Replacing head studs


4 replies to this topic
  • walshy

Posted August 21, 2008 - 01:04 AM

#1

About to put the head back on the old 03 WR450!
This is the second time I've had the head off, and have heard that the head studs should be replaced!
Not a huge expense, but maybe a bit of a wait for the things to show up!
Probably should have ordered them with the other bits but wasn't thinking!!! :thumbsup:

  • matt4x4

Posted August 21, 2008 - 03:58 AM

#2

Dealer should be able to get them in a day or two, ordering on line will take longer, but for 4 bolts, your shipping would likely bring the on-line cost to the same or higher than the dealer.

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  • walshy

Posted August 21, 2008 - 03:27 PM

#3

I can't find any information about the head studs in the Yamaha manual...
Doesn't say whether they should be replaced or not!
They give the torque to yield "TTY" type specs for the head bolt tensioning, but don't state whether or not to replace the studs>>>:worthy:
But then the manual also states that you should "LAP" the valves, and we all know that to be a NO NO with TI valves...:thumbsup:

  • grayracer513

Posted August 21, 2008 - 04:02 PM

#4

The studs in the YZ/WRF heads are subjected to very little stress from torque. You could go either way with them.

They torque values for the head bolts are not Torque To Yield specifications, but Angle Torque specs. These are used to assure more uniform clamping force by working around the possibility of incorrect torque wrench readings caused by thread friction at high torque levels.

The bolts are torqued once to a value high enough to pre-compress the gasket, then backed off and retorqued to a lower base value not likely to produce the friction related errors. From that presumably uniform base, the 4 bolts are rotated an identical distance, which will produce the same clamping force on each bolt. The torque applied to these bolts in this process is well below the yield strength of either the bolt or the threads in the crankcase.

  • walshy

Posted August 23, 2008 - 02:37 AM

#5

The studs in the YZ/WRF heads are subjected to very little stress from torque. You could go either way with them.

They torque values for the head bolts are not Torque To Yield specifications, but Angle Torque specs. These are used to assure more uniform clamping force by working around the possibility of incorrect torque wrench readings caused by thread friction at high torque levels.

The bolts are torqued once to a value high enough to pre-compress the gasket, then backed off and retorqued to a lower base value not likely to produce the friction related errors. From that presumably uniform base, the 4 bolts are rotated an identical distance, which will produce the same clamping force on each bolt. The torque applied to these bolts in this process is well below the yield strength of either the bolt or the threads in the crankcase.


Thanks grayracer!!!
That all makes perfect sense! I'm thinking of my old ford six cylinder where the manual actually tells you to toss the old studs!!!




 
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