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tpars121

Cylinder Head Tightening

17 posts in this topic

Can someone explain to me the proper way to tighten the head on my 08 YZ450F? I dont understand this part of the manual:

Put a mark on the corner "1" of the

bolt (cylinder head) and the cylinder

head "2" as shown.

Tighten the bolts 90° in each of the

two steps to reach the specified angle

of 180° in the proper tightening sequence

as shown.

Do you tighten the bolts another 180 degrees after you torque it to 14 ft lbs?

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Yes, that's what the book says:

  1. Apply a thread lube to the bolts and torque them evenly in the prescribed order to 22 ft/lb. This preconditions the gasket.
  2. Remove the bolts and reapply lube, then retorque to 14 ft/lb. This creates an accurate base point from which to "angle torque" the bolts on the pre-crushed gasket. If they called for starting at zero, everyone's zero would be a little different.
  3. Mark the bolts and turn each one in order another 90 degrees.
  4. Then turn each bolt in order yet another 90 degrees, for a total of 180 degrees tighter than 14 ft/lb.

Note that if you are doing the head in the frame of an '06-'09, it will not be possible to remove the bolts in step two without tilting the head out of place. I recommend skipping that part and instead just loosening them to zero, then retorquing to 14 ft/lb.

Got it? :cheers:

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I haven't bothered to check that. The process is called angle torquing, and the purpose of it is to avoid having the friction of the threads or the torsional resilience of the bolts become a variable.

The gasket is first pre-crushed by torquing to a value high enough to flatten it to a uniform state across the sealing surface. Then the bolts are loosened and re-tightened to a level of torque high enough to be accurately measurable and repeatable, but low enough that friction and bolt twist don't come into play. That sets the stage for the tightening process with a uniformly seated gasket and four bolts at a virtually identical state of tightness. The bolts are then rotated a prescribed number of degrees to the final torque setting.

Since the pitch of the bolt is known, the amount of stretch produced by any amount of rotation is a known value. Since the amount of clamping pressure the bolt will produce when stretched any certain amount is also known, the number of degrees the bolts should be rotated can be precisely chosen by the engineers. It's a much more accurate and consistent approach that has come into use throughout the automotive and aircraft industries over the past couple of decades.

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Wicked info grey, you are a life-saver when it comes to questions about procedures for these bikes. Thank you for explain why the manual does it this way as well.

What would you recommend for a lube? Just oil?

Can you add this thread to the FAQ? this is info that I'm sure people skip or don't understand and run into problems down the road.

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I use a black moly anti-seize from Perma-Tex. The manual specifies moly disufide grease.

And yes, I'll add it.

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I haven't bothered to check that. The process is called angle torquing, and the purpose of it is to avoid having the friction of the threads or the torsional resilience of the bolts become a variable.

The gasket is first pre-crushed by torquing to a value high enough to flatten it to a uniform state across the sealing surface. Then the bolts are loosened and re-tightened to a level of torque high enough to be accurately measurable and repeatable, but low enough that friction and bolt twist don't come into play. That sets the stage for the tightening process with a uniformly seated gasket and four bolts at a virtually identical state of tightness. The bolts are then rotated a prescribed number of degrees to the final torque setting.

Since the pitch of the bolt is known, the amount of stretch produced by any amount of rotation is a known value. Since the amount of clamping pressure the bolt will produce when stretched any certain amount is also known, the number of degrees the bolts should be rotated can be precisely chosen by the engineers. It's a much more accurate and consistent approach that has come into use throughout the automotive and aircraft industries over the past couple of decades.

Damn...I'm not going to throw an answer out there on the torque number...but I have it written down somewhere.....Funny thing is when your installing an Athena big bore kit....They give you the number........if you dont wanna do the angle torque thing. Snap on angle torque guage works nice though.

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this is a big help, I wasn't sure about tightening, (crushing the gasket) then loosening and not knowing why aside from just being able to put more lube on the threads, but its to (condition the gasket). but my question now is this, will this same procedure work for the 2010 which has slightly different torque specs, my manual says to tighten to 22 ft. lbs, remove and relube threads/washers, then retighten to the same 14 ft. lbs. then this is where it is different, the 2010's require only 150 degrees, in steps of 90, then 60. or is this thread recommending that i go to 180 degrees even on the 2010's. and also mine says to use molybdenum disulfide grease, or is that the same thing as moly disulfide.

thanks, this site has been amazing for useful info.

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I suggest you follow the manual. If it says 150, that's what you should use.

BTW, the final torque numbers for the '06 I was working on last night ended up being right around 50 ft/lb. It was interesting to watch the variance in indicated torque at the same angles from one bolt to the next. It was about a 10 ft/lb spread over the 4 of them, centering on 50. Shows the reason for angle torquing.

Regarding the thread lube, the product they are referring to as moly grease is commonly called "anti-seize compound". There are 3 principal kinds; copper bearing, aluminum/tin/lead bearing, and moly bearing. The color is a giveaway as to the content, you want the black kind. Another nearly identical product is called "assembly lube". It's good, but far more expensive than the antiseize per ounce because of the smaller packaging.

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Yeah, I used the yamalube molybdenum stuff. 8$ nor a big tube. I used it on my valve stems and piston pin. As per manual. But would it be better to use actual antiseize for my head bolts?

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i soaked my head bolts in engine oil .. hope this doesnt affect anything too much .. ive built a couple of bike like using oil on headbolts , instead of proper grease ..

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I just performed the 14 ft lbs and 180 degrees tightening procedure and thought I would share the final torque numbers I ended up with

 

Front left 50.75 ft lbs     front right  50.25 ft lbs

 

 

rear left 52.75 ft lbs      rear right 54.0 ft lbs

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The variation you found on a follow up check is why angle torque is used instead of wrench torque.  Good example.

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