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Hi everyone,

I'm having my machinist re-size the con-rods for the new bearing sizes on my six cylinder. He called questioning the torque specs. on the bolts. My book (and his) says 55-60 lbs. It's his opinion that is too much for a 3/8 bolt. He said that the metallurgy in those days wasn't up to the standards of today and that 55-60 lbs. is for 7/16 bolts.

Seems to me that the book wouldn't give out the wrong specs.
Any ideas or suggestions?

-Erik

Looks like there may be two different sizes used for connecting rods. Don't know if any help on your engine but the 47 and the V8's have a 3/8-24 size listed for the connecting rod. Torque on those is 45-46 on the 47's and 40-45 on V8's. The 47 and the 51-4 specs also mention a 7/16-28 size used for connecting rods. Spec on that is 60-65.

In Motors Manual, pic below, 6 cylinders for '37-'39 listed as 55-60 and '40-'42,46 & 47 and later as 45-46.

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If I recall correctly there is a torque specification chart in the service manuals. The chart specifies the torque rating for bolt sizes and thread types. Might be worth checking the chart to verify. Motors Manual and other publishers repeat specs given to them by the various makers.

Packard made a mistake in describing the bore size of the 320 cu. in. V-8s in various manuals. They said it was 3 3/16". This is incorrect, it is 3 13/16". Coincidentally, the 3 3/16" bore size is that of the pre-war 320 cu. in. straight-8s.

Good catch by your machinist.

(o{}o)

So it seems...I've done a little research and it looks like the torque specs. for the six cylinder (245 cu) is for 7/16 in. bolts. My rods have 3/8 in. I know that in 1938 the rod bearings were increased size...perhaps the bolts were too??

This machinist is new to me, but seems to be paying attention. I think I'm in good hands.

-E

Metallurgy today is more developed, but the metal in those bolts is very high quality.

A machinist should be checking the yield (aka bolt stretch) if he is concerned about those bolts. I've never heard of them being failure prone.

Just because they didn't have cell phones and the Junknet at Packard doesn't mean they were inferior. In fact cell phones and the junknet are one of the reasons the world is getting stupider and stupider.

I hear they are even trying make grammar school paperless and getting rid of blackboards.