Re-engineering the Shift Spring

[docc]

So, what is the target durability? 300,000 downshifts? 500,000?

 

Seems the Euro guys consider 200.000 km to be high usage on a motorcycle. With my scenario that would be ~ 372,000  downshifts.

[swooshdave]

So, what is the target durability? 300,000 downshifts? 500,000?

 

Seems the Euro guys consider 200.000 km to be high usage on a motorcycle. With my scenario that would be ~ 372,000  downshifts.

 

The target is any spring that will survive your bike. How many springs have you broken?

[docc]

 

So, what is the target durability? 300,000 downshifts? 500,000?

 

Seems the Euro guys consider 200.000 km to be high usage on a motorcycle. With my scenario that would be ~ 372,000  downshifts.

 

The target is any spring that will survive your bike. How many springs have you broken?

 

Only one, on my warranty replacement gearbox. The original box went 26,662 miles with no spring trouble. Warranty replacement box broke a spring just shy of 27,000. That was a tick over 51,000 miles ago . . .

 

Maybe it's just this birthday thing, but at this point, a 372,000 downshift rated spring would have me all set.

[Chuck]

So, what is the target durability? 300,000 downshifts? 500,000?

 

Seems the Euro guys consider 200.000 km to be high usage on a motorcycle. With my scenario that would be ~ 372,000  downshifts.

Honestly, Docc.. I don't know. *Assuming* it's still going tomorrow morning, it'll have more than 200, 000. I didn't expect it to last his long.

[docc]

With respect for the Original Poster, and The Spring Whisperer, I would suggest a change to the Topic Name of this extraordinary thread (?)

[Scud]

... a change to the Topic Name of this extraordinary thread (?)

 

How about:

 

"Re-engineering the Shift Spring"

 

Or whatever other title you like... the topic has certainly moved beyond the original title.

[Chuck]

207360 and counting at 6 o'clock this morning. Still showing no obvious sign of fatigue. (!) We need an energizer bunny emoticon. In related news, after filling the little gearbox with rear drive lube, it's quieter and the motor and box are running much cooler. (Guzzi content.)

[Bill Hagan]

Ah, this thread brings back some nostalgic memories of the Ballabio.  Lordy, I did love that beast, but my first encounter with this issue cost me $600+ when I was stranded in BFE, Missouri.  Not wanting to ride to Atlanta in 2d gear, I tried to rent a small truck.  U-Haul said, nope, can't put a m/c inside a truck -- I have since wondered if honesty is always the best policy   -- and made me rent a trailer, too. 

 

Anyway, it's been "fun" reliving that adventure through this and the related threads.

 

Wait ... perhaps time for a class-action lawsuit?  Don't spend the settlement just yet. 

 

Seriously, good luck with your fascinating research and skunkworks fixes.  You'll break the code; too bad Mandello didn't.

 

Bill

 

P.S.  Weather is looking mighty fine this week for late November at the top of Virginia.  Now to decide which member of my moto-harem gets the nod.  Choices, choices, but, if still there, this thread would mean I'd saddle up the Ballabio ... with spare spring.    

[Chuck]

Gave up this afternoon at 289386. It wasn't going to break.

2017-11-27_03-50-39 by Charles Stottlemyer, on Flickr

Cleaning things up reveals the reason.

2017-11-27_05-06-32 by Charles Stottlemyer, on Flickr

The cam had eaten it's way into the lever. That combined with the spring doing the same thing, it's not been twisted the entire 39 degrees. More like 34.

The best laid plans and all that. I need to insert some 4130 into the lever, and try again. This spring is still in great shape, though.

[Scud]

Ha - well it's not supposed to break if it's not over-extended. But still, you'd think it was over-extended for a while - before the groove got cut in.

[Chuck]

Ha - well it's not supposed to break if it's not over-extended. But still, you'd think it was over-extended for a while - before the groove got cut in.

True.. but apparently *some* springs don't break. This is probably one of them.

I've also tested many variations with my gram scale in the neutral position. *Nothing* is as powerful as the Guzzi spring, but I doubt this much torsion is necessary. After all, the spring only has to hold the pawl against the pin at the start of the upshift. The eccentric will take it from there.

 

I should take that back. The .071 spring with 25 degrees preload is about the same.. 1600 grams.

Comma But

25+39 degrees is getting back to the "beyond safe travel" of that spring.

Make sense?

 

Even the weakest .071 spring still has positive pressure on the up shift, compared to a stock spring that is sacked.

My gut feeling is that the .071 spring with 10 degrees preload is the one we want. It's what I'd put in my bike at this point.

Third from the top in this picture.

2017-11-25_05-45-36 by Charles Stottlemyer, on Flickr

Testing will continue, just the same.

I'm afraid of the .080 spring stock with another active coil. Theoretically, it should be the best, but with tolerance stack up, it *might* not fit all bikes. .080" X3 equals .240". Scud's shifter gizmo measures .240". It works, somehow. If someone else's measures .230" it probably wouldn't.

Do I see any eyes glazing over yet? Sorry. I've dealt with manufacturing tolerances all my life, and I'm ruling out the .080 wire with extra coil. 

[Scud]

I'm tracking and learning. So the .071" wire with 10 degrees less than 2.5 coils (890 degrees of coil). While this configuration gives less torsion on downshifts, it gives more on upshifts... so the torsion is more uniform across the range. That's what we get with a little more "preload" on a thinner wire. Is that right?

 

My oldest daughter's boyfriend is studying mechanical engineering. He is entertained by this topic... too bad he is not a motorcyclist.

[swooshdave]

My oldest daughter's boyfriend is studying mechanical engineering. He is entertained by this topic... too bad he is not a motorcyclist.

 

If anything he needs to learn the difference between engineering and making it work. Not always the same thing.

[MartyNZ]

Gave up this afternoon at 289386. It wasn't going to break.

One thing that is difficult to design against is vibrations. Could the spring buzz itself to death? Are there any wear marks where the spring sits in the shifter mechanism?

If, for example the spring resonates at 4000rpm, then the fatigue cycle count could get into very high numbers without much shifting. Changing the resonance frequency could make a steel spring last forever if the design stresses were below the fatigue limit. A resonance change could come from different thickness wire, different length spring, different oil in gbox. 

Just a thought. I know it doesn't help your design, but it may explain why you can't break that spring by shift cycles alone.

[Chuck]

I'm tracking and learning. So the .071" wire with 10 degrees less than 2.5 coils (890 degrees of coil). While this configuration gives less torsion on downshifts, it gives more on upshifts... so the torsion is more uniform across the range. That's what we get with a little more "preload" on a thinner wire. Is that right?

 

My oldest daughter's boyfriend is studying mechanical engineering. He is entertained by this topic... too bad he is not a motorcyclist.

That's the long and short of it.