Gearbox Oil.

[Yorick]

Just has one of them brain fade moments and forgot what I've been using last 40 years

I think when I was racing I put any old crap in the gearbox of my 2 strokes.
I need some new oil for the Husky tmrw and CBA to go to garage to see the manual.
Google chucked up loads of folk saying to use 80 grade gear oil and never use normal engine oil. That made sense.
But I got off my arse and consulted the Husky manual. That goes against all the Internet experts and says 15/50.

So that'll be going in tmrw. And that's what it says on the clear 1 litre bottle I got from the bike shop last time.

Why so vastly different opinions?

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[Tricky]

Vastly different opinions simply as people are people and some of us have different opinions to each other

It won't really matter too much what you put in there (I used to use that pink ATF oil in my LCs ) , so whatever you've last put in the Gixxer motor would be fine if that's in the garage, otherwise what the manual suggests- I'd definitely stay away from the 80/90w gear oil though, unless you particularly want a draggy clutch that is.

[KungFooBob]

Gets some R40 in it!

[Le_Fromage_Grande]

I'd put in what Husky recommend, the clutch will be less likely to slip, who do you trust, internet experts or KTM/Husqvarna who've been building dirt bikes since before you were born.

[Mr. Dazzle]

I would bet it's cause there's a high degree of commonality between the 4T and 2T clutch and gearbox technologies they use. Not in the sense that they use the same parts, but they will use the same manufacturing techniques, same materials, clutch friction coating, surface treatments etc. It might not even be a conscious decision on their part, it could simply be that's what the market can provide (i.e. lots and lots of suppliers will offer "4T type" stuff and hence it's cheaper).

The 4T gearboxes will be made on the assumption they're sharing engine oil, thus the boxes are built to run in engine oil - so the 2T transmissions just use the same thinking.

Plus as Tricky says, the clutch will be built assuming you're using engine oil (for similar reasons) so heavier oil will make it behave differently.

[KungFooBob]

What about heat?

A 2T gearbox oil isn't going to get anywhere near as hot as a 4T because it doesn't touch the parts involved in combustion?

[Mr. Dazzle]

I don't think they'd be THAT different temperature TBF - you're right that 4T oil goes through the engine, but that's part of the reason you have more of it and an oil cooler. I suppose it's fairer to say that the maximum temperature they might reach would be very similar, but you're more likely to get there in a 4T. But you have to design to the same limits anyway.

It's probably worth mentioning that in modern vehicles with a separate gearbox it's not uncommon to have much lighter oil than you might expect. For example the Bonneville (built using 50's tech) uses gearbox oil which you can hardly even pour at garage temp, you have to stick it in a bucket of hot water. My wife's car on the other hand uses stuff which is not much thicker than Castrol 3 in 1. The stuff we used to make for supercars was filled with oil that's basically water. All made possible by better manufacturing. 'Thin' oil reduces drag and hence improves efficiency, at the cost of needing better manufacturing to prevent things breaking.

Anyone who's used to working with slightly older stuff might be surprised to see it.

EDIT: Should also point out that the grade scales for gear and engine oils are different anyway! That's a much more fundamental thing I.e. 80 grade gear oil is not the same 'weight' as 80 grade engine.

[Mr. Dazzle]

Actually...just idly thinking about this...last year I was doing some work with a big jet engine manufacture on carbon fibre gearbox a parts. These were gears right up at the cold end of the engine, well away from combustion. We were talking oil temperatures averaging 130°C and peaking at 180°C right in the hot spots IIRC. So you can see, gear oil can get pretty toasty just from the action of the gears.

[Yorick]

I'd put in what Husky recommend, the clutch will be less likely to slip, who do you trust, internet experts or KTM/Husqvarna who've been building dirt bikes since before you were born.

Oh yes I will. Just wondering why varying opinions.

And I do know that car engine oil and bike oils are different

[Le_Fromage_Grande]

I'd put in what Husky recommend, the clutch will be less likely to slip, who do you trust, internet experts or KTM/Husqvarna who've been building dirt bikes since before you were born.

Oh yes I will. Just wondering why varying opinions.

And I do know that car engine oil and bike oils are different

Because opinions are like arse holes, every one has one

[Count Steer]

The stuff we used to make for supercars was filled with oil that's basically water. All made possible by better manufacturing. 'Thin' oil reduces drag and hence improves efficiency, at the cost of needing better manufacturing to prevent things breaking.

Slight derail, but isn't the stuff they use in F1 so thin and so 'tortured' they have to build something into the car to de-foam it?

[Mr. Dazzle]

That's true of lots of oils TBF, they've got additives in to stop them foaming up. Kinda makes sense when you picture a gearbox, the gears aren't submerged in the oil so they make really good whisks. But yeah, you can also put mechanical features in to de-foam it as well. It also tends to occur when you get water in the oil, which is part of the reason boxes are sealed for life (nominally ).

[Yorick]

At the shop, I remembered

Last time I bought 4 litres in a plain plastic bottle.
I asked for 2 more litres 15/50 and the new lad broke onto machine gun Spanish
Other lad came and explained that they only use 10w40 on the island.

Then he added that's what they put in the Suzuki at last service, so all is well with the world again

[Demannu]

My answer would be based on how noisy the bottom end is!
4t bike oil if all is well, if the mains/output shaft is rough, sae70 to quieten things down a bit!

[DefTrap]

The geezer at the local motor factors wanted me to put the far more expensive weight-correct-as-per-manual oil in my auld Peugeot. I told him it was ancient and has already done 200k on rock-bottom supermarket oil. No, no, it's very important he said.

I put it back and got the cheapo dino oil when he had gone. Just did another 1500 miles in one hit.

My random anecdotal evidence is free of charge.

[Mr. Dazzle]

The geezer at the local motor factors wanted me to put the far more expensive weight-correct-as-per-manual oil in my auld Peugeot.

A guy I used to work with had an old 405 diesel with stellar mileage on it. He used to dispose of his old oil by waiting for the tank to be nearly empty, then pouring said oil in and topping it up with fresh diesel.

[DefTrap]

A guy I used to work with had an old 405 diesel with stellar mileage on it. He used to dispose of his old oil by waiting for the tank to be nearly empty, then pouring said oil in and topping it up with fresh diesel.

Dispose of the old oil as fuel?
I don't think even I'm that tight/thrifty.

Those old 405 motors were great. I bet the chassis and electrics were what saw them all off ....

[Le_Fromage_Grande]

I had a 405 SRi it had a load of electrical faults, best one was the central locking unlocking all the doors apart from the drivers door by itself.

[KungFooBob]

My 406 had central locking with a mind of it's own too.

I did like the little pop-down keypad for deactivating the immobiliser.