how do I torque a bolt that keeps "snapping"?

[KMinAF]

Sometimes when tightening a bolt to torque specs, I have come across one that as it is tightened will make "snap" sound and spring forward. This concernes me because I believe I am only getting the torque reading of what I would call "frictional force" instead the actual "stretch" of the bolt. To overcome this condition I have cleaned the threads and head of the bolt, applied engine oil to the threads and head and made sure the recieving threads are clean, all to no avail. Why does this happen and how can it be overcome?

 

[TheGrooveking]

Any possible chance the hole is too shallow and you are bottoming out prior to reaching full torque? Since you listed that you cleaned the threads and even oiled them it is either physical limitations space wise or substandard fasteners.

TheGrooveking

 

[PCO6]

I would try using new hardware.

 

[mattmankow]

Have you tried a different torque wrench?

 

[darkk]

Interested in the answer to this also. I have had this happen in the past also. I have never figured out why either, I just re torqued until I got the correct readings and moved on...

 

[byoungblood]

The problem might be the oil/lubrication. At least the way that I was taught you should not use oil on a bolt that you are tightening to torque. I agree with the previous comments about clean threads and making sure that it is not bottoming out.

FWIW - Frank

It depends on the application. Some bolts require lubrication, and the torque specs will reflect that. However, if it doesn't mention it, then it should probably be installed dry.

 

[scouting]

Posting so I can watch this, cause it's a mystery to me. I've had this happen, even after running a bottoming tap into the hole and hitting the bolt with a die. I wasn't using a torque wrench, but the bolt was 'slipping' as described. If it matters to any engineers reading this, grade 5 bolt into an aluminum casting, 10-32 thread.

Edit: I should add, there's no chance of bottoming out, I measured 3/16 clearance below the bolt. I could be off by 10-20 thou with the crappy caliper, but that's definitely adequate clearance.

 

[road]

I once rebuilt an old 1970 3 cyl. 650 Merc O/B. The previous owner had hit a rock shelf at hi speed. That ruined the prop, bent a few shafts and sheard the flywheel hub. Long story short.
As I was torquing the new 7/16" flywheel bolts I kept snapping them ( 2 sets )
Stupid me !! I was using the Wrong scale on the torque wrench !!

 

[GTA Matt]

Make sure you are using the proper lubricant. A small amount on the threads and plenty under the head of the bolt and washer if it has one. I see it most commonly when torquing head bolts on aluminum blocks. Using smooth, fast pulls on the torque wrench helps too. Going slow is asking for trouble. I would recommend ARP moly lube, but it changes the torque spec when compared to using motor oil so you have to adjust accordingly.

I should add that using different lubricants won't affect torque specs with TTY bolts.

 

[michael murder]

Someone mentioned getting new hardware, maybe worn or stripped threads. I had something similar happen when I over tightened bolts holding down a carburetor. Bought some new bolts, no problems

 

[Lurch67]

The problem might be the oil/lubrication. At least the way that I was taught you should not use oil on a bolt that you are tightening to torque. I agree with the previous comments about clean threads and making sure that it is not bottoming out.

FWIW - Frank

Adding lubrication decreases the required torque value. IE, reducing friction. Therefore you come closer to stretching the bolt and/or snapping it. Don’t lubricate the bolt unless required by OEM.

+2 for new bolts

 

[TheGrooveking]

When you listed that you clean the threads, did you run a bottoming tap all the way down the hole? If a taper tap was used the last so many threads may be undersized. Also when the fastener breaks the portion left in the threaded hole is it tight? And if so how are you removing it? Stud remover? Also where is the fastener breaking? Right under the head? I've had a bolt hole one time that very sharp after being regroups that was causing a lot of stress in a small area this causing extremely high pressure to generate which caused the head of the bolt to what snap.

TheGrooveking

TheGrooveking

 

[Eds_tls]

Galling can make this happen. Its common in aluminum and stainless. Some oil will help will help but then you'll need to lower your torque

http://en.wikipedia.org/wiki/Galling

 

[ex-x-fire]

I see this all the time when torqueing lug nuts, people put antiseize on the studs. When you torque them them the stud is stretching a lot b/c of the lube. Do the test yourself, it seems like the nut will turn a full 360* more after its seated then the dry one. That's the stud stretching.

 

[cookefab]

Make sure you are using the proper lubricant. A small amount on the threads and plenty under the head of the bolt and washer if it has one. I see it most commonly when torquing head bolts on aluminum blocks. Using smooth, fast pulls on the torque wrench helps too. Going slow is asking for trouble. I would recommend ARP moly lube, but it changes the torque spec when compared to using motor oil so you have to adjust accordingly.

I should add that using different lubricants won't affect torque specs with TTY bolts.

^^^this^^^....also plausible when dealing w/ grade 8+/12.8m into cast iron...i.e. hard bolt into softer metal....

 

[scouting]

When you listed that you clean the threads, did you run a bottoming tap all the way down the hole? If a taper tap was used the last so many threads may be undersized. Also when the fastener breaks the portion left in the threaded hole is it tight? And if so how are you removing it? Stud remover? Also where is the fastener breaking? Right under the head? I've had a bolt hole one time that very sharp after being regroups that was causing a lot of stress in a small area this causing extremely high pressure to generate which caused the head of the bolt to what snap.

TheGrooveking

TheGrooveking

Not the OP, but I posted about the tap. I used a bottoming tap, and measured the hole. The bolt came out fine, it just refused to torque properly. I was using a ratchet, but had the same symptoms. No extractor issues; it came out no problems, but didn't torque down right and led to an oil leak.

 

[pepi]

Someone mentioned getting new hardware, maybe worn or stripped threads. I had something similar happen when I over tightened bolts holding down a carburetor. Bought some new bolts, no problems

Holly recommends 18 inch pounds..

 

[SCTony]

Interesting article on tightening critical fasteners here- Threaded Fasteners Torque-to-Yield and Torque-to-Angle

 

[cookefab]

I see this all the time when torqueing lug nuts, people put antiseize on the studs. When you torque them them the stud is stretching a lot b/c of the lube. Do the test yourself, it seems like the nut will turn a full 360* more after its seated then the dry one. That's the stud stretching.

I have to ask...aluminum or steel wheel? If aluminum, does it have full or partial steel inserts, or none?

 

[GTA Matt]

I keep 2 old fashioned "ketchup" squeeze bottles filled with oil. One with 10w30 and one with 75w90 for when I do rear ends. I usually put just a single drop of oil at the end of wheel studs if the stud is rusty and allow the lugnut to run the oil in. Too much will cause the stud to stretch regardless of wheel or lugnut type. It is far more obvious when you are using a torque wrench as opposed to a torque stick when the stud is stretching. I use the oil drop method on just about every bolt or nut I touch unless it should be installed dry or have some type of loctite on it. Makes reassembly and dis-assembly in the future much quicker. Keep in mind that too much can be a bad thing here.

 

[KMinAF]

Most recently this occurred while tightening Subaru head bolts which are rather long, approx 13mm shank size and they are going into an aluminum case. I have had this happen on many other makes that I have worked on as well.

 

[Kracin]

you need to find out the specifications for the bolt first. its more of science than people make it out to be when you are torquing things to a precise amount. if it doesn't need to be precise, then you probably shouldn't worry.


applying engine oil to the threads of a bolt may make it glide in easier, but it certainly isn't acceptable for all kinds of bolt assembling as some oils have far better lubrication properties than others regardless of weight.

some bolts require moly lube which is use commonly on high torque bolts/studs because it helps to remove that friction lock you get before the bolt is actually up to the proper torque.

just because a torque wrench clicks, does not mean that the bolt is actually torqued and stretching enough, anyone who has assembled that requres specific torques and has ended up with a bad head gasket at one time can attest that the friction between the bolt/nut, the washers and the surface need to be lubed properly, or you will end up with a lot of torque on the wrench, and not as much force pulling it together.

it is about the same as putting a dirty bolt into a dirty hole and torquing it, it will never read correctly.



i would purchase new fasteners and some bolt/nut assembly lube (or moly lube depending on what it is). and go from there.

 

[pilotman81]

If there are OEM specs, I would follow them. If not you can usually find a general torque spec sheet that will give you general specs for the size/type of fastener that you are using. Just depends on how precise you need to be.

 

[Steinmetz]

Sometimes when tightening a bolt to torque specs, I have come across one that as it is tightened will make "snap" sound and spring forward. This concernes me because I believe I am only getting the torque reading of what I would call "frictional force" instead the actual "stretch" of the bolt. To overcome this condition I have cleaned the threads and head of the bolt, applied engine oil to the threads and head and made sure the recieving threads are clean, all to no avail. Why does this happen and how can it be overcome?

It happens because the threads are seizing. You cannot get an accurate torque until you overcome this. Try using Never Seez and alter the torque setting accordingly.

 

[ChevyEFI]

Wheel studs are intended to be dry and the torque ratings recommended by OEMs are determined accordingly.

I should add that using different lubricants won't affect torque specs with TTY bolts.

Your statement is too broad as it doesn't address the different kinds of TTY installation methods.

Unless you're able to accurately measure bolt stretch such as with a mic. on a connecting rod bolt, this isn't necessarily correct. Different lubricants do change overall torque on a "torque to X lb-ft plus ** degrees additional turn" bolt.

 

[mebuildit]

A lot of times there are a few things to take into consideration. The thread lube you are using. If it's for an engine, I like using ARP moly lubricant. It works so well and gives you a very accurate torque reading. If you are just torqueing other fasteners use a good thread lubricant, C5A is one of my favorites since you can take the bolt back apart after time has passed.
The other reason you may get a snapping sound is that your twisting either the bolt or if you are using an extension, and how tight the fastener is will twist, snap, turn. Use the shortest set up you can, and make it sturdy. Basically, if you are using an allen T handle and get the snapping sound, try using an allen bit driver. Huge difference.

Hope this helps.
Just my .02¢