know the proper term), before the relevant bits got re-machined as they should be.

 

They are probably fairly bulletproof if you adjust them right, and don't do as we did!

[RLWP]

Oh my god, this isn't helping!!

 

D'you want to buy a differential to help you visualise this? I've got one in the shed from an MG Metro

 

Richard

[alan_fincher]

D'you want to buy a differential to help you visualise this? I've got one in the shed from an MG Metro

 

Richard

The principle can just as easily be shown with Meccano or even Lego Technic, and would cost far less to post to Sarah!

[Chertsey]

I remember having to change the rear axle on our CF camper because the diff had gone (while I was driving it; I never had any luck with that thing) and that was sun and planet gears iirc, so now I'm even more confused.

 

OK, for starters, basically how many different ways of achieving reverse are there?

[Guest]

The principle can just as easily be shown with Meccano or even Lego Technic, and would cost far less to post to Sarah!

 

 

Personally I don't think it helps but worth a shot

Edited October 10, 2011 by MJG

[RLWP]

I remember having to change the rear axle on our CF camper because the diff had gone (while I was driving it; I never had any luck with that thing) and that was sun and planet gears iirc, so now I'm even more confused.

 

OK, for starters, basically how many different ways of achieving reverse are there?

 

Wow, you're going to be really confused now!

 

Sun and planet gears belong to an epicyclic box, a differential had four bevels in a square - and a back axle would usually have a crownwheel and pinion too (which are also bevel gears)

 

Richard

[David Mack]

 

Personally I don't think it helps but worth a shot

 

Some videos of car differentials in use on the straight and when steering at How Stuff Works.

 

However, I'm not sure how helpful these are for someone for whom this is all new!

 

David

[Chertsey]

OK, I can easily see how you can achieve reverse using cogs (Ladybird book of Levers, Pulleys and Engines). But my box doesn't appear to have any. Everything is in a straight line, if that makes sense. So what, by moving to a different position, makes the propshaft turn the other way, and how does it do it?

[RLWP]

The principle can just as easily be shown with Meccano or even Lego Technic, and would cost far less to post to Sarah!

 

I'm not sending off Meccano or Lego Technic to Sarah, it's far more valuable than the diff

 

Seems to me we need to wait for Tim to have some spare time

 

Richard

[Chris Pink]

The principle can just as easily be shown with Meccano or even Lego Technic, and would cost far less to post to Sarah!

 

My Christmas List:

 

 

http://www.amazon.co.uk/Tomy-TY6995-Gearation-Refrigerator-Magnets/dp/B00004U95L

[Chertsey]

Some videos of car differentials in use on the straight and when steering at How Stuff Works.

 

However, I'm not sure how helpful these are for someone for whom this is all new!

 

David

I can understand that, but I can't see how it relates to my reversing box, if it does.

Is that the principle mine operates on, but hidden, or is it on an entirely different principle?

Edited October 10, 2011 by Chertsey

[bizzard]

I'm not sending off Meccano or Lego Technic to Sarah, it's far more valuable than the diff

 

Seems to me we need to wait for Tim to have some spare time

 

Richard

Dear old Tim is probably still recovering from a bit of set to with me yesterday over machining a belt groove in a flywheel. bizzard.

 

So during this interlude i shall explain in simple terms how to convert an Aston Martin ZF 5 speed,all synchromesh gearbox for marine use with chains and sprockets,or perhaps another time. bizzard.

Edited October 10, 2011 by bizzard

[Evo]

Another Parsons-with guts exposed

 

 

Edit....you can just see the crownwheel and pinions.

Edited October 10, 2011 by Evo

[cereal tiller]

Here is a picture:

 

Alan, you've frightened me now... I was told they were bombproof!

right,on the right of your picture you can see a bronze bit that is a rowlock ,but upside down.it is commonly called a YOKE/

 

ahead is engaged when the shiny silver tapered bit is forced forward by the yoke and the three TOGGLES are splayed out as they rise up the ramp.

 

when the TOGGLES are splayed out the lock up the CLUTCH PACK inside the big rotating lump in the middle of the gearbox housing.

 

 

when astern is required,another lever,which cannot be seen in your picture,as it's working part are suberged in oil at the bottom of the gearbox,causes a BRAKE BAND to lock the the big rotating lump and hold it still.

 

 

within the big lump there is a set of gears which do function in a similar manner to a vehicle differential.

 

if you put a vehicle in gear with the driving wheels off the ground and prevent one of them from rotating,the other wheel would rotate in the OPPOSITE direction.

 

so,when you lock up the big lump with the BRAKE BAND,the inner geartrain causes the OUTPUT SHAFT to rotate in the opposite direction,thereby giving you reverse THRUST.

 

 

this is not easy to explain without a good deal of engineering terminology.

 

so ,are you any the wiser?