Gear oil

[Tone]

Chaps, what's the consensus on gear box oil, straight 50, 20W/50 or ep80/90, Id like to know what you all think, cheers

[bsa-bill]

lots of opinions Tone.
Some oils apparently contain substances that are harmful to bronze bushes over time?
Time is the big factor, if like most of us here you're no longer in the first flush of youth and you CHANGE the oil once a year it's very doubtful anything is going to harm your box at all let alone in the time frame we have left (sorry to bring up the maker full stop).
So for what it's worth my advise - put in whatever your wallet is happy with making sure you've enough for petrol to enjoy rather than worry about your pride and joy

PS engine same

[KiwiGF]

I use castrol 20/50 in the gearbox...mainly because that's what I use in the engine, and forks for that matter, so there's always some around.

I don't think you will get consensus on oil use   

In the primary I use sae 30 Briggs and Stratton lawn mower oil, it's red so I can see when the case is leaking, as opposed to anything else!

[u28909z]

I would caution against gear oil, ie EP80, EP90, as it does seem to degrade bronze bushes.

When I was hunting for parts for a 1940s Triumph, I bought half a dozen gearboxes, when they were still cheap to buy at autojumbles (mainly Newark in the 90s). The ones that were no use when stripped down invariably had the gear oil smell about them. The ones that had presumably been used as per book, with engine oil, were generally in good condition.

Gear oil may be ok for later boxes, but presumably the handbook recommendations should be followed. 

[KiwiGF]

I am wary of "urban myths" concerning certain oils and bronze bushes but there seems to be enough "noise" out there to avoid using EP (extreme pressure) oils in our BSA's e.g. This link below seems to confirm we shouldn't....but I know wiki is not always reliable......

https://en.m.wikipedia.org/wiki/Gear_oil

Modern sae 90 or even certain brands may very well be fine with bronze or whatever the bushes are made of (how would one know?) in your gearbox but maybe it's not worth the risk 

[Tone]

The engine on my plunger was built by SRM, in 2002, and funnily enough they recommend EP gearbox oil!

[BSA_54A10]

Some things just never seem to die
Way way way back when you were pooing in your nappies all gearboxes were crash.
These gearboxes needed lots of gunk to cushion the blow.
Sulphur compounds were found really good for this and even better a lot of crude oils actually contained them.
Downside was these copounds attacked the grain boundry regions of the Alpha phase of brasses & bronzes causing them to crumble


Fast foreward to about the time you got out of short pants and some cleaver dick invented the syncromesh gear box for use in light vehicles.
However these boxes used a funny cone chaped gera which could only be economically machined from bronze or made from a brass powder pressing so we needed new gearbox oils that would not attack the copper based alloys. Enter the era of zinc & lead addatives.

However trucks still ran crash boxes and the new oils just did not cut the mustard so they kept using the heavy sulphated oils and cars got the new SYNCRO SAFE gear oils, around 1960 if memory serves me well. Eventually these new fang dangle stupid lazy driver boxes became standard fitment so the words SYNCRO SAFE vanished from the lighter oils used in cars AND MOTORCYCLES.

As a general rule any gear oil SAE 120 and under will be syncro safe and the light grease still used by trucks will not be SYNCRO SAFE but inplace of marking the 300,000,000,000 bottles of CAR & MOTORCYCLE gear oil SYNCRO SAFE they marked the 100,000 5 gallon drums of truck gear oil "UNSUITABLE FOR SYNCROMESH GEARBOXES"

So any CAR gearbox oil will be fine in your bike

[Greybeard]

...So any CAR gearbox oil will be fine in your bike

Wow, you really are 'Wise & Enlightened' 

[Tone]

Wow indeed.

[morris]

I run my boxes on Penrite's gear oil;
http://www.penriteoil.com.au/products.php?id_categ=14&id_subcateg=70&id_products=78
Tried engine oil at first but found it foaming. Encountered the same phenomenon in the Morris, so now have all running happily on the above...

[KiwiGF]

Hi Trevor, is it possible things have gone full circle? The wiki article seems to be saying GL grade up to GL4 is ok to use, but not the latest GL5?

[BSA_54A10]

...So any CAR gearbox oil will be fine in your bike

Wow, you really are 'Wise & Enlightened' 

Umm no just been riding for near 50 years, daily , almost every day.
Rode to work then latter on rode for work , rode for pleasure been riding BSA's all my life, first registered bike was a moungrel A10 mixture of long & short stroke  parts with 11:1 pisons no mufflers no brakes jambed shocks and so I found out 30 years latter front forks that were cracked nearly all the way through and odd springs.

The chemistry of what was happening came through my studies and particularly through failure analysis.
Oil labeling came about from buying the bloody stuff for 40 years and when you rode the type of shit boxes I usually did, you used a lot of gearbox oil, in fact you used a lot of engine oil and no one gave a stuff. It was just something you did to keep the bike on the road.

[BSA_54A10]

Hi Trevor, is it possible things have gone full circle? The wiki article seems to be saying GL grade up to GL4 is ok to use, but not the latest GL5?

Don't know.
Gerry Bristow, a fellow metallurgist who went on to work for BP & Duckhams was my oil guru but he sadly died soem time ago.
Lead and copper were removed for oils a long while ago so now we need some other demon for the self appointed saviours of the planet to save us from and it looks like zinc is going to be the next target
You know galvanizers and welder get "metal fume fever" which can be fatal so obviously if you have never done any chemistry all zinc must be removed from contact with humanity.
You may have noticed that tin seems to have vanished from tin cans.
This is due to fatal stannious compounds that are impossible to be formed from tin plate in a can poisioning innocent members of the public.
You have to be a greeny with qualifiacations in humanities and history to understand how this works because scientists can not.

[bsa-bill]

yes I remember Gerry's mails fondly.
I go by my understanding of Prof Brian Cox and bits of the good book  - so everything in the universe is made of the same stuff and originally there was nothing so everything being at one time nothing i use mid to low cost oil in engine and gearbox.
That said I do know a couple of funny welders

[Greybeard]

That said I do know a couple of funny welders

That reminds me of a dodgy joke about a kid wearing welders goggles!