Broken Torque Rod Bolt

[audiomick]

16 minutes ago, docc said:

 M10x1.5 is tightened 45-50 Nm (with no reference as to hardness ratings).

Have another look at this:

https://www.anzugsmoment.de/anzugsmoment/

45-50 corresponds to the value listed there for an 8.8 bolt, so the general table is right, as far as that goes. Given that the bolt in the torque rod is apparently a 10.9, it can deal with a bit more welly. I'm with you and Pressureangle that the thing should be properly tightened up to prevent wear. That's gone onto the to-do list for mine for when I get it into the garage for a good look at everything.

[docc]

36 minutes ago, audiomick said:

Have another look at this:

https://www.anzugsmoment.de/anzugsmoment/

45-50 corresponds to the value listed there for an 8.8 bolt, so the general table is right, as far as that goes. Given that the bolt in the torque rod is apparently a 10.9, it can deal with a bit more welly. I'm with you and Pressureangle that the thing should be properly tightened up to prevent wear. That's gone onto the to-do list for mine for when I get it into the garage for a good look at everything.

This means that when I change my early V11 8.8 pivot bolt to the later 10.9 replacement, the tightening torque must be increased to this new value of 70Nm?

Harper's also told me the new bolt (GU01357731) is a 1.5 thread pitch. My early(1999-2001) Parts Catalog specifies the nuts as M10-1.25 (with both washe and spacer) for the "1st Series" and M10x1.5 for the "2nd Series" (no washer, only spacer on the bolt head side). Both of those bolts are apparently superseded by GU01357731.

So, also, pitch change(s). [edit: The 2004 Le Mans parts diagram @p6x linked on page one once again shows a 1.25 thread pitch with both a washer and a spacer.]

[audiomick]

45 minutes ago, docc said:

This means that when I change my early V11 8.8 pivot bolt to the later 10.9 replacement, the tightening torque must be increased to this new value of 70Nm?

I would rather say "can" and "up to" than must, but yes, the 10.9 can deal with a good bit more torque.

 

I just had a look at the parts lists at Wendel and Stein-Dinse. The nut is a bit confusing. At both of those sites I found the reference you mentioned to "1st series" with 1.25 and "2nd series" with 1.5, but also later models with allegedly 1.25. I also looked at a site showing listings for ISO standard pitch. An M10 *should* have 1.5.

 

I don't know if Guzzi swapped back and forth between a standard and a fine pitch, or if the parts lists are misleading. I would say care needs to be taken in getting the right nut.

 

By the way, it seems that the bolt at the final drive end of the torque rod has a 1.25 pitch.

[Speedfrog]

6 hours ago, Joe said:

 

I really miss @Lucky Phil right now... he would have had a field day 

[MartyNZ]

I wonder if that bolt failure is related to the condition of the needle bearing in the RH side of the bevel box? 🤔

Obviously stiffness in this bearing will increase fatigue loads on the reaction rod & bolt during suspension movement.

[LowRyter]

3 hours ago, leroysch said:

Is there a cover charge too?

When I reread that, I knew that would get me in trouble.    

[activpop]

Are the forces the same on bolts at both ends of the rod? I have the aft one out and it was dry as a bone...no sign of lube. I wonder it that falls into the same need of upgrade as the forward one.

[80CX100]

I've personally seen how devastating the forces can be in these torque arm set ups.

One of the VRRA racers I got to know, A.J.Simiana sp? was just starting a fresh build/setup on an older Tonti frame Lemans3? race bike.

AJ is an experienced racer and a decent builder within his limited budget. He designed and built a torque arm set up similar in appearance,to the Magni Parallel swing arm setup.

I'm not sure what aspect of the build caused the problem,but his very first race,he tore the welded front support completely off the swingarm/frame area.

It was a complete catastrophic failure,luckily didn't cause a crash.

AJ redid some math calculations,angles etc,redesigned it,rewelded the support and solved the problem,but for sure there's some serious forces involved.

Iirc I removed and greased or put anti seize on the back bolt,but I'm almost positive I didn't touch the front one.

Tks for the warning and discussion,I'll be taking a close look at that.

[MartyNZ]

11 hours ago, activpop said:

Are the forces the same on bolts at both ends of the rod? I have the aft one out and it was dry as a bone...no sign of lube. I wonder it that falls into the same need of upgrade as the forward one.

Yes, identical loads on each end of the reaction rod, as a single bolt forms a "pin joint". However I think that the forward end of the rod is more exposed to road spray, which explains the number of reports of the forward bolt breaking.

Assembly with an anti-corrosion jointing compound like Duralac or Mastinox will reduce rust without encouraging bolt rotation as grease would.

Since stress corrosion cracking is more likely on high tensile bolts, I believe that staying with the original spec bolt is a better idea, if you want it to last another 20 years.

[Joe]

8 hours ago, Speedfrog said:

I really miss @Lucky Phil right now... he would have had a field day 

 

[docc]

8 hours ago, MartyNZ said:

I wonder if that bolt failure is related to the condition of the needle bearing in the RH side of the bevel box? 🤔

Obviously stiffness in this bearing will increase loads on the reaction rod & bolt during suspension movement.

A very interesting concept. No doubt, each of us should be acutely aware of keeping the needle bearing cage serviced . While destruction of the seal surface of the pinion nose has already been noted as an adverse consequence of neglecting the outboard needle bearing cage of the reardrive, the possibility of it contributing to the forward bolt pivot failure is worth investigating.

@LowRyter and @kalev11, take note to have this failure point inspected and serviced . . .

 

[kalev11]

Docc yes my front torque bolt was sheared off when I discovered it. Only the nut and a short stub of the sheared bolt remained. Lucky for me the pork chop had the nut and bolt stub captured so they could not fall out and that little bit of luck is what got me and the bike home where I could repair the bike. 

[p6x]

I am super late in the topic, as I am back from NM;

Guzzi should have computed the shear force that load bearing component would be submitted to. Usually, you send the blue prints to a specialized company and they tell you what force that component will have to sustain.

That bolt should have been manufactured to precise specifications, using a given metallurgy and maybe thermal treatment. Guzzi would have ordered a large batch to support manufacturing.

The important factor is that, the shearing strength seems inadequate for a normal usage. For such an important component, it would be probably better to have one purpose made; if we knew what the maximum shear force it has to see.

I found a paper from Portland Bolt, that could be helpful:

How do I determine the yield and tensile strength of a specific diameter of bolt?

Quote

Shear Strength

First, find the ultimate tensile strength using the formula above. Take that value and multiply it by 60% (0.60). It is important to understand that this value is only an estimate. Unlike tensile and yield strengths, there are no published shear strength values or requirements for ASTM specifications. The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-8) states that shear strength is approximately 60% of the minimum tensile strength. For more information, please see our FAQ on bolt shear strength considerations.

 

[p6x]

On 3/16/2023 at 10:15 AM, docc said:

According to this French site posted by @p6x, the part looks available, but the part number is different than from my 1999-2001 catalog (GU37357706):

https://www.pieces-motoguzzi.com/guzzi-laverda-scarabeo/affectation_pieces_detachees/GU01357731

While MGCycle doesn't bring this number up (nor the number I posted), Harpermoto does show the -7731 part at $1.20US. This does NOT mean they have it! A call to Curtis is the only way to know:

https://www.harpermoto.com/screw-10mmx59mm-01357731.html

@LowRyter and @kalev11, where did your bolts break: at the head or at the base of the threads?

I used the catalogue for my V11 2004 Le Mans. I could ask them some details. The price +11 Euros feels correct for a bolt which is not stock manufacturing.

The different P/N maybe a pitch change? 125 or 150? (in college we would name the pitch as a whole number. Easier.

[Speedfrog]

Screw, 10mm x 59mm - GU01357731  —  AF1 Racing, Austin Texas  —  $2.91

https://www.af1racing.com/GU01357731-Screw--10Mmx59Mm---GU01357731