Quick Bro­ken Bolt Fix

Don’t panic! Sum­mit Rac­ing and Har­bor Freight have fastquick so­lu­tions for your bro­ken bolts and da­m­aged threads.

Street Rodder - - Contents - By Jim Smart Photography by the Au­thor, Sum­mit Rac­ing & Har­bor Freight

When a bolt or screw breaks off it leaves the hot rod­der feel­ing be­fud­dled and with­out hope. But take heart, Sum­mit Rac­ing Equip­ment, Har­bor Freight, and Dave Akard of Bur­bank Speed are here to help get you back on the road.

Fas­ten­ers typ­i­cally break off due to ma­te­rial fail­ure, im­proper in­stal­la­tion, cor­ro­sion, and the galling of threads. Ma­te­rial fail­ure is a weak­ness in the fas­tener where it fails and breaks off at the weak­est point. This is nor­mally caused by a weak­ness in the ma­te­rial to be­gin with or im­proper torque (tight­en­ing), caus­ing un­due stress.

Cor­ro­sion is nor­mally gal­vanic in na­ture (dis­sim­i­lar met­als such as a steel fas­tener in an alu­minum cast­ing) where cor­ro­sion eats away at the fas­tener and cast­ing, caus­ing a weak­ness in the fas­tener.

If con­di­tions are dry you’re less likely to ex­pe­ri­ence Gal­vanic cor­ro­sion. When con­di­tions be­come wet the ci­vil­ity be­tween dis­sim­i­lar met­als goes right out the win­dow. Flu­ids such as wa­ter and acid serve as elec­trolytes to cre­ate an elec­tro­chem­i­cal re­ac­tion be­tween dis­sim­i­lar met­als. Salty air is an­other cul­prit and highly cor­ro­sive. Elec­trons be­gin their jour­ney from one metal to the other and met­als be­gin to break down. When a fas­tener and cast­ing have been screwed to­gether for years and ex­posed to the el­e­ments fail­ure of the fas­tener is in­evitable.

There are also stress is­sues that go with fas­ten­ers be­cause they’re un­der con­sid­er­able ten­sion for a long time. Stress cor­ro­sion comes from ex­po­sure to the at­mos­phere, load­ing, ten­sion, and cyclic fa­tigue. En­gine, driv­e­line, and chas­sis com­po­nents are sub­jected to ex­treme loads and cyclic fa­tigue. This is an­other rea­son why bolts and screws fail and break off. En­gine fas­ten­ers, as a prime ex­am­ple, ex­pe­ri­ence a tremen­dous amount of stress and heat cy­cling, which is why they can fail when it’s time for re­moval.

A fas­tener’s pur­pose is to pro­vide a clamp­ing force be­tween two com­po­nents to hold them to­gether. If the proper fas­tener is used and is not torqued be­yond its de­sign lim­its the fas­tener should per­form as en­gi­neered.

Once you know why fas­ten­ers fail it be­comes eas­ier to un­der­stand how to choose and prop­erly in­stall them to be­gin with. Fas­tener in­stal­la­tion should al­ways be­gin with clean, un­dam­aged

threads on both the fas­tener and bolt hole along with proper lu­bri­ca­tion dur­ing in­stal­la­tion. Thread type and pitch should be uni­form, mean­ing coarse threads in a coarse thread bolt hole or fine thread in fine thread. Ide­ally, you will be­gin with new fas­ten­ers in­stead of work­ing with bolts that have al­ready been stretched and stressed. This may seem te­dious at first glance, but which is more te­dious, painstak­ing at­ten­tion to de­tail now or bro­ken bolts when it’s time to take it apart?

Bolt threads should be lu­bri­cated dur­ing in­stal­la­tion to re­duce stress and achieve an ac­cu­rate torque read­ing. ARP Ul­tra Torque Fas­tener Assem­bly Lubri­cant should al­ways be used when you’re in­stalling fas­ten­ers be­cause it helps yield a proper torque read­ing with­out stress­ing the fas­tener. If you in­stall fas­ten­ers dry you’re not go­ing to get an ac­cu­rate torque read­ing be­cause you can get into thread bind­ing and galling.

When bolts and screws fail you’re faced with how to get them out. How­ever, bolt, screw, and plug ex­trac­tion need not be dif­fi­cult if you’re pa­tient and think the process through. If the fas­tener or plug can­not be driven out with a punch or chisel, you will have to drill it out in phases un­til it can be re­moved with an ex­trac­tor. Some­times, heat has to be ap­plied to the area around the fas­tener or plug, which causes the area to ex­pand and loosen up. Soak­ing the area with a pen­e­trat­ing lubri­cant days ahead of time of­fers some hope and re­duces the like­li­hood of fail­ure. An­other ad­ver­sity can be a nut seized on a stud or bolt, which can be res­cued with pen­e­trat­ing lube, ap­plied heat, or a com­bi­na­tion of both.

Why Bolts Break

Au­to­mo­tive Rac­ing Prod­ucts (ARP) tells us there are com­mon causes for fas­tener fail­ure. In fact each type of fas­tener has unique iden­ti­fy­ing phys­i­cal char­ac­ter­is­tics that de­fine them—and ARP can tell you all about them.

Ten­sile over­load will cause the bolt to stretch and “neck down” prior to break­age. What this means to the lay­man is ex­ces­sive ten­sion or stretch to the fas­tener. You get tor­sional shear (twist) in a fas­tener when galling takes place be­tween the male and fe­male threads (nor­mally due to us­ing the in­cor­rect lubri­cant or no lubri­cant) or when the male fas­tener’s threads (bolt) mis­align with the fe­male threads (bolt hole).

Im­pact shear is sim­i­lar in ap­pear­ance to tor­sional shear with flat fail­ure faces and ob­vi­ous di­rec­tional traces from the im­pact. With im­pact shear the failed bolts not only had to clamp the parts, they were asked to also lo­cate these parts, which is nor­mally a job for the hum­ble dowel pin. Most of the time these bolts were not suf­fi­ciently pre­loaded dur­ing in­stal­la­tion, mean­ing they were im­prop­erly torqued.

An­other rea­son for bolt break­age is Cyclic Fa­tigue in two forms: rust pit or im­proper in­stal­la­tion, ac­cord­ing to ARP. Many of the high-strength steel al­loys are sus­cep­ti­ble to stress cor­ro­sion. L-19, H-11, 300M, and Aeromet met­als are par­tic­u­larly sus­cep­ti­ble to stress cor­ro­sion and must be kept well lu­bri­cated. They can never be ex­posed to mois­ture, in­clud­ing hu­man sweat. By con­trast In­conel 718, ARP 3.5, and Cus­tom age 625+ are im­mune to both hy­dro­gen em­brit­tle­ment and stress cor­ro­sion.

ARP adds that many bolt fail­ures

are caused by in­suf­fi­cient preload (proper torque). When a fas­tener is in­suf­fi­ciently tight­ened and loaded dur­ing in­stal­la­tion the dy­namic load may ex­ceed the clamp­ing load re­sult­ing in cyclic ten­sile stress and even­tual fail­ure. In other words the bolt moves (cy­cles) back and forth and round-and-round con­stantly be­cause it was not prop­erly torqued to spec­i­fi­ca­tions.

If a fas­tener is not tight­ened prop­erly to be­gin with, it can­not ap­ply the re­quired preload (pres­sure) on the com­po­nents it is en­listed to clamp to­gether. By the same to­ken, if a fas­tener is over­tight­ened and stretched be­yond al­low­able lim­its, it is likely to fail by ex­ceed­ing its max­i­mum yield point, ARP tells us.

Bolt break­age can be avoided with the use of the cor­rect fas­tener, clean threads, bolt lubri­cant, and the proper use of a torque wrench. Never over­tighten. Never jerk a torque wrench. And never un­der-tighten. Al­ways use a cal­i­brated torque wrench and torque fas­ten­ers in one-third torque val­ues in or­der to bring on ten­sion grad­u­ally. ARP also stresses the use of new fas­ten­ers in­stead of re­cy­cling old ones. In some in­stances it is safe to re­use old fas­ten­ers. En­gine builds, as one ex­am­ple, should al­ways be treated to new fas­ten­ers, es­pe­cially in high-stress ar­eas like cylin­der heads, main caps, con­nect­ing rods, and val­ve­train. Chas­sis com­po­nents should al­ways get new Grade 8 fas­ten­ers.

When Bolt Break­age and Thread Dam­age Are Be­yond Sal­vage

Some­times bolt break­age goes be­yond sim­ple bolt ex­trac­tion to where the bolt and threads must be com­pletely drilled out. Da­m­aged threads can some­times be chased and

cleaned up with a thread chaser or tap. When they’re so badly da­m­aged they can­not be cleaned up your only choice is to drill out and re­place them with a Heli-Coil insert or a Time-Sert.

The dif­fer­ence in Heli-Coil and Time-Sert is both con­ve­nience and cost. The Heli-Coil insert is the more af­ford­able of the two and more eas­ily found lo­cally. Time-Sert is an in­cred­i­ble in­no­va­tion and, there­fore, more ex­pen­sive. Both Heli-Coil and Time-Sert re­pair kits are avail­able from Sum­mit Rac­ing Equip­ment.

When you are per­form­ing thread re­pair or re­place­ment you have to pay close at­ten­tion to de­tail. Make sure you’re us­ing the cor­rect-sized drill bit for the stripped-out hole. The drill bit must be ab­so­lutely par­al­lel to the hole. You may use a straight­edge or a pre­ci­sion steel block as a guide or even a drill press and vise if the part can be re­moved from the ve­hi­cle. Al­ways con­firm ac­cu­racy be­fore drilling be­gins.

Once you have drilled the da­m­aged threads out, re­move all de­bris from the hole with com­pressed air or a vac­uum. When you grab the cor­rect-sized Heli-Coil tap, lu­bri­cate the threads with a Per­ma­tex Fast Break Su­per Pen­e­trant and slowly run the tap in and out. Run the tap a full rev­o­lu­tion and slowly back out one-half turn to clear de­bris. Con­tinue run­ning the tap un­til threads have pen­e­trated the full depth of the hole. Wash the hole out with brake cleaner and al­low it to dry.

The Heli-Coil insert is screwed into the tapped threads un­til seated.

It is sug­gested you use Per­ma­tex Thread locker on the out­side di­am­e­ter of the Heli-Coil insert to en­sure se­cu­rity. Once the Heli-Coil is seated, break the tang off and you’re ready for assem­bly. https://bit.ly/2LkSmMg

■ A fas­tener’s job is to pro­vide clamp­ing pres­sure be­tween two parts to hold them to­gether. Ten­sion on the bolt is what ap­plies pres­sure. How we choose and in­stall fas­ten­ers de­ter­mines the suc­cess or fail­ure of the fas­tener. You must choose the right fas­tener for the job to be­gin with. Proper in­stal­la­tion then de­ter­mines suc­cess or fail­ure.1

■ Choos­ing the right fas­tener for the job di­rectly af­fects suc­cess or fail­ure. Get ed­u­cated on bolt grades and strength and choose the right fas­tener for the job. En­gines, as one ex­am­ple, get no less than Grade 8 fas­ten­ers.2

■ These high-car­bon steel cylin­der head bolts can tol­er­ate tremen­dous loads and come back for more. How­ever, these gummy threads should be cleaned up for re­use or dis­carded in ex­change for new ARP head bolts.3

4 ■ A new fas­tener is “stretched” a spe­cific amount while pro­vid­ing clamp­ing pres­sure. What’s more, the fas­tener’s abil­ity to “re­bound” like a spring is what gives you the clamp­ing force it was de­signed to pro­vide. When you ap­ply torque and stretch to a fas­tener, you are ap­ply­ing clamp­ing pres­sure. Ev­ery fas­tener has a break­ing point. ARP tells us the max­i­mum amount of al­low­able bolt stretch is 0.0005 inch be­fore the bolt be­comes com­pro­mised and needs to be dis­carded. The best pre­ven­tion against bolt break­age is fresh hard­ware with ev­ery en­gine build. ARP of­fers com­plete en­gine hard­ware kits. And what isn’t in­cluded in the kit can be sourced in­di­vid­u­ally. Proper in­stal­la­tion go­ing in is what pre­vents bolt break­age.

■ The best in­sur­ance against bolt break­age is clean threads, lu­bri­ca­tion, and proper torque. Never torque fas­ten­ers with­out lu­bri­ca­tion. Al­ways use a torque wrench. Not only do bolt and re­ceiver threads need to be lu­bri­cated, so do any con­tact sur­faces, like the bolt head where ten­sion is ap­plied, and you need an oil wedge.6

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■ Per­ma­tex Form-A-Gas­ket has been around a long time and it re­mains an in­dus­try fa­vorite be­cause it works so well. Ap­ply Form-A-Gas­ket to bolt threads and get a good pos­i­tive seal where bolts pen­e­trate wa­ter jack­ets. Form-A-Gas­ket pro­vides lu­bric­ity while torque is ap­plied then cures to pro­vide a seal. Where deep seal­ing is re­quired, Per­ma­tex Thread Sealant with Te­flon is ap­pli­ca­ble to cylin­der head bolts in wet decks and rocker arm studs that go into wa­ter jack­ets. Cool­ing sys­tems pro­vide a very cor­ro­sive en­vi­ron­ment, which is why bolt threads need to be pro­tected. You may also use Per­ma­tex’s The Right Stuff on bolt threads.8

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