bowtie4.gif (2065 bytes) 1931 Chevrolet - Torque Settings
 

Updated: 05/05/2009

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
  • 35-40 ft-lbs
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

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

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Bellevue, WA, USA