When
rebuilding your car today, it is standard practice to torque most bolts to
a specified rating (usually in foot-pounds). But back in 1931
they hadn't yet developed this method. Instead they used
castle-nuts and cotter keys (for example on the connecting rods) to
prevent nuts from getting loose. Sometimes they
"punched" a mark along the edge of the bolt, or screw, which
then prevented road vibration from loosening the bolt (for example the
door hinges).
In this section, I have started to collect information about torque
settings that you can use instead of these older methods. (or,
in addition, to these methods) One of
the easiest places to first apply torquing specs is when you are
tightening the head
bolts. While there are NO torque references which specifically
apply to the 1931 Chevrolet, I've asked a lot of people and condensed
their best
guesses based upon the size and use of the bolt. To the best of
our knowledge, the range of settings are proper. Please let me
know if you find otherwise.
One other comment. Most good mechanics today use a thread-locker
product called Loctite when assembling nuts and bolts in critical
locations. We recommend that you use the semi-hard 242 version (Blue) when
tightening most bolts. With this applied, along with
the proper torque, you should have no problems with your bolts
becoming loose. Thanks.
|
Location |
Torque |
Use
Loctite? |
Camshaft
Collar |
- Original input was 1/4" bolts - use 25 ft-lbs?
- Comment: 25 ft-lbs on a 1/4 inch grade 8 bolts is
too much (1/4 Grade 8 is 10-12 ft-lbs.)
- Conclusion: Use 10-12 ft-lbs on "old"
bolts.
|
Yes with lock washer
|
Flywheel
|
- 3/8" bolts - use 40 ft-lbs
|
Yes with lock washer |
Head
bolts |
- ~75 ft-lbs (some guys say don't go over 60 lbs. These old
bolts tend to "stretch" and then snap. Don't over-tighten!!)
|
No
loctite.
and No lock washer. |
Connecting
Rod Nuts |
|
Yes
without lock washer |
Wrist
Pin |
- 3/8" bolts - use 35-40 ft-lbs
|
Yes
with lock washer |
|
|
|
Here
is some "industry" information regarding "modern"
bolt specifications. Use caution when applying this to "old
steel" bolts. When in doubt, test a similar bolt first in
your vice so that you don't snap it off in your engine block.
Otherwise finish it at a lower amount than shown below. |
Grade Identification Marking on Bolt Head
|
SAE Grade
|
Nominal Size Diameter (Inch)
|
Tensile Strength
|
None
|
1
|
up to 1 1/2
|
60,000
|
None
|
2
|
up to 1 1/2
|
74,000
|
3 line star
|
5
|
1 to 1 1/2
|
120,000
|
5 line star
|
7
|
1/4 - 1 1/2
|
133,000
|
6 line star
|
8
|
1/4 - 1 1/2
|
150,000
|
|
See here for another table of
this data. |
|
Thanks
to Jim Knopp, Chardon,
Ohio for this info! |
THREAD SIZE
|
Grade 2 TORQUE (lb-ft)
|
Grade
5 TORQUE (lb-ft) |
1/4 - 20
|
5-7
|
7 - 9 |
1/4 - 28
|
6-8
|
8 - 10 |
5/16 - 18
|
10-13
|
13 - 17 |
5/16 - 24
|
11-14
|
15 - 19 |
3/8 - 16
|
23 - 26
|
30 - 35 |
3/8 - 24
|
26-29
|
35 - 39 |
7/16 -14
|
35 - 38
|
46 - 50 |
7/16 - 20
|
43 - 46
|
57 - 61 |
1/2 - 13
|
53-56
|
71 - 75 |
1/2 - 20
|
62 - 70
|
83 - 93 |
9/16 -12
|
68 - 75
|
90 - 100 |
9/16 - 18
|
80 - 88
|
107 - 117 |
5/8 - 11
|
103 - 110
|
137 - 147 |
5/8 -18
|
126 - 134
|
168 - 178 |
|
COMMENTS: |
If you
find a table of torque values vs. bolt size, the problem is that the
tables assume high quality steel fasteners and base materials.
For example, on my 1946 216 wrist pin bolts 35 ft-lbs would have
broken the bolts because they are soft steel compared to a grade 8
modern bolt. I ended up torquing them at 28 ft-lbs - the lower
range for a 3/8 bolt (30-35 ft-lbs).
--- J KNOPP 12/2000
|
Quick Chart for General Shop use |
Bolt Diameter (inches)
|
Plain Steel (early 1930's standard bolt
material) (lb-ft)
|
1/4 - 20, 28
|
8 |
5/16 - 18, 24
|
16 |
3/8 - 16, 24
|
28 |
7/16 -14, 20
|
44 |
1/2 - 13, 20
|
67 |
9/16, 18
|
95 |
5/8 - 11, 18
|
131 |
3/4 |
228 |
7/8 |
361 |
1"
|
524 |
|
Mechanics?
|
Do you have
other information that should be listed here?
Send it to me by email and I'll add them.
Thanks. Bill Barker |