Gearbox oil

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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Red Gauntlet
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Gearbox oil

Post by Red Gauntlet »

The manual suggests SAE50 oil for the gearbox and F. Neill's book also suggests EP90 and somewhere else I read EP80, cannot remember what I used to put in mine 40 years ago but I would think SAE50 is correct. I am wondering why EP oils are suggested as the sulphur in the EP oil has a tendency to damage the phosphor bronze bushes in the gearbox, the copper content of the phos. bronze does not like sulphur.
Last edited by Red Gauntlet on Thu Apr 15, 2021 6:54 pm, edited 1 time in total.
56G80S
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Re: Gearbox oil

Post by 56G80S »

There's been lots of discussion on this topic, if you do a Search (magnifying glass top right of your screen).

Personally, I stick with SAE50 but apparently there is now contrary evidence to the "damage to bushes" point when using EP90. And perhaps that's only relevant if the gearbox still has phosphor bronze bushes?

When I first got the Matchless in the mid 1970's I used to put in Duckhams 20/50! I've only just stopped using that (incorrect for year) AMC gearbox and it was used hard including running up and down the country with a sidecar. I did keep it well topped up and changed on the theory that any oil is better than no oil.

JohnnyB
Red Gauntlet
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Re: Gearbox oil

Post by Red Gauntlet »

I did do the search before the post but could not find reference to the Roy Bacon book spec. Anyway I will use 50 weight as suggested although some of the 75w90 oils don't contain the same additives and have much better shear properties so are probably just as suitable, oils have moved on a long way since these bikes were built.
SPRIDDLER
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Re: Gearbox oil

Post by SPRIDDLER »

I'm not entering the Which oil? debate as it has been much covered and there are many opinions.
Here are just 4 of the many Forum pages on the subject which cover the same old, same old discussion:

http://www.jampot.com/forum/search.php? ... words=ep90

However, from a personal perspective.......

- In 16 years on this site I have never read any posts about corrosion/erosion/premature wear problems with g/box bushes regardless of which oil was being used.

- I have always used without any issues the originally recommended oils. Straight 50 for the gearbox (all year) and engine (summer) and 30 for the engine in winter and even for the primary drive. Just using 50 and 30 grades is convenient.

- With a typical power output of the H/W 350's of around 16bhp and the 500's of around 25bhp the gearbox components are never highly stressed. The L/W G5 is quoted at 15kW (circa 20bhp). The Burman B52 and AMC 'boxes were/are used reliably in far more powerful bikes with straight 50 oil. E.g. the 750cc G15 CSR producing 60bhp (AMC 'box).

(AMC were very reluctant to state engine power outputs officially (or to loan bikes to the Press for tests) so some of the above figures are taken from several magazine Reviews).
'There is a tide in the affairs of men
Which taken at the flood............'
Red Gauntlet
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Re: Gearbox oil

Post by Red Gauntlet »

Yes I didn't want to get waylaid in a great oil debate by a long chalk, I know there are some differing opinions, however working with a company that deals with F1 oils, I do get involved with many related researches, anyway back to the G5, 50 weight seems the way to go and as you say there is not enough power there in a straight cut gear box to really worry and I am not going to do a massive trip on it, unlike my other British bike which I did 150k miles. I just wondered why the F. Neill book suggests ep90 and everyone else 50 weight, in the long term any oil is better than no oil and if the gearchange is smooth then it is probably the right stuff.
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Duncan
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Re: Gearbox oil

Post by Duncan »

Mighty Max wrote:Y I just wondered why the F. Neill book suggests ep90 and everyone else 50 weight,
Not quite everyone, I use EP90 in my AMC and self levelling grease in my CP boxes, I do use SAE50 in another bike but that is a different make and has needle roller bearings. One advantage of EP90 is if the oil leaks out the smell makes identification easy.
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