TURN, TURN, TURN:
TORQUE
WRENCH
TECH
BY MIKE MAVRIGIAN
When fasteners
must be tightened, many are
too important to
rely on a sense
of feel. In these
situations, the
correct use of a
torque wrench
is essential.
34
June 2009
stationary needle that runs the length of
the shaft handle. The needle indicates
applied torque against a printed scale located at the base of the handle. This type
of torque wrench offers no preset limit,
and there’s no felt or audible “release”
when a specific torque value is reached.
The dial indicator type of torque wrench
features a readout for visual display. Both
the flex bar and dial indicator types provide visual displays of applied torque.
The sound-indicating type signals applied torque by momentarily releasing
the wrench a few degrees when the preset torque value is reached. The release
is usually accompanied by a “click”
sound. However, some release-type
torque wrenches will release upon reaching the preset torque, but may not provide an audible click. The release/click
type wrench is adjusted by means of a
micrometer scale on the handle.
When a torque wrench releases momentarily and/or clicks, this is referred
to as a signal type. Indicator type refers
to the visual display units such as the
flex bar or dial indicator style.
Any adjustable torque wrench should
be set at its lowest torque reading when
not in use. If left stored for long periods
at a high-torque setting, the accuracy
may be affected. When you’re done
with a torque wrench, readjust it to
the minimum setting before storing it in the toolbox.
A torque wrench is a precision
instrument that should never be
used—abused!—as a pry bar or
disassembly/assembly tool. It
should be used to achieve final
clamping load only. Handle
all of your “wrenching”
duties with common
wrenches, and use
the torque wrench only as the final adjuster to reach a specific torque level.
When using an adjustable torque
wrench, be careful not to overtighten by
applying torque past the release point.
At very low settings, the “click” may not
be heard, especially in a noisy shop. It’s
best to become familiar with the feel of
the release, rather than to rely only on
the sound of a click.
When using an indicating type torque
wrench (such as a flex bar or dial indicator type), try to read the indicator with a
straight-on view of its surface. Reading
the indicator at an angle will provide errors due to incorrect line of sight.
Most torque wrenches operate accurately only when held at the center of
their handle grips. Don’t use cheater
bars to extend your grip farther away
from the wrench head, and don’t grab
the handle closer to the wrench head.
Pick the Right Tool for the Job
Not all torque wrenches are universally
adaptable to all jobs. It’s important to
choose one that features your torque
value requirement in the middle of its
range. For instance, if you need to tighten a fastener to 100 ft.-lbs., don’t use a
torque wrench model that has an upper
range limit of 100 ft.-lbs. Instead, use
one that features a range of, say, 25 to
250 ft.-lbs. If tightening a fastener to 50
ft.-lbs., use a torque wrench that has an
upper limit of about 100 ft.-lbs., and so
on. So you may need torque wrenches
with different ranges, depending on the
type of work that enters your shop.
To some technicians, this may seem
like an unnecessary expense, but if you
use torque wrenches at all, the whole
point is to attain accurate and repeatable clamping values. So go the extra
mile and maintain several torque
wrenches, each with a different low-tohigh value range. The moral of the story: If you own only one torque wrench
June 2009
35
Photos: Mike Mavrigian; visual effects: Harold Perry
A
torque wrench measures
the amount of turning
(rotational) force applied
to a threaded fastener
(nut or bolt). Torque
wrench scales usually
read in foot-pounds (ft.-lbs.) or inchpounds (in.-lbs.) and Newton-meters
(Nm). Many torque wrenches provide
dual scales, for reading in either English
or metric format. With the foot-pounds
scale, one foot-pound equals one pound
of pull on a 1-ft.-long lever arm.
There are three basic types of torque
wrenches commonly used for automotive applications: flex bar, dial indicator
and sound-indicating (micrometer). The
flex bar type
(also called the
scale type or
beam type)
features a
TORQUE WRENCH TECH
Owning a selection of torque wrenches is a good idea.
Shown here are (top to bottom) a 1⁄4-in.-drive in.-lb.
wrench, a 3⁄8-in.-drive micrometer type ft.-lb. with a
range of 10 to 100 ft.-lbs., a 1⁄2-in.-drive beam type and a
1
⁄2-in.-drive ft.-lb. with a range of 20 to 250 ft.-lbs.
that you try to use for a wide variety of
work, you won’t be able to achieve accurate clamping loads for all jobs.
Precision Instrumentation
Another, very high-tech approach is to
use an electronic torque wrench, an example of which is Sunnen’s computerized ETW-125 Sensor I. This high-precision torque wrench brings laboratory
accuracy into the engine repairer’s and
builder’s shop.
This tool allows you to tighten a bolt
to its torque-tension yield point without
even knowing what the specs are. The
wrench has four different tightening
modes—angle control, where you can
tighten to a prespecified angle (from the
initial “snug” torque); torque control,
where you can tighten to a prespecified
torque; yield control, allowing you to
tighten until the torque-tension yield
point is reached; and dynamic torque
A torque wrench that has been recalibrated and serviced
should feature a label that indicates the service location
and date of service. This will help to remind you of when
the next recalibration service might be needed.
audit, which allows you to determine the
existing torque of a tightened fastener.
The head of the tool features a strain
gauge and a potentiometer that detects
torque and angle, respectively. The
body of the tool features an easy-to-read
digital display and four control knobs. A
reset button clears the memory and
readies the tool for the next tightening
task. A series of LED status lights provide instant information about the
torquing operation.
This is more than a glorified torque
wrench, since the tool is capable of actually determining where bolt yield
takes place, eliminating guesswork. The
tool will not only find the precise yield
point of a fastener, it will verify if a fastener is acceptable. In other words, it’ll
find bad bolts. This tool eliminates the
need for a connecting rod bolt length
gauge, and offers the opportunity to
reuse some torque-to-yield (TTY) bolts.
If you can accurately verify that a TTY
bolt is good, then it’s safe to reuse it.
More on TTY bolts later.
An electronic torque wrench also has
the uncanny ability to determine the existing torque of a tightened bolt. It actually audits the torque of a fastener without the need to loosen it! According to
Sunnen, the most effective way of auditing a fastener’s torque is to tighten
the fastener further by a small, precise
angle, then measure the instantaneous
torque. It’s all a matter of complicated
mathematical algorithms but the bottom line is that it does the job, and it’s
very easy to use.
Another firm, RS Technologies, offers
an array of fastener verification equipment, referred to as “Torque-Angle Signature Analysis.” This sophisticated electronic equipment is compact (laptop
size), and allows you to monitor fastener
torque, angle, bolt elasticity and clamp-
Always support the head of the torque wrench with your other hand (left photo), to help stabilize the socket angle at the
fastener head. And always grip the wrench at the center of the grip area only (right). This provides increased accuracy.
36
June 2009
TORQUE WRENCH TECH
ing force, with a special torque wrench
fitted with a transducer hard-wired to
the computer. I saw one of these units at
the Perfect Circle machine shop school,
and it was pretty wild. Watching the
monitor, you can see exactly what the
bolt is doing, as it happens. You can also
save the information, make a printout or
download it onto a disk. RS Technologies makes several of these systems. The
most compact is the Model 960 Hand
Held Transient Recorder.
Thanks to advancements in technology, torque wrenches are now available
that allow you to achieve both torque
value and applied rotation angle without
the need for a separate angle gauge.
One example is Snap-on’s Techangle series of wrenches. Featuring sensor electronics and digital control and readout,
you can preset (program) the torque value you want, or both torque value and
final applied angle, depending on your
needs. The electronic control allows you
to also choose between in.-lbs., ft.-lbs. or
Nm, plus angle. Two models are cur-
rently available—ATECH2FR100, with
a torque range of 5 to 100 ft.-lbs., and
ATECH3FR250, with a torque range of
12.5 to 250 ft.-lbs.
Torque wrenches with similar capabilities are available from Mac Tools,
Matco, GearWrench and others.
Recalibrating Torque Wrenches
A busy shop should plan to have its
torque wrenches recalibrated once each
year at a minimum. Also, anytime a
torque wrench has been dropped, it
should be rechecked for calibration.
Torque wrenches are delicate, precision
pieces and, like the strings of a guitar,
simply will not remain in perfect tune
without care and routine maintenance.
By virtue of the environment in
which they operate, torque wrenches
can be subjected to a great deal of wear.
When used in an engine rebuilding shop
that lives and breathes precision torque
values, this wear level is at its zenith,
even in the best-intentioned hands.
While it’s certainly not recommended
Circle #18
38
June 2009
to toss this precision instrument around
the shop like a soccer ball, an occasional
oops! may not cause severe calibration
changes (we say “may” because it’s always possible for any hard impact to
damage the tool). If badly abused, the
wrench can be internally damaged if the
impact force is severe enough. Bottom
line: Don’t bang the thing around. Treat
it for what it is—a precision instrument
that deserves respect and care.
The most compelling reasons to send
your torque wrenches out for recalibration include life cycle and overtorquing.
If the wrench is used very infrequently,
it may require recalibration only every
five years or so. However, if it’s used on
a regular basis in a professional shop,
the operating cycles increase dramatically. Depending on how much engine
work your shop performs on a regular
basis, the number of torque wrench cycles could easily reach 10,000 to 20,000
per year. When you add in the other
miscellaneous torquing applications (oil
and water pumps, exhaust manifolds,
repairing shop equipment, etc.), even a
small shop can easily run well over
20,000 cycles per year.
When installing wheels (OE or custom aftermarket), final tightening of the
wheel fasteners should always be done
with a torque wrench, to manufacturer
specifications. This is especially true
with late-model thin-hat brake rotor
hubs, since uneven tightening can lead
to rotor disc warpage and a pulsating
brake pedal. If your shop installs wheels
at a rate of ten vehicles per day (for the
sake of example, let’s say all of the
wheels feature a five-bolt pattern), your
torque wrench will experience about
200 cycles per day, or about 4000 cycles
per month or 48,000 cycles per year.
If a torque wrench is not used properly, accuracy can be affected, possibly resulting in overtorque (stretched cylinder
head bolts or stripped bolt holes in the
block, etc.), inadequate torque or uneven
torque. Remember, when tightening a
cylinder head’s fasteners, uneven or excessive bolt stretch can result in uneven
or inadequate clamping. This uneven
clamping force can lead to cylinder head
warpage, coolant leaks, combustion leaks
and even cylinder head cracking.
When using any style of torque
wrench, it’s critical to stop as soon as the
desired torque value is achieved. In the
case of a click-type torque wrench, stop
applying force the moment the click is
heard or felt. The typical user tends to
stop too late, achieving about a 10% increase in applied torque. On a critical
application such as engine assembly,
this can create a real problem. For example, if the specified value is 110 ft.lbs. and the operator continually exceeds the “stop” signal, he could be applying 121 ft.-lbs. or more (and often in
an uneven format, with multiple fasteners on the same component).
Click-type micrometer style torque
wrenches have an internal spring that’s
preloaded via a screw adjustment when a
new wrench is calibrated. When you feel
or hear the click, you’re working against
the spring and a cam mechanism. Overtorquing past the selected setting abuses
the spring and will definitely cause an
out-of-calibration problem.
Torque wrench calibration has a finite
life span. Every click on a torque
wrench represents one cycle of use. All
torque wrenches probably need to be
recalibrated or at least retested after
5000 cycles (although some manufacturers recommend recalibration after as
many as 10,000 cycles). Granted, 5000
cycles may seem like an extraordinary
amount, but as we mentioned earlier,
that level of use can easily occur in less
than six month’s use in a machine shop.
Most torque wrench manufacturers recommend that their products be recalibrated at least once each year under
normal use. However, torque wrench
operation in a busy engine rebuilding facility hardly qualifies as “normal” use. A
Circle #19
June 2009
39
TORQUE WRENCH TECH
A torque-plus-angle tightening specification involves first tightening the fastener to a specified torque using a torque
wrench, then rotating the fastener head by an additional number of specified degrees. An angle gauge, such as this one by
Lisle (shown in the left photo), will speed up the job (it’s faster and more accurate than painting a dot on the bolt head and
guessing at the angle change). The photo on the right shows the angle gauge sandwiched between a socket wrench and a
ratchet. The gauge body is anchored to a nearby stationary object via a flexible arm and clamp, to prevent it from rotating.
routine recalibration schedule should be
established for any shop’s torque
wrenches.
Another aspect of torque wrench use
that can seriously affect calibration is
bidirectional use—using a torque
wrench in a counterclockwise direction
in addition to clockwise rotation. When
applying counterclockwise force through
a torque wrench that was designed for
clockwise rotation, you’re fighting a losing battle, because everything is stressed
internally to favor the clockwise side.
This left-hand application of force must
overcome the built-in right-hand stress.
Calibration on the left-hand side can be
severely out-of-spec. The result is that
you not only potentially damage the
right-hand calibration, you also arrive at
an unknown torque value when applying left-hand force. If you require lefthand operation, this can be specified
when ordering a torque wrench (or
when one is being recalibrated). If calibrated for left-hand pulls, the same
wrench should not be used for righthand pulls. If your shop performs lefthand torquing on a fairly routine basis,
it’s best to dedicate that torque wrench
as your left-hand device, and label it accordingly, although I don’t see this as a
common requirement for the average
shop.
Recalibration is required for all types
of torque wrenches. Regardless of the
design, all feature moving components
that can stress or wear out. A great misconception with regard to torque
wrenches relates to the ratcheting fea-
40
June 2009
ture of the click-type version. Some users
commonly believe that the tool is a ratcheting wrench that also measures torque
value. As a result, some users tend to use
it to install as well as final-tighten fasteners. In reality, a torque wrench should
never be used to initially install a fastener. The bolt or nut should be installed to
“finger-tight” or “snug” force with a conventional wrench (fixed wrench or ratchet and socket), and final-tightened to value using the torque wrench.
As for the cost of recalibration, not
every recalibration service shop will
charge the same amount. However, in
order to gain a ballpark idea of this cost,
I contacted the folks at Angle Repair
Service (a premier torque wrench recalibration and testing facility in Beckley,
WV, that’s used by a number of the leading wrench manufacturers). Angle’s typical recalibration fee is $25. Turnaround
time is 24 to 48 hours, which means that
for only $25, your torque wrench will be
back in service in a heartbeat.
Use of Adapters & Extensions
As long as the adapter (socket extension, etc.) is in-line with the torque
wrench drive, no compensation is required. However, if an adapter that effectively lengthens the wrench is used
(such as a crowfoot wrench), a calculation must be made in order to achieve
the desired torque value.
For those occasions when a straight
socket can’t be used, a special attachment might be needed (such as a crowfoot). The use of an offset adapter
changes the calibration of the torque
wrench, which makes it necessary to
calculate the correct torque settings.
Following is a method of calculating
this change:
E⫽Effective length of the extension,
measured along the centerline of the
torque wrench.
L⫽Lever length of the wrench, from
the center of the wrench drive to the
center of the adapter’s grip area.
TW ⫽Torque setting on the wrench.
TE⫽Torque applied by the extension
to the fastener.
Formulas:
L ⫼(L⫹E)⫻TE ⫽TW (where the
adapter makes the wrench longer)
or:
L ⫼(L⫺E)⫻TE ⫽TW (where the
adapter makes the wrench shorter)
If you want to know where to set the
torque wrench when using an adapter
that alters the effective length of the
wrench, you must calculate to compensate for the adapter. If the distance from
the wrench drive to the center of the
bolt makes the wrench longer, the final
wrench setting must be adjusted to a
lower value. If the distance from the
wrench drive to the bolt center makes
the wrench shorter, the wrench must be
set to a higher value.
Let’s say you want to torque a bolt to
140 ft.-lbs. but you’re using a crowfoot
adapter. Let’s say the length of the
torque wrench is 12 in. (from center of
the handle to center of the drive). Let’s
also say that the crowfoot is aiming away
from the wrench drive, making the distance from the center of the wrench
drive to the center of the bolt 1 in. This
makes the wrench 1 in. longer. In this
case, you’d divide the length of the
torque wrench (L, from the center of
the handle to the center of the drive) by
L+E, then multiply that ratio by the desired value.
In this example, the formula is:
the connecting rod base material, at
least consider the potential compression
of the material itself during bolt clamping. As the bolt is tightened, the head of
the bolt tends to embed itself into the
rod, slightly compressing the stock material. Production rods are typically softer, allowing the head of the rod bolt to
sink in, until the material under the bolt
head work-hardens under compression.
Torque-to-Yield Bolts
12⫼(12+1)⫻140⫽.923⫻140⫽129
So in this case, where the crowfoot
adapter has made the torque wrench 1
in. longer, the wrench would be set at a
value of 129 ft.-lbs. to achieve the desired value of 140 ft.-lbs.
If the crowfoot is aimed toward the
handle (turned 180° from the prior example), and we still want to achieve 140
ft.-lbs. of torque, we know that the
adapter has now made the wrench
shorter (because the center of the bolt
is now closer to the center of the
wrench handle), then the formula is:
Using an extension extends the leverage point further than the torque
wrench’s calibration, so you must use
a simple formula to compensate for
this extended leverage factor. Not
compensating for the extension results in overtightening.
12⫼(12-1)⫻140⫽1.0909⫻140⫽152.7
So in this case, where we want to
achieve 140 ft.-lbs. of torque but the
wrench has been made 1 in. shorter, we
adjust the wrench to a setting of 152.7
ft.-lbs. to actually achieve the desired
torque of 140 ft.-lbs.
In sum, if the adapter makes the
wrench longer, you must back off on the
adjustment setting. If the adapter
makes the wrench shorter, you must
raise the adjustment on the setting.
The Friction Factor
If a bolt is tightened using straight
torque, the desired preload may not necessarily be achieved due to the variable
of friction. Since we can’t predict the
frictional loss, measuring rod bolt stretch
provides the most accurate method of
ensuring that the clamping loads will be
sufficient for the task and that each pair
of rod bolts will achieve equal loads.
Bolt stretch is affected by a number
of factors, including tensile strength and
mass (the length of the bolt being
stretched). The effective diameter of the
bolt contributes to this. For example,
let’s consider two 3⁄8x1-in. bolts. One fea-
Wheel fasteners should be snugged
initially. Here a speed wrench is used
to initially tighten the wheel nuts, to
make sure the wheel is mated flush
with the hub face. Never use an impact gun for fastener installation. Final tightening should always be done
with a torque wrench—no exceptions! Apply tightening in the appropriate crisscross pattern to evenly
distribute the clamping load.
tures threads on the full 1 in. of shank
length. The other features only 1⁄4 in. of
thread length at the tip, with 3⁄4 in. of the
shank full diameter and smooth. The
bolt with partial thread will stretch less,
because the 3⁄4-in. shank area between
the head and nut engagement area has a
thicker cross section. The partial-thread
bolt has a .375-in.-diameter shank, while
the all-thread bolt has only a .324-in.diameter shank (due to the smaller root
diameter inside the thread path).
While we can’t control the reaction of
Once, it was common practice to retorque cylinder heads after an initial engine break-in period. This was necessitated by the expected relaxation of the
compressed head gasket after initial
clamping. In far too many of today’s engines, this procedure of retorquing simply isn’t practical, due to the extremely
difficult access to cylinder head bolts in
a crowded engine bay. While it’s still
easy to access the head bolts on a carbureted performance engine in a restored
muscle car, it’s a real pain to perform this
service on a late-model engine that features direct injection, a cumbersome upper intake plenum and a maze of wiring
harnesses, plumbing and vacuum hoses.
The engineering answer to this was
the advent of the torque-to-yield (TTY)
cylinder head bolt. When any bolt is
tightened (any threaded bolt or stud,
not just head bolts), it stretches by design. This is referred to as the bolt’s elasticity. This stretch creates clamping
force; the more the bolt stretches, the
greater the clamping force becomes...to
a point. When the stretch enters the
bolt’s yield point, the stretching (and
therefore its clamping force) stops, and
in fact begins to diminish.
A TTY bolt will stretch to a point, retaining its elasticity, and will be able to
spring back when tension is released.
Once it’s stretched to its yield point, it
stops generating tension. Stretched beyond that point, it will break.
The same phenomenon takes place
whenever a bolt is tightened. Ideally, we
want to stretch the bolt to just short of
its yield point. In that way, we take full
advantage of its clamping force without
yielding the bolt. When loosened, it will
spring back to its original length, retaining its elastic property.
A torque-to-yield bolt is designed to
June 2009
41
TORQUE WRENCH TECH
provide maximum clamping load on its
initial tightening, since we don’t expect
to return to the job by retorquing the
bolts in order to provide more crush for
a now-compressed head gasket. With a
TTY bolt, we arrive at full “long-term”
clamping load during the initial tightening process. When the gasket does relax, TTY bolts continue to provide sufficient clamping load to maintain an effective gasket seal.
TTY bolts are designed to be tightened within a small window of tension—just short of their yield point. The
torque spec for a TTY bolt is generally
higher than that of a standard (nonTTY) head bolt, because we’re taking
full advantage of the TTY bolt’s designed elastic range. If a TTY bolt was
used in an older engine, using old, nonTTY torque specs, that bolt probably
won’t stretch enough to provide the
clamping force it’s capable of. The likely
result is head gasket leaks. Likewise, if
new TTY specs (involving both torque
and bolt angle) are used on non-TTY
bolts, chances are you’ll stretch these
bolts beyond their elastic range, or
break them, or damage the female
threaded holes in the block. In short,
TTY bolts are designed to stretch more,
providing a long-term clamping load
without the need to retorque.
Most TTY cylinder head bolt specs
will involve both an initial torque (in ft.lbs. or Nm), plus a specific degree of
bolt head rotation, called torque plus
angle tightening. Regardless of how silly
the extra step of angle tightening may
seem to some people, there’s a legitimate reason for this approach.
Since bolt engineers already know
how much stretch, and therefore clamping load, will occur based on how far a
bolt head rotates, they use the angle of
bolt head movement to determine exactly how much load is being exerted.
A torque spec alone cannot be used
to exactly determine bolt stretch because of the friction variables that
come into play during tightening. A
certain amount of torque loss is caused
by the friction of the bolt head underside to the cylinder head contact surface, and by the friction of thread engagement. The type and amount of oil
or lubricant on the threads provides
42
June 2009
yet another variable in terms of friction.
Depending on how smooth and burrfree the bolt head contact area is, and
on how smooth and uninterrupted the
threads are on both the bolt and the female threaded hole, a torque reading
alone really can’t provide accurate and
consistent clamping load information.
The resistance caused by bolt head or
thread friction is read by a torque
wrench in the same way bolt stretch is
Top: This digital torque wrench display shows the selected torque value,
in this case, in Nm. Center: With the
press of a button, the window display
quickly converts to ft.-lb. format.
Above: For torque-angle applications, the display can show selected
angle as well. Whenever the selected
torque value or angle value is reached,
the tool emits an audible signal.
read—it’s all resistance to movement. If
enough friction is created by these variables, a reading of 40 ft.-lbs. on a torque
wrench may in reality provide the
equivalent of only 20 ft.-lbs. that actually works to stretch the bolt. And if the
bolt was designed to stretch to its justshort-of-yield point at a true 40 ft.-lbs.,
this inadequate bolt stretch will mean
insufficient clamping load on the gasket.
So, although some of us may not like to
deal with TTY torque and angle specs,
we really don’t have a choice.
Should TTY Bolts Be Reused?
This is an issue that will stir debate. A
TTY bolt is designed to stretch to a
point immediately prior to its yield
point. On that basis, it’s theoretically
possible to reuse them. Some carmakers claim it’s okay to reuse TTY bolts a
specific number of times. However, that
recommendation is based on the assumption that each bolt has been properly tightened in the past. Since you
have no way of knowing whether a TTY
bolt has been improperly tightened,
perhaps past its yield, the safest course
of action is to always use new TTY bolts
in every single application. This recommendation is also made by the leading
gasket makers, including Fel-Pro and
Victor-Reinz. In fact, Fel-Pro has released a number of tech bulletins on
this very subject, emphasizing the need
to replace TTY bolts in every case (refer
to Fel-Pro bulletins 4522-91, 4774-93,
4904S and 5052-96; and Perfect Circle’s
Machine Shop Service Bulletin CH-7).
Considering the cost of the bolts, it’s
cheap insurance to protect a costly engine rebuild.
When tightening a TTY bolt, you’ll
invariably have to meet both torque and
angle published specs. For instance, the
spec may dictate that the bolt is torqued
to 45 ft.-lbs., then tightened further by
degrees of bolt head rotation (let’s say
45°). Some bolt specs may ask you to
reach an initial torque, followed by several steps of rotation (20°, followed by
20°, followed by 10°, for example).
To apply a specified torque, obviously you’ll need to use a torque wrench
(needle type or click type). To tighten
the bolt further by angle, you’ll need an
angle meter. These are available as separate units that attach to the wrench.
They feature indexable needles and
provide a means of holding the meter
base in position (so that only half the
meter moves—either the needle or the
meter scale). This hold-down may be in
the form of a mechanical stop built into
the meter or a remote cable secured to
a convenient location on the cylinder
head via a clamp or magnet.
This article can be found online at
www.motormagazine.com.