Torque is a force applied to an object that tends
to rotate that object. When parts are fastened together with screws,
the torque applied to these screws determines the pressure holding the
parts together. The more torque we apply, the tighter the parts are
held together. The correct torque takes into consideration factors
such as strength of the screw, the threads engaged, the cylinder material,
thermal expansion, etc. Equally important as the correct torque is
the sequence and stages by which these screws are tightened. Follow
the proper tightening sequence and tighten the fasteners to 50%, then to
75%, and finally to 100% of the desired torque.
Torque is measured as the amount of force times
the length of the lever arm. As an example, 12 in-lb. means 12 lb.
applied to the end of a 1" lever (or 1 lb. applied to the end of a 12"
lever). The Tork-It Model 36 is a release type device that releases
at the preset torque. It complies with ANSI Type 3, Class A, Style
1, Screwdriver Grip torque wrench standards. You cannot apply more
than the preset amount of torque.
Specific torques for model engines run from 7.5
in-lb for 2.0mm (valve cover) screws to 24.0 in-lb for 4.0mm (cylinder
head) screws. If you apply 5 pounds of force to the end of a typical
L-shaped (2 3/8" long - 3.0mm) socket head wrench, you have applied approximately
11.9 in-lb of torque to that screw. If you apply that same force
1/2" from the end of that wrench you have applied about 9.4 in-lb of torque.
That is a 25% difference in torque applied. To properly torque the
head of your favorite 1.2 engine to 21 in-lb, (using the L-shaped wrench
above), you should first apply 4.63 lbs. to each of the head screws in
alternate rotating sequence, then 6.73 lbs., and finally 8.84 lbs. to reach
a final torque of 21 in-lb. Who can tell the difference between 4.63,
6.73, and 8.84 lbs. of force as well as the exact place you are applying
force on the L-shaped wrench? The entire procedure is very
simple with a torque screwdriver. You simply set the amount of torque
desired and the device releases at that torque. In the above case
you would tighten the head screws to 12 in-lb on the first pass, 16 in-lb
on the second pass, and 21 in-lb on the final pass (observing the alternate
rotating sequence). No professional mechanic would consider working
on your automobile, your lawn mower, or even your weed eater without the
appropriate torque equipment. Chances are your model engine cost
more than your weed eater and perhaps more than your lawn mower.
Why settle for less with your model engines? Although many factors
affect engine performance, correct assembly is the first step to longer
engine life, improved reliability, and more consistent performance.
Torque Considerations
-
Never use your torque instrument to hammer or pry.
-
Never use a torque device as a breaker bar.
-
Always store your torque instrument set below 25%
of capacity.
-
Loosen all screws before re-torquing.
-
Clean fasteners and apply a film of lubricant (anti-seize
compound).
-
Be sure threads and threaded holes are clean.
-
Use alternate diagonal tightening sequence.
-
Tighten in at least three stages, 50%, 75%, and finally
100%.
-
Never torque hot equipment - let it cool first!
|
Recommended Maximum Torque
(steel screws into aluminum)
|
Screw Size
|
Torque
|
Socket Size
|
| 2.0 mm |
5-7 in-lb |
1.5 mm |
| 2-56 |
6-8 in-lb |
5/64" |
| 2.5 mm |
8-10 in-lb |
2.0 mm |
| 4-40 |
12-14 in-lb |
3/32" |
| 3.0 mm |
13-15 in-lb |
2.5 mm |
| 5-40 |
14-16 in-lb |
3/32" |
| 6-32 |
17-21 in-lb |
7/64" |
| 4.0 mm |
20-24 in-lb |
3.0 mm |
| 8-32 |
22-26 in-lb |
9/64" |
| Use the higher values for head screws with longer
thread engagement and the lesser values for back plates, valve covers,
carbs, etc. |
|
Glow Plugs
|
1/4-32 Standard Glow Plug: 20-24 in-lb (with
gasket)
More torque may be needed for glow plugs in
high performance / high RPM applications (18,000+) |
| There are many small sets of 1/4" drive hex bits
on the market. I sell top quality (US made) 2"-long bits. The 2" length allows you to get
past cooling fins.
Good Luck, Good Flying, and Thanks,
John W. Snider (Owner)
It's easy to order from TORK-IT!
Just call 770-736-0613
Fax: 770-736-0916
or click on the e-mail button.
1250 Kelvington Way
Lilburn, Georgia 30047
|
©1998-2000
John Snider
|
