Situation is that a few of my crankcase bolts stretched when I was trying to torque them properly to 19 ft-lbs. I was thankful that I realized what was up and pulled them before they snapped in the crankcase. I'm getting replacement bolts, but was curious in the mean time whether this is normal for some bolts to stretch, or is this implying something else is up with my reassembly of the crank halves? Any insight? Trans shafts and crank spun smoothly without any noticable issues after reassembly. Thanks in advance.

 

What do you mean the bolts stretched?

 

What bike/motor is it in?

 

It is an 1997 CBR600 F3 motor. 3 bolts from the lowercrank case, and 2 from the upper, started "necking" as I tried to torque them to a relatively low 19 ft-lbs.Bascially a section of the bolt started getting thinner. If I still am not describing the effect successfully, image the threaded section of the bolt having more of a coke bottle shape rather than a cylindrical shape. Of course, I only saw this after I realized the bolts just kept spinning without hitting the torquewrench setting. I learned something about torque wrenches...even if the lowest setting is 10 ft-lbs,low values don't alwaysclick to let you know the torque is reached (yeah, that is real useful). So I ended up getting another torque wrench that had a more appropriate range, but still had this "necking" happen on the latter 3 bolts. I put motor oil on the threads of all the bolts (suggestedfor more accurate torqing), and applied sealant - Hondabond 4 - to only the lower half of the crankcase before joining (as described in the manuals). I'm starting to wonder whether the bolts where bad when I first dissasemble the motor - necking is something expected in a metal piece is getting stretched.I'm not sure how thatwould happen tightening boltsin a crankcase. I'm just going to make sure the holes are clean, and try it again when my replacement bolts show up.

 

I have had this happen to me on a few of the valve cover bolts. They started stretching out and one of them actually broke. Luckily I was able to thread out the remaining portion with a punch! I don't know what caused this stretching to happen other than they were old. Like you… I was well within the torque spec. I know what you're talking about when you say the stretch though. I don't think you'll have the issue with the new ones because when I replaced the valve cover bolts, there wasn't an issue.

 

If your not overtightening, which it sounds like you know what your doing, must be bad bolts. Let us know.

 

Also, make sure you're not just tightening one at a time down to the torque setting, you're supposed to do them in steps, rotating around and getting progressively tighter. If it's the original honda hardware, or crap knockoffs it's possible that they're just not up to snuff and will stretch, but new 7's or whatever they use there shouldn't stretch when torquing them.

 

Thanks all for the feedback!

Do you think I'm risking much by continuing with my re-assembly withthose few crankcase bolts not yet installed? All the others are torqued, but I hate to get held up because of those few bolts. I at least want to slap the headon tonight.

 

I'd probably wait on that, and replace all the crankcase bolts for a peace of mind. And dont forget what rabbit said.