By the way, here's some common stretch specs for ARP bolts, along with a
little more discussion on torque VS stretch from a website I found. The
angle method scares the heck out of me--I don't know why. It feels like
"tighten it down till it breaks and back off half a turn". I don't
remember the URL, I saved it as text in my Triumph resource file:
For any fastener to supply clamp loads high enough to keep the parts
bolted together, it must be stretched the proper amount. Torque does not
measure bolt stretch, it measures friction. This is why we prefer the
stretch method or the torque and angle method for tightening rod bolts.
To use the stretch method, measure and note the free length of each bolt
before tightening with a stretch gauge or a micrometer with ball end
attachments. Then, using the chart below, tighten the bolt until the
proper stretch is achieved.
The torque and angle method uses the lead of the thread to stretch the
bolt the proper amount. To use this method, simply torque the bolts the
amount listed in the chart below (this low amount of torque snugs up the
bolt and removes lash). Then, using a Snap-On #TA360 torque angle gauge,
turn the bolt the listed number of degrees.
Bolt Type Recommended Stretch Torque & Angle
5/16 - Oliver/ARP 3.5 .0052" to .0057" 10 ft lbs + 55 deg
3/8 - Oliver/ARP 2000 .0052" to .0057" 25 ft lbs + 50 deg
3/8 - Oliver/ARP 3.5 .0057" to .0061" 25 ft lbs + 55 deg
7/16 - Oliver/ARP STD (Black Bolt) .0048" to .0055" 30 ft lbs + 40 deg
7/16 - Oliver/ARP WSB .0053" to .0058" 30 ft lbs + 40 deg
7/16 - Oliver/ARP 3.5 .0060" to .0065" 30 ft lbs + 50 deg
As a final check to make sure no bolts were missed: Before bolting the oil
pan on, set a torque wrench at 50 ft lbs (use a wrench set at 30 ft lbs
for 5/16" bolts), and check all rod bolts. If any bolt turns before
reaching the preset torque, it has not been properly tightened. You must
loosen these bolts and tighten them properly.
-----Original Message-----
From: Bill Babcock
Sent: Tuesday, February 11, 2003 10:39 AM
To: 'John Wilkins'; FOT@autox.team.net
Subject: RE: Retorquing head gaskets
I think everyone is on the right track. The complicating factor is how
much everything moves. These are very strange engines. We have a cast iron
block, steel sleeves, cast iron head, some very long and relatively short
bolts, none of which are through-bolts. All these things are heated
differently and cooled differently. Then we have a wide array of
gaskets--composition, copper clad, steel clad, steel shim, steel shim with
copper wire, and solid copper.
One answer for all? I doubt it.
I always retorque the heads--why wouldn't you? I'm not that committed a
spectator, so I tend to fuss around my car in the pits. If I set the
valves I usually torque the heads first. Every so often you find a bolt
that has loosened a little somehow. If you use either composite or shim
steel with a copper ring, you'll see a substantial change after a heat
cycle. Not just once--you see it six months later.
A bigger question is are the bolts dry or lubricated. That's a much bigger
variable than the heat cycle. If you torque a bolt to it's published spec
dry the chances of pulling out the threads or breaking the bolt are very
low. If you use a very effective (for sliding friction) lubricant then the
same torque will rip out the threads or break the bolt. I got obsessive
about this issue after I broke a long head bolt at the base of the thread
way down inside the block in the pits before the Monterey Historics.
Most torque specs assume a motor oil lubricated bolt. If you want to
really do it right, you need to find the stretch specification for each
bolt you are using, lubricate it with the lube you intend to use, put the
bolt in a fixture that will allow you to measure stretch, torque it to the
stretch spec and read the torque value. Then always use that lube with
that bolt.
With bigger or longer bolts, motor oil or dry torquing will give highly
variable numbers when you torque to a stretch spec. The torque jumps as
the bolt sticks and slips. The super slick stuff supplied with high
quality bolts is too scary to use--on a cheap bolt you'll exceed stretch
specs way before you see any significant torque.
Gear oil works okay, but I've settled on a cheap, readily available
anti-seize compound that I use for everything. I've also gotten allergic
to split lockwashers. Spending any time investigating bolt torque and
stretch will convince you they are a tool of Satan. Instead I have big
bottles of every type of locktite. I'm gradually eliminating lockwashers
from everything.
For simplicity sake I torque the long and short head bolts the same, even
though they really do require different torques to reach spec stretch.
With a shim steel gasket and copper wire rings with anti-seize on the nuts
and good, hard washers (no nicks on them either) 65 pounds is good. After
a heat cycle I remove the nuts one at a time, re-lube lightly, and
retorque to 65.
So far, so good.
Sounds like too much trouble, but it only took me a couple of nights to
make a fixture and test the bolts (I just drilled lengthwise through a 2"
thick chunk of steel I had, put a nut and locknut on the bottom end of the
bolts, and borrowed a big micrometer to measure bottom to top of the bolt
at five pound increments), and retorquing takes about an hour.
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