why my bands always came loose

fishlessman

Jeepster47 said:

@poster ... neat analysis ... thanks for posting.

The band arrangement on the egg has got to be one of the most marginal designs possible.  The egg surface has a slight taper where the bands grip.  As poster pointed out out; the tabs on the bands aren't perpendicular to the bolt shaft, thus the bolt bends under load.  The thermal expansion of steel and BGE ceramics are different enough to aggravate the issue.

Quick analogy first:  Imagine a sphere with a 25,000 mile circumference ... that sphere would be close to the size of the earth.  Now imagine a "band" around that sphere that hugs the surface.  Let's add a measly 6.2832 feet to that 25,000 mile long band and imagine that the band stayed circular.  How much clearance would you guess is between the band and the sphere?  Would the band now fall off the sphere?  Would you believe that the band-to-surface clearance is one foot?  It is!  The point of the analogy is to show that it doesn't take much additional stretch in the band or the bolt to cause it to come loose from the egg.

When you torque a bolt, some of that torque goes towards overcoming friction in the threads, some goes towards overcoming the friction between the bolt/nut and it's mating surface ... and finally a small portion actually goes into stretching the bolt so that it keeps the joint tight.  Add a surface that isn't perpendicular to the bolt's centerline and even less goes towards stretching the bolt. Allow the bolt to bend, and again, less goes towards stretching the bolt.  My feeling is that the actually band tightness obtained with the same torque value would have a wide distribution around target.  Thus, some eggs bands stay tight and some don't.

Oh yes, don't forget the friction between the band and the ceramic.  I'm guessing that that friction inhibits the tightening of the band evenly around the perimeter of the egg.  Cycle the temp in the egg and it probably equalizes some.  Since it doesn't take much extra length to loosen the band (analogy above) it comes loose after a high temp cook ....... maybe!  Wonder if tapping all on the band around the perimeter of the egg with a rubber mallet and then re-torquing would help?

When the steel bands and the BGE ceramics heat up, they both expand.  I'm guessing that steel expands more than the ceramics ... thus, the bands are a little looser when hot than when cold.  If you toque the bolts with the egg hot, I'm guessing that the bolts yield some when the system cools off.  If so, then during the next heat cycle, the bands are not as tight as when you originally torqued them hot, but still tight enough to keep them in place.

Oh yes, one other thought; do you simply close the lid softly or do you close it somewhat harshly?  Closing it hard might cause the dome band to shift downward.  And, if you push down on the handle to insure that it's tightly closed, well stop doing that!

Double nutting:  Double nutting is an inexpensive solution to stop loosening caused by vibration.  It doesn't help in this application.

something ive never seen in writing on thermal expansion and metal is that though the expansion rate is fixed, with repeated use over time it doesnt always shrink back uniformly, it actually gets bigger over time. ive seen this on large industrial boilers and on heat treatment chambers where the expansion joints were fine for years and later on im lengthening the expansion areas or cutting the lengths and diameters down on the innards. might explain after years of use that all of a sudden the bands got loose

Focker

Carolina Q said:

I don't know, guys. I assembled my egg over six years ago. It was, and remains, in perfect alignment. Clean burns, 900° pizza cooks, -12° to 100+° ambient temps, sometimes daily cooks, sometimes 2-3 months with NO cooks.  

Finally checked for band tightness once, sometime last year. They were just like they were when I put them on. I have no idea what the torque value is. I tightened them until they bent. Grade 5 OEM. I guess I'll have to check again... in another 5 years.

My eggs have been similar, no alignments needed.  Many buried needles.  I do double nut. 

4Runner

Jeepster47 said:

@RRP ... @4Runner ... @Darby_Crenshaw ... why do you double nut in this application?

I tried it and my bands haven't loosened since.  Not saying that is the reason but I have plenty and it worked.  

RRP

Focker said:

Carolina Q said:

I don't know, guys. I assembled my egg over six years ago. It was, and remains, in perfect alignment. Clean burns, 900° pizza cooks, -12° to 100+° ambient temps, sometimes daily cooks, sometimes 2-3 months with NO cooks.  

Finally checked for band tightness once, sometime last year. They were just like they were when I put them on. I have no idea what the torque value is. I tightened them until they bent. Grade 5 OEM. I guess I'll have to check again... in another 5 years.

My eggs have been similar, no alignments needed.  Many buried needles.  I do double nut. 

You know just wondering out loud here. My oldest egg is 16 years old and my youngest is 11. I've never had my bands get loosey-goosey and I've always attributed that to the old BGE instructions of just tightening until the bolts bent and then my belief in double nutting. I wonder if BGE itself changed its supplier of bands, nuts and bolts in recent years. Fall out never used to be as newsworthy as it seems in recent past. I'm just sayin...

stv8r

good info

nolaegghead

Loose bands sink ships.

Jeepster47

When I was growing up, all the Catholics had a plastic Jesus on the dash board of their auto ... they said it protected them from accidents.  Those who hadn't had an accident swore up and down that it was working.

Please understand that double nuts on the band bolts are simply a different form of a plastic Jesus on the dash.

Argue some of the other points I suggested ... many of those are suppositions.

Zmokin

Double-nutting is the "expensive" overkill solution to a lock washer.
Overkill because it works, never seen it fail.  Expensive is tongue-in-cheek reference to the cost of a second nut vs. the cost of a lockwasher.  Maybe if you did it a million times on a production job, the added cost could be significant, but for us home DIY, it's cheap insurance against a nut working it's way loose.

theyolksonyou

Som time I should visit this thread sober...all these words!

nolaegghead

Thread.  huh...huh huh..

fishlessman

RRP said:

Focker said:

Carolina Q said:

I don't know, guys. I assembled my egg over six years ago. It was, and remains, in perfect alignment. Clean burns, 900° pizza cooks, -12° to 100+° ambient temps, sometimes daily cooks, sometimes 2-3 months with NO cooks.  

Finally checked for band tightness once, sometime last year. They were just like they were when I put them on. I have no idea what the torque value is. I tightened them until they bent. Grade 5 OEM. I guess I'll have to check again... in another 5 years.

My eggs have been similar, no alignments needed.  Many buried needles.  I do double nut. 

You know just wondering out loud here. My oldest egg is 16 years old and my youngest is 11. I've never had my bands get loosey-goosey and I've always attributed that to the old BGE instructions of just tightening until the bolts bent and then my belief in double nutting. I wonder if BGE itself changed its supplier of bands, nuts and bolts in recent years. Fall out never used to be as newsworthy as it seems in recent past. I'm just sayin...

the 16 year old spring band may have been made in mexico, the newer ones are made in usa. the telltale is if the handle is welded or bolted on  the band, the welded ones are mexican. maybe these new eggs have bands made someplace new because in all these years ive never seen all these alignment issues since the old mexican bands. my original mexican band made atleast 10 years before it failed and bge shipped me a new one

Jeepster47

fishlessman said:

the 16 year old spring band may have been made in mexico, the newer ones are made in usa. ... maybe these new eggs have bands made someplace new because in all these years ive never seen all these alignment issues since the old mexican bands. my original mexican band made atleast 10 years before it failed and bge shipped me a new one

That would be about par for the course.  We used to spend millions of dollars developing a new product.  Testing for hours and hours on multiple prototype machines with components manufactured by the end supplier.  And purchasing would switch suppliers after the start of production to save a dime.  Just 'cuz they look the same, doesn't mean they are the same ... does it?

HeavyG

The easiest solution to all this fuss and worry and messing with bands and bolts is to just buy a Komodo Kamado.

PSC

My head hurts, LOL

LKNEgg

Tried out my newly installed bolts this weekend.  Ace Hardware had grade 5 bolts and grade 8 washer and nuts.  So far so good. Thanks again for the testing and analysis. Used the red spacers that came with the grill to line everything back up and did a high temp pizza cook.  


Made fajitas saturday night and added leftovers to the pizza Sunday night.  Chicken, onions, peppers, with spicy queso, spicy sausage, mushrooms, and topped with mozzarella cheese to bind it all.  Phenomenal results!  Everyone wanted another, but ate all the fajita toppings Saturday night!

Jeepster47

@LKNEgg ... the bolts aren't bent ... did you torque to specs?  If so, how about checking the torque after the egg cools down.

LKNEgg

@Jeepster47  they were starting to bend (not really visible in pix) and things started to creek and pop so I stopped.  Must admit I don't have a torque driver to test it, but feels a lot tighter than the original bolts would allow without flexing.  
Thanks for looking out for me!  I don't want to end up with the lid falling out like the pix floating around here!

pgprescott

They should have a very visible bend in them. 

LKNEgg

Ok, sounds like the consensus is to crank them down.  I will crank them down a little more!  I just figured the higher grade bolts wouldn't bend as much or easily!

RRP

LKNEgg said:

Ok, sounds like the consensus is to crank them down.  I will crank them down a little more!  I just figured the higher grade bolts wouldn't bend as much or easily!

Anyway you cut it the angle of the band ends are already showing the bands are suffering from the tightening and will continue to bend before your new bolts probably will. Personally I would rethink using those grade 5 bolts without at least trying to heat and rebend the bands back to being closer to a 90 degree bend. Am I making sense? 

LKNEgg

@RRP  makes sense to me.  It is obvious they are fatigued and lost the original 90 degree bend.  Not an expert, but I try not bend metal back due to additional weakening.  Any thoughts? 

RRP

LKNEgg said:

@RRP  makes sense to me.  It is obvious they are fatigued and lost the original 90 degree bend.  Not an expert, but I try not bend metal back due to additional weakening.  Any thoughts? 

Heat! 

Jeepster47

@LKNEgg ... the OEM bolts are Grade 5 carriage bolts.  So, you have the same strength bolt now as when you had the OEM bolts installed.  The width of the head on the carriage bolt is probably a little more than on a hex head bolt, so that might contribute a little more to the bending.  But, still ... I'd torque it till you had a noticeable bend.

Here's a pretty good write-up on band tightening ... and discusses a MacGyver torque wrench method.

http://www.grill-repair.com/blog/2013/big-green-egg-spring-assisted-band-replacement-instructions/

Jeepster47

@LKNEgg ... I respectfully disagree with heating or straightening the bends in the bands.  Here's a fuzzy (phone focused on the ground) picture of the ends on my bands:



Those ends may have started out at a 90 degree angle, but they bend along with the bolts to yield a less than perfect angle.  If you heat the ends, then any temper that the bands have will be lost ... softer and more prone to bend.  If you cold bend them, then you are fatiguing the bend and they may break.

Tighten them up to specs and you'll be as good as can be.

RRP

Jeepster47 said:

@LKNEgg ... I respectfully disagree with heating or straightening the bends in the bands.  Here's a fuzzy (phone focused on the ground) picture of the ends on my bands:



Those ends may have started out at a 90 degree angle, but they bend along with the bolts to yield a less than perfect angle.  If you heat the ends, then any temper that the bands have will be lost ... softer and more prone to bend.  If you cold bend them, then you are fatiguing the bend and they may break.

Tighten them up to specs and you'll be as good as can be.

Then I humbly retract my suggestion of heat and re-bending. Obviously as an engineer you are far better versed than I am - my suggestion was based on what worked for me on my small when I had a similar issue years ago and they are still fine. BTW do you feel those bands really are tempered?

Jeepster47

RRP said:

... BTW do you feel those bands really are tempered?

Don't know for sure ... but, being conservative, I wouldn't risk the cost of new bands.