Re-engineering the Shift Spring

[Scud]

Yeah, they'll make one or two springs, for about the same price as 50. Gotta pay for set-up. I'll call the guy again tomorrow and share our final specs:

 

Make it like the sample (including same inside diameter of coil), but with the following differences:

1. Use .071" piano wire (I'll ask what the "spec" is)
2. Make the coil 895 degrees, instead of 540
3. 90-degree bend on short arm should have bend radius of 2x wire diameter

I can have them all shipped to me, and then send you a bunch of springs along with the preselector, which you can torture.

 

 

Edit - to include point # 3 per Chuck

[Chuck]

Sounds like a plan. Don't forget the 1 1/2 dia bend radius on the short leg. 

[Scud]

Sounds like a plan. Don't forget the 1 1/2 dia bend radius on the short leg. 

 

I'm going to send a new spring for reference.

 

Are you suggesting something different than the original for that end? If so, can you describe it more clearly?

[Chuck]

The bend radius for music wire is 1 1/2 X the diameter. On the one I have, it is 1X diameter. That could be why they are breaking there. 

[Scud]

Got it - went back to edit the instruction above.

[footgoose]

Well, I'm late to the party. For 5 days notifications have gone to spam for some unknown reason.

 

Here's what I've done with the extension spring. http://www.v11lemans.com/forums/index.php?showtopic=19827Works great btw, and no leaks. All parts are stainless, tho they don't need to be, and are from McMaster Carr. I did it this way so it can be ordered from the same place, and a "kit" of sorts could be assembled. Bolts and nuts are 8/32. I can get you the bit and tap size for the hole. There is a small bit of grinding required on the inside of the cover plate. Some nuts and  washers came in multi packs, and I ordered different size spacers to experiment with, so I have misc extras if someone else wants to do this mod. Maybe get a new set of eyes on it.. make it better, simpler? I works fine for me, and I didn't see much interest, so the thread fizzled.

 

My comment to Docc, in reference to changing the spring next time I'm in there was for this reason. When unscientifically comparing the spring tensions of the oem lever spring against two extension springs, I used a pull scale of 2 lb. Apples to apples pulls show the lever at 2 lb and my stiffest extension spring at 1.5 lb. I couldn't wait for a stiffer spring to arrive before the Spine Raid, so I went with what I had. As mentioned, It works. Occasionally, when coasting to a stop... the type when you are caught in too high a gear and must downshift 2 or 3 gears quickly without releasing the clutch, it would not "complete" one of the shifts. I can only attribute this to the lighter spring tension. I will know when I upgrade it.

 

The only other possible reason I can think of, may be as Lucky Phil mentions, regarding the variable pull angles that the spring goes through in a cycle. Something I don't fully understand.

[luhbo]

... Occasionally, when coasting to a stop... the type when you are caught in too high a gear and must downshift 2 or 3 gears quickly without releasing the clutch, it would not "complete" one of the shifts. I can only attribute this to the lighter spring tension. I will know when I upgrade it....

Owning a bike with a rather soft "Japanese Mod" I can watch the same. Quick shifts have become tricky, but it's a different gearbox anyway, so the reason for that can be anything.

[Chuck]

Scud.. if Footgoose thinks a 25% reduction in spring pressure is causing the quick shift issue we should hold up on making the new springs. We're over that..

[Scud]

OK, I'll hold... and I'll try to get a more precise measurement of spring travel. It's hard to see the exact angles of the springs when they are installed, so I assumed a right angle for the short arm. As I calculated on the last page, a little less than 2.5 coils translates into more pressure (which I've been calling preload, even though that's probably not the right term).

 

Using the variables you provided, I can find the degrees of travel with the thinner wire to produce the same pressure as the original spring (in the at-rest position). That works out to an 886.5 degree coil (just 13.5 degrees less than 2.5 coils).

 

What's that funny quote about being a member of Moto Guzzi's post-production R&D program?

[swooshdave]

What's that funny quote about being a member of Moto Guzzi's post-production R&D program?

 

Pretty sure that every Guzzi owner is in that club. Even the new bikes. 

[Chuck]

OK, I'll hold... and I'll try to get a more precise measurement of spring travel. It's hard to see the exact angles of the springs when they are installed, so I assumed a right angle for the short arm. As I calculated on the last page, a little less than 2.5 coils translates into more pressure (which I've been calling preload, even though that's probably not the right term).

 

Using the variables you provided, I can find the degrees of travel with the thinner wire to produce the same pressure as the original spring (in the at-rest position). That works out to an 886.5 degree coil (just 13.5 degrees less than 2.5 coils).

 

What's that funny quote about being a member of Moto Guzzi's post-production R&D program?

Scud, I don't mean to sound like a know it all, but I think it's time for me to get more involved before we spend (cough cough) money.    It's been uhh close to 50 years since I've made springs, and I *don't* have access to a spring winder, but can probably make some prototype springs on the lathe and test them to see whether we need to continue pursuing new torsion springs or continue developing the extension spring "kit." 

I need to spend some time in the shop breaking in a new pup on the cnc mill for the next 2 or 3 weeks, (yuck, work) so if you send me the preselector, I'll order some music wire and get right on it. (yay, play.) 

[Scud]

Well, Brer Rabbit, I'd hate to have to throw you into the briar patch. 

 

Translation: Thanks, I will gladly send the preselector to you.

[Lucky Phil]

Scud.. if Footgoose thinks a 25% reduction in spring pressure is causing the quick shift issue we should hold up on making the new springs. We're over that..

You know Chuck what Footgoose discribes is not uncommon in many motorcycle transmissions and my view is its down to gearbox revolutions. In the scenario mentioned the box often isnt rotating at a speed high enough for proper reliable dog alignment and it gets balky and misses shifts.

I can tip in a few bucks if necessary to help the cause.

 

Ciao 

[Chuck]

 

Scud.. if Footgoose thinks a 25% reduction in spring pressure is causing the quick shift issue we should hold up on making the new springs. We're over that..

You know Chuck what Footgoose discribes is not uncommon in many motorcycle transmissions and my view is its down to gearbox revolutions. In the scenario mentioned the box often isnt rotating at a speed high enough for proper reliable dog alignment and it gets balky and misses shifts.

I can tip in a few bucks if necessary to help the cause.

 

Ciao 

 

Sure, I've seen that on many transmissions where you are caught off guard  in a higher gear and suddenly *need* to get down into first. Footgoose is an experienced rider, though.. and no doubt knows what is normal and what is not.

At any rate, I have some .071 and .080" music wire ordered. It's cheap. With any luck at all, I'll have some test springs made this coming week.

[footgoose]

 

 

Scud.. if Footgoose thinks a 25% reduction in spring pressure is causing the quick shift issue we should hold up on making the new springs. We're over that..

You know Chuck what Footgoose discribes is not uncommon in many motorcycle transmissions and my view is its down to gearbox revolutions. In the scenario mentioned the box often isnt rotating at a speed high enough for proper reliable dog alignment and it gets balky and misses shifts.

I can tip in a few bucks if necessary to help the cause.

 

Ciao 

 

Sure, I've seen that on many transmissions where you are caught off guard  in a higher gear and suddenly *need* to get down into first. Footgoose is an experienced rider, though.. and no doubt knows what is normal and what is not.

At any rate, I have some .071 and .080" music wire ordered. It's cheap. With any luck at all, I'll have some test springs made this coming week.

 

Good description LPhil. That's what it fells like. And it's not normal for me and this bike. I also changed to the Phil/Chuck linkage arm at the same time. I would think that would make positive shifts easier, but this and a newly acquired hyper sensitivity to shifting right after the mods, may have played a part.

 

Fwiw, I still feel that a better torsion spring is the better idea. I couldn't find one, and I can't make one. The extension spring mod is a great way to bypass the pita stock spring. And dead easy to do. The one advantage as I see it, is the extension spring mod eliminates the points of friction, and the 'twist and bind' stresses that will remain with any torsion spring. I always felt the oem spring looked too thin and spindly for the application. I'm confident you'll build it better.

 

I'll buy one of the new Scud/Chuck springs just to carry as a lucky charm so mine will never break!