broken cylinder head cover bolt

I finally got the parts to rebuild the motor in my '97 XR600R. So tonight I assembled it and was simply tightening the head cover bolts to spec when the 10mm bolt at the outside of the cover let go. You gotta be kidding me, I've been waiting 6 weeks to get back on this thing. When I look at the bolt pattern, there is not a corresponding bolt on the opposite side from the one that broke; the 10mm bolt I broke is on the front right side of the motor, and there is no 10mm bolt on the front left. I'm trying to use this fact to justify a break in ride tomorrow, thinking that the worst case scenario is some minor, not catastrophic, leakage past the head cover. Any one disagree? Am I sacrificing my gaskets if I do take it for a ride?

On a side note, the bolt that snapped was corroded; in retrospect, I shouldn't have reused it. Even so, this is not the first factory Honda bolt I have broken using factory torque specs. I am using a Craftsman torque wrench, the kind that clicks when the specified torque is reached; I thought it was quality. Did I break the bolt because it was corroded and no longer good? Or is my wrench suspect?

Thanks for the input,

What model of torque wrench do you have and what is the size of the bolt?

It's hard to tell if it's the torque wrench or the bolt unless you take the torque wrench in for calibration to verify if its within spec. In general though you should use a torque wrench that corresponds to the size of the fastener. A large torque wrench that has a range of lets say 20 to 100 lb/ft will be more accurate within a certain range of those numbers (usually in the middle of those numbers) and less accurate towards the ends of those numbers. So if your torque for a fastener is 20 lb/ft and you're using a torque wrench that says it's good from 20 lb/ft to 100 lb/ft, then you're probably using the least accurate portion of your torque wrench and it may be off as much as 10% where as the torque accuracy may be much more accurate at 50 lb/ft (in the middle of the range. On all my torque wrenches (made by Proto), I get a print out of exactly how accurate they are at given steps throughout their torque range so I know exactly what my margin of error will be, which can be critical for some fasteners.

One thing that you should make sure of with your click type torque wrench is to make sure that you never store it while it's set to a torque setting or it will loose accuracy and need to be recalibrated. Always keep it stored with the torque removed :cry:

You may have also just encountered a weak bolt. If a bolt looks bad or is corroded, it's good practice to just replace it.

Bummer about that bolt...I broke one in my clutch access cover a few months ago... let me guess honda says 9lb. ft.? right? Well I have a friend that is a master mechanic, who swears that 9 lb. ft of torque for such a small bolt is WAY TOO MUCH!!! I know where your coming from I'm a torque freak myself!!!! I argued with him, I said why would honda make a book with that spec if it wasn't right???? But eventually I took his advice, and just tighten them til snug, and give another 1/4 turn. Never had a leak yet!!! And no more broken bolts! I hope you at least had enough sticking out to remove the bolt. :cry: :cry: :cry:

Another thing that comes to mind is if the bolt was lubricated or not. For instance, if anti-seize is used, then the torque values must be reduce by 20% or else you'll snap the bolt. It's just something for everyone to keep in mind if they're not familiar with it.

The grade of the bolt is also something else that determines the torque value of the bolt and so does the surface condition of the nut. For instance, if you're using a nut that's zinc plated, you'll have to use different correction factors when determining the torque value for a nut that was plated with cadmium because they both have different coefficients of friction and these things become important when using aftermarket fasteners.

malevolant73 brings up another good point because the torque wrench isn't the only way to properly tighten a bolt. The 'part turn' method as he mentioned is also a proven way to tighten fasteners. He mentioned 1/4 turn, but I've always used the procedure of tightening the bolt until joint surfaces are in close contact and at the point where just before solid tightening starts, I'll turn the nut 1/2 or up to 3/4 turn. You can also measure the elongation of the bolt, which is yet another method of determining correct torque, but it's not usually practical for many common applications.

No matter how careful a person is, it's just a matter of time before a person snaps a bolt if they're working with fasteners. I hope you're able to quickly & easily remedy your issue and that you get your bike going soon.

Here's a link to a torque guide for metric bolts.

And if you really want a kool bolt, then check out DTI's Smart Bolts with built in stress indicators that visually tells you when the bolt is properly torqued based on the fasteners elongation. This is a kool propduct!

I have a Craftsman model 8152, I think, and I sure did store it in a torque setting; I didn't know that I shouldn't. The bolt head is 10mm, which makes the shank 6mm? The manual called for 17 ft/lbs, which this particular bolt obviously couldn't take. And, thinking I was being smart, I did lube the bolt.

I just picked up Carroll Smith's "Engineer to Win", and have read enough about fasteners to get myself in trouble, apparently. A little knowledge is a dangerous thing. Lack of knowledge notwithstanding, it seems to me that there is good reason to tighten a fastener to a published spec, but very difficult to control all the variables in order to get the fastener exactly to spec. Maybe I should leave exact values to Formula 1 and aerospace guys, or at least guys with Proto torque wrenches, and use Malevolent's technique.

Everytime I make a painful mistake, I tell myself, "that's the price you pay to learn," but when the price involves tearing my engine down again, my mantra loses much of its power. Thanks for all the info,

I tell myself, "that's the price you pay to learn,"

I've learned a lot at the school of hard knocks :cry:

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