Torque spec below torque required to thread bolt in

[vavavroom]

I have run into this problem a couple times. I can't recall the specifics because it was years ago. I remember a fairly long bolt to be tightened to something like 15 ft-lbs. Although I had thoroughly cleaned the threaded hole and despite a new bolt, just threading the bolt in required more than 15-ft-lbs. When I noticed this I tried the old bolt to see if may the new bolt was out of spec. The old bolt also required excessive torque.How do you deal with a situation like that?

 

[The Critic]

Threads may have damage. Use a tap of the appropriate diameter/pitch to clean the threads before attempting.
Bolts should always thread-in smoothly. If they do not, STOP....otherwise you may break off the bolt.

 

[Leo99]

Be sure it's not cross threaded and it's not too rusty. I know in my younger days, I'd just crank that bolt down until it stopped and was hopefully seated and nothing broke.

 

[JeffKeryk]

Sounds like the threads are boogered up.
I keep a couple of Honda and Toyletta oil drain plugs on hand for just this purpose.
If they won't thread in by fingers only, I throw 'em away.

As the Critic says, break out the taps.

 

[Trav]

Take a old bolt and with a cutting wheel in a Dremel cut 3-4 flutes (just straight lines) lengthwise about twice the bolt diameter (eg M10 bolt cut about 20mm up from the end) then thread it in. This will act as a thread chaser without actually cutting the threads like a tap instead rolling them like original.

 

[ABN_CBT_ENGR]

As many have said, you have a problem so isolate it and fix it ( real easy to say) but don't pull the taps out just yet.

Based on your assessment, you have a joint problem ( maybe not a bolt problem)

You need to examine everything for binding first, to include: mating surfaces, bore/hole alignment, proper sized fastener.

Lets assume all that's good.

Now check the bolt, is it: straight, the RIGHT THREAD ( count/pitch/angle etc?) and the right ISO FIT CLASS?. Is it the right finish and grade? Is the thread/shank length ratio right?

you say you cleaned it? How? Is there stuff packed in it? Bad finish? ( need to check it carefully and clean it with a bore brush and blow it out good.)

Lets assume all that's good.

Now you probably have damaged threads and many gauges wont fit in parent threads. If you have it available, you want to use a bottom tap as opposed to a starter tap.

You want the tap as the last resort because almost all thread chasing/cutting changes the fit, geometry and mass of the threads which significantly de-rates the joint strength and at 15 lbs. ft., you aint got much to begin with.

I probably would go helicoil if the joint is a critical one

 

[ABN_CBT_ENGR]

Take a old bolt and with a cutting wheel in a Dremel cut 3-4 flutes (just straight lines) lengthwise about twice the bolt diameter (eg M10 bolt cut about 20mm up from the end) then thread it in. This will act as a thread chaser without actually cutting the threads like a tap instead rolling them like original.

I recommend this method over the tap IF you are familiar with it and can go by feel

 

[Astro14]

Take a old bolt and with a cutting wheel in a Dremel cut 3-4 flutes (just straight lines) lengthwise about twice the bolt diameter (eg M10 bolt cut about 20mm up from the end) then thread it in. This will act as a thread chaser without actually cutting the threads like a tap instead rolling them like original.

I have an assortment of thread chasers made of old bolts in exactly this manner.

In working on a 1975 MB 450 SL recently, they have been used extensively, many of those old bolt holes have corrosion, some to the point that new bolts won't hand thread to full depth.

The thread chaser is a critical tool for those situations, cleaning corrosion and debris from the old bolt holes so that new bolts can be properly threaded and torqued.

They clean what bore brushes and solvent alone can't remedy.

 

[Trav]

Yes, I made a bunch of them from 12.9 bolts (they last longer) but the ones that can really save the day are the brake line nuts. I got a job one time come on a hook, the guy buggered the threads putting in a brake line, no tap locally available so I cut some flutes down a longer brake line nut, got it started and it went like a champ, threaded perfectly after that.

 

[ecotourist]

I have an assortment of thread chasers made of old bolts in exactly this manner.

Could you post a photo of one? I understand the concept but it's hard to visualize exactly what you mean.

When you cut across threads don't you have rough threads right at the cut? Or do you file off the roughness?

 

[Astro14]

I can post tomorrow.

Basically, three slots up the length of the bolt. Cut just past the depth of the shank, leave the edges sharp, so that it’s like a tap with very narrow flutes.

It’ll clean the threads without removing metal.

 

[wpod]

Take a old bolt and with a cutting wheel in a Dremel cut 3-4 flutes (just straight lines) lengthwise about twice the bolt diameter (eg M10 bolt cut about 20mm up from the end) then thread it in. This will act as a thread chaser without actually cutting the threads like a tap instead rolling them like original.

Trav is the master !!!

 

[vavavroom]

The bolt was the right size and straight, the threaded hole was clean. The bolt was not cross-threaded. I remember thinking that the part the bolt had to go into was probably a bit bent. Just bent enough to increase friction. I just can't remember what part it actually was but it was not something I could have easily replaced.
.

 

[ABN_CBT_ENGR]

Could you post a photo of one? I understand the concept but it's hard to visualize exactly what you mean.

When you cut across threads don't you have rough threads right at the cut? Or do you file off the roughness?

Let me give you some additional "advice" for the beginner because the method you will be shown pictures does work ( very well in many cases) but has some caveats that can make it turn left in a hurry.

You must only use strong high end bolts to begin with ( not hardware/Wal Mart grade) preferably plated. This is because bolts are rarely hardened ( defined as resistance to deformation such as a tap or drill) but actually designed to "stretch" ( pull tension). You want the "chaser" hopefully harder than the parent thread you are cleaning. ( you don't want it to twist and break or gall)

You most likely will need to chase the bolt threads after you cut your flutes ( can be as simple as running a nut down then backing off when complete). You may need to dress ends as well.

You also need to inspect the suspect threads. "Chasing" and "Cleaning" threads is basically either scraping off "stuff" and/or straightening something deformed. ( wedging it back in place. If the suspect threads are galled or bradded down, its best to not even try chasing in the first place and go straight to thread repair/replacement. ( last thing you want is to jam/break the chaser in the hole)

Back and clean out frequently- those grooves collect "stuff" they are not helix's that will evacuate them like a drill.

Do NOT use a lubricant- use a cutting oil or anti-galling compound. ( traditional lubricants tend to want to make cutting surfaces "slide" along the surface like traditional tribology demands- you want to scrape clean but at the same time not become a galling agent so those products are better suited for that)

Hope that helps.

 

[Trav]

Could you post a photo of one? I understand the concept but it's hard to visualize exactly what you mean.

When you cut across threads don't you have rough threads right at the cut? Or do you file off the roughness?

I round the nose a little so it starts easier then put 3-4 cuts in it, bigger bolts eg M12 and bigger I cut 4, this is an M10 so it has 3. It took 4 minutes to make this one.
If you use hardened bolts and cut the flutes wider and longer it makes a working emergency tap for soft metals but I wouldnt recommend it if a real tap is available. Do not take a file to the flutes, they need to be sharp.

 

[ecotourist]

I round the nose a little so it starts easier then put 3-4 cuts in it, bigger bolts eg M12 and bigger I cut 4, this is an M10 so it has 3. It took 4 minutes to make this one.
If you use hardened bolts and cut the flutes wider and longer it makes a working emergency tap for soft metals but I wouldnt recommend it if a real tap is available. Do not take a file to the flutes, they need to be sharp.
View attachment 32590

Thanks Trav and ABN. I appreciate the discussion and the photo.

 

[OilUzer]

I've used WD-40 on rusty bolts and thread holes. Spray some in there and let it drip and repeat ... also clean the bolt with WD-40 (I soak it in a cup and leave it for few hours or overnight) then slowly try to thread a few times and repeat ... Sometimes I also use compressed air to get the stuff and the leftover WD-40 out.

so far this has worked out for me But sounds like lubricant may not be recommended based on the above posts but I clean the lubricant.

 

[ABN_CBT_ENGR]

But sounds like lubricant may not be recommended based on the above posts but I clean the lubricant.

No, lubricant is a good thing ( and cutting oils do lubricate but that's not their primary purpose in cutting) but these are extreme cases described up there.