Gearbox oil and phosphor bronze

Hi, use EP90 gear oil to g5 spec. Hypoid oil sometimes reacts with phospher bronze, it leaches the trace metals out. Drain the box and fill it with a 20 grade engine oil, leave for a few days, drain and refill with EP90. In the sixties everyone used GP50 or straight 40 engine oil. There is a lot of tosh spouted about oil. Sixties engines lasted 15 to 20 thousand miles because oil was crap. Look at car engines, they all run at 90 degrees C, yet oil manufacturers talk about ambient temperature for oil grades. It is only relevant for when you start up. Norton used to use GP50, and run it in for 5k miles on old oil. Aircooled engines need thick oil to stop them rattling. If your gearbox has lasted this long, you have nothing to worry about, it deserves a medal!. Best regards, Paul

The issue is the sulphur compounds in GL4 and GL5, these were added to early EP90 and most have been reformulated to remove the sulphur. Even if the sulphur compounds were not taken out they are only an issue above 100C, which separate gearboxes do not get to. Source for the 100C is Glacier Industrial Bearings.

Some distrust GL5 gear oil preferring GL4 but I gather that GL5 is unlikely to attach phosphor bronze bushes.

I have always run my 99 gearbox on EP90. 200,000 miles and the only failure has been a layshaft ball bearing. And the odd kickstart spring of course.

hello Well the old Hypol 40 0r 50 is the same as Extreme presser oils 80 or 90 and any of them can be used even car gear boxes have bronze bushes I use hypol 50 in my morris minor for years yours anna j

dont know if this will help.

https://www.opieoils.co.uk/p-68916-millers-oils-pistoneeze-classic-gear-oil-ep-80w-90-gl4.aspx

Barry

Having used GL5 Lubricant for some time now and suffered no problems, the above is correct as some mentioned

The the higher level of sulphur additives in GL5 can attack yellow metal bushes. These additives are also present in GL4, but at lower levels - They have always been there.

The oil needs to be considerably well used, usually beyond change cycle, AND the temperature of the gearbox very high for this attack to occur - As indicated above Norton gearboxes hardly get warm. You can find test results done at 100 Centigrade with GL5 oil.

Bushes are still used in modern transmission assemblies which will all use GL5 spec oil if it can be used due to the EP package within the oil, not the bush compatibility. The content of bushes has not changed for years. The way the oil is now designed will hold in suspension the wear particles better than GL4 is what some notice - they run out of the box when the oil is drained instead of settling out at the bottom of the gearbox. Yes, I hear say, but then they are circulated through the box repeatedly, do you not think the blenders have thought of this, the oil will still settle at the bottom of the gearbox, but each piece is encased in oil and thus able to run out when drained. This is what concerns some owners, as in the past the golden sludge was found on stripping the box, not on changing the oil.

What is really important, it to use the correct grade which has the best anti-foaming properties. This is better for the gearbox and will ensure less oil can travel down the clutch pushrod. Strangely the old spec GL4 straight EP90 oils seem to be better the GL5 oils, which foam quickly - have a look next time you have the gearbox inspection cap off with the bike running.

Use either and do not worry.

Hello Paul,

i use the Castrol Classic EP90. It's GL4.

stefan