Stelvio main engine mount bolt broken

[randy yocum]

I just washed my 2012 Stelvio NTX and discovered the main engine mount bolt on right side completely snapped off at the bolt head,I can see the screw thread portion clearly in the hole.I hope to be able to drill and easy out whats left of the bolt.Does anyone know the correct Guzzi part number for this bolt ,or can I just go to my local hardware store and find one.Also if I remove the good bolt on the other side to get a good match will the front of the engine fall down.I mean are there other mounting points that will hold the engine in place? Is this a fluke,or some what common .I've check these bolts in the past and found both to be a little loose,then tightened them .It's possible I over torqued this bolt  I didn't use a torque wrench  .I will buy  two new bolts and tighten them to the correct torque.

[Daniel Kalal]

are there other mounting points that will hold the engine in place?

Randy, there is an attachment between each cylinder and the upper frame rail (left and right), but, those have been known to have never been tightened at the factory (as was the case on two bikes that I've seen).  What's the long-term effect of that happening?  I don't know, but perhaps you've just found out.  Of course, your upper bolts could be fine and your failed bolt is from something else...

[randy yocum]

Thanks Danial,
   I will need to pull the tank and check those other mount bolts you spoke about,as luck would have it I just topped off the fuel tank,were talking 8.5 gallons of fuel.That monster tank which I love for obvious reasons is a pain to get off when it's this full and so heavy.

[Daniel Kalal]

I will need to pull the tank...

While you're at it...  The dash panel is attached with a strange sort of bolt that also attaches the clear plastic wing.  The bolt screws into a bit of steel that is glued into the plastic tank.  All the fastener does is keep the loose bits from rattling around; there's really no load on it.  Do not over-torque this bolt.  The part that is potted into the tank has been known to spin, and then you're stuck--now you'll need a drill and a small Dremel grinder to get it all out.  I'd advise a fair amount of anti-seize on the threads just to make sure that the bolt always comes out easily--it doesn't matter if it come loose just because you've been so gentle with it.

[randy yocum]

good tip thanks...

[Rolf Halvorsen]

A standard drill rotates to the right.

Buy some that rotates to the left. You can then see that while drilling - the rest of the screw can come out by itself.

Rolf

[leafman60]

Ditto on what other postings say.

More info on the loose top motor mounts -

https://wildguzzi.com/forum/index.php?topic=65635.0

Very poor quality control. 

Unfortunately, there's  a long list of other such items.

https://wildguzzi.com/forum/index.php?topic=88274.0


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[molly]

These bolts came loose (one came out altogether) on my 1100 Griso. Best of luck getting the broken bolt out, from memory it is M10 x 1.5.
The torque setting on the Griso is 60NM.
 I drilled and tapped a M6 hole in the side wall of the frame mounting lug and used a M6 stainless grub screw to lock against the M10 bolt head for extra peace of mind.

[randy yocum]

all great ideas,thanks guys.I will try to get the broken bolt out today.wish me luck.

[pauldaytona]

These bolts came loose (one came out altogether) on my 1100 Griso. Best of luck getting the broken bolt out, from memory it is M10 x 1.5.
The torque setting on the Griso is 60NM.
 I drilled and tapped a M6 hole in the side wall of the frame mounting lug and used a M6 stainless grub screw to lock against the M10 bolt head for extra peace of mind.

It is GU98682650 M12x50. I'm even not sure if is standard speed or smaller. Look at the numbers in the head for the strongness. You can get one in local hardware store, but it isn't a common size.

AF1 racing has it in stock:
https://www.af1racing.com/store/Scripts/prodView.asp?idproduct=48331

[randy yocum]

Good news,I got the bolt out.I was lucky to have a bushing that fit perfectly in the frame boss and the drill hole in the bushing was 3/16 inch so that's the size bit I used .The bolt must be pretty hard as it took forever to drill about 1/4 deep.I kept going back for more cutting oil on the drill tip.Once I drilled the hole deep enough to attach the easy out (I think using the bushing as a drill guide to keep the drill hole centered) screwing the broken bolt out was a piece of cake.
    There is a place called Fastenal near by that has two zinc coated M12-1.75 x50mm in stock he said they are class 8.8 steel.I hope that means they will be hard enough.Does anybody know what that code means?

[acogoff]

     I would be paying attention if the parts that that bolt holds together are well fitting and not dependent on the bolt to pull them into register. I.E. some creative shimming may be required to avoid stress. May be a caused of the bolt breaking in the first place. Just an observation of why things break sometimes.

[Rolf Halvorsen]

8.8 is standard hardness for screws
10.9 is used on flywheel to the crankshaft screws
12.8 is the hardest hardness in screw family

Rolf

[randy yocum]

Thanks Rolf,
   I when to pick up the bolts today the guy there seemed to know allot about metal hardness for fasteners.I ended up buying a harder bolt then I intended it's 12.9 on the hardness scale verses the 8.8 that I was going to buy.( like my old biker friend Gene used to say I don't want to be this side of Alburquergue and have the darn thing break again)There are a couple down sides I did consider,one the harder bolts are not zinc coated ,black oxide which I know from experience does rust. I painted the bolts silver that should help for awhile.The other thing is being so hard what if a bolt snaps off again I doubt that I will be able to drill a hole in the end to fit an extractor,or on the other hand maybe that could never happen with a bolt this hard I have no idea.The good thing is the bike is back together so I can ride again.Wednesday is going to be 67* and sunny,now lets see what back roads  can I go explore? 
It's nice to be retired

[Wayne Orwig]

Once I drilled the hole deep enough to attach the easy out (I think using the bushing as a drill guide to keep the drill hole centered) screwing the broken bolt out was a piece of cake.

You had an easy out work?
 
Sorry, April 1st is a few days away.

[John A]

You had an easy out work?
 
Sorry, April 1st is a few days away.

I like it when they break off....

[molly]

     I would be paying attention if the parts that that bolt holds together are well fitting and not dependent on the bolt to pull them into register. I.E. some creative shimming may be required to avoid stress. May be a caused of the bolt breaking in the first place. Just an observation of why things break sometimes.

When I fitted new bolts to my Griso I checked the gap between the frame lug and engine it was about 0.5mm, so the bolts pull the frame onto the engine, slightly stressing the frame. Whether this matters I'm not sure because there needs to be clearance for assembly of the engine to the frame.
Personally if I had a couple of 0.5mm thick circular shims at hand I would have used them.

[randy yocum]

You are correct,there was about a 5mm gap on both sides,It pulled together as I tightened the bolts.Do you think that this is a problem? should I create a spacer to fill the gap?I'm still waiting to burn off about 5 gallons off fuel before I try to remove the fuel tank to check the upper engine mount bolts.The funny thing is I never had a clue that the bolt was missing.I mean I like to keep my bikes tuned to perfection,So there was never an indication of unusual vibration, I've owned this bike for 3 years  it has 32,000 miles now and smooth as silk going down the road I regularly blast up to 100 mph on the highway, nothing ,no vibration .I don't know if that bolt broke yesterday or 3 months ago. 

[molly]

You are correct,there was about a 5mm gap on both sides,It pulled together as I tightened the bolts.Do you think that this is a problem? should I create a spacer to fill the gap?I'm still waiting to burn off about 5 gallons off fuel before I try to remove the fuel tank to check the upper engine mount bolts.The funny thing is I never had a clue that the bolt was missing.I mean I like to keep my bikes tuned to perfection,So there was never an indication of unusual vibration, I've owned this bike for 3 years  it has 32,000 miles now and smooth as silk going down the road I regularly blast up to 100 mph on the highway, nothing ,no vibration .I don't know if that bolt broke yesterday or 3 months ago.

The funny thing is if I tightened the mounting bolts to 60Nm there was more vibration on the Griso.  I finished up going to only 20Nm and using the locking  grub screws I mentioned earlier.

[Rolf Halvorsen]

I advise against to use 12.9 when the manual states 8.8

8.8 is more tensile than 12.9

Rolf

[randy yocum]

Hey Rolf,
   What does that mean more tensile ? I would imagine ,though I'm not a metallurgist that 12.9 is better then 8.8  when it comes to hardness. Can you explain? why would a softer bolt in a high stress application would be better? 

[Daniel Kalal]

…Can you explain why a softer bolt...

use the higher grade bolt; they're all the same stiffness, regardless, and the higher grade will have better fatigue properties (at a higher cost, of course). 

Note that none of these SAE grade bolts are considered especially great (and you won't find them on any factory-built airplane), but they are perfectly fine for this (and a whole lot cheaper than the aircraft quality version).  Last I checked, the SAE spec only calls out a minimum hardness to match their rating, so bolts in the SAE 5 box could have the same tested hardness as those in the 8.8 box, regardless of what is stamped on the head.

Note, too, that hardness is just an easy value to check, and it's only a corollary to strength, which is what you really care about.

Guzzi called out the lower spec bolt because they thought it was adequate and because it's cheaper, which is how all bolts are determined in a design.

[jwinwi]

I advise against to use 12.9 when the manual states 8.8

8.8 is more tensile than 12.9

Rolf

THIS. As hardness increases the fastener becomes more brittle. Of course I don't have any proof to back this up but, in general terms, I believe this is true. If only there was a way I could type words on a machine to look up information...

[Daniel Kalal]

If only there was a way I could type words on a machine to look up information...

you can type "fracture toughness vs strength in steel" and you'll get the information you're looking for, but that's not really the property that we're trying to improve. 

Of course, if you're cutting a notch in a bolt and whacking it with a hammer to break it then high fracture toughness is what you want to prevent fracture, but we want something with excellent fatigue properties in shear, and for that you want to focus on high strength and a smooth (non-corroded) finish.

[randy yocum]

Got it Danial thanks,60nm torque on the bolts .I went ahead replaced both bolts ,I could see after careful examination of the remaining good bolt had some threads worn down, the edges weren't sharp like they should look.I'm thinking like you said the metal is too soft or fatigued due to age .I feel better now having replaced them with a higher quality bolt.I've been riding the bike ,no vibration.
   I'm curious about the comments that Molly made about his Griso and how fully tightening 60nm these engine mount bolts would cause more vibration so he went with 20nm .How is that possible?

[leafman60]

Randy,

On the Stelvio go around all fasteners to the frame and tighten the hell out of them, particularly the engine guard fasteners. Doing this to mine made a noticeable improvement in vibration control.

I like some vibration but it was an issue for me when my stock Hella aux lamps and signal mirrors were shaking apart.  Making sure you still have upper mount bolts in place will also help, lol.

[randy yocum]

Duly noted about loose fasteners ,by the way I found a good solution  to the pesky- vibrating to death- Hella auxiliary light problem.I rubber mounted them ,I can lay my hand on the light at highway speed and no vibration, zip,I remember before when I did that my hand would tingle from serious vibration,it's no wonder the lights fall apart and the bulbs don't last.Since my mod I haven't replaced a bulb in those lights in over two years.
   A side benefit is when the bike falls over when I'm riding of road,the light just gets pushed out of the way and doesn't break.

[leafman60]

Good mod!

There are many reasons to change from the stock aux lamps other than the shaking apart issue.

The stock aux lamps are woefully weak in light output when compared to modern led units.  I am partial to the very high-quality and reasonably-priced Rigid products.  Their D Series Heavy Duty lamps with rubber isolation brackets are fantastic.  Light output is many times greater than those stock halogen pieces.

I have posted about this with pictures in the past.

https://www.rigidindustries.com/d-series-pro-specter-diffused-heavy-duty-black-2-lights-522313.html

While you're at it, stick in a pair of the Cyclops H-4 led bulbs to your stock headlights.

More here-

https://wildguzzi.com/forum/index.php?topic=75440.0



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[molly]

Got it Danial thanks,60nm torque on the bolts .I went ahead replaced both bolts ,I could see after careful examination of the remaining good bolt had some threads worn down, the edges weren't sharp like they should look.I'm thinking like you said the metal is too soft or fatigued due to age .I feel better now having replaced them with a higher quality bolt.I've been riding the bike ,no vibration ,as was before.
   I'm curious about the comments that Molly made about his Griso and how fully tightening 60nm these engine mount bolts would cause more vibration so he went with 20nm .How is that possible?

God point. When I bought the bike the mounting bolts were loose so I tightened them up. There was  a bit more vibration so I played around with various torque settings.
For some reason 20Nm was the sweet spot on my bike but I added the locking grub screws to ensure the bolts did not come loose.
I have no useful explanation why this worked.