Hi fellas, what would be the heaviest/weight oil I could put in my BSA gearbox without going to semi fluid grease. Also how do you tell which modern oils will chew out the gearbox bushes?

regards Neil

Hello Neil,

There were many oil discussions on the forum,
And if you search, you can find them, but basically,

The correct oil is like the one for the engine:50 grade oil.

I used for 12 years 90W-140 mineral gear oil with no issues,
And I guess a thicker one can also be used.
The oils should NOT be synthetic, as it corrodes the bushes.

Hope it helps,
Noam.

It should be noted that Noam is in sunny (and hot) Israel...I ran SAE50 in the engine of my Ariel Square Four in the summer but there was noticeably more resistance to movement as soon as the weather cooled down in the late Autumn...

I run SAE40 in my M20 gearbox without any issues and I should think you could run an SAE50 as well if your not running in too cold a climate or if you give it some time to get moving...

Overly heavy oils should be avoided IMO due to the number of smallish drillings that allow the oil to reach the bushes in the box and I consider semi liquid grease a complete 'no no'....

If leaking is the issue behind your enquiry fitting a sealed bearing at the drive end is the best cure....If you think about it, any oil that won't leak out probably won't reach the bushes either...Ian

email (option): ian@wright52.plus.com

And gear oils are measured on a different scale to engine oils.
30W engine oil is roughly equivalent to 75W gear oil so the 90W 140 will be around SAE 60 engine oil.

email (option): bsansw1@tpg.com.au

Hello all.

Thanks Ian and Trevor.
This is also interesting for me..
I thought that the oil I use (90-140) is more remote in viscosity than the 50...

In the newer M21 project bike, I did install a sealed bearing,
And as I see almost no leakage, after topping with the 90-140,
I started to add mono 40, when needed

I have also a question please:
Many times we discussed if it is worth to run the engine on synthetic oils,
But the cons and pros were mostly the price.

My question is-
If a synthetic oil can harm the gear bushes, isn't it also bad for the engine's smallend?

Thanks,
Noam.

I was chatting to Rex Ward a few weeks ago when we went to collect my friends GMC 6x6 gearbox after he rebuilt it. (A lot of the UK guys will know of Rex and his years of being a military vehicle engineer, especially well known for rebuilding DUKW's)

We asked him about the correct oil to use as we were under the impression that there were 'harmful to bronze' additives in EP (Extreme Pressure) gear oil. He said that, that is a thing of the past and EP and Hypoid oils are quite safe and he uses it all the time.

OMG! Not another oil debate

Ron

email (option): ronpier@talk21.com

That has put my mind at rest.

I used EP90 for a few years as I had lots of it. I stopped when people told me it could eat bushes.

From memory it leaked out as well as any other oil I have put in the box.

Regards

Pat

email (option): sacombsashtrees@hotmail.com

(Hypoid)GL5 rated gearbox oils have a high sulphur content which is the element doing the damage to the bronze...

(GL1 to) GL4 spec. gearbox oils do not contain this element...Some, but not all, GL5 spec. oils have a chemical inhibitor to prevent the corrosion...

As no one here has described any proven benefit that might accrue from the use of hypoid gear oil it begs the question why take the risk?...

GL4 grade oils are available from Halfords under the 'Comma' trade name (and from other manufacturers) or you could just carry on using engine oil which does the job perfectly well...

'If it ain't broke, don't fix it' is the phrase that comes to mind...Ian

email (option): ian@wright52.plus.com

One of the reasons for my query with Rex is that WW2 Jeeps have "FILL WITH HYPOID OIL" cast into the axle casings by the filler plug. Ron

email (option): ronpier@talk21.com

'Hypoid' refers to the tooth forms of the helical cut 'hypoid' gears within the box/transfer case...EP (extreme pressure) additives in hypoid gear oils are there specifically to cope with the high pressure 'sliding' motion between such gears...

The M20 gearbox contains no such gears so logically, doesn't require an oil of that specification...Ian

email (option): ian@wright52.plus.com

I have been trying to put this one to bed for decades.
Syncro cones are brass.
Thus oils designed for syncro gearboxes are safe for brass ( and therefore most bronze as well )
Since just about every car made since 1970 has a syncromesh gearbox almost every gear oil made for CAR use will be fine.

Trucks are different.
They really only went fully syncro around 2000.
So truck oils that are safe are marked "Syncro Safe" as ther are a lot of old crash box trucks out there.

As for synthetic oil being a problem. Total and utter crap.
Synthetics are a problem for cast iron rings on cast iron bores and this is a well proven fact . Only old bikes & cars run cast iron rings in cast iron bores .
There for by the logic of a 3 year old's brain, synthetic oils must be a problem for old bike gearboxes x 1 tweet x 1,000 retweets x 1,000,000 retweete of a retweeted retweet and google says it is a fact so it must be true.

email (option): bsansw1@tpg.com.au

Morris oils list non EP oils under the 'classic' gear oils section of their product range...However, they have a range of products ( synthetic/semi synthetic etc.) which do not definitively list application details...

I've e mailed a specific enquiry to their technical help dept. and I'll post the reply here when I get it...Hopefully that will resolve this question...Ian

email (option): ian@wright52.plus.com

Thanks guys.

Another oil debate, but a very interesting one.
I do not recall the harmful attitive issue being raised before. (?)

So, the engine synthetic engine oil is safe for the bronze smallend bush?
It doesn't contain that "bad" components?

Thanks,
Noam.

Sulphur & phosphorous compounds were added ( or in come cases not removed ) from lubrication oils.
Hypoid oils were used extensively in WWII because a lot of gearboxes had minimal heat treatment so the hard wearing surfaces, if there at all were very thin.
I had an associate who was into Jeeps & he fond out the hard way that some were made simply to storm the beach head thus had no hardening on the gear teeth and the latter was cut from free machining steel ( to save time & money )so they gears would wear out and start screaming in very short time, if they did not all strip strait off the shafts the first time you dropped the clutch.

Both Phos & sulpur attack the grain boundry regins of copper based alloys ( and zinc ones too ) causing them to crumble and fall apart.
This is not good for a load bearing surface.

email (option): bsansw1@tpg.com.au

Really?
Synthetic oil attacks cast iron?
I've been using it in my Commando but was not aware of this issue.

email (option): mfarnay@bigpond.net.au

Below is the reply from Morris's Oils ref. oil for BSA gearboxes...It's pretty much self explanatory and confirms that it is still possible to experience the problems that are the subject of these posts...


Good Morning,

Thank you for your enquiry.

Yes this is a regular question asked as it can get a little confusing. Basically what was classed as EP back in the 40’s and 50’s is very different to today’s standards so yes, you have to be careful. GL-5 is used mainly in Axle type applications in today’s world and will as you correctly stated have an effect on Yellow Metal due to the levels of Sulphur. GL-4 is ok but to be very honest the use of an SAE 40 Engine oil as originally specified is the right application even today.

If you were to ring me today I would give you our Golden Film SAE 40 for the gearbox as this is still the optimum choice.

I hope this helps.

Kind Regards

Wayne Devonport

Technical Advisor

email (option): ian@wright52.plus.com

So another oil thread were at the end of all this typing its found to be best to use what BSA said in the first place! Ha Ha

Who'd ave thought it!!

Exactly.. ...Ian

email (option): ian@wright52.plus.com

Did I say "attack" ?
I said it was a problem and the problem only exists when bedding in new rings.
Synthetics actually stick to CI much better than the complete oil they are made from.
This makes it difficult to wear in the rings to the bore on CI to CI systems.
Once run in it is fine.

In fact you can run in an engine on fully synthetic if you like , it just takes 50 times as long.

email (option): bsansw1@tpg.com.au

Correct.

What I like to use in the box is a funny colour oil.
Currently I have some nice purple agtrans which I am using .
Firstly because I got it really cheap
Secondly because it is a funny colour I can tell by the spots on the floor where the oil is coming from .
Not that oil spots on the floor worry me , these bikes were designed to leak from new and leaking when they are 70 years old is fine by me but it helps to know and even better it reminds me to do what the book says and regularly check the oil level.

email (option): bsansw1@tpg.com.au

As for some gear oils attacking the brass or bronze in the gearbox, yes that can happen. But what is always left out of the discussion is the fact that this only happens if the temperature of the oil exceeds 350 degrees F. I have been running these harmful oils in Triumph, BSA, Matchless, Ariel, Norton and Velocette for 40 years with no ill effects. If you gearbox is getting to this temp, you have bigger problems. When you hear from people to avoid these oils, you will find out that none of them have ever actually seen the bronze bushings being attacked. The gearbox does not need Hypoid oil but using it is fine. In most of my bikes I usually run 140W gear oil as we get very warm here in summer and it does not leak out as fast.

Bruce

Trevor as we were discussing high sulphur content oils attacking bronze gearbox components I (wrongly ) assumed your reference to synthetic oils being a problem for cast iron bores and rings was along the same lines. My apologies mate.

email (option): mfarnay@bigpond.net.au