Re-engineering the Shift Spring

[nobleswood]

From what I remember of my Greek mythology those who answered the Siren's call ended up dead !

[Chuck]

"We.. thought.. you was a toad.."    Gotta watch them si reens.

[brubache]

 

Again... this is just so interesting. Again... thank-you.

 

It is almost impossible to resist the Scura's call. But unlike the false promises in the sirens' songs, the Scura delivers.

 

Until the spring or clutch breaks. 

 

 

Now that was funny right there!  

[Chuck]

I very seldom watch movies.. and almost never watch one again. I've seen O Brother several times.   One of my all time favorites. 

[docc]

I can identify with the point at which the feller in the back row sez, "Whaaa?"

[PJPR01]

Skill and ingenuity! You guys are amazing! A doff of the cap in recognition of the creativity!

[Chuck]

 

 

I can identify with the point at which the feller in the back row sez, "Whaaa?"

Yeah, I just cracked up the first time I saw it. 

In related news, 155520 downshifts and upshifts on the seriously overstressed .071 spring as we speak. I'll let it run a while longer and test it to see if it's lost it's ju ju.

[Chuck]

Alright, stress test complete. 250,000 down and up shifts without issue on the spring with 28 degrees preload. (over stressed)

Here is my report from the reliability lab. 

This is what I'll recommend.

.071 dia. spring with 2.45 active coils. The spring calculator says this spring has 62.5 degrees safe travel. Total travel of this spring in service is 39+15= 54 degrees.

Max safe torque of this spring is 6.8 inch lbs.

At 54 degrees, this spring generates 5.88 inch lbs.

At 54 degrees it's inner diameter is .622"

The post it rides on in the Guzzi part is .590" diameter. (15mm) Shouldn't be any coil binding.

 

Now, it needs to go to the Winter Desert Proving Grounds in the deep southwest for "real world" testing to see if it actually works. 

I'll make up a couple and send them out to our test engineer,  along with the preselector, early next week. 

[Chuck]

One other thing: I moved the lever out so there was only about 1/16" of the end of the spring riding on it to test whether it would break there. That is the other place the stock spring breaks. I think I can say with reasonable certainty that this spring won't break. Will it work? It certainly works fine in the preselector on the bench. It's still TBD whether it works in the real world.

2017-12-02_10-52-07 by Charles Stottlemyer, on Flickr

[swooshdave]

If I learned one thing from Mythbusters it's that if something doesn't fail you change the perimeters until they do. That and they had the best job ever.

 

You say that you're using a 15mm mount, what is the other size that people are reporting that was supposed to break springs? Perhaps try that set up with a stock spring and a new spring and see if you can get one to break.

 

We want carnage!

[footgoose]

I have a stock pawl arm thats over 16mm. Was going to show a pic but imgzeit is down for some reason

 

Chuck and Scud have put in far more r&d than Guzzi did on this part. I think it'll work fine

[Chuck]

If I learned one thing from Mythbusters it's that if something doesn't fail you change the perimeters until they do. That and they had the best job ever.

 

You say that you're using a 15mm mount, what is the other size that people are reporting that was supposed to break springs? Perhaps try that set up with a stock spring and a new spring and see if you can get one to break.

 

We want carnage!

 

16mm is .630" 

 

 

At 54 degrees it's inner diameter is .622"

especially, if it is *over* 16mm like Footgoose says, it would break. 

 

Honestly, I'm getting tired of doing this.    I haven't kept track but have many hours in it. I hope it works. If it doesn't, we'll have to explore the coil spring, but getting something together that the average home mechanic could install would be difficult, at best.

[swooshdave]

Totally understand. You’ve done more than your fair share.

 

 

Sent from my iPhone using Tapatalk

[Lucky Phil]

If I learned one thing from Mythbusters it's that if something doesn't fail you change the perimeters until they do. That and they had the best job ever.

 

You say that you're using a 15mm mount, what is the other size that people are reporting that was supposed to break springs? Perhaps try that set up with a stock spring and a new spring and see if you can get one to break.

 

We want carnage!

16mm.

 

Ciao

[czakky]

Thanks so much for the hard work Chuck! I learned a lot! You are a true pillar of the spine frame community.