Engine Oil in Gearbox??

[lmanton]

I am looking for some experienced advice please?

I experienced a loss of power when cruising at steady pace, with BMC 1.5 reconditioned engine with an older PRM Gearbox.

Before setting off I had checked oil level in engine and gearbox and all was correct. When lost the power I stopped and check the levels. I was amazed to find the engine oil level had reduced and the Gearbox had excess oil level.

Any ideas please? Thank you.

[Keeping Up]

I can't think of any direct connection between the oil systems.

 

Is it possible that the gearbox level has been increased not by oil but by water via the oil cooler, through a leak which could have been either the cause or the effect of the loss of power and the engine oil problem (overheating? head gasket?)

[alan_fincher]

Like Allan, I can't see how engine oil could end up in the gearbox.

 

Generally gearbox oil looks virtually like brand new oil, but engine oil loos contaminated and black.

 

If it were somehow possible that the increase in your gearbox was from engine oil, (and I still can't see how!), you might expect the oil in there to now bo looking less than pristine. Does it still lok like it did before these problems ?

[lmanton]

Like Allan, I can't see how engine oil could end up in the gearbox.

 

Generally gearbox oil looks virtually like brand new oil, but engine oil loos contaminated and black.

 

If it were somehow possible that the increase in your gearbox was from engine oil, (and I still can't see how!), you might expect the oil in there to now bo looking less than pristine. Does it still lok like it did before these problems ?

 

Thank you both for your replies.

It was definitely from the engine as I had to drain about 750ml of black engine oil from the gearbox as it was nearly full to the top of the gearbox. It was still steady black consistency without water mixed in.

It was also weeping out of small 1/2" diameter hole in flywheel housing just above the gearbox.

[cheshire~rose]

I am hopng to learn something here so excuse me if I cloud the issue with another question but if the rear crankcase oil seal in the engine was leaking where would that oil go?

[alan_fincher]

OK, but to be fair to Allan and I you had not spelled out that you had identified it definitely as engine oil, nor mention the large size of the quantities involved.

 

In my ignorance I would have thought that to get from one to the other it needed to pass two different seals, and the likelihood of both being failed at the same time was small.

 

Also that if the rear crankshaft oil seal on the engine has failed big-time, (clearly possible), the oil would simply drain quickly from the bell-housing.

 

Obviously I don't understand how things work, because I'm failing to see how it could get into the gearbox!

 

I'll leave it to someone who can.......

 

I am hopng to learn something here so excuse me if I cloud the issue with another question but if the rear crankcase oil seal in the engine was leaking where would that oil go?

I have always understood it would end up in the bell-housing, probably thrown around by the flywheel, but that there are places on the bellhousing it would drain out of.

 

As the bell-housing is usually a marinisation part on a BMC, not part of the original engine, I guess the presence of drain points (or not) could be down to who made that particular type ?

 

But I've a feeling I may know less than I think I do, and am also about to get an education in all this!.......

Edited October 28, 2012 by alan_fincher

[bizzard]

This could be possible if the engines rear main bearing seals have blown out possibly caused by excessive crankcase pressure caused by a blocked breather. Oil then forced into the bell housing picked up by the flywheel, flung about and worked its way along the gearboxes input shaft, through a worn oil seal and into the box, aided by a downward sloping angle of the engine and box.

[alan_fincher]

This could be possible if the engines rear main bearing seals have blown out possibly caused by excessive crankcase pressure caused by a blocked breather. Oil then forced into the bell housing picked up by the flywheel, flung about and worked its way along the gearboxes input shaft, through a worn oil seal and into the box, aided by a downward sloping angle of the engine and box.

 

Wouldn't the oil seal need to be more than a bit worn for the reported three quarters of a litre of randomly flung oil to all find its way along the shaft, and into where it should not be ? Sounds a phenomenal amount of oil to manage to do that, doesn't it ?

[RLWP]

This could be possible if the engines rear main bearing seals have blown out possibly caused by excessive crankcase pressure caused by a blocked breather. Oil then forced into the bell housing picked up by the flywheel, flung about and worked its way along the gearboxes input shaft, through a worn oil seal and into the box, aided by a downward sloping angle of the engine and box.

 

Were you in the escape committee for Colditz?

 

I cannot see how the oil would pass from the engine, through a dry bellhousing filled with flywheel, then into the gearbox

 

Do you have some strange oil cooler set up via the engine sump?

 

Richard

[lmanton]

Apologies, yes, I should have added that info in the OP.

Thanks to all for the replies, it does seem I have a major fault and an unusual on at that!

For sure it sounds expensive and difficult

[bizzard]

Wouldn't the oil seal need to be more than a bit worn for the reported three quarters of a litre of randomly flung oil to all find its way along the shaft, and into where it should not be ? Sounds a phenomenal amount of oil to manage to do that, doesn't it ?

Yes it does, but imanton says that the box is older than the engine so that could mean many many years old so the seal would be an old plastic type with lip spring, these old seals were not very impervious to oil and fairly quickly became hardened and or the spring snapped. Its a long time since i worked on those BMC 1500 engines now but i'm pretty sure that they like almost all engines of that era had rear main oil seals consisting of half moon graphite seals and cork strip seals that always leaked a bit of oil. The vehicles in those days always had a bell housing drain hole at the bottom usually with a ''Giggling pin'' inserted to keep gunge from blocking it and allow oil to build up and contaminate the clutch linings. Some modern vehicles still have a hole there, just in case.

If you remember even new vehicles in showrooms always had a drip tray beneath the engines to catch oil drips.

Modern neoprene based seals are of course much more reliable.

 

Were you in the escape committee for Colditz?

 

I cannot see how the oil would pass from the engine, through a dry bellhousing filled with flywheel, then into the gearbox

 

Do you have some strange oil cooler set up via the engine sump?

 

Richard

Depends on how oil tight the bell housing is.

[RLWP]

C'mon Bizzard. To really get oil from a BMC into a PRM box, you'd have to have the bell housing half-full of oil

 

Something doesn't add up here

 

Richard

[bizzard]

C'mon Bizzard. To really get oil from a BMC into a PRM box, you'd have to have the bell housing half-full of oil

 

Something doesn't add up here

 

Richard

Worn rear main bearing and blown out rear main seals with excessive pressure behind it could quite quickly fill a bell housing.

Hang on though hasn't he just stated he has some sort of odd oil cooling from the engine similar to what you've just suggested.

[RLWP]

<snip>

It was also weeping out of small 1/2" diameter hole in flywheel housing just above the gearbox.

 

 

<snip>

Hang on though hasn't he just stated he has some sort of odd oil cooling from the engine similar to what you've just suggested.

 

Ahh, yes he has - well sort of

 

I wonder if this 'power loss' is due to massive oil shear?

 

No - wait a bit - what about the starter motor? Wouldn't there be a horrendous oil leak there together with a failure of the starter?

 

Richard

[bizzard]

Ahh, yes he has - well sort of

 

I wonder if this 'power loss' is due to massive oil shear?

 

No - wait a bit - what about the starter motor? Wouldn't there be a horrendous oil leak there together with a failure of the starter?

 

Richard

Could have been on the point of seizure.

He's not yet reached the point when he tried restarting the engine.

[lmanton]

Not sure what an oil shear is...but engine still starts fine and runs ok, there is just little power on the driveshaft. When you empty he oil from gearbox back to dipstick level the power is better until the oil returns to gearbox. The housing may well be half full of oil as I had to put some more back in the engine to keep te levels up on dipstick. At least 2-3 litres i would guess.. Thanks for the replies.

 

Forgt to say engine sounds ok, with no unusual noises. Thanks

[bizzard]

Not sure what an oil shear is...but engine still starts fine and runs ok, there is just little power on the driveshaft. When you empty he oil from gearbox back to dipstick level the power is better until the oil returns to gearbox. The housing may well be half full of oil as I had to put some more back in the engine to keep te levels up on dipstick. At least 2-3 litres i would guess.. Thanks for the replies.

 

Forgt to say engine sounds ok, with no unusual noises. Thanks

Does your engine have a plunger type hand operated oil change sump pump? as often these are arranged with a change over tap to pump out and change the oil in the gearbox too. If the change over tap is positioned low down and with its lever left positioned between the pipe from the engine and the pipe from the gearbox oil could possibly transfer between the two.

[LEO]

Hi,

 

I used to have a 1.5 and it always leaked oil from the rear oil seal - until it had reached an oil level (usually halfway between full and empty) and then it would stop and run happily at that level for ages. If filled to the 'full mark' on the dipstick it would repeat this messy proceedure.

 

I found running it to the level at which the engine was happy was the best course of action and passed this info on to subsequent purchasers and as far as I know the engine still runs well.

 

I recall you mentioned the engine has been rebuilt - if done by a large concern it is posible that 'dipsticks' have been mixed up and you may have one for another Mk of engine.

 

On my engine the oil leaked from the rear bell housing, I can't see how it gets into the gearbox (oil in here can go black and burnt due to clutch slip).

 

Are you sure you are not over filling these reservoirs?, hope this helps, if running an oil cooler on the gearbox I would check that for leaks carefully.

 

L,

Edited October 29, 2012 by LEO

[by'eck]

This could be possible if the engines rear main bearing seals have blown out possibly caused by excessive crankcase pressure caused by a blocked breather. Oil then forced into the bell housing picked up by the flywheel, flung about and worked its way along the gearboxes input shaft, through a worn oil seal and into the box, aided by a downward sloping angle of the engine and box.

 

Wouldn't there be a tell-tale hole in the bottom of the bell housing to show up a rear crank oilseal leak. If not why not

[alan_fincher]

Wouldn't there be a tell-tale hole in the bottom of the bell housing to show up a rear crank oilseal leak. If not why not

I'm not convinced they all do have.

 

But something still sounds very odd here.

 

Even if there is no drain hole on the bell-housing, there isn't going to be a gasket between it and engine, is there, so I'd expect it to leak out anyway.

 

Also, unless I'm remembering wrong, don't 1500s have their starter motor set pretty low down ?

 

With the volumes of oil being talked about here, I'd expect the starter to be flooded out, quite possibly no longer working (?) and oil to be dripping out allover the place.

[Tony Brooks]

Yes it does, but imanton says that the box is older than the engine so that could mean many many years old so the seal would be an old plastic type with lip spring, these old seals were not very impervious to oil and fairly quickly became hardened and or the spring snapped. Its a long time since i worked on those BMC 1500 engines now but i'm pretty sure that they like almost all engines of that era had rear main oil seals consisting of half moon graphite seals and cork strip seals that always leaked a bit of oil. The vehicles in those days always had a bell housing drain hole at the bottom usually with a ''Giggling pin'' inserted to keep gunge from blocking it and allow oil to build up and contaminate the clutch linings. Some modern vehicles still have a hole there, just in case.

 

 

I seem to remember that most 1.5s had a lip seal for the rear main but the bearing cap was sealed to the block by some sealing strips which could also leak. I also recall being told that some industrial 1.5s used an oil thrower an scroll for the rear main so if that engine is set at a steep angle such a setup would leak oil - especially when stationary.

 

I like your sump pump tap theory and find it by far the most likely explanation, especially given the 1.5s "most excellent" crankcase breather system. If the oil drain pump is a duel inlet type then definitely make sure the idiot breather system is clean and working.