Broken Crank bolt removal
10-03-2007, 02:34 AM
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Broken Crank bolt removal Removal of broken off harmonic balancer bolt in LS engines
I started reading the forum pages as a way to pass the dead time while over here in Iraq. Alarmingly, I’ve seen quite few folks who’ve had to deal with fasteners shearing off inside holes when attempting to remove them, specifically harmonic balancer bolts. Hopefully, this will help some people with getting back on the road.
I’ve been a custom gunmaker for the past 8 years. Prior to building rifles, I was a machinist working in the aerospace, nuclear, medical, and auto racing industries. Repairing and reconditioning threaded holes comes with this work quite often.
So, let’s get started.
The LS engines use a torque to yield type fastener for retaining the harmonic balancer. What is a torque to yield bolt? How is it different from other fasteners? This is taken directly from another site, http://www.boltscience.com/pages/faq.htm and it defines TTY fasteners:
Torque to yield is the method of tightening a fastener so that a high preload is achieved by tightening up the yield point of the fastener material. To do this consistently requires special equipment that monitors the tightening process. Basically, as the tightening is being completed the equipment monitors the torque verses angle of rotation of the fastener. When it deviates from a specified gradient by a certain amount the tool stops the tightening process. The deviation from a specified gradient indicates that the fastener material as yielded.
The torque to yield method is sometimes called yield controlled tightening or joint controlled tightening.
What we learn from this is that the bolt is being stretched as it is tightened so that it applies a high tensile (think spring) load on the parts it is holding together. This is where the problem lies when taking it apart. Overcoming the shear loads and friction coefficients on the fastener is what is breaking the thing when attempting to remove it. As a preventative measure, perhaps a shot of Kroil on the bolt head prior to removal will aid in the success rate and make the rest of this thread just recreational reading.
Below is a list of suggested tools. The quality of your tooling has a direct result on the outcome of your problem. Cheaply made tooling will more than likely result in greater frustration. Home Depot and Sears are not the best choice for the cutting tools. Take the time to locate a machine tooling supply shop or go to a mail order like MSC Industrial Supply, Granger, or McMaster Carr. Harbor Freight and the flea market should be avoided at all costs.
1. Can of Kroil brand frozen bolt lubricant.
2. Electric drill with sufficient power to drill steel for prolonged periods (if cordless, charge your batteries!)
3. Transfer punch set.
4. #2 High Speed Steel (HSS) Center drill. DO NOT BUY SOLID CARBIDE THINKING IT’LL WORK BETTER, IT WON’T. YOU’LL JUST BREAK THE TOOL AND BE REALLY SCREWED.
5. High quality Torx bits on 3/8 socket drives
6. Split point (118*) Stub or Jobber length drill index
7. Ball Peen hammer
8. Hot air gun
9. Clean rag soaked in water
10. Patience (most important)
11. Small container with 30 or 40 weight oil (High sulfur content cutting oil like “Mobile Vactra” is the best choice but not an absolute requirement)
Begin by selecting a transfer punch that just slips inside the hole on the crank snout (assuming your bolt is broken off inside the hole) One firm smack with a ball peen hammer will make a mark for your center drill.
Chuck up your center drill and using moderate pressure and rpm, drill your hole to a depth of about an eighth (.125”) of an inch. Use some oil on the tool to aid in cutting and to manage the chips.
Select your drill. As you do this, there are some things to before starting. If you notice, I did not suggest using an EZ out in the tooling list. EZ outs are great but they can work against themselves sometimes too. An EZ out attempts to expand the material as it screws into the fastener. It does this because the diametric pressure helps the tool to bite into the material. An EZ out is also tapered. In order to gain a good amount of surface contact, you must drive it into the bolt a fair amount. This further complicates the expansion into the hole.
I like torx bits because they provide good purchase with minimal expansion. The flute shape of the tool promotes good surface contact. This also requires good tools made from high quality, heat treated tool grade steel. (Craftsman is ok, but Mac/Snap-On is better) as cheap ones will just shear off and break.
You want to use the largest torx bit you possibly can while being mindful that you need to maintain some material around the outside of the bolt hole to support the inserted tool. If you strip out the hole you will have even bigger problems.
Look at the face of the torx bit. Now, common sense applies. Your drill cannot be smaller than the root diameter of the tool. The root diameter is measured across the root of two flutes directly across from one another. Imagine a circle around the root of the bit. Your drill cannot be a great deal smaller than that circle. A tiny bit is ok and will promote good purchase, too much and you might as well try to drive the tool through a brick wall. It just won’t work.
Now that your drill size is selected, begin carefully drilling your hole using moderate pressure and rpm. About a thousand rpm should work well for most applications. High speed just means more heat and the danger of either dulling the tool which increases heat and this can work harden the material. A BIG NO NO!
Use plenty of oil and be sure to remove the drill from the hole to evacuate the chips. Chips in a hole do two things. It enlarges the hole because the drill will run off center and it breaks tools. Two things cannot occupy the same space at the same time. Obviously, you want to do everything you can to ensure the hole is drilled straight and concentric with the bore. The ideal solution being having a guide made from mild steel that slips over the crank snout and has a hole on center with the crankshaft. A machine shop can do this, but may charge you a pretty penny. Profit from it and rent it out on the forums. . .(hmm?)
Hopefully your bolt has a space behind it and is not bottomed out into the crank snout. This space will work for us.
Now squirt a good dose of Kroil into the hole. Kroil is the fluid of choice here because it has a high capillary action. WD 40 doesn’t have this quality so don’t use it. More than likely, you’ll only get one shot at this so stack the deck in your favor every chance you get.
Now take your torx bit and drive it into the hole with a ball peen hammer. Seat it as deep as you can to gain as much purchase as possible.
Take your wet rag and wrap it around the base of the crank snout around the seal. This is to keep the hot air gun from cooking the rubber seal on the timing chain cover.
Hot air gun time. Begin heating the crank snout. Hot air is the cats meow because it is not an open flame that can damage the surface finish or start a fire in an engine compartment. It won’t oxidize things. I’ve used hot air to remove stuck barrels from $20K custom built African Dangerous Game rifles without damaging the blued finish a bunch of times. Works great!
Heat evenly and concentrate around the periphery of the snout in the location of the broken bolt. After a few minutes, you should see white smoke begin to appear when you remove the hot air. This is what you want. The Kroil is being heated and it is expanding. This expansion is pushing the fluid between the threads. The torx bit is acting as a partial plug right now to aid in this.
Once you have a good deal of smoke, allow the crank to sit for about 5 or ten minutes. This will allow some additional time for the lube to creep into the threads.
Heat the crank snout again and then begin applying an even, deliberate pressure with a breaker bar. Make sure you go the right way. Lefty Loosey, righty tighty.
With any luck the bolt will drop the attitude and back itself out of the hole. Don’t rush, if you have time to do it twice, you have the time to get it right the first time.
Assuming things go well. . .
Once the bolt is out, chase the threads with either a tap or a thread chaser (preferred) and then flush with brake clean and compressed air. Get a flashlight and physically look down inside the hole to ensure the chips are gone and that the threads are in good shape. This is when a 45 caliber bronze pistol bore brush is a great asset for scrubbing the hole. If the threads are garfooned, you may have to consider pulling the crank and having it enlarged to the next size up bolt. This’ll require pulling the engine. No fun, so lets hope you got lucky. Yes, it could be drilled with a hand drill and then retapped. I won’t advocate this. My advice is to either get a new crank, or take it to a machine shop. If you go that route, have a key way cut into it at the same time and kill two birds with one stone.
That about covers it. I hope this helps someone and wasn’t too boring a read.
Some additional information that might be helpful:
Tap and drill sizes. Metrics are the easiest to use because you don’t need an elaborate chart. Not for a car anyways.
You just take the diameter and subtract the pitch.
Example: 10X.5 mm bolt. 10mm diameter, .5mm pitch, Ten minus .5 equals 9.5. 9.5mm is the drill size you’d want to use.
Conversions. One millimeter is .03937” inches long. It takes 25.4 millimeters to equal and inch. So, if you have an 8mm hole and want to convert to inches, just multiply 8 times .03937 and you’ll have your decimal fractional equivalent. (.31496” or just .315”)
I wish I had some photos but fortunately, I haven’t had to repair one of these yet.
Good luck and hope this helps someone out.
I started reading the forum pages as a way to pass the dead time while over here in Iraq. Alarmingly, I’ve seen quite few folks who’ve had to deal with fasteners shearing off inside holes when attempting to remove them, specifically harmonic balancer bolts. Hopefully, this will help some people with getting back on the road.
I’ve been a custom gunmaker for the past 8 years. Prior to building rifles, I was a machinist working in the aerospace, nuclear, medical, and auto racing industries. Repairing and reconditioning threaded holes comes with this work quite often.
So, let’s get started.
The LS engines use a torque to yield type fastener for retaining the harmonic balancer. What is a torque to yield bolt? How is it different from other fasteners? This is taken directly from another site, http://www.boltscience.com/pages/faq.htm and it defines TTY fasteners:
Torque to yield is the method of tightening a fastener so that a high preload is achieved by tightening up the yield point of the fastener material. To do this consistently requires special equipment that monitors the tightening process. Basically, as the tightening is being completed the equipment monitors the torque verses angle of rotation of the fastener. When it deviates from a specified gradient by a certain amount the tool stops the tightening process. The deviation from a specified gradient indicates that the fastener material as yielded.
The torque to yield method is sometimes called yield controlled tightening or joint controlled tightening.
What we learn from this is that the bolt is being stretched as it is tightened so that it applies a high tensile (think spring) load on the parts it is holding together. This is where the problem lies when taking it apart. Overcoming the shear loads and friction coefficients on the fastener is what is breaking the thing when attempting to remove it. As a preventative measure, perhaps a shot of Kroil on the bolt head prior to removal will aid in the success rate and make the rest of this thread just recreational reading.
Below is a list of suggested tools. The quality of your tooling has a direct result on the outcome of your problem. Cheaply made tooling will more than likely result in greater frustration. Home Depot and Sears are not the best choice for the cutting tools. Take the time to locate a machine tooling supply shop or go to a mail order like MSC Industrial Supply, Granger, or McMaster Carr. Harbor Freight and the flea market should be avoided at all costs.
1. Can of Kroil brand frozen bolt lubricant.
2. Electric drill with sufficient power to drill steel for prolonged periods (if cordless, charge your batteries!)
3. Transfer punch set.
4. #2 High Speed Steel (HSS) Center drill. DO NOT BUY SOLID CARBIDE THINKING IT’LL WORK BETTER, IT WON’T. YOU’LL JUST BREAK THE TOOL AND BE REALLY SCREWED.
5. High quality Torx bits on 3/8 socket drives
6. Split point (118*) Stub or Jobber length drill index
7. Ball Peen hammer
8. Hot air gun
9. Clean rag soaked in water
10. Patience (most important)
11. Small container with 30 or 40 weight oil (High sulfur content cutting oil like “Mobile Vactra” is the best choice but not an absolute requirement)
Begin by selecting a transfer punch that just slips inside the hole on the crank snout (assuming your bolt is broken off inside the hole) One firm smack with a ball peen hammer will make a mark for your center drill.
Chuck up your center drill and using moderate pressure and rpm, drill your hole to a depth of about an eighth (.125”) of an inch. Use some oil on the tool to aid in cutting and to manage the chips.
Select your drill. As you do this, there are some things to before starting. If you notice, I did not suggest using an EZ out in the tooling list. EZ outs are great but they can work against themselves sometimes too. An EZ out attempts to expand the material as it screws into the fastener. It does this because the diametric pressure helps the tool to bite into the material. An EZ out is also tapered. In order to gain a good amount of surface contact, you must drive it into the bolt a fair amount. This further complicates the expansion into the hole.
I like torx bits because they provide good purchase with minimal expansion. The flute shape of the tool promotes good surface contact. This also requires good tools made from high quality, heat treated tool grade steel. (Craftsman is ok, but Mac/Snap-On is better) as cheap ones will just shear off and break.
You want to use the largest torx bit you possibly can while being mindful that you need to maintain some material around the outside of the bolt hole to support the inserted tool. If you strip out the hole you will have even bigger problems.
Look at the face of the torx bit. Now, common sense applies. Your drill cannot be smaller than the root diameter of the tool. The root diameter is measured across the root of two flutes directly across from one another. Imagine a circle around the root of the bit. Your drill cannot be a great deal smaller than that circle. A tiny bit is ok and will promote good purchase, too much and you might as well try to drive the tool through a brick wall. It just won’t work.
Now that your drill size is selected, begin carefully drilling your hole using moderate pressure and rpm. About a thousand rpm should work well for most applications. High speed just means more heat and the danger of either dulling the tool which increases heat and this can work harden the material. A BIG NO NO!
Use plenty of oil and be sure to remove the drill from the hole to evacuate the chips. Chips in a hole do two things. It enlarges the hole because the drill will run off center and it breaks tools. Two things cannot occupy the same space at the same time. Obviously, you want to do everything you can to ensure the hole is drilled straight and concentric with the bore. The ideal solution being having a guide made from mild steel that slips over the crank snout and has a hole on center with the crankshaft. A machine shop can do this, but may charge you a pretty penny. Profit from it and rent it out on the forums. . .(hmm?)
Hopefully your bolt has a space behind it and is not bottomed out into the crank snout. This space will work for us.
Now squirt a good dose of Kroil into the hole. Kroil is the fluid of choice here because it has a high capillary action. WD 40 doesn’t have this quality so don’t use it. More than likely, you’ll only get one shot at this so stack the deck in your favor every chance you get.
Now take your torx bit and drive it into the hole with a ball peen hammer. Seat it as deep as you can to gain as much purchase as possible.
Take your wet rag and wrap it around the base of the crank snout around the seal. This is to keep the hot air gun from cooking the rubber seal on the timing chain cover.
Hot air gun time. Begin heating the crank snout. Hot air is the cats meow because it is not an open flame that can damage the surface finish or start a fire in an engine compartment. It won’t oxidize things. I’ve used hot air to remove stuck barrels from $20K custom built African Dangerous Game rifles without damaging the blued finish a bunch of times. Works great!
Heat evenly and concentrate around the periphery of the snout in the location of the broken bolt. After a few minutes, you should see white smoke begin to appear when you remove the hot air. This is what you want. The Kroil is being heated and it is expanding. This expansion is pushing the fluid between the threads. The torx bit is acting as a partial plug right now to aid in this.
Once you have a good deal of smoke, allow the crank to sit for about 5 or ten minutes. This will allow some additional time for the lube to creep into the threads.
Heat the crank snout again and then begin applying an even, deliberate pressure with a breaker bar. Make sure you go the right way. Lefty Loosey, righty tighty.
With any luck the bolt will drop the attitude and back itself out of the hole. Don’t rush, if you have time to do it twice, you have the time to get it right the first time.
Assuming things go well. . .
Once the bolt is out, chase the threads with either a tap or a thread chaser (preferred) and then flush with brake clean and compressed air. Get a flashlight and physically look down inside the hole to ensure the chips are gone and that the threads are in good shape. This is when a 45 caliber bronze pistol bore brush is a great asset for scrubbing the hole. If the threads are garfooned, you may have to consider pulling the crank and having it enlarged to the next size up bolt. This’ll require pulling the engine. No fun, so lets hope you got lucky. Yes, it could be drilled with a hand drill and then retapped. I won’t advocate this. My advice is to either get a new crank, or take it to a machine shop. If you go that route, have a key way cut into it at the same time and kill two birds with one stone.
That about covers it. I hope this helps someone and wasn’t too boring a read.
Some additional information that might be helpful:
Tap and drill sizes. Metrics are the easiest to use because you don’t need an elaborate chart. Not for a car anyways.
You just take the diameter and subtract the pitch.
Example: 10X.5 mm bolt. 10mm diameter, .5mm pitch, Ten minus .5 equals 9.5. 9.5mm is the drill size you’d want to use.
Conversions. One millimeter is .03937” inches long. It takes 25.4 millimeters to equal and inch. So, if you have an 8mm hole and want to convert to inches, just multiply 8 times .03937 and you’ll have your decimal fractional equivalent. (.31496” or just .315”)
I wish I had some photos but fortunately, I haven’t had to repair one of these yet.
Good luck and hope this helps someone out.
These are some great tips and ideas. I'm going to make myself a copy, I'm sure I'll need it again in the future. 
10-03-2007, 04:07 PM
#3
I have seen many broken bolt threads. There seems to be a common theme in my opinion, that is not using correct tools.
Using the old bolt to hold the load required for pulling the old unit off is a bad way to do this. You have no control over how many threads are loaded and any thread damage, while not apparent, may become so during re-installation.
A longer bolt is not the correct way to re-install. You want full thread engagement before loading them up with the forces required to press on the new unit.
On aftermarket pulleys (and the stock unit), an interference fit is required. Typical interference is 0.0007 - 0.0011" or in that vicinity. Point being, the hub is smaller than the crank by several ten-thousands of an inch. No one measures, which you are supposed to. If you fall out of the tolerance range, you have to hone the hub to obtain the correct interference fit. I have stated this in several threads and several times gotten negative responses.
You mention the bolt preload, not many understand this and tend to smother the bolt with red Loctite. This is another bad approach as we have now completely locked the threads of a bolt that has exceeded it material yield point.
I have changed several of these. I never push on the threads with the puller, rather I made a thick 1-1/4" diameter disc of steel that sits on a socket and I push on the end of the crank. No threads involved for removal at all. For re-installation, you can make your own tool for under $20 that engages all the threads and will press the pulley on quite nicely. Finally, so far I have been fortunate with the aftermarket pulleys, the interference has fallen within the required range.
PS: Stay safe over there !!!
Using the old bolt to hold the load required for pulling the old unit off is a bad way to do this. You have no control over how many threads are loaded and any thread damage, while not apparent, may become so during re-installation.
A longer bolt is not the correct way to re-install. You want full thread engagement before loading them up with the forces required to press on the new unit.
On aftermarket pulleys (and the stock unit), an interference fit is required. Typical interference is 0.0007 - 0.0011" or in that vicinity. Point being, the hub is smaller than the crank by several ten-thousands of an inch. No one measures, which you are supposed to. If you fall out of the tolerance range, you have to hone the hub to obtain the correct interference fit. I have stated this in several threads and several times gotten negative responses.
You mention the bolt preload, not many understand this and tend to smother the bolt with red Loctite. This is another bad approach as we have now completely locked the threads of a bolt that has exceeded it material yield point.
I have changed several of these. I never push on the threads with the puller, rather I made a thick 1-1/4" diameter disc of steel that sits on a socket and I push on the end of the crank. No threads involved for removal at all. For re-installation, you can make your own tool for under $20 that engages all the threads and will press the pulley on quite nicely. Finally, so far I have been fortunate with the aftermarket pulleys, the interference has fallen within the required range.
PS: Stay safe over there !!!
Last edited by vettenuts; 10-03-2007 at 05:43 PM.
