Cam Cap bolts


8 replies to this topic
  • motodiver13

Posted December 13, 2011 - 09:05 AM

#1

I know from previous posts the cam cap bolt torque spec is 7.2 ftlbs. Can any one tell me why the bolts seem to be cranked on at about 15-20 ftlbs from factory? I had to break them loose with quite a bit of force. Are the locktited at the factory? Anyone else notice this?

  • Mr. Neutron

Posted December 13, 2011 - 09:08 AM

#2

Sometimes they seem to get tighter after a whole buncha heat up/cool off cycles. You're not the first guy to notice this.....

Jimmie

  • grayracer513

Posted December 13, 2011 - 10:07 AM

#3

Simple. They stick to the head. Basically all bolts do this. Vibration, heat, etc., collaborate to form a bond between the plating or coating of the bolt and the threads they sit in, and this "adhesion" must be defeated along with the normal friction and the original torque when removing them.

BTW, I personally do not use the 7.2 ft/lb (86 in/lb) torque figure on my own bikes, and I haven't for several years. I assemble them with oily threads as called for, but torque them to 75 in/lb (6.25 ft/lb) in 3 progressive steps.

  • motodiver13

Posted December 13, 2011 - 11:19 AM

#4

thanks Grey, that makes sense. I've noticed this on several different bikes.

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  • crf450319

Posted December 13, 2011 - 11:32 AM

#5

but torque them to 75 in/lb (6.25 ft/lb) in 3 progressive steps.


Why 6.25 in/lbs as opposed to 7.2 ?

  • grayracer513

Posted December 13, 2011 - 01:46 PM

#6

Why 6.25 in/lbs as opposed to 7.2 ?

Because I don't like the physical feedback I get from the fasteners at the specified level of torque. It simply feels like too much torque for the assembly. The degree of rotation to the next 5 in/lb begins to become inconsistent, and I believe it begins to involve a certain amount of yield within the thread zone of the head and in the caps.

Standard torque for dry M6x1.0 threads is 7.2 ft/lb, but the cam cap bolts are spec'd at 7.2 with oiled threads. Oiling the threads creates variably 15-30% more clamping force than dry threads at the same torque, which is something else to bear in mind.

I'm not saying I know more than the Yamaha engineers in this matter, and I understand that my reasons for this are not backed up by hard, measured data. I'm not even going to outright say that I recommend it, but I will say that it's what I do to my own equipment and will continue to. It's just what they feel like, but that's feel as developed over 40 years of professional wrench turning, for whatever that's worth. I think 6.25 is tight enough, and that the caps and head in the cam bore area remain truer over multiple tear downs and reassemblies at that level.

  • RiderX

Posted December 13, 2011 - 02:38 PM

#7

Because I don't like the physical feedback I get from the fasteners at the specified level of torque. It simply feels like too much torque for the assembly. The degree of rotation to the next 5 in/lb begins to become inconsistent, and I believe it begins to involve a certain amount of yield within the thread zone of the head and in the caps.

Standard torque for dry M6x1.0 threads is 7.2 ft/lb, but the cam cap bolts are spec'd at 7.2 with oiled threads. Oiling the threads creates variably 15-30% more clamping force than dry threads at the same torque, which is something else to bear in mind.

I'm not saying I know more than the Yamaha engineers in this matter, and I understand that my reasons for this are not backed up by hard, measured data. I'm not even going to outright say that I recommend it, but I will say that it's what I do to my own equipment and will continue to. It's just what they feel like, but that's feel as developed over 40 years of professional wrench turning, for whatever that's worth. I think 6.25 is tight enough, and that the caps and head in the cam bore area remain truer over multiple tear downs and reassemblies at that level.



I wonder if they torque them dry at the factory, and don't take in to consideration that the threads are going to be oily when disassembled and reassembled, so they didn't change the spec?

  • crf450319

Posted December 13, 2011 - 03:28 PM

#8

Sounds good, I thought you might have had some mystical reason for it.. that I wouldn't have been able to figure out.

grayracer513

Because I don't like the physical feedback I get from the fasteners at the specified level of torque. It simply feels like too much torque for the assembly. The degree of rotation to the next 5 in/lb begins to become inconsistent, and I believe it begins to involve a certain amount of yield within the thread zone of the head and in the caps.

Standard torque for dry M6x1.0 threads is 7.2 ft/lb, but the cam cap bolts are spec'd at 7.2 with oiled threads. Oiling the threads creates variably 15-30% more clamping force than dry threads at the same torque, which is something else to bear in mind.

I'm not saying I know more than the Yamaha engineers in this matter, and I understand that my reasons for this are not backed up by hard, measured data. I'm not even going to outright say that I recommend it, but I will say that it's what I do to my own equipment and will continue to. It's just what they feel like, but that's feel as developed over 40 years of professional wrench turning, for whatever that's worth. I think 6.25 is tight enough, and that the caps and head in the cam bore area remain truer over multiple tear downs and reassemblies at that level.



  • grayracer513

Posted December 13, 2011 - 03:43 PM

#9

I wonder if they torque them dry at the factory, and don't take in to consideration that the threads are going to be oily when disassembled and reassembled, so they didn't change the spec?

That would not explain it. If they were torqued dry, the clamping force on the bolts would be less than specified. All torque values are given assuming "clean dry threads" unless specifically called out differently. The manual specifies oiling the threads for these bolts, and then in the same page and section calls for 7.2 ft/lb. If what you suggest were to take place, the bolts would be looser on the first removal than at any subsequent time.

It is not unusual for specific fasteners to be called out at higher than standard torque values, especially in more critical applications such as this, so that's not really at issue. It's just what feels right to me based on my experience.





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