MG MGB and MGB GT Tech Talk
Had a devil of a time getting the bolts back in the crossmember but finally succeeded. My question is, what should they be torqued to? I'm a bit concerned as I have 2 bolts at 15 lbs but then they don't seem to tighten further. Afraid I might be stripping something though they threaded properly. They're all new bolts but would sure hate to have them shear off. Anyone know what the proper torque setting is for these?
Bentley's shop manual says 54 to 56 ft. lbs.
Those bolts are like 7/16", you're not going to strip them.
Are the nuts new too Bob? If not the threads may not match up correctly. Just a thought...
Shawn Escue
The nuts have a locking thread, the other end of the bolts have a taper fit so the bolt is probably spinning due to the locking thread in the nut. If you had the suspension parts off the car you could reach the bottom nuts with a holding wrench. If you cannot reach them find a non locking nut with a good thread and you may be able to pull the taper up enough to keep the bolts from spinning. After the taper is pulled up you should be able to remove the plain nut and install the lock nut.
Clifton
I can see I wasn't clear enough. I was referring to the transmission cross member. No nuts here, the bolts thread into a tapped bar within the frame member. These bolts are about 5/16".
Sorry for the confusion.
These are probably all stupid questions but ....
Did you chase the weld nuts with a tap to clean the rust and crud from them? (highly recommended everywhere)
Did you replace with the same size fasteners? Is it possible that they are longer?
Anti-seize compound?
If these are the outboard bolts that attach the crossmember to the sub frame rails, I believe these are 3/8" dia and most sources specify that 3/8 NF GR5 be torqued to 35 ft-lb dry and about 25-30 if lubed. I have never seen a specific value listed for them in any of the manuals etc.
I think they are 5/16 NF (1/2" hex head). Might be 9/16 hex (3/8"-NF). 1/2" should be fine in the range of 15-25 depending on grade of fastener. 9/16 shpould pull tighter. as noted.
I'm not of the belief that Grade 8 is any better in 95% of the cases, and here you have a "soft" weld nut not a hardened G8 nut. So if with a std 8-10" ratchet you give it a tug almost as hard as you can, that is plenty.
I do tend to use new nuts and cap screws most of the time, with hardened flat washers (G8, cheap by the box) not the split washers (which i believe, over time, are worthless).