How to never snap a bolt?
Discussion
Chimune said:
The heat option has always confused me and seems more like an 'all else has failed' action.
If you heat the top of the bolt, Shirley:
1.you are making the bolt expand into an already very tight hole. Does that actually squeeze the head away from the surrounding metal by a mm?
2. Weakening / fatiguing the bolt metal. A glowing bolt will be softer and more likely to fail.
I can see how heating the surrounding metal might help, but i don't understand the physics of heating. What's the theory here?
You are actually partially right, because people don’t understand the full process. The actual process as it was since the beginnings of time in the motor trade was to ‘cherry’ a bolt/stud/nut using an oxyacetylene, then douse with water. It was never heat up then try and undo whilst still hot. The douse with water cracks the seal between the two parts. The best thing is an induction tool, but they are still a bit pricey, especially for the hobby mechanic. Using heat-quench you can get cylinder head studs out that have been in for 40+ years without breaking a sweat. If you heat the top of the bolt, Shirley:
1.you are making the bolt expand into an already very tight hole. Does that actually squeeze the head away from the surrounding metal by a mm?
2. Weakening / fatiguing the bolt metal. A glowing bolt will be softer and more likely to fail.
I can see how heating the surrounding metal might help, but i don't understand the physics of heating. What's the theory here?
The classical 'experiment' demonstrated by your physics teacher, the ball and ring, where the ball that would go through the ring, does after the ring is heated, does not express real life! See: https://www.youtube.com/watch?v=nA-WJyq19H8&ab...
The Prof heated just the ring, the ball stays cool. You can't do that with a bolt seized in a hole, as you must heat both at once. Thermal expansion affects both parts equally and the hole and bolt change size equally as they rise in temperature equally. A hot ball will still not go through a hot ring!
Sure, a small hole in a large casting or panel may be impeded in growth as the cooler parts around it will compress the material. Maybe heating the bolt will crush the corrosion around it in the hole, loosening it when it cools. And if the bolt and panel are in different materials - aluminium expands twice as much as steel - then heat may produce a dramatic loosening.
The 'cure' that hasn't been mentioned is the candle! Heat the bolt, and rub it with a candle end so that the wax runs over it. Allow to cool, and you can expect some loosening! Melted candle wax seems to be a good penetrant, and provide lubrication once it gets into the threads.
JOhn
The Prof heated just the ring, the ball stays cool. You can't do that with a bolt seized in a hole, as you must heat both at once. Thermal expansion affects both parts equally and the hole and bolt change size equally as they rise in temperature equally. A hot ball will still not go through a hot ring!
Sure, a small hole in a large casting or panel may be impeded in growth as the cooler parts around it will compress the material. Maybe heating the bolt will crush the corrosion around it in the hole, loosening it when it cools. And if the bolt and panel are in different materials - aluminium expands twice as much as steel - then heat may produce a dramatic loosening.
The 'cure' that hasn't been mentioned is the candle! Heat the bolt, and rub it with a candle end so that the wax runs over it. Allow to cool, and you can expect some loosening! Melted candle wax seems to be a good penetrant, and provide lubrication once it gets into the threads.
JOhn
[quote=tapkaJohnD
The Prof heated just the ring, the ball stays cool. You can't do that with a bolt seized in a hole, as you must heat both at once. Thermal expansion affects both parts equally and the hole and bolt change size equally as they rise in temperature equally. A hot ball will still not go through a hot ring!
[/quote]
Depends what they're made of. A steel ball could go through an aluminum ring as the aluminum will have expanded twice as much as steel. In theory this should mean a steel bolt in an aluminum block gets looser with heat, but I'm not sure how much heat it would take.
Similarly putting things like motorbike wheel bearings in the freezer should make them easier to fit but in practice I don't think it's a big enough temperature difference and a big hammer works better.
The Prof heated just the ring, the ball stays cool. You can't do that with a bolt seized in a hole, as you must heat both at once. Thermal expansion affects both parts equally and the hole and bolt change size equally as they rise in temperature equally. A hot ball will still not go through a hot ring!
[/quote]
Depends what they're made of. A steel ball could go through an aluminum ring as the aluminum will have expanded twice as much as steel. In theory this should mean a steel bolt in an aluminum block gets looser with heat, but I'm not sure how much heat it would take.
Similarly putting things like motorbike wheel bearings in the freezer should make them easier to fit but in practice I don't think it's a big enough temperature difference and a big hammer works better.
Just having differential expansion and contraction due to a temperature gradient can help break the thread loose, even if you can't get much of a temperature difference across the thread. Heating and cooling will also draw in the penetrating oil as air in the joint expands and contracts.
Nads02 said:
g3org3y said:
Should one preferably use an impact wrench rather than a breaker bar if concerned re the possibility of snapping the bolt?
That's what I think as wellEdited by Evoluzione on Saturday 13th March 20:45
Evoluzione said:
Nads02 said:
g3org3y said:
Should one preferably use an impact wrench rather than a breaker bar if concerned re the possibility of snapping the bolt?
That's what I think as wellThe other thing to remember is - is it really necessary to save the fixing or the item it's holding?
Sometimes it's a lot quicker and easier to have new bolts\parts to hand, and just cut the old ones off without even trying to undo them. Perfect example, exhaust clamps. About £2 each, and can be zipped off in seconds.
Sometimes it's a lot quicker and easier to have new bolts\parts to hand, and just cut the old ones off without even trying to undo them. Perfect example, exhaust clamps. About £2 each, and can be zipped off in seconds.
shtu said:
The other thing to remember is - is it really necessary to save the fixing or the item it's holding?
Sometimes it's a lot quicker and easier to have new bolts\parts to hand, and just cut the old ones off without even trying to undo them. Perfect example, exhaust clamps. About £2 each, and can be zipped off in seconds.
What like a cylinder head or a hub?Sometimes it's a lot quicker and easier to have new bolts\parts to hand, and just cut the old ones off without even trying to undo them. Perfect example, exhaust clamps. About £2 each, and can be zipped off in seconds.
shtu said:
The other thing to remember is - is it really necessary to save the fixing or the item it's holding?
Sometimes it's a lot quicker and easier to have new bolts\parts to hand, and just cut the old ones off without even trying to undo them. Perfect example, exhaust clamps. About £2 each, and can be zipped off in seconds.
Yep this. I have zero intention of refitting the rusty old fixings back on my Landy as I move along with the chassis swap. The removal process for many bolts has been:-Sometimes it's a lot quicker and easier to have new bolts\parts to hand, and just cut the old ones off without even trying to undo them. Perfect example, exhaust clamps. About £2 each, and can be zipped off in seconds.
Hit it with the impact - 60% success rate
Try with the breaker bar - 10% removed
Angle grinder - remainder
Evoluzione said:
What like a cylinder head or a hub?
no one is going to snap off head bolts on purpose , like someone else said its about having the kit and know how to deal with broken stuff when it happens , quality set of drills , center punch , sharp chisel etc end of the day some bolts will snap anyway , soaking in penetrant for 6 weeks was never going to save it
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