Hypoid oil? …why?

[Tapio]

Maybe they did specify it just steer us towards better "quality" oils, but to me that smacks of a slightly cavalier approach for a German engineer! You have a certain design requirement, you specify the gear oil to satisfy it, surely?

Sometimes, in any kind of mechanical design, if the manufacturer recommends oil that is not typically used for that specific application, it's a sure sign that there is something fundamentally wrong with it in the first place.

//T

[Corvus]

I believe a hypoid gear has a degree of sliding, similar to a worm gear, whereas a helical gear, spur gear, bevel gear and I think also a spiral bevel gear all have a rolling action on a constant pitch circle.

A bit of hair-splitting maybe, but no, teeth faces are not sliding against one another, but rather turning. If you think of the teeth faces as segments of a cylinder, you get that the cylinder segments are not only rolling, but also turning with respect to each other. This is with involute design:
http://en.wikipedia.org/wiki/Involute_gear
Hope that made sense.

//T

Straying slightly off topic, but consider a worm gear, especially one with a very high ratio. The teeth are involute form (usually anyway), but would you agree there is a degree of sliding of surfaces? The proportion of sliding versus "pushing" gets higher as the ratio increase generally speaking, although the number of starts of the worm thread alters this somewhat. But my point is to try to illustrate how I think you can have sliding with an involute tooth form.

I always thought that the fact that the pinion shaft is offset on a hypoid gear caused a little of this effect and separated this type from the spur, helical, bevel and spiral bevel? I'll have to do some reading!

Loving the thread though.

[Corvus]

Maybe they did specify it just steer us towards better "quality" oils, but to me that smacks of a slightly cavalier approach for a German engineer! You have a certain design requirement, you specify the gear oil to satisfy it, surely?

Sometimes, in any kind of mechanical design, if the manufacturer recommends oil that is not typically used for that specific application, it's a sure sign that there is something fundamentally wrong with it in the first place.

//T

Not sure about that. For the moment I'm going with the clue on the bottle. EP. Extreme pressure.

The pressure on a gear tooth depends primarily on the pitch circle diameter and tooth width. Also material quality. Smaller diameter for a given torque equals higher pressure. You can compensate by making the tooth wider, but you haven't the space. Put a lubricant in there capable of taking the extreme pressure and you can have narrower, smaller diameter gears, for a given load.

Bearing and shaft loads also increase with smaller gears. The pressure angle generated by the tooth will alter it very slightly.

Tapio, regarding hypoid gears, your own link to Wikipedia describes the sliding I was talking about. I've just consulted my very tatty 1981 issue of "the fundamentals of motor vehicle technology" and sliding (akin to a worm gear) is also stated there. I was beginning to think I'd dreamt it.

Which is also possible!

[Tapio]

You’re right. I only looked at the picture Still not sure if wikipedia is right though, but as opposed to you, I’m too lazy to do homework on it.

Anyway; talked to a friend of mine, whose wife has an R69, ‘62. He says that it too requires hypoid oil, according to BMW. The R69 that is, not the wife.

So, maybe BMW have had this recommendation since the times it was needed, and never got around to change it?

//T

[Corvus]

You’re right. I only looked at the picture Still not sure if wikipedia is right though, but as opposed to you, I’m too lazy to do homework on it.

Anyway; talked to a friend of mine, whose wife has an R69, ‘62. He says that it too requires hypoid oil, according to BMW. The R69 that is, not the wife.

So, maybe BMW have had this recommendation since the times it was needed, and never got around to change it?

//T

Ha ha. That's funny.

I don't know if I'm on the right track or not but, regardless, I enjoy the topics you put forward. They make me think.

Cheers.

[conkerman]

Helical gears in the final drive will require EP oil. Having the same oil in the gearbox makes servicing easier and stops techs putting the wrong oil in the final drive.

[Corvus]

Helical gears in the final drive will require EP oil. Having the same oil in the gearbox makes servicing easier and stops techs putting the wrong oil in the final drive.

If EP oil equates to hypoid oil, then that will part way answer tapio's original question. But it still doesn't explain WHY it needs it. As tapio says, there are no hypoid gear pairs anywhere in the transmission.

This is being pedantic I know, but wouldn't the final drive gears be classed as bevel or spiral bevel (I'm guessing they are actually spiral bevel)?

It also gives me an opportunity to ponder what I see as a peculiar feature of spiral bevel gears. Because the helical form starts on a smaller diameter towards the centre and winds its way out to a larger diameter pitch circle speed/angular velocity, whatever you want to call it, is not even along the length of the tooth? The same I suppose applies to straight cut bevel gears? But with spiral bevels the tooth load won't be constant along the length of the tooth either. The pressure nearer the smaller end will be much higher than at the larger end.

Have I got that right? Is that why spiral bevels need EP oil?

Hypoid gears seem to have all the above foibles, with the added burden of a degree of sliding (scuffing).

Any thoughts?

[conkerman]

I was told long ago that EP (Hypoid) oil is needed to cope with the sliding load on spiral cut gears.

What you propose could certainly be a contributing factor.

Horrible stinky stuff that it is.

[slparry]

I was told long ago that EP (Hypoid) oil is needed to cope with the sliding load on spiral cut gears.

What you propose could certainly be a contributing factor.

Horrible stinky stuff that it is.

I recall years ago several people trying to get me to "get rid of that dirty motorbike" (my beloved RD400) .....

I got a winter car, a Toyota Celica 1600ST, cheap because it needed a clutch fitting (little old lady had spent her time slipping the clutch every where).

Laying on my back with the car on ramps with cow crap and other detritus falling into my hair while changing the clutch and the gearbox oil while I was under there and having EP90 drizzled onto my face ... made changing the clutch on the RD400 a dream job, hell I even taught my then girlfriend how to do that job .... the RD was dyno'd at Dugdales to 64hp at the rear wheel

The porting was very excessive, it ate pistons and rings every month, but went like hot snot. Clutch plates usually lasted 3 months before giving up the ghost. High quality ones would last 4 months but were twice the price so the cheap ones where better value. Springs where usually changed at the same time and always packed with shims to apply more pressure. It also seemed to have an appetite for rear wheel and swing arm bearings every 6 months or so.

Add in the DG radial heads, Race Ace expansion chambers ... some different carbs (gone blank on what they where) .. Boyson reeds with wildly flowed cages etc etc.

After such a deep maintenance schedule with the RD owning my first 4T four, a Z650B1, was a revelation! Only ever seemed to need the occasional chain adjustment.

[McBoxer]

....I even taught my then girlfriend how to do that job....

You old romantic!

[Dog Tyred]

On subject of transmission case fluid changes, on the 11s drain plug is there meant to be a crush washer? I ask cos I bought a crush washer service pack for my bike from motoworks. It contained 6 washers but no large diameter one for the drain plug. Can not remember if one was on when I drained it weeks ago. I know it has a higher torque value (55nm) than other fill/drain plugs (23nm) with crush washers so perhaps it is a metal to metal friction job?

BTW I use Halfords GL4. Much cheapness when using my trade card

Can't remember its been soo long since I changed it Must do it soon.

The workshop manual states 'Fit new seal and re-install drain plug' so I guess the answer is yes. However the manual have been proven to be wrong before Just to prove the point review of the BMW parts page does not show a seal for the drain plug but does show one for the filler plug?

Good ol BMW!

Someone will be along in a minute with the definiative answer.

DT

[slparry]

....I even taught my then girlfriend how to do that job....

You old romantic!

it was like the pottery scene from Ghost ... except with clutch plates

[McBoxer]

....I even taught my then girlfriend how to do that job....

You old romantic!

it was like the pottery scene from Ghost ... except with clutch plates

Currently crying with laughter!!
The rest of the office think I'm having some kind of breakdown. Perhaps they'll let me go early.....probably in an ambulance!

I guess I'll have to clean this coffee up first....

[nab 301]

On subject of transmission case fluid changes, on the 11s drain plug is there meant to be a crush washer? )

There's never been one on mine, never really thought about it a poor quality pic I took today.

[fatnfast]

There is no crush washer on the gearbox drain plug. Other variants of the R11XX have another drain plug below the fill plug. These both use washers.