AJS & Matchless Owners Club

I've been using Halfords 20/50 Classic oil for quite a while in the engine and AMC gearbox
I notice the gear changes are a bit tighter during a longish run, with the engine hot.
Would this be down to using this oil rather than the recommended Castro's Sae 50 as stated in the manual.
Is there a lot of difference between the two.
If Sae 50 is heavier maybe this could help improve the gear change.
I was thinking about trying this...
https://www.ebay.co.uk/itm/Silkolene-Ha ... 2539129632

No, just the opposite. Note in extreme cold SAE 30 is recommended. Where is heaviness felt? If when using the clutch lever, perhaps your thrust rod is seizing. When was the last time you inspected and cleaned it. Could be the multi grade has loosened muck. If you put it in the gearbox without first given it a good clean. Why did you decide not to use the recommended grade. Could be that what's caused the problem. So the box now needs all the loose muck cleaned out and correct oil put back in. Let it drain over night and see what comes out.

Rob Harknett wrote: So the box now needs all the loose muck cleaned out and correct oil put back in. Let it drain over night and see what comes out.

I've never found any 'muck' in any of my gearboxes. In fact the drained oil is always as clean as when it went in. It's cleanliness is an easy way to tell whether oil drips on the ground are from the engine or the gearbox.
I cannot see any justification for using multigrade in the gearbox.

SPRIDDLER wrote:

Rob Harknett wrote: So the box now needs all the loose muck cleaned out and correct oil put back in. Let it drain over night and see what comes out.

I've never found any 'muck' in any of my gearboxes. In fact the drained oil is always as clean as when it went in. It's cleanliness is an easy way to tell whether oil drips on the ground are from the engine or the gearbox.
I cannot see any justification for using multigrade in the gearbox.

Could be because you use your bikes Neville. Standing bikes can get oil contaminated with moisture, the oil turn milky. May not even drain out easily. Always need a bit of oil in my old grease gear boxes after standing. Also spay WD 40 in oil boxes to lubricate parts that have stood dry.

Hi

The bigger the number the 'thicker' the oil. Theoretically 20 / 50 multigrade will have the same properties as straight 50 when both are at normal running temperature, however when cold the 20 / 50 equates to a straight 20, (eg thinner).

The range of operating temperature in a gearbox is probably lower than that of the engine and therefore a 20 / 50 multigrade is more than likely performing at less than 50 viscocity, (thickness), so in my opinion could be contributing to your tighter feeling gearbox.

I'm a bit of a traditionalist so am using Castrol XP50 in my gearbox and Castrol XL30 in the engine, (though if Scottish summers continue to get warmer I might change to SAE50 engine oil).

Regards Mick

Mick surely thinner oil will allow moving parts to run more freely, That's why in extreme cold 30 SAE is recommended for the gear box. So using 20/50 the box should run more freely. ( put thick oil in a clockwork watch would stop it ) One reason I went for oil being contaminated, as it was feeling heavy. Or of cause its the clutch thats heavy due to thrust rod seizing perhaps.

mikeydpippin wrote:I was thinking about trying this...
https://www.ebay.co.uk/itm/Silkolene-Ha ... 2539129632

Why? 'Ordinary' Morris mono oil is fine (and less expensive).

I and probably hundreds of thousands of others have used straight SAE 50 in AMC, Burman and other 'boxes quite happily ever since mother was a lad.
If the gearchange is unusually stiff I suggest the problem is not with the oil.
The AMC 'box is pretty bombproof. A factory tester who was visiting our section said that when he was sent out on a bike fitted with the first production 'box he was offered a fiver if he could break it. He tried, as a fiver was probably a week's wages.
Out of interest what oil do you put in the primary chaincase?

Thanks for the info Nev,
The gearbox changes gears as it should until after a good run.
Then as the gearbox warms up it changes gear albeit seems a bit dry and not so easy to change.
I use 20/w50 in the primary chaincase as well.
Think I will use up the 20w50 in the engine and when used I will change all the oil to sae50

Rob Harknett wrote:Mick surely thinner oil will allow moving parts to run more freely

Hi Rob

You're correct to a point, but thinner oils have a thinner lubricating layer and this is easier to break through resulting in metal to metal contact, more wear and friction, (stiffer operation). In a gearbox where there is no pressurised oil system I would prefer to use a more viscous monograde.

Regards Mick

Mikey, if its for your 350's then the general consensus is straight 50 for the engine mainly because it has big end roller bearings as opposed to shells. The gear box should also have a heavy grade as recommended straight 50. If its anything like any of my bikes then the gearboxes hardly warm up at all. So, the 20/50 will not reach its heavier properties more suitable for the heavy demands/loads of the g/box.