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Re: head torque+rocker arm end play
- Subject: Re: head torque+rocker arm end play
- From: Ben Barkow <dr.ben@xxxxxxxxx>
- Date: Mon, 11 Apr 2005 14:08:39 -0400
> Subject: head torque+rocker arm end play
> Clive wrote
>>> It is important to accurately establish the "starting" point of the
> 90+90 angle torque with the initial 20Nm.<<
> I think this starting point is the root of the stripped head stud problem,
> its rare but does happen. I have been to 2 different dealer to buy a head
> stud for testing purposes, and neither had one in stock.
> Plotted out, the relationship between nut rotation and torque is not
> linear, for instance, just as an example, say a nut is at 10 ftlbs and you
> turn it 30 degrees and thats put is it to 15 ftlbs, now with the nut at 30
> ftlbs, turning it 30 degrees puts it at 60 ftlbs.
> Some testing on this.
> I have only done rocker end play on 3 slightly used oil heads, which i
> owned at one time, all had the 600 check up done at different local dealers,
> i found the final torque and they were 34(95rs), 36(98gs), and
> This is a very small test lot, but it tells me even the trusted
> professionals have a 10% window.
> Why did i go with 400inch lbs.? about the middle of the page read what
> Hank writes,,
> There is a final torque window, i am not sure what the extremes are, on
> the low end you need to keep from blowing head gaskets and stop weeping oil,
> on the high end the weak link is apparently the engine case.
> The 20nm then 90+90 system works good and stretches the bolt in the
> elastic range, it bypasses the many variables in regular torquing like a
> burr on a thread or the amount and type of oil etc..
> But again, you have to have an accurate, calibrated torque wrench to
> establish the starting point.
> Anyway this is a complex subject with many aspects, which i am no expert
> at, or have alot of data on, however at regular job i am involved in bolt
> torque, but its in a structural sense, bridge/building etc.
> Do what you think is best for you, but in conclusion, after you do your
> 90+90, set the wrench at 37ftlbs, if it clicks off easily you may or may
> not have a problem. on the low end try 33, if you are under this you may
> want to double check your work.
> rod neff
Great post on a mysterious subject from Rod.
Having tried re-torquing the head studs this weekend, I think the 90+90
method is inherently unworkable and a method using a max torque figure, as
Rod suggests, makes more sense.
While I can't argue with the materials engineering which leads to angle
rather than torque specs, I can say, the angle can't be done as stated
especially on re-torquing. That's because when you are looking for a light
force set-point (like 20 Nm or 15 ft-pds), the torque wrench will have a
plausible range of maybe 90 degrees or even more. That means that the final
setting will be within 90 degrees of a rotation which is a big distance on
these large threads.
My impression was that setting to 35-40 ft-pds works just fine (and is
roughly what the 90-90 method leads to, roughly).
Yes, I know, if you use a clicker, it will click somewhere uniquely (that's
the click, right), but just how stable is that "somewhere" point? I'm not
saying that any torque setting is precise, but it gives me a bad case of
nerves to crank 180 degrees on a cylinder stud from a vaguely defined
BTW, I went to 8 and 13 on the valves (from 5 and 10) and the engine seemed
to have a welcomed added bit of mildness. Prolly just imagination. No extra
noise evident. Idle went up 200 rpm... just as well, you get less nasty
engine braking in first gear.
Replaced two-electrode Bosch FR6s with cooler trick NGK iridium BKR7EIX,
about $10 each. My impression is that shrouding the plug with numerous
electrodes is never beneficial (you get only one spark at the most) and was
done only to ensure long service intervals. With the pricey iridiums, the
service interval is long (not that any of us wait long) but the center and
side electrodes are very cut down thus aiding mixture and ignition flow.
Overall size seems identical. With my Techlusion 1031, prolly just gilding
the lily, but might help others who don't want to take the Techlusion route.
Denso iridiums have even a finer center wire electrode but hard to find.
End of oilheads-digest V2 #87