Parsons Reverse Gear type DA

[RLWP]

Like the Gleniffer RB this gearbox is fully mechanical, and derives it's reverse from a bevel gear cluster. This is the input bevel with the two idlers inside the bevel gear cage:

 

 

The output bevel has a large spline cut onto the hub at the back:

 

 

This spline is part of the forward gear locking clutch. It is keyed onto the output shaft and projects into the clutch drum:

 

Inside the drum are a set of alternating steel and bronze clutch plates. The bronze ones are connected to the drum by six bolts, one of these plates is shown in the picture above.

 

The steel plates have a spline cut on the inside and engage with the output bevel:

 

 

The pack is finished off with a steel pusher plate:

 

 

The endplate of the clutch drum carries three cranked levers that push three pins into the drum pack:

 

 

It is these levers and pins that lock the forward gear clutch, connecting the output gear to the bevel gear cage and locking the bevel cluster. This is the completed forward gear clutch pack:

 

 

The three levers are pushed outwards by a sliding sleeve on the output shaft. Here the levers are free and the clutch is disengaged:

 

 

Here the sleeve has been slid backwards, the levers are pushed out and lock the clutch:

 

 

Richard

[luctor et emergo]

I'm reading this with avid attention, as I am most curious as to how my gearbox actually works.

[RLWP]

Reverse gear is engaged by locking the bevel cage to the gearbox housing with a bandbrake:

 

 

which runs on the outside of the clutch drum:

 

 

So, this is the whole clutch pack, bevel gear cage and bandbrake:

 

 

All we need now is a way of operating it all. The Parsons box is very obliging, here are all of the workings:

 

 

At the top are the reverse gear parts, at the left the forward gear parts. The box is in neutral:

 

 

For forward gear, the lever and fork on the left slide the sleeve backwards, the levers ride up the cone on the sleeve and lock out on the large plain diameter:

 

 

Reverse gear is engaged by pushing the ends of the bandbrake together. This is done with the locking wedge at the top of this picture:

 

 

Here the wedge is in the neutral position:

 

 

Here it is in reverse:

 

 

The wedge has two parallel parts connected by a taper. Pulling the wedge to the left pushes the ends of the bandbrake together

 

Richard

Edited July 3, 2012 by RLWP

[RLWP]

This box has positive positions for each part of the mechanism in forward, neutral and reverse. However, it is a bit tricky to adjust.

 

When locked in forward, the ends of the levers must be on the large, parallel part of the sleeve:

 

 

The levers each have a hexagon headed screw and a locking nut. A fraction of a turn on this screw can make the difference between the gearbox locking properly or not. I ran the screws in finger tight, then added a sixth of a turn to each before checking I could still lock and unlock forward gear. I repeated this until I was happy, then locked the screws

 

Reverse is a bit more of a fiddle. The bandbrake is adjusted with the nut and locknut at the bottom of this picture:

 

 

However, as the nut is tightened up, it makes it harder to pull the reverse wedge into it's locking position. This is relieved by screwing out the adjustable stop in the casing at the top of the picture. So there is a repetitive process of tightening the nut at the bottom and loosening the stop until the clutch locks and the wedge locks out. The locknuts were then tightened.

 

So there it is, the Parsons DA reversing gear.

 

 

 

Richard

Edited July 3, 2012 by RLWP

[luctor et emergo]

How does one check the oil level?

 

Ahh, spotted it in the bottom pic...

Edited July 3, 2012 by luctor et emergo

[RLWP]

Dipstick, top left:

 

 

(straightened so it doesn't interfere with the oil thrower, fitted with dirt seal)

 

Richard

[Chertsey]

I'm guessing my F-type works on the same principle? I know I asked a while ago and had it explained then, but seeing this is really helping it sink in...

[RLWP]

I'm guessing my F-type works on the same principle? I know I asked a while ago and had it explained then, but seeing this is really helping it sink in...

 

It works on the same principle, the detail parts are different.

 

Richard

[BEngo]

It works on the same principle, the detail parts are different.

 

Richard

 

 

As far as I know there are three basic types of reverse arrangement in smallish sizes:

 

The type where there are two female cone clutches revolving in opposite directions driven by a combination of gears and chains and where the output shaft, with male cone is slid into the appropriate clutch for ahead or astern. Found in Kelvin/early Gardner boxes.

 

The epicyclic type where ahead is obtained by locking the sun wheel to the planets and the annulus gear and reverse by fixing the annulus gear and making the planets and the sun wheel revolve. Typified by Lister mechanical and hydraulic boxes.

 

The bevel gear type explained above by Richard- typified by Parsons and Glennifer. ISTR the small Dorman box worked like this too.

 

 

Anyone know any other types (apart from the big buggers with multiple gear trains and self-shifting clutches as found in HM's war canoes)?

 

N

[MoominPapa]

The epicyclic type where ahead is obtained by locking the sun wheel to the planets and the annulus gear and reverse by fixing the annulus gear and making the planets and the sun wheel revolve. Typified by Lister mechanical and hydraulic boxes.

I always assumed that this is how the Lister gearboxes worked until the famous Paul Catchpole gearbox incident, when we actually looked at drawings and worked it out.

 

 

Diagram here. (warning, big download).

 

There's in fact no annulus gear: what gets fixed by the reverse brake-band is the carrier, 5. The input is to gear 91 which meshes with and turns gear 25. Gear 25 meshes with gear 24 and turns it the same direction as the input gear. (Gear 24 is slightly further from the axis than 25, or slightly smaller diameter, so it doesn't mesh with the input gear, 91) Gear 24 meshes with the output gear 26, and turns it in the opposite direction to the input gear.

 

In neutral, the carrier 5 is free to rotate, allowing the input gear to rotate whilst the output gear stays still.

 

In forward, the clutch pack locks the output gear 26 and the carrier, 5 together. That stops gears 24 and 25 from rotating relative to the carrier so the teeth of the input gear, pushing on the teeth of gear 25, turn the whole carrier, clutch and output gear as one locked assembly.

 

There are actually two pairs of the 24,25 gears in the small boxes, and possibly more in the large ones.

 

This is a brilliant design. There's no bearing at the input end of the gearbox: just a bush (14) between a land on the input gear and the carries that keeps the bits in line. When the gearbox is in forward, that doesn't even move and the whole of the gearbox internals rotate, supported by the last engine main-bearing at one end and the output shaft thrust bearing at the other end. Dismantling is easy, the casing splits horizontally and the top half of the casing comes off, leaving the bottom half in situ, still attached to the engine. Then the output thrust bearing carrier is unbolted and the whole internals can be moved back to disengage from the input gear and bush and removed. There's never a need to lift the whole gearbox out of the boat as a unit.

 

MP.

[lucas88]

Hello everyone. What a wonderfull discussion above. I am Lucas from Holland and recently buoght and renovated an open boat (sloop) which was once a lifeboat (judging from the amount of dolly holes for oars I had to close/epoxy)

 

It came with an ancient looking Perkins 4.107 coupled to a Parsons gearbox, which thanks to this article I now know is an DA-type. The boat is from 1975, the engine from prior, since the Perkins nr is from before 1974 (when the traceable engine numbering started...) Engine is running like clockwork but the gearbox however doesnt sound so well. It makes a horrible and loud scraping sound when engaged (when still cold it actually makes quite less noise) and does not remain engaged by itself (althuogh deducting from the above epistel, I do not think that these two are related) When in neutral, it still gives thrust (no true neutral) and only after slightly pulling to reverse, shaft stops turning and the noise from the box completely stops and only the muffled sound of the Perkins is audible (which actually sounds very nice) I opened the top hatch on box, and inside looks normal. I only noticed the lining on the reverse band brake partly seperated and is now vissible/slightly coiled up in the sopen section of the band.

 

Following questions/theories I would like tested/commented on:

-1 Is this scraping sound maybe normal/common? (since all the gear wheels have straith teeth)

-2 From the above, I have ruled out the oil thrower being loose, since in Neutral, the oil thrower also spins (is this indeed the case)

-3 Could it be the forward shift fork (that operates the sleef)is broken? (this one I could replace from the top, withouth completely removing the engine/gearbox from the boat) From another forum (about an F-type Parsons) I noted these can break as well. This would also explain why the sleef for forward does not travel far enough to stay locked. It just travels over the corner to the parralel part, but then slids back.

-4 While I'm typing, I'm just realizing I did not check the reduction gear for the presence of oil.....who knows.

-5 Since the sound increases when the oil gets hotter, I suspect it is a worn out bearing somewhere in the box.

 

Any other ideas (that preferably do not invlove completely disassembling the box from the boat...) are very welcome.

 

I tried to attach a photo to this reply, but I am obviously computer literate enough....

 

Thanks in advance.

 

Kind regards,

Lucas

[RLWP]

I only noticed the lining on the reverse band brake partly seperated and is now vissible/slightly coiled up in the sopen section of the band

 

That sounds like your band brake has failed, which could give all sorts of problems

 

Richard

[lucas88]

Thanks Richard. I'll check your theory in winter when I'll take out the box. I am gambling it will hold out thruogh summer. In fact I am going on a 10 day trip on the boat tomorrow.

I doubt thuogh that the band brake would make this noise, but I check by engaging revers. The noise should then stop (since the bandbrake mechanism is then fixated) Reverse gear is actually working OK and locks.

 

Another question though: I notice on your pictures that your gearbox Identification plate is still on and states "..... engine oil for winter" and "......engine oil for summer", but I cannot make out the type specified. Can you advise what is stated on the box. (I am currently running on 20-W60 mineral oil, as specified in the Perkins 4.107M manual for the Parsons DA box)

 

R

Lucas

[RLWP]

Thanks Richard. I'll check your theory in winter when I'll take out the box. I am gambling it will hold out thruogh summer. In fact I am going on a 10 day trip on the boat tomorrow.

I doubt thuogh that the band brake would make this noise, but I check by engaging revers. The noise should then stop (since the bandbrake mechanism is then fixated) Reverse gear is actually working OK and locks.

 

Another question though: I notice on your pictures that your gearbox Identification plate is still on and states "..... engine oil for winter" and "......engine oil for summer", but I cannot make out the type specified. Can you advise what is stated on the box. (I am currently running on 20-W60 mineral oil, as specified in the Perkins 4.107M manual for the Parsons DA box)

 

R

Lucas

 

If that's what the book says, I'd stick with that

 

If I remember correctly, it was SAE 30 in summer

 

Do keep an eye on the band brake. If the lining has come adrift, it could shift and jam the box in reverse while still in forward. I haven't found a sensible source of new forward plates if you overheat them

 

Richard

[lucas88]

Richard,

I feel like the most stupid guy in the world... I'll be kiking myself for while.

It was indeed item 4, no oil (at all!!) in the reduction gear... It was running on dust and metal parts. I obviously badly damaged the bearings and gears, but after adding oil the noise completely disappeared. I'll take the reduction gear out in winter and see how the internals are.

But for now, smooooth boating withouth scraping noises.....(althuogh when warm, there comes a veery slight scraping. Same as withouth oil, when the scraping badly worsened when warm

 

Anyway, thanks for all assistence.

 

Lucas

[RLWP]

Richard,

I feel like the most stupid guy in the world... I'll be kiking myself for while.

It was indeed item 4, no oil (at all!!) in the reduction gear... It was running on dust and metal parts. I obviously badly damaged the bearings and gears, but after adding oil the noise completely disappeared. I'll take the reduction gear out in winter and see how the internals are.

But for now, smooooth boating withouth scraping noises.....(althuogh when warm, there comes a veery slight scraping. Same as withouth oil, when the scraping badly worsened when warm

 

Anyway, thanks for all assistence.

 

Lucas

 

It's a pleasure Lucas, glad you found something to explain the symptoms.

 

Richard

[luctor et emergo]

Goeieavond Lucas88, en welkom.

 

I'm affraid that it sounds like the box needs to come apart, as your symptons are quite similar to the ones I had. First thing, that you can, and must do now, is get the box adjusted correctly, as it sounds like the forward engagement at least, is not quite positive. This adds a lot of potential wear to the clutch plates. (Don't ask how I know this? )

 

Take Richards advice, he knows this box rather well...

[Peter Reed]

Richard please stop posting this engineering porn as i get breathless looking at it all.

 

Doubled up somehow

Edited August 1, 2012 by Peter Reed

[lucas88]

For sure the box will eventually come apart. If only for the brake band that has partially seperated.

 

But the box itself is at the moment functioning relativetly well (I only have to keep it fully engaged in forward. I suspect this must be the shift fork, since it appears the the three toes dont travel far enough past the cone) The reduction gear I have obviously badly damaged by boating for so long with the noise (no oil....) , but now with oil in it, at least it doesnt make any noise. And additonally I have installed a seperate thrust block, so the engine/box is isolated from any external forces (besides shaft torque)

Hopefully I can keep the reduction gear wheels and only replace the bearings. I assume I can get the brake band renewed/ recapped by a gear specialist.

 

All in all, I really enjoy this forum and will keep you posted. Hopefully with pictures, once I find out how to attach/include (I dig mechanics rather well, but with computers I feel like a pianist with only two fingers) Can someone maybe explain how to include/paste pictures in this media? If I try insert an image it asks for an URL (whatever that is), but I cannot browse in my computer.

R

Lucas

[David Mack]

All in all, I really enjoy this forum and will keep you posted. Hopefully with pictures, once I find out how to attach/include (I dig mechanics rather well, but with computers I feel like a pianist with only two fingers) Can someone maybe explain how to include/paste pictures in this media? If I try insert an image it asks for an URL (whatever that is), but I cannot browse in my computer.

 

 

Lucas, this should help: http://www.canalworld.net/forums/index.php?showtopic=38816

[Timleech]

For sure the box will eventually come apart. If only for the brake band that has partially seperated.

 

But the box itself is at the moment functioning relativetly well (I only have to keep it fully engaged in forward. I suspect this must be the shift fork, since it appears the the three toes dont travel far enough past the cone) The reduction gear I have obviously badly damaged by boating for so long with the noise (no oil....) , but now with oil in it, at least it doesnt make any noise. And additonally I have installed a seperate thrust block, so the engine/box is isolated from any external forces (besides shaft torque)

Hopefully I can keep the reduction gear wheels and only replace the bearings. I assume I can get the brake band renewed/ recapped by a gear specialist.

 

All in all, I really enjoy this forum and will keep you posted. Hopefully with pictures, once I find out how to attach/include (I dig mechanics rather well, but with computers I feel like a pianist with only two fingers) Can someone maybe explain how to include/paste pictures in this media? If I try insert an image it asks for an URL (whatever that is), but I cannot browse in my computer.

R

Lucas

 

One point to bear in mind is that Parsons strongly recommended that, if you have an external thrust block, you change the internal thrust bearing (a split ball race) for an equivalent sized plain ball bearing. Probably not worth worrying about now, if your bearings are already shot, but it'll save you a bit of money later because the split thrust races are expensive and can be hard to find.

 

Tim

[lucas88]

Richard,

Returned early from 10 day trip. but not due to technical problems (put on about 16 hrs and box is doing fine except for reduction gear box slightly leaking over the shaft seal. But luckily I had another major problem to wrry about, namely a diesel leak which caused about 20 liters of diesel to lean into my bilge, before I noticed it. This now fixed thuogh)

 

Anyway, in preparation of winter box stripdown, I studued the pics a bit closer, and noticed that the reduction is actually not a seperate item, but integrated in the box end plate, and sharing the same main shaft bearing, which is acually lubricated from the reverse gear side aso is now for sure also shot.

 

I saw in the other trail/forum topic a part of a cross-sectional drawing of the box. Any chance you have the full cross-section drawing available (hopefully with the bearings oand oil seals part numbers...?) The the bearings/seals special parts (Mathway marine) or are they available at specialized bearing suppliers? (where did you get them?)

 

In fact, in my case, since I added a seperate thrust block, in theory, I would not even necisarily need conical roller bearings for the output shaft. But obviously I prefer to stick to the OEM parts/design.

 

R

Lucas

[lucas88]

One point to bear in mind is that Parsons strongly recommended that, if you have an external thrust block, you change the internal thrust bearing (a split ball race) for an equivalent sized plain ball bearing. Probably not worth worrying about now, if your bearings are already shot, but it'll save you a bit of money later because the split thrust races are expensive and can be hard to find.

 

Tim

Tim,

Only just saw your reply on the bearings. Thanks, at least that will make the bearing hunt easier.

R

Lucas

[RLWP]

The seals and bearings are normal commercial ones - buy the best you can afford

 

Richard

[BEngo]

The seals and bearings are normal commercial ones - buy the best you can afford

 

Richard

 

 

I assume they are Imperial sizes?

 

If so Lucas may have difficulty obtaining them from local suppliers in Holland. Are there UK (or even US) suppliers ( bearingboys et al) who ship to Euroland?

 

N