Torquing bolts w/o specs

[Alex]

When you guys are torquing bolts and no specs are given, how do you determine how tight to go.

For example, do you use a general fastners table like

Bolt Depot - US Recommended Bolt Torque Table

Or a more engineering based (torque to yield less 60-70%)

Fastener Torque Table SAE Grade - Engineers Edge


I know some develop a feel for it over time, but if you don't have that skill, then what. For example, on SN95 spindle nuts on a cobra, torque is 250ft-lbs....so most people on the ffr site say just keep tightening until you're about to have a heart attack, and then you're good - only problem with that (for me), is i can torque them 1 handed, with my left hand (yaaay weightlifting), so when somebody says tight, it really doesn't mean anything to me

 

[Randy V]

Good post Alex!

Many bolts I use the clicking elbow on - the elbow has been calibrated over many years and a number of broken bolts and lost temper...

It's a good idea to do as you and use the charts/tables whenever possible.
:thumbsup:

 

[Brian Hamilton]

I go by the *Ugh* torque measurements. When tightening a bolt, sometimes you give it a full *Ugh*, sometimes a "Half a *Ugh*", sometimes a "Quarter *Ugh*". LOL


Great post btw...

 

[Ron Earp]

It's a good idea to do as you and use the charts/tables whenever possible.
:thumbsup:

I do the same. But I have to say I'm getting good and estimating torques based on bolt size, to the point I can get very close to the table without looking.

And then sometimes I use Brian's method, ugh.

And for things that "ought not ever come off and are really big" when I don't have a torque wrench I tighten until my nutz are tight and stop.

 

[Alex]

I'm beginning to get the feeling there's a reason some of you guys like to check every single nut and bolt on your vehicle every few hundred miles, hehe =)

Ironically (or maybe not so), none of the bolts in my cobra have loosened, except for 2 in the trunk (and i didn't install those 2, my bodyguy did.....I guess he only gave them an 'OMPH', instead of an 'UGH' :laugh: )

 

[Robsan]

This has been posted before but I have found it useful

FUTEK Bolt Torque Calculator | Bolt Torque Calculators

Bob

 

[Cliff Beer]

The tables are helpful, but only half the story from a practical standpoint. Meaning, it's just as important what you're torquing the bolt into - good quality steel, aluminum, pot metal, bronze, etc.

I'll put a lot less elbow grease into a bolt going into aluminum than good quality steel. Or, if the threads are tired and chasing them with a tap only marginally improves things.

You definitely do develop a sense for it over a number of years - mostly from stripping out threads or twisting the head off cheasy bolts. For example, a 5/8ths 12.9 brake caliper bolt is going to get a good "umph" with the 1/2 socket whereas a 10mm 1.0tpi grade 5 bolt holding the coil bracket isn't.....

 

[JD Doshti]

i believe that if you use the right size ratchet and have a good feel for it your alright. but i still double check with bolt grade specs and im always really close

 

[Rick Muck- Mark IV]

I do the same. But I have to say I'm getting good and estimating torques based on bolt size, to the point I can get very close to the table without looking.

And then sometimes I use Brian's method, ugh.

And for things that "ought not ever come off and are really big" when I don't have a torque wrench I tighten until my nutz are tight and stop.

Tighten 'em till they strip and then back 'em off half a turn...................

 

[Ron Earp]

I'm beginning to get the feeling there's a reason some of you guys like to check every single nut and bolt on your vehicle every few hundred miles, hehe =)

There is a reason for sure. On my race car the damnedest nuts back off and need re-tightening every few hours. In particular the half shaft bolts. I've used new bolts and I always torque to spec, but they just won't stay tightened. I'd like to loc-tite them but being is how the diff gets removed a couple of times each season that would cause some trouble.

Besides those there are always a few others here and there and just get loose. A good nut and bolting session is a must every few hours.

R

 

[Rick Muck- Mark IV]

I'd like to loc-tite them but being is how the diff gets removed a couple of times each season that would cause some trouble.


R

Use Loctite "Stud and Bearing Mount" and you will never worry about them comng adrift........of course you will need to torch the crossmember out to remove the diff, but the bolts won't loosen!

 

[Randy V]

Use Loctite "Stud and Bearing Mount" and you will never worry about them comng adrift........of course you will need to torch the crossmember out to remove the diff, but the bolts won't loosen!

Depends actually....

Bolts have been known to stretch - which all the Loctite Red in the world will not address...

The bolt probably won't be loose - but whatever it was clamping will be...

I nut-n-bolt my racecars after every event.

 

[Brian Hamilton]

There is a reason for sure. On my race car the damnedest nuts back off and need re-tightening every few hours. In particular the half shaft bolts. I've used new bolts and I always torque to spec, but they just won't stay tightened. I'd like to loc-tite them but being is how the diff gets removed a couple of times each season that would cause some trouble.

Besides those there are always a few others here and there and just get loose. A good nut and bolting session is a must every few hours.

R

Have you thought about safety-wiring them? There's a couple of different methods to do it, drill straight through the nut and bolt, then you can just drill through a portion of the nut and safety wire them all together in kind of a criss-cross pattern. Let me see if I can find a picture...

http://www.oldbritts.com/image/52_130202b.jpg

http://www.tpub.com/content/aviation/14014/img/14014_116_1.jpg

I'm sure you all know what I'm talking about though. LOL

 

[Cliff Beer]

McMaster has drilled socket cap bolts in a sufficient grade for U/CV jointed half shafts: McMaster-Carr Not sure if they have metric however.

 

[Alex]

Alright, stupid question time - I'm getting ready to re-torque the suspension, and was wondering something about the bolt that hold the control arms (rear) to the mounts.

The uppers are 1/2'', lowers are either 9/16 or 5/18 ..... this means the uppers (according to tables) are in at approx. 80ft-lbs, the lowers about 130ft-lbs.

This seems like a lot of torque to me, especially with heim joints in the middle - don't you risk bending the bracket ears in and crushing the heim joint?

 

[JimmyMac]

McMaster has drilled socket cap bolts in a sufficient grade for U/CV jointed half shafts: McMaster-Carr Not sure if they have metric however.

I use many safety wired or pinned fasteners and drill my own set screws and bolts using this jig for accuracy.

 

[Randy V]

Alright, stupid question time - I'm getting ready to re-torque the suspension, and was wondering something about the bolt that hold the control arms (rear) to the mounts.

The uppers are 1/2'', lowers are either 9/16 or 5/18 ..... this means the uppers (according to tables) are in at approx. 80ft-lbs, the lowers about 130ft-lbs.

This seems like a lot of torque to me, especially with heim joints in the middle - don't you risk bending the bracket ears in and crushing the heim joint?

Hi Alex,

Those bolts are in shear. You really don't need that much torque on them. If the bolts you have are using locking nuts (Nylocs came on my RCR40), I would bring them to 45-50 Ft Lbs and call it good - BUT - I would also put a dab of paint on the nut to the threads to show me (upon inspection) that the nuts are not turning on the bolts.

Bending the brackets - you should be using shims to remove most of the excess slack in the bracket to the heims. If you have to squeeze more than say .020" of slack out of the bracket - It would be advisable to find the correct shim.

 

[Chris P.]

On my race car the damnedest nuts back off and need re-tightening every few hours.

Sounds like maybe the threads are getting worn? Have you tried Heli-Coiling them? I would personally Loctite them. I also only bother torquing the really important ones that holding loads mainly in tension and compression.

3 things which many here know, but in case some don't:

1) If you are going to nut and bolt your car (check for loose nuts and bolts), don't give each one a little turn to check; just put enough force on it to see if it has loosened up. If you nut and bolt frequently and always give everything just a little turn each time, you will before long over tighten things. Sounds obvious, but people do that.

2) Torquing is not done to keep fasteners from loosening - it is just one of several methods available to "pretension" the fastener. If you were to take the time to look at a properly tightened bolt joint on paper, you will see that for jointed assemblies that see cyclical tension/compression loading, a properly pretensioned fastener will survive A LOT longer than one that is not. This is why rod bolts and head bolts are so religiously torqued - they live their entire lives with cyclical tension/compression loads.

3) Proper torquing requires some form of lubricant on the threads. The k-factor in those torque calculations is precisely for this reason. It is a factor to take in to account friction between not only the threads, but also friction under the head of the bolt / nut. Also - I have seen people (mechanics no less) jerk the torque wrench near the end of tightening to get it to click. :speechless: You need to get it right so it clicks while you're still turning it somewhat slowly, but more importantly at a constant speed.

Anyway, off my soap box.

 

[Alex]

Alright, further clarification time

There are 2 locations so far I've found for 5/8'' bolts.

1 is on the rear rocker arm (holds it to the frame; gigantic socket head screw)

1 is on the rear lower control arms, that holds it to the frame

Recommended torque for 5/8'' bolt is 150ft-lbs.

Now I can see 150ft-lbs for the rocker since it's to the frame, but 150ft-lbs for the control arm seems.....unusual. Why would the lower control arm (arm to frame mount) be at 150ft-lbs, btu the upper (arm to frame mount) is in at 80ft-lbs...................

 

[Ron Earp]

Sounds like maybe the threads are getting worn? Have you tried Heli-Coiling them? I would personally Loctite them. I also only bother torquing the really important ones that holding loads mainly in tension and compression.

They're shoulder bolts in shear that hold the half shafts to the stub axle, and the driveshaft to the diff input flange. I can't helicoil them, but I have tried new bolts but generally get the same effect. I'd safety wire them but every other weekend the diff gets changed for a different diff/ratio and that'd be a pain in the ass. The tightening every few hours works and isn't a huge deal. I need to be under there inspecting other things anyhow.