Re-engineering the Shift Spring

[Scud]

Can we pool our collective experience and semi-mass produce a kit to replace the problematic shift lever spring with a coil?

 

 

I just broke my second spring and am not looking forward to the possibility of another breaking in an inconvenient location (like the Mojave Desert).

 

If the Indiana R&D team (Chuck and Footgoose) can figure out how to source stuff, I will contribute the pre-selector. I'll even send you a whole transmission if you think you need it. Of course, I'd like it back... But you can take your time since it's a spare.

 

I've already done the polishing on this pre-selector per Phil's write-up. But I didn't get it adjusted correctly (ended swapping pre-selectors).

 

http://www.v11lemans.com/forums/index.php?showtopic=19547&hl=

 

I also installed a bearing on this one - instead of a solid disc for the detent gear.

 

http://www.v11lemans.com/forums/index.php?showtopic=19514&p=213785

 

And can somebody post the links to the coil spring modification? I tried a few searches and didn't find it yet.

 

 

[coreytrevor]

This one?

 

http://www.v11lemans.com/forums/index.php?showtopic=19827

 

[Scud]

That's the one.

 

Chuck offered, in another thread, to machine something if needed. It seems to me that a custom-made post would be in order. Something that is fairly wide at the base to prevent rocking - and with a standard diameter to go through the case so it could be drilled out by a home mechanic like me. If you have the correct spring in hand, then I suppose the top end could be machined to accommodate it securely.  So that's my wish... a custom-machined stud, a proper-strength and size spring, whatever mounting hardware is required, and some guidance about where (and what size) to drill the hole. That would make a fine kit.

 

And how did the spring attach to the arm? Did it use the existing mount - or did that need to be replaced? I think it was replaced. If so, that might require a second custom-machined bit.

[swooshdave]

spri by swooshdave, on Flickr

 

I see it as 3 main parts if you follow this model.

 

1. Drill a hole and mount a stud.

2. Spring

3. Drill a hole and mount a stud.

 

As is this example you can just use off the shelf parts.

 

How did Guzzi fix it on later bikes? Is this exclusive to the 6 speed V11s?

[docc]

footgoose has said he would use a stiffer spring on the next try:

 

"My "alternative" mod is working well, but when I go back in there, I will stiffen up the spring."

[coreytrevor]

Could you use a spring with a side hook and hook it to the existing spool thingy on the arm? Or would it not clear the selector wheel?

 

[Scud]

Something like that might work if the loop could fit over the button on the arm. There's more clearance under the bottom gear (which is the top, open position in the photo).

 

For the record, I had previously installed this shift pre-selector from 2004 V11. It had the "banana" upgrade. I previously thought the broken shift springs were mostly on the 2002 models. 

 

 

I put my LeMans back together with a standard spring, but I have the spare (2003 model) to play with and take measurements if needed.

 

There are at least 3 variations on the shift pre-selector mechanism. But they all use the same spring and I think this coil spring fix would fit all variations.

 

@Dave - yeah, I think it's conceptually as simple as you stated. But I think it all needs to get measured and tested. I'm just hoping we could either build a kit or describe the parts in enough detail that anyone could do it without further experimentation.

[Lucky Phil]

Of course the issue with this mod is 3 fold, lots of extra bits in the gearbox, the spring is now going to be extended in 2 directions during operation. A straight extension as the selector arm ramps ride over the wheel pins and a small rotating motion as the selector arm moves in a linier direction as it rotates the drum. Also we now have another oil leak point.

The first shouldn't be an issue if its all loctited up, the second can be overcome without too much difficulty and the third I'm not sure about in the long term. I would suggest that the ends of the spring be able to rotate on the anchor posts if they dont already. It should be easy to measure the original spring tension with a digital scale with the cover off to get an idea whats required of a coil spring.  

Would it not be possible to stick with the original design and look to have a higher quality spring made. I'm sure Guzzi didnt use the best available spring material at the time.

 

Ciao

[luhbo]

I'd be interested in why nobody can tell why they don't break on the early models. You can read of different diameters and how to fix this and that. However, they still keep braking on the later ones ...

[Scud]

gstallons mentioned that he had a Racecraft spring - stronger than the original (although it might no longer be available). I'd be happy with a stronger spring in the original position - I'm not excited about drilling another hole in the cover.

 

I just found this place that makes custom springs:

 

https://www.springsfast.com/custom-extension-springs.php?ex=eep549-chxfib-0&gclid=Cj0KCQiArYDQBRDoARIsAMR8s_SL-TDDqDrKHZ4DOJUOtzgCa0VtWWMW148EpRo3laV-ummOm5cgh3AaAnEXEALw_wcB

 

I'll send them a picture and measurements and see what's involved in making some thicker/stronger springs.

 

As for why they keep breaking - it could be a quality issue. I pre-emptively replaced the shift spring on my Scura with a new one (from Moto Guzzi). It broke within a few thousand miles. Luckily, I kept the original - put it back in and it's been OK for a while.

[Chuck]

Scud, if that doesn't pan out, I'd be willing to take this problem on.. with everyone's help. I think you may be right, though. A "better" spring might just cure the problem. 

It would be interesting to make a simulation with the correct diameter spring boss and rig up an electric motor that cycles the spring the same as the shift lever. Any reputable manufacturer would have already done this test, but I'll bet a dollar to a doughnut that Guzzi doesn't have a Reliability lab. 

I have an "Experimental department.."  

2016-02-20_03-20-56 by Charles Stottlemyer, on Flickr

[czakky]

Where are you guys seeing the break happen?

 

On mine it was the small 90 that rides on the arm. It seemed to wear a groove on that spot from the sharp edge riding on the soft steel of the arm, fatiguing the spring.

[Scud]

The new spring on my Scura broke as you described, Czakky. Perhaps it would be good to slightly round the edge of the arm where the small 90 of the spring makes contact. The one that broke Saturday is in my picture above. It broke on the coil. 

 

I rode it to work today. But I wasted Sunday afternoon on the repair.

 

I wonder if a U-hook at the arm would be more durable than a 90-degree bend. I'll look and see if there is enough clearance to install a U-hook.

 

Meanwhile, I sent a photo and inquiry to WB Jones Spring Co (link above) in Wilder, Kentucky.

[swooshdave]

Can someone post a picture of the stock spring in place, perhaps additional photos of the range of the spring?

 

I thought I had read something about the boss and spring not matching (15mm vs. 16mm) and perhaps the spring binds and breaks?

[Chuck]

Can someone post a picture of the stock spring in place, perhaps additional photos of the range of the spring?

 

I thought I had read something about the boss and spring not matching (15mm vs. 16mm) and perhaps the spring binds and breaks?

Spring binding was the problem with the 16mm boss. It seems this spring is capable of breaking about anywhere..