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Allis Chalmers Discussion Forum

Self-locking rod nuts

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todd hertel

12-26-2015 15:20:16

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Iím in the process of rebuilding an AC G-262 gas engine. The connecting rods use a marsden type self- locking nut. The AC specs for rod torque is 40 to 45 ft-lbs. The engine I am working on had 1 rod with the wrong nuts on it. It had cotter style nuts on it but the bolts for the connecting rods are not drilled for installing cotters. I have also rebuilt Buda B230 gas engines. The rods use a castellated nut with cotters and the torque spec for these is 50 to 65 ft-lbs. Why is there such a difference in torque specs? Does the AC engine use a lower grade of rod bolt?

I found a self-locking nut called Flexloc 21FC624. These appear to be similar in nature to the original AC nut type but are cadmium plated so they may not require as much torque as a dry nut. Has anyone out there found a good self-locking nut that may be used and if so, what torques do you use.

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12-26-2015 20:40:00

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 Re: Self-locking rod nuts in reply to todd hertel, 12-26-2015 15:20:16  
My AC manual calls for 20 - 25 ft lbs on the rods. That would be for self locking nuts. Bob

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Dick L

12-26-2015 17:00:23

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 Re: Self-locking rod nuts in reply to todd hertel, 12-26-2015 15:20:16  
Rod bolts are the same as grade eight bolts. The torque spec. will be by bolt diameter not by engine make. If you have a 60 foot pound torque spec it will be for a 7/16 rod bolt.

As Dr Allis stated on 3/8" rod bolts with castell nuts and cotter keys, my book calls to torque to 30 pounds and tighten until the cotter key will insert (if necessary).

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12-26-2015 16:27:32

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 Re: Self-locking rod nuts in reply to todd hertel, 12-26-2015 15:20:16  
I checked my Official A-C Service manuals, and the WD-45 and D-17 diesels are 30 to 40 ft lbs of torque. No mention of the castellated nuts, but I think they are. I guess I was always taught to go to 30 ft lbs and see if you could get the cotter pin installed and if not, continue until you could, not to exceed 40 ft lbs. Now, when I go to the D-19 book, the torque value is 40 to 50 ft lbs, and I assume no cotter pins. AGCO parts books isn't much help, as they sub you up to the newest P/N's for bolts (74515070) and nuts(74516821). I would sure never think of 60 ft lbs on a 3/8" NF bolt/nut.

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