Brittle Bolts, Coarse or Fine ? Grade 5 or 8 ?

[mike90045]

So, last 2 days, I've noticed some extra movement in the flex joints in the ex pipe and the valve cover stud is flailing around more.  All the bolts seemed tight, but a real close inspection showed movement between the upper frame and lower frame (not a motor mount) .  I pulled the bolt, and found a couple munged threads.
 It was a 7/16 coarse thread, grade 5 bolt, and a couple threads had deformed allowing movement. The nut looks OK, but it's hard to see inside it!
I went to the local store that claims to be a hardware store, and was only able to get some old dusty grade 5 fine thread bolts & nuts.  Tomorrow, I go to the big city (Ukiah) to get some real hardware (structural bolts with extended nuts).
 But the question of the day is ,  what should I get, Coarse or Fine ?
 I understand that coarse thread are "tougher to strip" but fine threads  leave more meat in the bolt for stronger bolt.

For listeroid applications, what should I search for ?  I also believe I should stay with grade 5, being less brittle than 8.  Or should I count on the steel frame absorbing shock and not matter about the brittleness ?

  Because of the web in the steel I frames, I can't get any larger than 7/16 bolts without the head and nut hitting the web.  I had to grind down washers to get them to fit.
 layup:
engine bolts to upper frame 
upper frame bolts to steel sleepers 
steel sleepers clamped to anchors in floor 

[Thob]

I think I would stick with grade 5 bolts and coarse threads, and put two nuts on each bolt, if you have room for them.  It may require longer bolts, but tightening up the first nut and then running down a second nut and tightening it up would give you a much longer thread engagement.  I'd also look up the torque recommendations and use a torque wrench to tighten them down - that way you KNOW they are tightened properly.  Again, if you have room.  If you don't have room for the torque wrench, then using the torque wrench on a nut/bolt held in a vise will give you a good feel of how tight to get the nuts with whatever wrench will fit.  Just tighten the nut with the torque wrench, mark the flats with a sharpie, and then loosen and re-tighten the nuts with the wrench that fits.

Any chance of getting in there with a welding machine and welding the top frame to the bottom frame?

[Tom]

Mike, can you tap the steel base for 1/2" 13 threads? Then just tighten the bolts from the top. Coarse threads hold better, but weaken the bolt a bit. Grade 5 will deal with the vibration loads better.

[mike90045]

the I beams are not thick enough for threads, at least not threads I would trust.  Pinching it with a bolt seems like the best.   I could try re-drilling on the other side of the I beam(s) and try to get the hole up to 1/2", but to leave space for the bolt head & nut, I'm getting further out on the horizontal web.  Maybe I'll mock it up with chalk and see if it looks sensible.  Too far out, and I'm afraid of the web starting to flex, or the hole tearing out.

[vdubnut62]

There is a washer made to fit the tapered flange on I-beams called a leveling washer. They straighten the bolts so the can exert the clamping pressure evenly. I have a link at McMaster-Carr.
http://www.mcmaster.com/#standard-washers/=10q9cgt
Ron.

[Tom]

OK, tap the threads, screw a bolt in to the hole with some threads extending below the frame. Screw a nut on extended threads and weld into place. Problem solved?

[mike90045]

There is a washer made to fit the tapered flange on I-beams called a leveling washer. They straighten the bolts so the can exert the clamping pressure evenly. I have a link at McMaster-Carr.
http://www.mcmaster.com/#standard-washers/=10q9cgt
Ron.

I have those on the actual engine mounts.  Squared up the washer alignment really well.  I'll have to look at the angles to see if maybe
I should use some more.

[deeiche]

another data point.  your "grade 5" hardware may not really be grade 5.

I work at a facility where we regularly test fasteners, this because of the high number of counterfeit fasteners.  Rigorous testing is done because our manufactured product go into areas where systems can't be repaired or replaced.

[mike90045]

another data point.  your "grade 5" hardware may not really be grade 5.

I work at a facility where we regularly test fasteners, this because of the high number of counterfeit fasteners.  Rigorous testing is done because our manufactured product go into areas where systems can't be repaired or replaced.

Boy, I know that problem. Had issues in aerospace with both hardware and electronic components, even had issues with "factory" distributors with bogus parts.
I do check for the 3 raised ribs for grade 5.

Yesterday, while at the Industrial Hardware (B & B Steel) I also came across grade A-325 hardware, which may be just a bit tougher than Grade 5
http://www.portlandbolt.com/technical/faqs/astm-a325-vs-grade-5-bolts/   definitely heavier heads and nuts with more thread engagement on the longer A325 nuts.

I think grade 8, is too brittle to be used for the engine mount bolts ( are folks using 1/2" bolts, 5/8 or 3/4 on the 4 base bolts ?)

I will try to see if I can get some new holes drilled (with a 90° close drill gear I can fit in between the the I beam webs)  I tried the bevel washers (actual name for the tapered washers for use on I beam stock to keep the bolt square) but I can't get them into the space for the holes as drilled.
 photo  https://www.facebook.com/photo.php?fbid=1981406573613&l=7e532ce0ae   or here 
 Should I use a larger bit and hog out a larger hole and rely on hardened washers to fill the void, or switch to the other side of the I and try a new hole there (which will be a lot harder to get into because of the space limitations) ?

[buickanddeere]

Forget about bolts. Run a square bottoming tap to the very bottom of the threaded bore. Used a little loc-tit green and turn a grade 8 stud to the bottom of the threads. Now just use nuts and washers to hold the exhaust pipes etc on.

[mike90045]

While dealing with this <again> this new year, I came across this informative page
http://www.boltscience.com/pages/twonuts.htm
 about double nuts as a locking gizmo.   

So, I'm going to ream out the holes and try to get to half-inch fasteners.  Not sure how/why 3/8 was the starting point, I've reamed them out last year to 7/16
and half inch should have so much more meat, grade or counterfeit will be less of an issue.

Question now, is the malleable iron bevel washers.  Putting grade 5 washers over them, will that make them flow like silly putty ?  Malleable sounds like it's going to be butter soft, comparatively.

[Tom]

The listeroid here is mounted to the frame with 1/2" carriage bolts. The holes in the 4" channel iron frame were filed square so they would not spin. The heads are captured by the wood beam the channel iron sits on. Never had a problem. Mike, I would highly recommend that you take those 1/2" bolts and weld them into place sticking up from the frame. Be sure to place them in the slots straight and square so that engine stays put. I still think this is the root cause of the belt issue and doing this will permanently resolve it.