Omega Owners Forum
Omega Help Area => Omega General Help => Topic started by: olm on 03 July 2021, 02:53:59
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Hi, I'm mounting the cylinder head of my y32se and I see that the tightening is 20nm +90+90+90+15. But when giving 90 + 90 the screw no longer works and I use a large long bar, if I try to give the 105 that remain it will break. . Has someone mounted it and given that tightness?
Thanks
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The "90 " part is degrees (a quarter turn) , NOT 90 NM
Lucky you stopped and asked
new bolts required now and probably a new head gasket
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The "90 " part is degrees (a quarter turn) , NOT 90 NM
Lucky you stopped and asked
new bolts required now and probably a new head gasket
Yes, is degrees, I know, sorry for not specifying
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Are you using new bolts?
Even worse, as I read it the correct spec is 25Nm + 90° + 90° + 90° + 15°. Not 20Nm ++++.
All bolts in turn in the correct spiral sequence.
Operate your torque wrench a couple of times on one of the wheel bolts before you use it on the head bolts. Might help accuracy.
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It is some time since I refitted a cylinder head, and then on 4 pots.
Back in the day the tightening of the bolts was done in sequence, in a cross pattern, from middle to ends.
As a point of interest, and ready for the day I may have to do it again, but on my V6, what is the prescribed pattern tightening down gradually to full torque? ??? ??? ;)
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It is some time since I refitted a cylinder head, and then on 4 pots.
Back in the day the tightening of the bolts was done in sequence, in a cross pattern, from middle to ends.
As a point of interest, and ready for the day I may have to do it again, but on my V6, what is the prescribed pattern tightening down gradually to full torque? ??? ??? ;)
The tightening pattern(and you loosen in reverse :y ) hasn't changed. It's like that to prevent distorting the part as the forces are applied. It's why you tighten opposite wheelbolts too. Modern heads have a lot less metal in them, usually aluminium, although the multi-pass approach means that the clamping is built up in stages.
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... Even worse, as I read it the correct spec is 25Nm + 90° + 90° + 90° + 15°. Not 20Nm ++++.
All bolts in turn in the correct spiral sequence.
.....
The difference between 20Nm & 25Nm is negligible .... ;)
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using a "large long bar" on a torque wrench isn't good practice though :o
sounds like the threads are bottomed out :-\ or maybe have oil or coolant in :-\
such extreme torque could distort the deck of the block round the bolt holes
clearly something is wrong
has he head been skimmed ?
using the foot/pound scale instead of newton meters :-\
re-using stretch bolts :-\
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using a "large long bar" on a torque wrench isn't good practice though :o
sounds like the threads are bottomed out :-\ or maybe have oil or coolant in :-\
such extreme torque could distort the deck of the block round the bolt holes
clearly something is wrong
has he head been skimmed ?
using the foot/pound scale instead of newton meters :-\
re-using stretch bolts :-\
I do hope his head hasn't been skimmed ;D
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using a "large long bar" on a torque wrench isn't good practice though :o
sounds like the threads are bottomed out :-\ or maybe have oil or coolant in :-\
such extreme torque could distort the deck of the block round the bolt holes
clearly something is wrong
has he head been skimmed ?
using the foot/pound scale instead of newton meters :-\
re-using stretch bolts :-\
I do hope his head hasn't been skimmed ;D
;D :P
would explain the issue :D
it should read "has THE head been skimmed" :-[
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The bolt tightening sequence, described as a spiral sequence from the middle outwards, can be viewed here (http://www.omegaowners.com/forum/index.php?topic=90500.0).
I would guess that an unskimmed head is 134mm, because that's the spec for X25XE and Y26SE, between the upper and lower planed surfaces. So if it's measurably less then it has been skimmed. If it was skimmed because it was warped then the material removed might be significant.
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The bolt tightening sequence, described as a spiral sequence from the middle outwards, can be viewed here (http://www.omegaowners.com/forum/index.php?topic=90500.0).
I would guess that an unskimmed head is 134mm, because that's the spec for X25XE and Y26SE, between the upper and lower planed surfaces. So if it's measurably less then it has been skimmed. If it was skimmed because it was warped then the material removed might be significant.
Excuse my ignorance, but would you then have to use shorter head bolts?
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The bolt tightening sequence, described as a spiral sequence from the middle outwards, can be viewed here (http://www.omegaowners.com/forum/index.php?topic=90500.0).
I would guess that an unskimmed head is 134mm, because that's the spec for X25XE and Y26SE, between the upper and lower planed surfaces. So if it's measurably less then it has been skimmed. If it was skimmed because it was warped then the material removed might be significant.
Excuse my ignorance, but would you then have to use shorter head bolts?
A cowboy might do that. I very much doubt you'd bottom out a standard new head bolt regardless of how much you skim (assuming less than 1mm). Much more likely to be the wrong bolts, or the wrong washers, or you haven't correctly cleaned out the bolt hole.
Skimming the head ALWAYS increases compression. ALWAYS. It also brings the valves into closer proximity with the top of the piston. I've no idea what the normal clearances are in our V6's, but IMV the skimming limits on heads are usually to do with maintaining compression ratios within acceptable limits.
If you've skimmed the head by more than the allowable limits then the two options are 1) find a new head, or 2) fit a thicker head gasket.
As for the torqueing sequence. It's only valid for NEW standard head bolts. I'd guess these are 8.8 grade steel? If you use a stronger steel bolt (10.9, 12.9 or ARP fancy stuff) then following the torque sequence WILL lead to tears.
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you can't skim much off a V engine head and expect the valley gubbins to fit back
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AIUI, there are no published limits for skimming the V6 heads.
Which suggests that they shouldn't be skimmed.
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The bolts are new and the head not be skimmed.
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did you compare the original bolts with the new ones ?
did you clean out the blind bolt holes in the block before reassembly ?(no oil or coolant)
are you confident of the calibration of the torque wrench ? and know for sure you have set it correctly ?
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It is some time since I refitted a cylinder head, and then on 4 pots.
Back in the day the tightening of the bolts was done in sequence, in a cross pattern, from middle to ends.
As a point of interest, and ready for the day I may have to do it again, but on my V6, what is the prescribed pattern tightening down gradually to full torque? ??? ??? ;)
The tightening pattern(and you loosen in reverse :y ) hasn't changed. It's like that to prevent distorting the part as the forces are applied. It's why you tighten opposite wheelbolts too. Modern heads have a lot less metal in them, usually aluminium, although the multi-pass approach means that the clamping is built up in stages.
Thanks Nick :y :y
I hope I will now never have to do that job again, but who knows! ::) ::) :D ;)
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The bolt tightening sequence, described as a spiral sequence from the middle outwards, can be viewed here (http://www.omegaowners.com/forum/index.php?topic=90500.0).
I would guess that an unskimmed head is 134mm, because that's the spec for X25XE and Y26SE, between the upper and lower planed surfaces. So if it's measurably less then it has been skimmed. If it was skimmed because it was warped then the material removed might be significant.
Good one :y :y
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someone one suggested to me, that after the initial torque setting to seat the bolt, to put a spot of paint pen at 12 o'clock on each bolt as an aid to where you're up to when you're then tightening down in 1/4 turns
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A sensible tip. :y
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or, if your memory is that bad then don't take your engine apart into 100 bits ;D
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We all make mistakes from time to time. And my memory is that bad these days. ;D
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but what if you forget to put the dot on with a marker pen :D
it's just adding more to the procedure
but fair enough ,whatever works for who's doing the job :)
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did you compare the original bolts with the new ones ?
did you clean out the blind bolt holes in the block before reassembly ?(no oil or coolant)
are you confident of the calibration of the torque wrench ? and know for sure you have set it correctly ?
It's hard to believe that the bolts are bottoming out unless there's crud or oil in the bolt holes. Surely there must be some allowance.
The GM bolts are described as M11 x 105mm (1.25mm pitch?). So worth checking that the new bolts you're trying to fit are the same.
That said the Victor Reinz 14-32104-02 bolt kits say M11 x 100mm. I don't know why. It might be they're substituting another standard part for a one size fits many approach.
EG. FAI says their bolts are M11 x 105mm.