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BMC gearbox.. and the fun continues...


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Hi Guys and the fun continues.... I have a BMC B type marine gearbox with a 2:1 reduction gearbox and a bad seal leak

 

the oil is leaking quite badly and is coming from where the gearbox bell housing joins the engine

 

it all seems a bit odd but its definitely the reduction as its leaking an EP oil and the main reversing box runs on SAE20

 

I'm picking its the shaft seal where the reversing box connects to the reduction

 

has anyone or does anyone know or have any suggestions on how to change this seal... ?

 

at one stage the reduction oil level was running overfull and when I opened the filler level overflow bung about 500mil of oil ran out so i was hoping the reduction may find a level and stop leaking but then discovered there's a seal on the shaft so knowing my luck it will need to be replaced

 

 

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leaking from here

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Edited by kiwiSteve
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3 minutes ago, kiwiSteve said:

I have a BMC B type marine gearbox

 

I never knew BMC made a marine gearbox. Looks a bit like a Velvet Drive to my eye, but obviously isn't.

 

Apols for going off at a tangent...

 

 

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32 minutes ago, MtB said:

 

I never knew BMC made a marine gearbox. Looks a bit like a Velvet Drive to my eye, but obviously isn't.

 

Apols for going off at a tangent...

 

 

I suspect they were made by a subsidiary or outsourced. Newage made gearboxes for others for instance. 

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Please note the below is based on well over 50 year old memories so some details may be incorrect.

 

I don't see how the EP oil can get into the bell housing because there is an intermediate plate between the bell housing and gearbox with an oil seal around the input shaft. That makes two oil seals between the bell housing and the reduction box oil. I suspect that someone may have put EP into the gearbox and the seal in the intermediate plate is leaking. I THINK that seal has to fit over a gear when rebuilding so it is easy to damage (don't take that as gospel).

 

To  answer your question:

 

I fear the reduction box has to be stripped so you can undo the nut on the gearbox output shaft so you can withdraw the gear. then you can take the front half of the reduction box body off so you can get at the seal. However, once the gear is off, you may be able to hook the seal out. So, drive coupling off, back half of reduction box off. You may well have problems locking the engine, so you can undo the coupling nut and the nut retaining the reduction input gear. I fear it is a two-man job with one person jambing the flywheel teeth.

 

40 minutes ago, MtB said:

 

I never knew BMC made a marine gearbox. Looks a bit like a Velvet Drive to my eye, but obviously isn't.

 

Apols for going off at a tangent...

 

You would not say that if you had seen one in real life, let alone lifted one. In any case the Velver Drive reduction box, although bolted to the end of the reverse gearbox like this one, has an almost domed appearance.

9 minutes ago, Tracy D'arth said:

I suspect they were made by a subsidiary or outsourced. Newage made gearboxes for others for instance. 

 

I agree, I suspect that it may have been licensed from Parsons. In the times we are talking about Newage did the BMC marinisations.

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5 minutes ago, Tony Brooks said:

 

I suspect that someone may have put EP into the gearbox and the seal in the intermediate plate is leaking. I THINK that seal has to fit over a gear when rebuilding so it is easy to damage (don't take that as gospel).

 

 thanks for your help Tony... I thought the same as theres an EP smell in the reversing box bung... but the oil in the box is clean SAE20 and the oil flowing down my pristine bilges is dark EP the same as the oil that overflowed from the overflow bung... its got me stuffed mate...

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Just now, kiwiSteve said:

 thanks for your help Tony... I thought the same as theres an EP smell in the reversing box bung... but the oil in the box is clean SAE20 and the oil flowing down my pristine bilges is dark EP the same as the oil that overflowed from the overflow bung... its got me stuffed mate...

 

Have you been running the engine, and have you had the gearbox off the engine (I suppose you must have to do the overhaul).  Assuming the red arrow in the photo indicates the oil leak, then it seems more likely to be oil in the bell housing being thrown around by the flywheel, which if an old leak could be thick and dark from oxidation and dust that has managed to get into the housing.  What is going on has got me stumped as well.

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31 minutes ago, Tracy D'arth said:

I suspect they were made by a subsidiary or outsourced. Newage made gearboxes for others for instance. 

 

I suspect the box was designed for use on an engine much smaller than a BMC1500, given the bulge for starter motor bendix on the gearbox that is obviously not needed when fitted onto a BMC bell housing.

 

 

 

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1 minute ago, MtB said:

 

I suspect the box was designed for use on an engine much smaller than a BMC1500, given the bulge for starter motor bendix on the gearbox that is obviously not needed when fitted onto a BMC bell housing.

 

 

Not if you had seen the size of the thing. They did fit it to the diesel and petrol B series engines, but also the larger 3.x engines as well. It may, but not 100% sure, have fitted it t some 5.1 litre Sea Lord engines. There was a smaller version known as the A type for the A series engines.

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29 minutes ago, Tony Brooks said:

 

Have you been running the engine, and have you had the gearbox off the engine (I suppose you must have to do the overhaul).  Assuming the red arrow in the photo indicates the oil leak, 

Yeah managed to get it started the other day... didnt remove the gearbox as I couldnt get hold of a set of mains or caps just checked the end float and put it back together.. an inframe rebuild i think its called or something like that... Ive got receipts for a box service done about 160hrs ago so I thought it would be fine... (and yet just another dumb move... if your rebuilding... check and clean, check and clean ) (Just a tight ass KIWI I guess  😋)  yes to the arrow and when you watch its got a bit of a trickle going on, but as i said it was over filled and maybe theres some kind of relief system that has caused it 

It dripped a bit of this when I ran it up on its stand after the rebuild from the same place and I thought then it must just be from an old leak so spent 30mins with the break clean and water blaster trying to clean the bell housing out (bit of a laugh now i think of it).. anyway the main problem of water in the oil seems to be fixed and she run up beautifully its on 3hrs now...

 

Edited by kiwiSteve
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Not a recommendation, a bodge, but I had a series 1 Landrover with leaking half-shafts and they are difficult to dismantle and reseal.

I bunged in a tin of Wynns auto transmission leak stopper and it worked.  So well in fact that when I sold the Landy 5 years later it still had not been repaired and still didn't leak.

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10 minutes ago, kiwiSteve said:

Yeah managed to get it started the other day... didnt remove the gearbox as I couldnt get hold of a set of mains or caps just checked the end float and put it back together.. an inframe rebuild i think its called or something like that... Ive got receipts for a box service done about 160hrs ago so I thought it would be fine... (and yet just another dumb move... if your rebuilding... check and clean, check and clean ) (Just a tight ass KIWI I guess  😋)  yes to the arrow and when you watch its got a bit of a trickle going on, but as i said it was over filled and maybe theres some kind of relief system that has caused it 

 

Gearbox service? Unless itemised, I would take that to be change oil and check/adjust the ahead clutch toggles and reverse brake band. The box would stay in place.

 

No relief system.

 

The front of the gearbox is sealed by an intermediate plate that is basically just a big disk with a hole and seal in the centre, although it has a land on the gearbox side into which fits a simple plunger type oil pump and an oil jet to direct oil into the reverse gear drum. The pump is operated by an eccentric on the input shaft that bolts onto the flywheel (no drive plate).  

 

So, looking at the input shaft starting at the flywheel and working backwards, we find the shaft is formed to provide:

1. a machined journal for the seal to run on (I can't remember a bearing, but if there is one, it would also fit on this journal.)

2. the oil pump eccentric

3 the sun gear to drive the reverse planet wheels.

 

The only way oil can get from the box into the flywheel housing is through the seal.

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8 minutes ago, Tony Brooks said:

The only way oil can get from the box into the flywheel housing is through the seal.

and that would still only be the SAE20... although it would be hard for me to tell if it was a mix of darker EP from the reduction and the SAE20 by the time it is in the bilge so maybe both seals have a problem... why not... every other thing has been a battle

 

I tell you this thing will be the death of me... at least some body is going to get a really good boat out of all this i suppose 😇

Edited by kiwiSteve
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Quite often if a boats marine engine has not used and run for a long time oil seals tend to get a bit stiff a let oil past. By running and warming up the seal can rejuvanate them. I had this when I fitted a s/h Lister ST2 and LH150 box and reduction box. At first oil was transfering from the gearbox into the reduction box. After a while it stopped doing it and has never done it since. That was about 15 years ago.

  • Greenie 1
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Resurrecting an old boat with old engine and gearbox is always going to be a challenge. Luckily you seem to have the nous and determination to see it through.

And the guidance of the Master with 50 year old memories, irreplaceable.

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10 minutes ago, kiwiSteve said:

and that would still only be the SAE20... although it would be hard for me to tell if it was a mix of darker EP from the reduction and the SAE20 by the time it is in the builge so maybe both seals have a problem... why not... every other thing has been a battle

 

Yes, but if it had EP in before and as you have not had the box off any leaks could have pooled in the flywheel housing until the flywheel threw it about. Also the SAE 20 might have added to if the seal is leaking.

 

Any oil leak from the reduction box front seal will end up in the gearbox, increasing the gearbox oil level, but not doing any damage as long as you are looking out for it. Therefore, I think the first step should be to sort out the seal in the intermediate plate. I have a faint idea it may have been a leather lip seal, so possibly not as simple as it would be if it were on ordinary lip seal I think a suitably sized lip seal would probably do the job.

 

Once you have done that, run it and see if what happens to the reduction box oil level.

 

In view of Bizzard's comment, if it is a leather lip seal, taking it out and boiling i in oil may soften it enough to allow it to seal again.

 

If you do take the box off, I would advise that you need something to lift and support the weigh of the box so the rear mounting plate clears the mount studs. Then undo the ring of bolts holding the gearbox body AND intermediate plate to the flywheel housing. Then, taking care not to allow the intermediate plate to move backwards, split the box from the intermediate plate and lift it clear. Then you can see exactly what you are dealing with without risking damaging the seal.

Edited by Tony Brooks
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2 minutes ago, Tony Brooks said:

 

Yes, but if it had EP in before and as you have not had the box off any leaks could have pooled in the flywheel housing until the flywheel threw it about. Also the SAE 20 might have added to if the seal is leaking.

 

 

 yes I see... so if it could have previously had EP in the reversing box that had leaked through the intermediate plate seal and now the new SAE20 that is leaking through has caused the the old oil to flow confusing the new leak with the smell of the EP...

 

it is still that thick slippery stinky oil that the ep usually is in the bilge though.. exactly the same consistency and look as what overflowed from the bung

 

Right... on with sorting the intermediate plate seal... thanks Tony

19 minutes ago, bizzard said:

Quite often if a boats marine engine has not used and run for a long time oil seals tend to get a bit stiff a let oil past. By running and warming up the seal can rejuvanate them. I had this when I fitted a s/h Lister ST2 and LH150 box and reduction box. At first oil was transfering from the gearbox into the reduction box. After a while it stopped doing it and has never done it since. That was about 15 years ago.

Man I hope I have your luck.. and yes I have been a little out front on this one as it was only a couple of hours running before I noticed it..

22 minutes ago, Tracy D'arth said:

Resurrecting an old boat with old engine and gearbox is always going to be a challenge. Luckily you seem to have the nous and determination to see it through.

And the guidance of the Master with 50 year old memories, irreplaceable.

 so true.. I'm lucky you fellers put up with me thats for sure.. maybe someone else will gain from my posts if there is still anyone that needs this olde information left.. I know we have covered the subjects pretty deeply so the infos good

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Once you have the box off and had a good look, you can see how to carefully take the intermediate plate off and clean out the flywheel housing.

 

Remember that I was on about the long bolts through the drum. With the box off it is a good time to take them out for inspection and put them back with the HEADS at the back of the drum, so if one fails at sea you can take it out via the rectangular inspection cover and carry on.

 

Edited to add: You will have to be OK at making a large paper gasket to seal between the gearbox and intermediate plate.

Edited by Tony Brooks
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55 minutes ago, Tracy D'arth said:

Not a recommendation, a bodge, but I had a series 1 Landrover with leaking half-shafts and they are difficult to dismantle and reseal.

I bunged in a tin of Wynns auto transmission leak stopper and it worked.  So well in fact that when I sold the Landy 5 years later it still had not been repaired and still didn't leak.

 once I sus out just whats actually happening... this might be an option,, (I just want to go fishing ffs... lol)

10 minutes ago, Tony Brooks said:

Once you have the box off and had a good look, you can see how to carefully take the intermediate plate off and clean out the flywheel housing.

 

Remember that I was on about the long bolts through the drum. With the box off it is a good time to take them out for inspection and put them back with the HEADS at the back of the drum, so if one fails at sea you can take it out via the rectangular inspection cover and carry on.

I have a second box here at home so can do some practise runs on dismantling with out having to drive the 70km to the boat every day and one box has the bolts already changed so I will do the same.. great idea thanks

Edited by kiwiSteve
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12 minutes ago, Tony Brooks said:

 

 

Edited to add: You will have to be OK at making a large paper gasket to seal between the gearbox and intermediate plate.

A large cereal packet is a great source of gasket card, works fine.

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9 hours ago, Tony Brooks said:

 

Y

 

 

If you do take the box off, I would advise that you need something to lift and support the weigh of the box so the rear mounting plate clears the mount studs. Then undo the ring of bolts holding the gearbox body AND intermediate plate to the flywheel housing. Then, taking care not to allow the intermediate plate to move backwards, split the box from the intermediate plate and lift it clear. Then you can see exactly what you are dealing with without risking damaging the seal.

... Ive just remembered the box was changed from my original engine so the box has been changed and by a mechanic who possibly damaged the seal as he put it back together (I found out from his boss that he was an experienced truck mechanic but new to marine engines... Bugger ) it was so long ago now (a couple of years or a bit more) I forgot. Thats why I didnt want to mess with it to much as I don't understand the planetary gear thing very well and dont know anyone that does.... He charged so much it led me to believe it must have been a really difficult and specialist job..

Edited by kiwiSteve
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3 hours ago, kiwiSteve said:

... Ive just remembered the box was changed from my original engine so the box has been changed and by a mechanic who possibly damaged the seal as he put it back together (I found out from his boss that he was an experienced truck mechanic but new to marine engines... Bugger ) it was so long ago now (a couple of years or a bit more) I forgot. Thats why I didnt want to mess with it to much as I don't understand the planetary gear thing very well and dont know anyone that does.... He charged so much it led me to believe it must have been a really difficult and specialist job..

 

The planet gears consist of two or three sets of two (can't remember). A long gear that meshes with the sun gear on the input shaft that drives a shorter one that meshes with another sun gear on the output shaft. The shorter gears act in the same way as the reverse idler gear in a conventional car gearbox to reverse the direction of rotation.

 

On that box the planet gears do absolutely nothing when in ahead and very little when in neutral. In ahead, the ahead clutch joins the output shaft to the drum containing the gears. This in effect locks the planet gears to the sun gears so the input shaft, all gears, the drum and output shaft are just one large lump of metal. The planet gears are stationary within a big drum but the drum just spins.

 

In neutral, the ahead clutch disengages so drum is disconnected from the output shaft, exactly what turns and how fast is down to oil, clutch and brake band drag, but whatever moves is under virtually no load.

 

In astern, the brake band locks the drum stationary so the input sun gear drives the long planet gears. The long planet gears drive the shorter ones that run in the opposite direction, and these in turn revolves the output shaft in reverse. It is all these gears meshing and running that makes these boxes very noisy in reverse.

 

You have to split the drum at the ahead clutch pack to deliberately remove the planet gears, so just taking the box off the engine will do nothing to the planet gears or drum - as long as when you refit it you ensure the teeth on the input sun gear align with the long planet gear teeth. If you don't you may chip a/some teeth, making it noisier than ever in reverse.

 

If the box is relatively silent in reverse but noisy in ahead, then you are driving it backwards - you have the wrong handed prop fitted - and the wear on the planet gears and their shafts will ensure a short service life. On twin engined boats, the reversal of shaft rotation for one is done with an idler in the reduction box.

 

PS for those familiar with other older boxes, but not this particular one, they are like beefed up Wortham Blake or WaterMota boxes beloved of the small Ford petrol engines fitted to many small GRP cruisers back in the day.

 

I am not sure if that helps because it is very wordy, but they are simple and robust boxes and you don't need to worry about the planet gears when you remove the box.

Edited by Tony Brooks
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  • 2 weeks later...

finally got a puller sorted and slipped off the rear bearing, oil pump cam and adapter plate... big rubber seal on the back of the main bearing..

I'm guessing the oil pump is pushing oil through the bearing seal and its pooling in the bottom of the bell housing and being picked up by the teeth on the fly wheel and spraying up top of the bell housing and running down the front at the join....

 

 

 

 

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Edited by kiwiSteve
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56 minutes ago, john.k said:

Is that oil grooves to lube the planetary set?

Yes.. the pump sits on a cam and pumps oil onto the planetary gear which then runs to the bottom of the box where its picked up by the pump again rather than spinning through oil.. looks like one of those endless threads on the inside of the pinion that carries the lube

 

theres no cooling on the reverse box and I guess the oil passes to the end runs back down the box and a lot of the heat in the oil would be lost to the cast iron housing then pools in the bottom ready to go round again

 

 

 

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Edited by kiwiSteve
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