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Posted

Could use some help folks!  Was assembling my rebuilt rocker assembly back on the rebuilt engine.  Used the original B bolts and new lock washers.  On about the third set, I twisted a bolt off with my torque wrench set at 35 ft-lb.  I had retrieved a couple charts off this forum showing the torque spec as 30-35.  All the torque specs appeared to be in ft-lb but it didn't actually spell that out for each category.  I got the bolt out with an easy out thankfully.  But now I'm spooked because I don't want to over-tighten the aluminum alloy stands to the head.

So does someone have a reliable spec on the torque for those bolts?  I thought I'd replace the old B bolts with grade 5 or 8 but now I'm worried about having too much clamping force at a given torque because of the higher tensile strength of the newer bolts.

Did I misinterpret the spec?  Should it really be 30-35 in-lb?  Dry assembly or lubed?

Any help would be appreciated .

Thanks

Tom

Posted

I found this chart online; seems consistent with a couple of others that I looked at.  If it is a 3/8" coarse thread, the table says 15 Ft-Lb.  I wouldn't go above 20 in any case...

 

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Posted

Also, sometime in past the broken bolt may have been over torqued and weakened making it more prone to failure.

                                                                                       Thanks leif

Posted

Hi 39 Again,

My MoToR manual agrees with the charts above for a torque value of 30-35 ftl lbs from 1935 - 1942 for all series Buicks.  Lock washers are generally used under a nut to prevent the nut from loosening due to vibration. Flat washers do a better job of distributing the torque load over a greater surface area. ARP fasteners recommends that lubricant be used on the thread and under the bolt head to ensure proper torque values are reached. The only exception would be for the threads of a fastener that is contact with liquids, (oil, coolant etc.) in that case a sealant should be used on a clean fastener, (still use a lubricant under the bolt head). Loctite products work very well as both a sealant and thread lock to prevent loosening due to vibration.

 

I was taught to follow this procedure, when assembling engines, transmissions and differentials.

  1. Determine whether the threaded hole is a blind hole or through into a passage where it contacts liquids as noted above
  2. Run a thread chaser in all bolt holes and clean holes out thoroughly. Compressed air is excellent for this, but use proper eye protection. Any debris can result in a false torque reading.
  3. Determine whether the bolt is the proper thread diameter, pitch, length and grade for the application.
  4. Ensure that the all rust, sealers etc are removed from the bolt thread and that no threads are damaged. A thread chaser works great for this.
  5. Use the proper lubricant and/or thread sealant as needed. 
  6. Assemble and torque to specifications

A final thought is to make sure your torque wrench is calibrated correctly. Good luck and happy wrenching.

Posted
Thanks to all that responded with good tips. After several waves of holiday guests left, I got back on my project. Checked calibration on my torque wrench and it was spot on.  My brother, who was a 50's hot rodder straight out of movie "Grease" was my car mentor growing up.  He spent his career with company building pumps and pressure vessels for nuclear and petrochemical industry.  He did a little research and sent me a reference on bolt torque....very technical and more than needed, but helpful.  Also consulted a couple of my old mechanical engineering books collecting dust on shelf.  So after all that, I used thread sealer and added a small dab of lube on end of bolts.  Set the torque at 30 ft-lb...low end of range spec because I was using grade 8.  Everything worked fine.
Also, I set the lash at .018" cold so hope this will work well for starting.  If anyone wants to opine on the lash, I'm all ears.
Again, thanks for your help.
Tom

 

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