I'm building a 928 hybrid engine which is comprised of a 5.0L 32 valve short block with 16 valve euro spec "S" heads, spyder and CIS from the 4.7L "S" engine.

I stole some time from my busy work schedule to prep my 928 block for the machine shop. The head studs need to be removed for the boring process.

Now I've pulled studs before without incedent. But as Murphy would have it, this time I broke one of the studs flush at the start of the threads.

So I have the threaded section ( 1 1/4"long ) hardened head bolt stuck in the block. Normally this wouldn't be a problem, but the stud is free standing in a 3 1/2" deep hole in the block!

Here's a crude drawing of the problem I'm faced with.

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Here's the stud.

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Here's the stark reality of the stud in and out of the block. The stud slides down a 3 1/2" deep hole in the block before it starts to thread in.

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I'm going to make a drill collet as a guide for a pilot bit. The problem is I need a long, reverse twist drill bit.

Most drill bits are approx 5" long. the hole is 3 1/2", the threaded section is 1 1/4" for a total of 4 3/4". See the problem?

Then, what the #$!! do you drill a hardened bolt with?

Anyone know of a good tool source? This is beyond most Mac and Snap on stuff I would think.

Let your machinist deal with it?

Probably end up drilling it out on a press, and then putting in an insert.

Zach

Looks like a "major malfunction".

What a bizzar manufactoring method....

Rick the guy I started out working for had the EXACT same thing happen while torqueing a head. His solution was to holler F*CK, throw his torque wrench on the floor, tell the engine what a M+%*$( %)@_%*%^@!(#)% piece of $#&$(^(#&@#*^(#!@$&^@#$% it was, and let the mahinist fix it. IIRC he clamped it in the mill and basically ate the stud away then put a time cert in the block. Sorry to hear. Sux big time

Could always use that spare block that came from California by way of Texas couldnt you Since your doing the hybrid thing and all

I have no idea what the cost of this is, but EDM (Electrical Discharge Machining) aka Spark Erosion may be the right tool for the job.

Maybe you can find someone local to you like this guy (found via Google search)...

http://www.brokentap.com/

Another Google search for EDM services, but this time for someone in MN...

http://www.twincityedm.com/

Good luck on getting the stud removed!

I believe the correct bit is made from Cobalt.
These or carbide bits.
Look at McMaster Carr, MSC, or Grainger for the correct bit(S)

You will need at least two bits to work up to the right size.
Drill press would be the way to go, but you can also use a hand drill.
Think about buying a long section of bronze to make a collar that keeps you straight.

The tap will be from the same industrial hardware guys also...it needs to be long.

Rich

Totally!

The drill guide should also work. The biggest problem is getting the drill to start in the center of the stud and not wander off center. Then you are drilling the case and not the stud. A properly setup EDM should be able to remove all the stud except the threads which may still be tricky to get out because of how deep the stud is in the block. Take the block to someone with equipment like EDM and / or a mill. Lots of luck Rick.

Larry, I broke that CA. block when I had a valve fail.

I found a EDM place. Their 180 miles away. Not the worse thing, at least there's one in the state.

http://www.twincityedm.com/contactus.htm

Rick,

There is a tool dealer in st paul, Norseman drill & tool, 651-227-8911 or 800-328 -4655 that has wonderful drills and cutters.

They have made mill tools to spec for me and might be able to help you.
Good luck!

Jule

Rick,

If you go the EDM route, I would be curious to hear what they charge for that type of work. Just for future reference. I think something like this is pretty much in the future of anyone who does their own engine work.

Richard

I contacted the EDM guy. He didn't think he could work 3 1/2" deep inside a 5/8" inside hole.

It's up to me. Thanks for the lead for the drill source in St. Paul.

I called them. They only have left hand bits in jobber length, (3/8"=5" long) and only sell to jobbers like the Tool Crib, etc.

Still looking. I need left hand drill bits approximatly 7" long. And a thread extractor as long

BTW: My machine shop offered to drill it out and install a time sert (sp) then remembered the threaded part is 3 1/2" in the block... Maybe not.

A good EDM guy can probably do it. I have a number for one, but he's in LA, CA. He does work for many of the bug Top Fuel guys, including Johnson Racing here in Santa Maria.

Aircraft work sometimes requires extra long drill bits- say 12 inches or so......

These are not reverse twist but they might be a workaround and the prices aren't too bad.....

Aircraft 12 inch long drills linky link

I do like the guide pilot idea if the bore isn't tapered.

Ken

OK, I did some deep thinking about this today. Unfortunately, I didn't have the light bulb moment until most places closed for the day.

Here's how I'm going to fix this. If it works I'll post pics.

I located left hand drill bits on http://www.mcmaster.com/

They also have left hand taps and bolts!

I'm going to machine a drill bushing that doubles as a chuck for a (short) left had drill bit. Sometimes during the drilling the threads will back out. If it doesn't,,,,,

I am going to use the left hand tap to cut threads in the pilot hole.

This sometimes will cause the threaded section to back out. If it doesn't,,,,

I am going to thread in a left hand grade 8 bolt. This will repair the broken bolt and give me a positive bite on the threaded section. If the bolt breaks I can just drill it again.

If I used an extractor and it breaks, I toss the block in the scrap pile.

Extractors = bad.... bolt = good...

I bet you could get a new block for cheap....seriously.
There was a 928 motor at Hershey for short money...

Rich

Have you called 928 international??? Maybe they have a cure for this???
Or Pevec (SP) the guy who hot rods these motors???

I am sure someone has dealt with this in the 928 community before.

Rich

I posted this problem over on the list where the 928 Int guys hang out, and the bird. The consenses seems to be if the stud breaks in the block it's junk. Granted, the guys in the know on the list seem to be luke warm when anyone asked a real question.... The guys on the bird are much more helpful but there are fewer of them. Not like this place.

What is the size and pitch? How hard is it? You can see how hard it is by filing or grinding. Drill and tap on the section you have in hand to see how hard it will be to drill and tap.

I plan to chuck one of the studs up in a lathe and run the drill bit in the end of it as a test. It's a head stud. It's designed to hold tension and resist torsion during torque.

The left hand bits are extraction bits designed to drill hardened steel bolts and studs.

Cross your fingers for me. I wish you were closer. I'd bring it over to your shop and we could tag team it.

With any luck the bolt will be a little softer in the middle. I am a little concerned about your getting the drill to start in the center. What would help the most is to use an end mill to machine the top of the broken stud. This would require another bushing for the end Mill. Long ones are expensive and a little hard to find (although I have a long .5" carbide one). After the stud is milled flat, center drilling would help. again the length would be a problem and that I don't have.

Yes its too bad you are not closer. I was thinking the same thing.

Lots of luck

The tools arrived today. All left hand or left twist. Now I just need some time to try the extraction...

To center the drill, find a piece of pipe with the OD the size of the hole and the ID of the drill bit. It should act as a guide and allow you to drill exactly in the center.

I have a friend with a lathe. I'm going to turn a an extension that will double as a guide for the O.D.

I hope this works out for you.

And have a second one made for the tap. The tap looks a little short. You can also get longer taps. They are called pulley taps (Maybe not in left hand). How deep will you be able to tap the stud.

That's the problem, Left hand, I felt very lucky to find the one I did. The broken section is all thread. Based on the other studs, it measures 1 1/4" long. I figured I would build in a drill stop on the extension that won't allow me to pass 1". I don't want to drill and tap through the stud and into the block. That would suck!

I ran a test tonight on the broken stud. The left hand Drill bit I purchased worked very well. It cut into the stud like butter.

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The real test is going to be the tap. I managed to cut threads into the bolt but it was scary. I feel somewhat confident in that the tap, being left hand thread may have enough cutting resistance to actually catch and back the bolt out without having to screw the left hand cap head screw into the bolt.

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I've had luck getting a stud out of a deep hole by slipping a tube down the hole with its bore roughly the same size of the stud. Then I feed down a 7014 rod and then arc weld the tube to the bolt letting it all cool. Fill the hole around the pipe with diesel for a few days so it can penetrate the thread. Heat the block in the area where the threads are locked and now try to wind out this mess.
Good luck!!!

That's a great suggestion! That's the first doable idea I've heard for a stud in a deep hole. I've welded washers to flush broken bolts before, then welded a nut to the washer and backed out the bolt, but I've never seen a broken stud in a deep hole before. I may need to try this one.

That's sounds like the best DIY idea. Other than that I second the EDM.

Well?

I can't get a break! I drilled the broken bolt perfect, I tapped the threads perfect, I threaded the cap head in perfect but the allen stripped. I pounded in a metric size allen wrench and removed the cap head bolt. I tried a second bolt but even with super heating the block I couldn't apply enough torque to the cap head to move the stud. Size does matter. I probably needed to move up to the next size drill and tap. I could literally twist the allen 1/8 turn without phasing the broken bolt. I tried to use the tap as an extractor as it was less likely to loose power in the flex the allen wrench was showing. But as luck would have it, just as I thought I felt the bolt move, SNAP! the tap shattered!

I'm going to try that welding idea now. I've got nothing to loose.

If the weld ing idea doesn't work, or as an alternative, can the stud be addressed from the bottom? If there is more access to drill it out from the bottom, or oversize drill it out, maybe the block can be tig welded to seal up the hole that is made. Have you let a machinist take a look at the block? Some are actually purty sharp and can devise alternative methods to get these studs out. Also if hour drill hole is "perfect" you might want to keep drilling it till it is t the base of the threads, then pick the threads out. Though I suspect this would be awful tricky deep down a hole.

No access from the bottom. It comes out through part of the main bearing saddle.

I probably could have drilled the bolt out all except the threads but now with the tap snapped off We'll see how the welding idea works. I like that one.

I tried welding a piece of square tube to the bolt about 10 times. I managed to crystalize the top of the tap section but couldn't get the weld to stick to the bolt. The slag from the rod blocked the edge of the tube leaving a poor weld connection. So, some day I may bring this engine to the machine shop to see what they can do with it. But until then it's scrap.