Anyone who has serviced engines (as well as certain driveline and chassis components) that date from roughly the early 1990s to the present is aware that many OE threaded fastener tightening requirements call for a combination of torque-plus-angle specifications as opposed to a torque-only spec. Common applications for this procedure include but are not limited to cylinder head fasteners, main cap fasteners and connecting rod bolts.
Regardless of how silly the extra step of angle tightening may seem to some people, there is a legitimate reason for this approach…it’s better.
Remember that clamping load relies on bolt stretch (taking advantage of the bolt’s elastic properties). Since fastener engineers already know how much stretch, and therefore clamping load, will occur based on how far the 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 parent material contact surface (for example, where the bolt head contacts a cylinder head), and by the friction of the thread engagement. The type and amount of oil/lubricant on the threads provides yet another variable in terms of friction.
Depending on how smooth and burr-free 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. If enough friction is created by these variables, a reading of, say, 60 ft. lbs. on a torque wrench may in reality only provide the equivalent of (for example) 47 ft. lbs. that actually works to stretch the bolt. And if the bolt was designed to stretch to its just-short-of-yield point at a true 60 ft. lbs., this inadequate bolt stretch will mean insufficient clamping load. (which, in the case of cylinder head bolts, for example) can lead to a gasket leak or gasket failure down the road.
Torque-plus-angle simply provides a more accurate method of achieving the needed clamping load.
If published tightening specs only call for torque, then tighten accordingly. But for later model (domestic and import) applications that specify a torque-plus-angle method, you MUST follow those procedures in order to achieve design clamping loads.
Previously in order to achieve final angle-tightening, common methods included placing a reference mark (paint or pen) on the bolt head, and observing the angle of rotation (a “close enough” guesstimate of a movement of 90 degrees, or 45 degrees, etc., which is “close” but certainly not repeatable or consistent, or accurate). Another method is to use an inexpensive specialty tool that consists of a plastic or metal incremented dial that is placed onto a wrench drive, between the drive square and the socket wrench (angle gauge or protractor). This works, but it’s time consuming (torque to the required spec, remove the torque wrench, grab another square drive wrench, place the dial gauge onto the drive, attach a socket wrench to the dial gauge, re-attack the fastener and tighten to the required angle). Plus, if you bump the angle gauge or protractor, you lose your reference point, which means that you need to loosen the fastener and start over.
Thanks to advancing technology and the efforts of quality tool manufacturers such as Snap-On, those days are gone, providing you pony-up and take advantage of a new precision tool system.
TECHANGLE MODEL SPECS:
MODEL SQ. DRIVE ft.-lb. Nm in.-lb. Overload Length
ATECH1FR240 ¼ in. 2.0-20.0 2.7-27.1 24-240 25 15 in.
ATECH2FR100 3/8 in. 5.0-100.0 6.8-135.6 60-1200 125 17 in.
ATECH3FR250 ½ in. 12.5-250.0 16.9-338.9 150-3000 312 26 in.
NOTE: When ordering your Tech-Angle wrench, be aware that different versions are available in terms of torque formats. If the model number ends in the letter “N,” this indicates that torque readings are only available in Nm (Newton meters). If you want to have a choice between Nm, ft-lb and in-lb, the model number should feature the letter “A” at the end (for example: ATECH3FR250N reads in Nm; while ATECH3FR250A provides options of Nm, ft.-lb. and in.-lb.). I learned this the hard way. The first unit I received was Model ATECH3FR250N. When I fired it up, I quickly realized that I didn’t have the option of switching to ft.-lb., since it only offered Nm. I swapped this out for ATECH3FR250A, which offers all three formats (Nm, ft.-lb. and in.-lb.). Of course, if your shop torques all fasteners in units of Nm, the dedicated Nm version (suffix N) would be ideal.
The Snap-On TECHANGLE wrench digitally displays and monitors both fastener torque and angular rotation. The wrench functions as an adjustable torque wrench, as you’d expect, and also functions as an adjustable angle wrench, simultaneously monitoring torque to prevent fastener or wrench overload.
The preset values are programmable from 5% to 100% of full-scale torque and 5 to 360 degrees of rotation. The scrolling digital display rolls over at both ends for convenient and quick setting.
If the wrench is used beyond 100% torque capacity, an audible tone will pulse rapidly to warn the user to stop.
To preset the wrench, select unit of measure (Nm, ft.-lb., in.-lb. or degrees). Use the UP/DOWN keys to set the torque value or angle degrees required.
In the torque display mode, the display shows the torque preset value until 5% or more of full scale torque is applied. The display then switches to TRACK mode, showing the applied torque in real-time. When applied torque is within 2% of the preset value, the buzzer will sound for ½ second and the handle will vibrate until the applied torque is released. At torque-release, the display shows the PEAK value applied (this flashes for 10 seconds). If torque is re-applied during this 10-desond period, the display will automatically switch to TRACK mode (again, to show applied torque in real-time). NOTE: If any button is pushed during this 10-second window, the PEAK value will be cleared.
In the angle display mode, the display shows the angle PRESET value. Angle measurement is held in reset until 5% of torque is applied. When applied torque is released, the accumulated torque and angle values will flash alternately for 10 seconds. The display will continue to accumulate if torque is reapplied within this 10-second period (this allows time for changing the wrench to reverse ratchet motion if needed). When the accumulated angle equals the preset angle, the buzzer will sound for one second and the handle will vibrate until torque is released. Once the angle preset has been reached, and once torque has been released, the total angle accumulation and the peak torque value will be displayed alternately for 10 seconds (or until any key is pushed). If the angle preset is reached and torque is released, angle accumulation resets to zero automatically. This provides time to move to the next fastener (this gives to 10 seconds to move to the next fastener without the need to re-program).
I first dropped three fresh AA batteries into the grip (unscrew the end-cap, insert all three batteries with positive end first and reinstall the cap, being careful not to cross-thread the cap. If you do cross-thread the cap, proper contact won’t be achieved and the unit won’t power-up). For the sample test, I chose a 1999 GM 5.3L cast iron block (LS type). The main caps utilize four 10mm primary bolts and two 8mm side bolts per cap. The inboard cap bolts call for an initial torque value of 15 ft-lbs, finished with 80 degrees of rotation. The outboard 10mm bolts (these feature stud tips for the oil pump pickup and windage tray) call for an initial 15 ft.-lbs. followed by 53 degrees of rotation. Once the 10mm main cap bolts are fully tightened, the 8mm side bolts are snugged to a value of 18 ft.-lbs.
During tightening of the inner and outer main cap bolts on this 5.3L block, I preset torque at 15 ft.-lbs. With the Tech Angle wrench set to the ft-lb mode and set at 15 ft-lb, I began to apply torque. The instant I hit 15 ft.-lbs., the alarm sounded, instantly followed by very noticeable grip vibration and a buzzing sound. I torqued all of the inner and outer cap bolts (in proper sequence) to this initial 15 ft-lb value. I then pressed the “U” button to switch to angle mode, and adjusted desired angle to either 53 or 80 degrees (remember: the LS calls for two different angle values, for inboard and outboard cap bolts). As I tightened each bolt, as soon as I reached the programmed angle value, the alarm sounded, instantly followed by grip vibration and buzzing. If all cap bolts called for the same angle value, I could have simply preset one angle value and finished tightening. However, because this wrench allows you to quickly re-adjust values, switching from 80 to 53 degrees (depending on which bolt location I needed to address), the task went quickly (immensely faster than if I was forced to use an angle gauge).
The audible and vibration alerts ensure that you’re instantly and clearly informed of reaching your preset value, even in the noisiest of shops. If you can’t hear the chirp or buzz (you’d have to be deaf not to hear this), you’ll definitely feel the vibration in the grip. I found this tool not only easy to use, but quick and repeatable. And because of the projection hump on the grip, I could lay the wrench onto my workbench without fear of it rolling off. The 15-degree pivot built into the drive head comes in handy too, especially when a nearby object is slightly in the way of your tightening path.
I won’t try to toss any BS here…. admittedly, this tool is expensive (at a suggested list of about $515), but as we all know, quality precision tools are never cheap. Considering it’s precision, construction quality and it’s time saving capabilities, it’s a solid investment, especially for the technician who cares about the quality of his work (notice how often I refer to the word “precision?” It’s not an accident. This is one of the crown jewels in my engine assembly room).
The grip features not only a rubber surface for non-slip and comfy operation, but a forward “nub” stand is placed at the front of the grip area. This prevents the tool from rolling off of a table (very cool feature that all torque wrenches should have). Also, the sealed key pad prevents dust and grit. Actually, construction of the entire tool is designed to be splash proof, protecting the tool from water and most shop chemicals (I don’t recommend using the tool underwater during submarine maintenance, but it should survive your shop environment).
Also, the flex head pivots 15 degrees in either direction (up/down), for convenient fastener access, without screwing up torque or angle calibration. Also, once you’ve pre-set your torque and angle once torque is reached (the alarm sounds and the handle vibrates and buzzes), simply press the “U” button to switch to angle mode and continue to tighten. Once the preset angle is reached, the alarm sounds and the handle vibrates and buzzes. And, you can actually ratchet during angle tightening. According to Snap-On, this is achieved by using angle calculations based on the same gyroscope technology featured in helicopters (how cool is that?).
I love tools. I use them, and sometimes abuse them, but I still get excited when trying out a new tool (hand tool, pneumatic, electric, etc., it doesn’t matter). This new torque/angle wrench is an absolute funfest. It’s handy, it’s a quality precision tool and it works as designed. It just doesn’t get any better than that. In the future, every time I need to perform a torque-plus-angle tightening on a bunch of head bolts, I’ll be smilin’.
TO AVOID WRENCH DAMAGE
- Never use this wrench with the power turned off.
- Do not press the ON/RESET button while torque is being applied or when the wrench is in motion.
- Never use this wrench to break fasteners loose (the same holds true for any torque wrench).
- Do not use extensions (such as a pipe) to extend the length of the handle.
- Check that the wrench capacity matches or exceeds each application before proceeding.
- If the wrench is dropped, calibration must be re-verified.
- Always make sure that the ratchet direction lever is fully engaged in the correct position.
- Don’t force the head of the flex-head against the stops.
- Always pull (never push) on the wrench handle, and adjust your stance to prevent a possible fall if something slips/fails.
OUR TEST TOOL SPECS
HEAD TYPE………………Sealed flex head
GEAR ACTION…………….10 deg.
HEAD WIDTH……………1 5/8-in.
RANGE IN-LB…………….150 – 3,000 in.-lbs.
RANGE FT-LB…………….12.5 – 250 ft.-lb.
RANGE Nm………………..17.5 – 340 Nm
ANGLE RANGE……….5 – 360 degrees
OPERATING TEMPERATURE…..40 – 110 degrees F
STORAGE TEMPERATURE……..0 – 122 degrees F
DISPLAY……………Four-digit LCD, unit of measure, angle, CCW and battery condition
OVERALL LENGTH…….26 in.