Gear Braking?

Corvus · Post by **Corvus** » Fri Oct 25, 2013 6:28 pm

BMbler: "Its good we are having every aspect discussed through, but, but, but....
again (in different words) main contact on forward moving Pinion(transfer) starts at one end Force- torque and impact- quite significant to that one end.... "

Assuming I've understood you, I made this point on a different thread. One started by tapio I think? Anyway, even if we are both right, this is a function of how spiral bevel gears work. Not confined to bmw final drives.

BMbler:"Then in engine braking mode teeth of main knuckle are banging by bigger angle and absolutely surely loading the other end of a pivot... "

I think you are saying the reaction reverses? I'm not sure it does.

BMbler: "Hope it is designed to take such punishment, else apart from experience of BM and your assurances the only factors as how will I sleep?"

Answer=some Pink wine this evening...

Job done.

Cheers!

el-nicko · Post by **el-nicko** » Sun Oct 27, 2013 6:26 pm

.

Corvus wrote:
I'm not at all confident of being right........... so I guess that's end of it!

Cheers.

Phew! Glad that's over.

Corvus · Post by **Corvus** » Sun Oct 27, 2013 7:08 pm

el-nicko wrote:.

Corvus wrote:
I'm not at all confident of being right........... so I guess that's end of it!

Cheers.

Phew! Glad that's over.

Well I GUESS that's the end of it.

But I've guessed wrong before.

bikesnbones · Post by **bikesnbones** » Mon Oct 28, 2013 12:32 am

Just ride the bloody things and enjoy.

Corvus · Post by **Corvus** » Mon Oct 28, 2013 7:06 am

BMbler wrote:
ah well, I'll say (to myself), that its OK'ish to gear Brake, but "'ll be warned" of potential FD failure or at the very least increased wear

It's a mechanical device, so at some point, something will fail. I agree with merecat's comment regarding gearboxes, that bearing failure due to ingress of debris is the most likely cause in a lot of cases. I think the bearing manufacturers pretty much say as much themselves, based on statistical data? I thought I read that once, but I might be mistaken.

I'm sorry I never quite understood your last point. At least I tried to engage in some kind of debate and I quite enjoyed the challenge of thinking about it. Perhaps you can re phrase the question and we can try again. Beats talking about sat navs.

el-nicko · Post by **el-nicko** » Mon Oct 28, 2013 12:39 pm

el-nicko wrote:.

Corvus wrote:
I'm not at all confident of being right........... so I guess that's end of it!

Cheers.

Phew! Glad that's over.

Hmmm... guess I spoke too soon.

Corvus · Post by **Corvus** » Mon Oct 28, 2013 12:55 pm

BMbler wrote:Hi Corvus,
On the one hand it is a bit of riddle, that I got stuck on...
on the other, as most say- just ride and worry about it as whenever something happens.
The point I am still stuck- is weather it sensible to do gear Braking all together

)Due to the fact as how knuckles unload the forces and play in between altering the angle of impact BUT being spiral... I have almost given up in getting my head round that.)
____________________________________________________

Bearing load:

upon thrust (HP or Torque ) transfer forward, main resistance/impact is on red indicated areas.
Upon braking it is in burgundy (needle bearing)
?

My own (I stress) feelings or interpretations of technique:-

I think the "classical" style of riding involves a certain amount of engine braking (gear braking). It can lead to smoothest control of the bike if done sensibly, with regards to road riding. Done with too much abuse, engaging too low a gear too early, not only leads to mechanical abuse but is also likely to lead to less control of the vehicle, with regards to normal road riding. The mechanical abuse is more likely to be to the clutch though. Track riding and the advent of slipper clutches are a different kettle of fish.

My own (I stress) interpretations of theory :-

With regard to your thoughts about tooth loading, I think you are wrong, with all respect. The whole idea of a spiral bevel gear pair is to smoothly distribute tooth load as one tooth leaves mesh and the next one engages. More than one tooth is in partial mesh at any one time.

What happens during engine (gear) braking is that the opposite flank of each tooth carries the load instead. When driving forward the engine is driving the wheel, when engine braking (gear braking) the wheel is driving the engine. But the reactions imposed on the bearings is still the same direction because this is relative to direction of rotation.

Make sense? Is it wrong?

Like merecat, I've had a little experience with industrial gearboxes in a past life, but all the spiral bevels I've seen have had a taper roller bearing pair to carry axial loads in either direction. But then they would. They're not designed for just one specific application, as I wrote on an earlier post. The bmw FD is designed for one specific job and, with the exception of wheeling the bike around, only rotates in one direction.

I have seen examples of gear failure, although in most cases it is probably true that the bearings have been replaced previously (have failed first), but not always.

I don't go around worrying if my bikes are about to fail, but I do wonder how they work. A lot.

Corvus · Post by **Corvus** » Mon Oct 28, 2013 5:34 pm

BMbler wrote:
Corvus wrote: What happens during engine (gear) braking is that the opposite flank of each tooth carries the load instead. When driving forward the engine is driving the wheel, when engine braking (gear braking) the wheel is driving the engine. But the reactions imposed on the bearings is still the same direction because this is relative to direction of rotation.

Make sense? Is it wrong?
I don't agree....
Corvus wrote: I don't go around worrying if my bikes are about to fail, but I do wonder how they work. A lot.

I do agree!

One out of two ain't bad!

Notice I said "the same direction" whereas you only highlighted "the same"?

I didn't mean the same magnitude (necessarily). Confirm you meant to highlight "direction" and I'll go away and think again.

Corvus · Post by **Corvus** » Tue Oct 29, 2013 7:01 am

http://www.bostongear.com/litportal/pdf ... 33-153.pdf

More information, some which is relevant to our topic. Page 13 has a statement which bears out what I've said:

"For spiral bevel gears the direction of axial thrust loads will depend upon the hand and direction of rotation"

There, it's not only me who thinks it!

It explains (to me, at this stage) why bmw only cater for (heavy) axial pinion loads in one direction only, doesn't it? They know their final drive will only rotate (under load) in one direction. Whether it be forward driving torque or back drive torque during engine braking (what you're calling gear braking).

Come on my friend, I'm doing my best in providing proof. You'll need to do the same.

Ps. The above was written in friendly manner and not aggressive, so please interpret as such.

Corvus · Post by **Corvus** » Tue Oct 29, 2013 7:29 am

http://www.bmwra.org/otl/finaldrive/

In reading the article which I've re attached from the second post, Largiader seems to attribute most likely cause of bearing failure (large ball brg on output shaft behind crown wheel) to incorrect shimming. This makes a lot of sense. One small error with a shim and a huge force could be applied. The absence of an opposing taper bearing is then asking for trouble. To my mind.

He also attributes other reasons for higher bearing loads (since the first airhead r80 mono lever) to tyres becoming wider. True and let's also no forget that power has gone up significantly too. The loads imposed on the bearings from power transmission won't be insignificant.

The Teutonic Tangerine · Tue Oct 29, 2013 4:46 pm

oooooo I am confused - pass the Sherry

Corvus · Post by **Corvus** » Wed Oct 30, 2013 6:46 am

The Teutonic Tangerine wrote:oooooo I am confused - pass the Sherry

Which bit?

BMbler is in charge of the sherry, but he's got a pretty tight grasp of it.

Corvus · Post by **Corvus** » Wed Oct 30, 2013 5:06 pm

BMbler wrote:
Corvus wrote:
The Teutonic Tangerine wrote:oooooo I am confused - pass the Sherry
Which bit?

BMbler is in charge of the sherry, but he's got a pretty tight grasp of it.
Yup, Nope! no Sherry's rounds , disagree with me!

Unless one is very persuasive and would change my ming about the way of gear braking not being a bad'ish idea

I reckon you could make a very good mock up using nothing but two sherry bottle corks and a pen knife. Of course you'd have to finish off both bottles then.

Corvus · Post by **Corvus** » Thu Oct 31, 2013 8:05 pm

BMbler wrote:
Corvus wrote:
BMbler wrote: Yup, Nope! no Sherry's rounds , disagree with me!

Unless one is very persuasive and would change my ming about the way of gear braking not being a bad'ish idea
I reckon you could make a very good mock up using nothing but two sherry bottle corks and a pen knife. Of course you'd have to finish off both bottles then.
Are you trying to get me drunk sir?
... now I get the meaning of bad bikers influence!

All in the name of science.