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I was changing the rear springs on my wife's CRV earlier and one of the bolts holding the strut to the bottom are sheared. Removing the captive nut and remains of the bolt was slightly awkward but not insurmountable. However I'm left with the question of what to replace the snapped bolt with.
It's just an M10 bolt and captive nut. It goes through the arm, through the bottom shock mount, and into the captive on the other side of the arm. Effectively, the bolt holds up one corner of the car. My plan is to weld on a new captive but what tensile strength bolt should I use. The original has no markings to help and a Honda one from Honda may take a while. I have 8.8 bolts ready to use but am wondering if 10.9 wouldn't be better.
Any thoughts?
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Jaguar S-Type 3.0 SE
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Hi, The likely tensile strength of the bolt is as you say grade 8.8 but your load on the bolt is a shear loading which is different. The weakest point of the bolt is the junction of the shank and the thread but the load on your bolt is on the shank the stronger part of the bolt. With some research that size bolt has a shear capacity of circa 4000kgs. As that is more than twice the weight of the car do you think that's enough?
Colin
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My internet research suggested that it should be ok but the internet is awash with experts so I'm always a bit cautious. 4000 kg would be sufficient for the crv with my half on the roof rails.
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Jaguar S-Type 3.0 SE
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get some 10 or 12.9 for pennys ....might as well do it right and not have the worry that its gona snap off
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91 golf g60, 89 golf 16v , 88 polo breadvan
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Having thought about it, I think that's the peace of mind option. I seriously doubt that the 8.8 bolt will break but it'll nag at me anyway. I've ordered a 10.9 one as back up. |
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Jaguar S-Type 3.0 SE
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Fungus
Part of things
Posts: 960
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I would use a 12.9 for sake of 50p or so.
Do you have a local fixings and fasteners supplier?
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I would use a 12.9 for sake of 50p or so. Do you have a local fixings and fasteners supplier? There used to be a brilliant engineering supplier locally who would tell you what to use then sell you one. Sadly my 6 monthly visits weren't enough to keep him in business. All we really have are DIY stores. It's back together with the 8.8 bolt for now so it's mobile rather than moored on the drive. I'll ring Honda tomorrow. I read on the internet last night that Honda use 10.9 for pretty much everything. I also read that in some uses, 10.9 is more inclined to break than 8.8. I'm none the wiser and don't have time to do a metallurgy degree so I'm going down the factory route. |
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Jaguar S-Type 3.0 SE
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richr
Part of things
Posts: 119
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As has been said you don't necessarily need a higher tensile strength when the application is in shear.
In fact a higher tensile strength can be negative when not used in its intended application.
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j4m35
Part of things
Posts: 70
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As has been said you don't necessarily need a higher tensile strength when the application is in shear. In fact a higher tensile strength can be negative when not used in its intended application. Yes, greater strength in tension means higher carbon steel, which in turn means greater hardness and a greater succeptability to shear rather than bend if exposed to loads well beyond the allowances of the application. |
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For the bolt get the right one from Honda, its not worth taking a risk on safety critical fasteners.
For the nut go for a 1 1/2 height one of the best grade you can get.
Also check the tightening procedure many moderns now use torque + angle, the right bolt is critical for this.
The loads can be very high 6g (i.e. 6 x the static loading) is not uncommon when braking into a pot hole or striking a kerb, you don't want the wheel coming off!
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It's just a torque setting in this case, done with the car on the ground. I shall be on the blower to Honda this morning and have ordered suitable nuts.
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Jaguar S-Type 3.0 SE
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Oct 16, 2016 19:45:21 GMT
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To bring this to a close, Honda rustled up a bolt for £4. After some M10 fine thread based confusion, it's back together again. The bolt in question is basically just a 10.9 one with a pointy end to make it easier to fit.
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Jaguar S-Type 3.0 SE
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8.8 will not break. Although 10.9 and 12.9 have a higher tensile strength they are more brittle.
Make sure the markings on the bolts are proud and not engraved. Engraved ones are usually fake. Also, threads should be rolled and not cut.
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düdo
Part of things
wide as house
Posts: 770
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I was in a similar situation last week with the mounting bolts for the stabiliser/anti-roll bar on the Tigra and I ended up going to the Opel dealer to get the exact replacements as they had to be torque plus two stage angle tightened.
But the main dealers don't always have a clue as I had to go back twice to swap some other bolts he'd given me for the lower arm/roll bar connection. I think they work better with part numbers than actually thinking about load factors etc
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Oct 19, 2016 10:33:19 GMT
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Hi, Yes, the parts guy is a storeman not an engineer.
Colin
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düdo
Part of things
wide as house
Posts: 770
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Oct 19, 2016 20:27:00 GMT
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Hi, Yes, the parts guy is a storeman not an engineer. Colin When I went to the local Opel HQ they summoned the parts guy from some dark recess and he came out blinking as though he'd never actually met a customer. I think very few private punters call in and none arrive on a bicycle. But he was friendly and invited me into his private recess/warren/80s timewarp place store. He'd forgotten that the Tigra A even existed but he did some good rummaging on my behalf and spontaneous discounting of stock he was hoping to clear. |
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Do you know why the bolt had sheared was it due to the shock bushes being worn or is there another reason?
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