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MG Midget and Sprite Technical - g/oil

hi all,
got a very slight whine in 1 2 and 3 in ribbed gearbox. i know it recommends 20/50 oil but would it benefit or do any damage to use the old ep80 oil.
regards bob.
trebor

If all you have is a slight whine, take it apart and replace the layshaft and bearings - could well save yourself a gearbox.

FRM
FR Millmore

Bob,
I'm not too sure how much it would help or not as I don't know how the thickness/weight/rate EP80 compares to 20/50, the 80 isn't 30 more than the 50 if you follow me, FRM knows as this was discussed in a rec ent thread but as ususal I can't remember

slight whine on 1st is normal and if it's slight something to be pleased about whine on 2nd and 3rd isn't so normal but it depends how slight it is

how much whine is there, how long have you noticed it, have you got the soundproofing and carpets out of the car, are you perhaps fixated on the whine, do you notice it with the hood down

have you tried changing the existing gearbox oil with fresh good quality 20/50

if not get the g/box oil as hot as you can and leave to drain as long as you can as this with give a through drain of all the muck and old oil in the g/box

when you've thoroughly drained the existing g/box oil you can also check it for metal bits as a warning

you can get additives to add to the g/box to quieten it down by many don't think they should be used and they don't help much and could mask a problem (but only a bit)

FRM posted whilst I was typing
perhaps you need to compare your whine with another g/box to see how slight it is or how it compares
Nigel Atkins

Don't use 80s. Your gearbox is designed to run on 20/50 engine oil only.

Bernie.
b higginson

Not sure about the ribbed case g/box but the smooth case was designed to run on a straight / monograde SAE 30. Although copes fine with a multigrade. The usual reason for a gearbox or axle recommending a 'NON EP' oil is because the additives in EP (extra pressure) oils attack any bronze bushes/ bearings present, whereas a multi or mono oil will not.
Ed H

>>The usual reason for a gearbox or axle recommending a 'NON EP' oil is because the additives in EP (extra pressure) oils attack any bronze bushes/ bearings present, whereas a multi or mono oil will not.<<

I think you're mixing things up there a bit, I think you are thinking of GL4 spec oil being ok and GL5 not - which in itself is wrong GL5 is just the higher later spec

I'm certain you could try different oils and different thicknesses/weights/rates (within limits), the multigrade is probably to help with gearsh*ts at a range of temperatures

with the manual Leyland V8 boxes IIRC it was ATF in some
Nigel Atkins

Peter Cavanagh of Classic Gearboxes Marple came to a recent meeting of MASC North West to give a talk. He does other 'boxes, but is a specialist in our smooth and ribcase transmissions.
He brought along cutaway gearboxes and bits of horrendous gearbox failures and one of the things that he mentioned was that the smooth and ribcase 'boxes were designed to run on 20/50 engine oil. The thicker oils do not get to some of the bearings on the lay shaft and thicker oils start to clog up in use.
The handbook says 20/50, the Haynes manual says 20/50 and the manufactures designed them to run on 20/50, so I think that is the elephant in the room.
As FRM says, rebuild the layshaft then use the correct oil.

Bernie.
b higginson

Viscosity ranges are not strictly comparable, but SAE 40 engine oil is in the same range as SAE 90 gear oil. Found that out 50 years ago when I tried to get a few more miles out of my 47 Ford with loose bearings - the SAE90 gear oil made no difference - but 140 did! An 80W90 gear oil is pretty close to 20W50 engine.

Gearboxes could not have been designed for 20W50 - because there was none when the gearbox was designed. Some multigrades were becoming available, but they were not very common, and they only covered two or three grades. like 20W30, or 10W30.

The only reason for not using gear oil is the high EP additives affecting bronze bushes and synchro action - which certainly does not need to be reduced. "Gear oil" does not necessarily mean "EP", and the degree and type of EP additives is all over the place and extremely difficult to get information on - and the formulae change constantly. The GL4 - GL5 ratings also do not necessarily tell you what you need to know. All this stuff is proprietary info from the manufacturers, who will tell you that it is OK but they do not know what our old toys are made of.

For these reasons, which were even less controlled back then, but probably simpler and better understood, BMC recommended engine oil. Plus, they only had to stock one grade of oil!

FRM
FR Millmore

How much noise should a late 1275 gearbox make, mine is quite noisy, ecspecily with the hood up, but having never driven another midget I don,t know how it should sound. Its been like that for the last 10 years, I guess its original, so will have done over 100 000 miles.

Dave
Dave Barrow

FRM and Dave hitting the nails on the head

oils aint straight forward and diiificult to fully pin down

and

how noisey is noisy

Dave has a good point unless you drive other Spridgets you have nothing to compare yours against

that's why I always suggest potential buyers test drive good examples out of their buying budget to see how well the cars should be and that the buying budget may need to be increased

I've not driven someone else's Spridget for 18 months to 2 years back, I wonder how many owners have never driven another example of their model since or even before buying their Spridget

my original Spridget g/box had the noisiest 1st gear I've ever heard or my mate's ever heard and he grew up with cars from the 50s and 60s

I couldn't face a g/box rebuild after all the hassle I had with my previous Spridget 15+ years ago and I'd always intended getting a 5th gear for touring and everyday use

so Bob, meet up with another nearby Spridget owner go out in each others' car, drive each others' if acceptable and possible and I bet you both learnt something from the experience and have fun
Nigel Atkins

Just for info attached is a copy of the bmc workshop manual (1972) recommended oil chart so this would apply to ribbed case box.
As stated before the Sprite MK1 manual states monogrades as multigrades were not readily available, so smooth case would have been different spec oils. That said I've used 20/50 in engine & gearbox on the Frog just like everyone else with no issues.
Ed


Ed H

Ed,
you obviously miss me when I'm (very often) quoting from and telling everyone to buy the (owners) Driver's Handbooks and also the factory workshop manuals and parts catalogues

that page would also be in the (owners) Handbook - makes me smile to have it quoted back to me :)

note there is a range of oils quote not just 20/50 and as was pointed out to me oil have moved on in the last 40 years

as FRM has pointed out BMC quoted what was conviently available to them and possibly their customers at that time and lets be honest they weren't into radical developement work with the car particularly from the late 60s onwards and that's being generous to them

20/50 would be a reasonable compromise for the gearbox oil but not necessarily the only solution

as you've put you've divaited from spec with your Frogeye with no issues so why rule divaiting from spec for later models

then we have to ask are all 20/50s the same spec :)
Nigel Atkins

Ed-
Yes, and that is entirely compatible with what I said - they were keeping it simple. It is clear that multigrades are superior any place with a wide temp range = the reason for no single grades recommended by then. If you understand that the "W" number is a cold (O F)spec, and the second is a hot (210F)spec, then you can see that the oil meets all the specs for any grade in between.

Nigel-
"then we have to ask are all 20/50s the same spec"
Yes, because that is what they are tested for - to meet the spec. That does not mean they are the same, as the spec ranges are very wide - you can have a "thin" 50, or a "thick" 30, and they might be the same at the test temp. We used to use Valvoline for engines that leaked a lot, clattered, or were run very hard, because it was noticeably thicker than Castrol of the same spec. Was good for Jaguars which liked to drink oil - which is what Castrol originally developed 20W50 for. Once there was 10W50 Castrol, but it was unstable and not very good at either end of the range, and was dropped after a short time.

FRM
FR Millmore

Nigel

Yes missed those posts !! And yes I agree not all 20/50 oils are the same. I use Penrite in my vintage cars and they have now rebranded their Monograde SAE 30 & 40 oils to 20/60 but say the formula is still the same. Your guess is as good as mine ? :-)

ed
Ed H

Right or wrong.....

When i had my ribby box i used 20/50 with lucas oil additive, andit made my box mega quite and it shifted much nicer i used about a 1/3 of a quart

Now i have 5 speed datsun...and i used lucas tranny oil
Prop and the Blackhole Midget

FRM,
yeap that's what I meant by 20/50s not being the same plus their wear charateristics

Ed,
you've done well to miss those posts

I saw the Penrite (plus 10?) oils when search for engine oils and as above I mean the same rated multigrade oils act differently

personally I'm a big fan of fully synthetics but I've found that there are different interpretations (might not be the right word) of what a sythetic oil is
Nigel Atkins

OK, here's another thought:

There's a lot about lower zinc levels in oils now (including 20/50) and the negative effect on camshafts and followers in pushrod engines where the contact loading is high.

Basically, most of the engine oils on the market now have zinc levels much lower than they did when BMC specified it as the gearbox lubricant. So is this an issue when the same oil is used in gearboxes, where tooth contact loadings are alos high?
Paul Walbran

Paul-]
Tooth loadings in helical or spur gears are nowhere neat those in worm or hypoid gears or cam applications. It is the sliding accompanied by heavy pressures that requires EP additives. Normal gears are a rolling contact.

FRM
FR Millmore

Thanks FRM. I realise the loadings are less than hypoid gears, but the cam comparison is the one I don't have a feel or any hard data for.
Paul Walbran

Paul-
If you think about the hypoid or worm gears, you will see that the contact is predominately sliding, just like any flat tappet cam. Also just like a baulk ring or cone clutch, another reason for no EP in the gearbox.

FRM
FR Millmore

Just nervous - these boxes don't have much up thier sleeve!
Paul Walbran

This thread was discussed between 17/08/2012 and 20/08/2012

MG Midget and Sprite Technical index

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