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  #1  
Old 03-24-2002, 02:19 PM
jon isgreen
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replacing head...degrees of rotation to foot/pounds.

Sirs,
Replacing the head on an'85 2.2L diesel. The manual, for the last two sequences of torque application, dictates two 90 degree rotations with a 10 minute rest period between the first and second.
Does anyone know what final torque this converts to?
Is this, in your collective experiences, the best way to go, or is a more gradual increase, by foot/pounds, more dependable?
I will, of course, be using new bolts, with anti-seize cmpd.
Thanks.
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Old 03-24-2002, 04:13 PM
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Why would you do it any other way?

Do what the book says -- two 90 degree torques, in sequence. I have no idea what NM or ft lbs these torques require, but it is alot because you are stretching steel as you are torquing.

Get a grease pencil or paint pen and mark your bolts before you do the two torques, so you'll know when you've reached exactly 90degrees each time.

Good luck!

~Paul

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Old 03-25-2002, 09:11 AM
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Angle of rotation means just that! On MB engines starting around 1979 the head bolts are "stretch to yield". So follow the torque sequence as specified. 25nm= 18ftlbs & 40nm=28ftlbs. Then use a breaker bar with socket & perform the 2 90deg angle rotation. IN other words turn each bolt 1/4 turn (two times in sequence). AS long as you have good(or new) head bolts the final torque doesn't matter.
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Old 03-25-2002, 12:13 PM
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Is the 10 minute rest period important? I had never heard that before.
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Old 03-25-2002, 12:16 PM
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What manual are you using?
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Old 03-25-2002, 01:04 PM
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The most important part of using Sretch Bolts is to pay attention to having a uniform sequence on the called for 'snug torque' specs. This is as important as the angle spec. as it creates the baseline for the latter.

I think the resting period you mention may be to let the bolts stabilize between sequence as they heat up when streached.

Here is the basic info:
http://www.robbos.com.au/myweb/Tech_Bolts.htm
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Old 03-25-2002, 01:10 PM
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You will literally be resting 10 mins if you torque these down with a ratchet -- maybe that's what they mean

~Paul

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Old 03-25-2002, 02:01 PM
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I have done a couple of heads using the 90+90 torque sequence and pmizell is right on. The first 90 degree sequence was not too bad the after I finished the second sequence my arm felt like it was about to fall off.

90+90 is very tight but I've had no problems with any head that I have assembled using this spec.
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Old 03-25-2002, 08:40 PM
jon isgreen
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Sirs,
I would assume 90 degrees, once all bolts are torqued in stages to 45Nm, is demanded because how accurate would, say, 45 degrees X4 be? Hard to measure.
My concern is the sudden demand placed on the bolt and the warping effect of a 90 degree rotation on the head...after all, only one bolt at a time can be rotated, unless one had 18 assistants.
A 90 degree rotation exceeds the elastic limits of the steel, and flows into the plastic limit, as the bolt is engineered to do...but wouldn't a more gradual torquing, with appropriate rest periods, give the crystal lattice time to realign and 'heal" somewhat?
Besides, bolts, like people, are not identical...some will deform while others will resist deformation. Torquing, vis a vis degrees of rotation, would sense the behavior of individual bolts and compensate accordingly...not to mention manufacturing fluctuations in the head gasket from front to back.
The head, upon installation, is being warped...just warped in a manner that minimizes built-in stresses.
Just pondering...
Parenthetically, I think the bolt will heat up from the friction, and cool down from the stretch...with a net rise in temp, therefore length, momentarily.





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Last edited by jon isgreen; 03-25-2002 at 08:54 PM.
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