2003 Head Bolt Torque Specs


12 replies to this topic
  • wflee26

Posted February 26, 2008 - 10:55 AM

#1

I was going through the Yamaha shop manual about torque-ing the head bolts.

Interesting process, torque each one to 33 Nm, then remove, and re-torque to 22 Nm.

Then the manual states to torque the head-bolts to 180 degree's from there.

I don't understand the torque-remove-retorque sequence. Please elighten.

Thank you in advance.

Frank

  • grayracer513

Posted February 26, 2008 - 11:22 AM

#2

The process is called angle torquing. The intention is to eliminate the variations in clamping force that often result from using long bolts at high torque values. As the bolts are tightened, the friction at their threads increases. This friction is an uncontrollable variable, even when lubed. When the friction is higher at one bolt than at another, the bolt will not be rotated as far to reach a specified torque value as the bolt with less friction will, and the actual applied clamping force will vary as a result.

The first step pre-crushes the compound head gasket and settles the head/cylinder stack to get a more uniform result in the second phase, since the angle rotation can be started from at point at which none of the clamping will be "used up" in crushing a gasket.

The second phase asks you to remove and relube the bolts because you are starting over with pre-crushed gaskets. You don't absolutely have to remove the bolts, but you should, and you at least need to back them completely off to a zero torque state. Since angle torquing will only produce an accurate result if it starts from a predictable, repeatable point, the bolts are first run down to 14 ft/lb. This is a value that is high enough to be unquestionably snug and settled, but low enough that thread friction is not yet a significant factor in the real clamping force. The head is now snugged up squarely on a pre-crushed surface, and ready to be torqued.

Finally, the bolts are rotated a specific distance, which will produce a consistent, predictable force holding the head, bypassing any errors caused by head friction.

  • todds924

Posted February 26, 2008 - 06:51 PM

#3

The process is called angle torquing. The intention is to eliminate the variations in clamping force that often result from using long bolts at high torque values. As the bolts are tightened, the friction at their threads increases. This friction is an uncontrollable variable, even when lubed. When the friction is higher at one bolt than at another, the bolt will not be rotated as far to reach a specified torque value as the bolt with less friction will, and the actual applied clamping force will vary as a result.

The first step pre-crushes the compound head gasket and settles the head/cylinder stack to get a more uniform result in the second phase, since the angle rotation can be started from at point at which none of the clamping will be "used up" in crushing a gasket.

The second phase asks you to remove and relube the bolts because you are starting over with pre-crushed gaskets. You don't absolutely have to remove the bolts, but you should, and you at least need to back them completely off to a zero torque state. Since angle torquing will only produce an accurate result if it starts from a predictable, repeatable point, the bolts are first run down to 14 ft/lb. This is a value that is high enough to be unquestionably snug and settled, but low enough that thread friction is not yet a significant factor in the real clamping force. The head is now snugged up squarely on a pre-crushed surface, and ready to be torqued.

Finally, the bolts are rotated a specific distance, which will produce a consistent, predictable force holding the head, bypassing any errors caused by head friction.


Hey there Gray! Just came across something you might find interesting today. I was putting an Athena Big bore kit on a WR 450 and in there instructions they just gave a straight torque spec. for the bolts.....not what is specified in the manual. It seemed a little on the light side to me also.

  • grayracer513

Posted February 26, 2008 - 08:46 PM

#4

How much was it?

  • kubamtx

Posted February 27, 2008 - 07:58 AM

#5

Gray I'm rebuliding my yzf 426 and my manual says that I have to torque the bolt to 44Nm . Nothink about torque-remove-retorque sequence. Should I use 44Nm or do the sequence like 450 manual says?

  • grayracer513

Posted February 27, 2008 - 09:16 AM

#6

You should follow the manual.

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  • wflee26

Posted February 27, 2008 - 02:36 PM

#7

When I put the head together, I just torqued to 33Nm, then did the 180 degree torque from there. Do you think that might be my problem?

  • King_Air

Posted February 27, 2008 - 03:33 PM

#8

Are you having problems after a rebuild? What are you problems?

  • King_Air

Posted February 27, 2008 - 03:37 PM

#9

All right, I just now noticed you other thread on water in the oil. One of my basic rules of troubleshooting is to look hard at where the last hands were. In this case the head gasket seems a likely cause. Then considering that the head was tourqed improperly, that is what I would change first (head gasket) and touque it per the maintenance manual.

  • grayracer513

Posted February 27, 2008 - 04:56 PM

#10

When I put the head together, I just torqued to 33Nm, then did the 180 degree torque from there. Do you think that might be my problem?

Could be, but have the head and cylinder surface checked, anyway.

  • todds924

Posted February 27, 2008 - 05:00 PM

#11

How much was it?


45 Newts.......I believe that equates to 30 ft lbs. It just seemed lighter than doing it the 22ft lbs, back it all the way off, 14ft lbs, then 180.

  • grayracer513

Posted February 27, 2008 - 05:14 PM

#12

45 Newts.......I believe that equates to 30 ft lbs. It just seemed lighter than doing it the 22ft lbs, back it all the way off, 14ft lbs, then 180.

That's 33 ft/lb. The 426 called for 32. Who knows? If you think of it, use a torque wrench to do the 180 on the next head and see what it ends up.

  • todds924

Posted February 27, 2008 - 09:07 PM

#13

That's 33 ft/lb. The 426 called for 32. Who knows? If you think of it, use a torque wrench to do the 180 on the next head and see what it ends up.


I have a nice Snap On digital that will tell me where its at after the 180...I just never thought about it until yesterday. After I torque to 14 ft lbs I dont use a torque wrench to do the 180. Yamaha is the lightest on Head torque between the 4 jap brands for the 450's.





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