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Subject: Locknuts on the rod bolts

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Kent S.    Posted 01-15-2019 at 00:22:49 [URL] [DELETE]        [Reply] [Email]  
  • Locknuts on the rod bolts
  • The IT shop manual FO-4 says on page 31" tighten connecting rod nuts evenly to a toque of 35-40 ft.-lbs., then install new locknuts(pal nuts) and tighten to 4-5 ft.-lbs. torque.
    The May 1950 parts book describes the nut as 3/8"x24 hex and the locknut as 3/8"x24(9/64 x 9/16")hex locknut. the locknut is about half as tall (or less) in the depiction.The March 1994 Assembly Manual and Service Parts Catalog doesn't list the locknut.
    I guess locknuts make the most sense to me, but why does the newest parts manual omit them. Is red locktight good enough?
    Kent

    Rustyal    Posted 01-18-2019 at 19:00:49 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Locknuts on the rod bolts
  • I like the little stamped lock nuts. Not sure you can still find them. You can use Loctite but Iíd try not to.

    TheOldHokie    Posted 01-15-2019 at 11:18:37 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Locknuts on the rod bolts
  • You really don't need anything more than the hex nuts but If you want to use a thread locker it will work fine. Red Loctite (263) is overkill but won't hurt anything. Blue (243) would be more than adequate. If you use a thread locker make sure both male and female threads are free of oil.

    TOH

    Tim Daley(MI)    Posted 01-15-2019 at 08:05:13 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Locknuts on the rod bolts
  • Don't put much faith in the later parts books -when NH took over they mucked up the numbering system and made their own changes. I'd go by the original MPC's. I have no idea what a March 1994 Service Parts Catalog is and don't want to know. Look in the 39-53 MPC as it lists and shows the locknut -p/n 45218-S -it is a 3/8-24 stamped part and probably no longer serviced. the 7HA-6212 Con Rod nut is sold by Dennis Carpenter and Just8Ns and is just a 3/8-24 castle nut. I wouldn't use any thread locking substance at all.

    Tim Daley(MI)

    Rustyal    Posted 01-15-2019 at 07:37:57 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Locknuts on the rod bolts
  • You donít need lock nuts on the ones with the lock built into the nut. You need them otherwise.

    Jim    Posted 01-16-2019 at 08:46:10 [URL] [DELETE]        [Reply] [Email]  
  • Re: Locknuts on the rod bolts
  • Would using loctite or something similar interfere or change the torque value? thanks

    TheOldHokie    Posted 01-16-2019 at 10:30:57 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Locknuts on the rod bolts
  • Short answer is yes. Long answer is more complicated.

    Torque values are a crude measurement of the tension (clamping force) produced in the fastener. It is this tension and the friction it creates that keeps the fastener from working loose. This tension is typically chosen to be 60-75% of the fastener proof load. The torque needed to produce this specific tension is then calculated using an equation that contains a "K factor". The K factor represents the loss in tension attributable to friction between the threads and head of the fastener. This loss is typically 75-90% of the applied torque!!! So anything that chances that friction can substantially alter the torque needed to produce the desired tension.

    Most automotive service manuals specify torque values calculated assuming oil lubricated threads. According to Henkel's technical data sheets Loctite 243 has the same K factor as engine oil so no adjustment would be needed. On the other hand an inserted or deformed thread lock nut will have a higher K factor and require a small (WAG 5%) increase in torque in order to obtain the same clamping force.

    Keep in mind that torque wrench measurements as a means of measuring tension have an accuracy of +/- 25% to begin with so tiny variations in K factor become academic in most applications. Be more concerned when using torque values for dry versus lubricated threads where the difference in K factor becomes significant.

    TOH

    Jim    Posted 01-16-2019 at 12:50:29 [URL] [DELETE]        [Reply] [Email]  
  • Re: Locknuts on the rod bolts
  • thanks

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