I'm in the midst of my TB/WP replacement. Everything was going pretty well until...all the WP except the one on the right side of the impeller came out very easily. I snapped this one. Damn. I should have stopped and drilled off the bolt head. Anyway, it snapped almost even with the block. I read this tip:


Anything to add? I plan on progressively drilling and trying to retap.
It's rusted in pretty well, so the last message in the tip (broken easy outs) is ominous.

89 S4


I had this happen on my TB/WP replacement last year.

Tried the easy out method - only to break the *&$$( easy out.

I ended up (gasp!) using a very steady hand with the Dremel too and a tungsten bit to remove the remnants of the old bolt and easy out. Then I used a tap to remove the threads out of the block. If you do this, be very very careful.

Be sure to use the tap anyway to chase out the threads and clean up the holes for all of the bolts. It'll make re-assembly a breeze and hopefully the next time you have to do the TB/WP maintenance, you should have no
problems with any of the bolts.


87 S4 Auto


I am drilling it out. These bolts are not too hard and I think I got the drill centered pretty well. I have it almost all drilled out and HOPE that I can retap it at M6 x 1.0. If not, maybe up a size?

89 S4


Everything was going well. I drilled out the old bolt to the ID size.
That was pretty easy going. I was tapping the new hole and was about half way done when...the tap snaps off. Of course the tap is some kind of impervious (although brittle) metal. This has turned into a nightmare.
Will see if I can center punch it and drill enough to extract it. Damn.



Current status of the broken tap:

Unfortunately, the tap is holding up fine. It is sitting just below the surface of the block. I can see the flutes but as it is a small 6MM tap, I can't get enough leverage with a chisel or punch to turn it. I tried heating the area to help loosen it, but it hardly got warm. The block is a big heat sink. I'll try more heat later.

I bought some carbide tipped masonry bits. I guess those are about even with the tungsten tap in terms of hardness, right (same material)?

I bought a helicoil kit and would be happy use it, but you can mooch it too much since the 6x1 helicoil is hardly larger than the original bolt. I used a product called TimeSert once. They are solid and thick walled (in fact they have an insert called BigSerts which are very thick walled).
I may call them and see if they can FedEx a few.

I just need to get this done so I can go racing on Thursday.

Another fella wrote me to say his 928 was missing 5 bolts and still was water tight. I wouldn't want to leave it that way, but I may temporarily leave it out.

For tonight, I'm going to sleep on it.

Tomorrow I may try a diamond Dremel bit and try to cut a trough across the top so I can screw it out.

Keep the suggestions flowing.



I know two ways to get out a broken tap, but unfortunately most of us won't be able to get the equipment.
1) Someone (don't remember who) makes a tool to remove a broken tap. it consists of a rod that has three or four small protrusions on the end. The rod fits down in the hole, and the protrusions fit into the tiny spaces where the tap flutes are cut away. Won't work if the tap is truly stuck, requires a size for each tap, probably impossible to find.
2) Large shops may have an EDM (Electrical Discharge Machining) system.
Using a small electrode, you can burn a super-hard tap out of an aluminum work piece, while leaving unharmed the threads that the tap has cut. The system that we had was portable, since you can't carry a 3000 pound mainframe that is built into a C-5 into the shop.

Sorry that this is of academic interest only - unless you get desperate enough to find a large machine shop that has an EDM machine with the right attachments.




Good post.

I have successfully used a grinder sharpened set of cheap needle nose to simulate the first choice. The secret is to loosen the chip that has hung the tap up. Tapping and wiggling with a ton of patience while blowing the hole out with aerosol solvents is what the guys at the foundry showed me how to do it. Guys that do this every day of their lives are the ones that know the tricks. But patience and feel are key. Little tap with a center punch.
Little wiggle, little tap, little wiggle, shot with the air, wiggle, tap, squirt of wd40... etc. eventually the chip jumps into the flute and the thing just unscrews.

Brad Orr is a fount of this sort of trivia. He is one of the Zenn machinist types :)

Jay Kempf
79 US 5ish speed


Some additional info on "broken tap/fastener" syndrome.
This really is a preface to my last post.
Please note that my references below are to a hand-held, propane bottle type torch as many people have these at home. If you have a portable oxy-acetalene torch setup (or easy access to one) you will likely have better results as you can choose an optimal tip and these offer more BTU's to do a more efficient job.


Because the tap is made from a high carbon steel, you can soften it by a reverse heat-treatment process known as "normalizing".

First take some kind of non-flammable, no-residue cleaning agent to the broken tap/hole area and remove any traces/residue of oils or cutting fluids you may have been using in the process. Be thorough, we don't want to start a fire here!
Take your propane torch and try to adjust the flame to a very small, concentrated cone, about 1/2" long or so. Carefully heat the exposed end of the tap. Keep heating it, you want to make it glow a cherry red color - and you must keep it at this temperature/color for at least three or four minutes. Try to avoid letting the flame "wander"
to the adjacent aluminum alloy block. More time won't hurt, but less time will not allow for the metallurgical reaction to take place. You must get the entire broken tap piece glowing.
Remove the heat, and allow to slow cool in the air.
This will NOT hurt the surrounding aluminum alloy block material!

This will soften the tap to the point where a drill bit will now be able to cut it. Left-handed drill bits are ALWAYS better in any of these situations (obviously you will need a reversible drill).

Also, because of the different expansion rates between aluminum (all alloys) and steels, the act of warming the faster-expanding aluminum can often "release" a stuck steel part.... but we're a little late in the game for that now. In this case, you heat the surrounding aluminum alloy part and avoid the steel part as best as is possible.

In the event that something may catch on fire, keep something nearby to smother the flames. Smother, NOT douse!

There are also tools called "tap extractors" for removing broken taps.
These have "fingers" that slide down the flutes of the tap coupled to a square drive on the top of the tool. These will sometimes work, but usually only in cases where you can already partially turn the broken tap.
Another alternative if you have a welding machine: if enough of the broken tap (or broken fastener) remains outside the hole, often you can weld a hexnut onto the broken piece. Center the hexnut over the broken "stub" and weld into the hole in the nut, filling it up. Allow to cool slowly in air. Use a wrench to turn the hexnut and remove the broken piece.

Incidentally, the tungstun carbide drill bits I was talking about are also known as "masonry drills" (for drilling through concrete). If you can soften the tap by the method I described, these may not be necessary - you may be able to make due with a cobalt or titanium- coated drill bit (visually these have a distinct gold hue or colour to them).

Brad Orr
'78 euro 5 speed


More on the "broken tap/fastener" syndrome.
This is specifically written to apply to situations in which the item to be repaired can be transported to a machine shop, like a disassembled engine block in this example.
This information is also more pertinent to a broken bolt than it is to a broken tap.


Although it is a pain in the a$$, take the block to the machine shop.
Get them to set it up on a milling machine, where they can accurately position the spindle (part that holds and rotates the cutting tools) in two axis, side-to-side and front-to-back. They will have to "dial in" the block surface to make sure they have it positioned exactly perpendicular (square) to the milling machine spindle in both axis, and then find the center of the tapped hole. This is easier if the bolt has broken off "deeper" into the hole than the 1mm that you have in your situation, but a careful and experienced machinist should still not find this too difficult.
Alternately, the block could be set up on a "radial arm" drill press that has provision for a very "fine" (as opposed to coarse) hand feed - this is usually a small handwheel on the spindle head, not the "big locking arms" that engage the power feed. Using a radial arm drill press is an easier setup, but it is harder to "lock" the machine's radial "arm" in the exact "centered" position.
Because a screw thread is a helical form, when they break the top surface "left in the hole" is never flat but will be on an angle. The machinist should first use a cutting tool called a SLOT MILL (or he may call it a "two flute end mill") to cut this surface flat.

With a 6mm thread, he should use a 4.5mm or a 11/64" slot mill for this operation.
Next he should drill a small hole of approximately 3/32" size through the center of the broken bolt. The previous step of cutting the top surface of the broken bolt flat is necessary so that the small drill will not "wander" (deflect from "center" when fed against an angled surface).
The next step requires a "LEFT HAND" drill bit. These are identical in design to a standard twist drill - just opposite, as they must rotate counter-clockwise. The machinist must REVERSE the direction of spindle rotation on the milling machine (or radial arm drill press).
For a 6mm thread size, the best size of left hand drill bit to use would be again either a 4.5mm or 11/64".
Many machine shops will have these left hand bits as they are a very handy item, and most tool supply businesses should be able to get one for you for only a few dollars.
Use the left hand drill bit with a HAND FEED ONLY, *NOT* power feed!
It is also recommended to use a very SLOW spindle speed, something in the neighborhood of say 20-50 rpm.
Because you have pre-drilled the small diameter hole in the center of the broken bolt, the drill "point" does not apply any downward force or pressure on the broken bolt (the drill point only contacts "air", not metal!). What happens here is that the two cutting "lips" on the end of the drill bit will "bite" into the broken bolt material and apply sufficient torque that, rather than drill into the broken bolt, the left hand drill bit will actually cause the broken bolt to "un-screw" itself right out of the hole for you. THIS IS WHY HAND FEED AND LOW SPINDLE RPM ARE *ESSENTIAL*. You will have to allow for the "rapid" upward movement of the broken bolt as it comes out of the hole!
If you don't, you will break the drill bit... or worse yet, damage the female" threads in the softer aluminum block.
This is the BEST method possible to remove a broken fastener, and I have yet to encounter a single instance when this method would not remove the broken fastener WITHOUT damaging the surrounding female threads (and I've been involved in the machining and tool-and-die trade for *way too many* years!).

The machinist should still produce a flat surface on the top of the broken bolt after centering the machine spindle to the bolt. He has two alternatives at this point. He can try to true up the hole that you drilled (I'm assuming you used a hand-held portable electric drill for this) by using a milling cutter, and then use the left hand drill bit as per the method above.
Alternately, he can use the milling cutter to cut away at the remainder of the broken bolt. He MUST use a milling cutter that is SMALLER than the "minor diameter" of the screwthread (he will know what this means!) and accurate centering is *essential* so as not to "break through" the outer edge of the bolt threads and cut into the female threads in your engine block. If he has his setup perfectly centered, after he has cut away the "body" of the broken bolt he will have left only the "thread" portion in the tapped hole - it will resemble a "slinky" (you *do* remember that child's toy, don't you?) that can be grabbed with a pair of needle-nose pliers and "uncoiled" from inside the hole.

After you remove the broken bolt, be sure to use the proper size tap to "chase" the internal threads so that they are clean and (hopefully) undamaged for reassembly. This is a good practice to use on all drilled and tapped holes anyway during any kind of a rebuild.

Brad Orr


Lots of great suggestions! Here's my plan for the day:

1. Countersink above the tap to reveal it better. I can only see 2 of the three flutes. This may give me better access to clean and punch drive it out after applying some heat. The countersink can't hurt (there's plenty of sealing surface) and it should give me a better look at things.

2. Buy some Diamond drills. Look at this:
There's a lapidary supply house on the way to work. Anyway, I will try to dremel a slot with the bit. This tap is really just barely started a couple of turns. I have a special screw (head) extractor that says it can remove stripped Philips and slotted screws. It just needs a partial slot to bite into.

3. Order some stainless steel (for anti-corrosion more than strength)
Timeserts FedEx with a bottom tap. This will be a special order. I used them on my 82 CBX motorcycle when it spontaneously pulled two head studs. They worked great, and the TimeSert people custom made a kit for me. Nice
folks. I like the fact that they are solid and that extra wall thickness allows me to mooch the hole more than the Helicoils.
Check out their BigSerts too. When I did not get the original TimeSert perfectly aligned for the super long studs on my CBX, the BigSerts came to the rescue. To see the bike in question and a picture of the studs I had to insert, go here:

4. If things don't go well, I will button this up without the 14th bolt and not worry about it for a few months.

89 S4


Plan B is in effect. The old Plan B (leave the 14th bolt out for a while) is now Plan C.

I was assembling my resources, looking for machine shop suppliers that might have a tap extractor, diamond drills, whatever, when what rolls up on Yahoo's Yellow Pages search but a "Tap Removal Service" located maybe 10 miles from home. Called them up. They'll be out at 8:30am tomorrow.
Will remove the tap and do a helicoil. Sure I could have spent the night trying to get it out (I may work on it a little more) but I didn't want to royally futz it up, despite all the great advice given here. Sorry if that disappoints anyone. I'm a comitted do-it-yourselfer, but with no experience handling this, I'm happy to let someone else do this part.
Anyway I will report back.

I was surprised to see a business as narrow as "tap removal", especially in the midst of non-industrial East SF Bay Area. I was feeling pretty low, but it seems like there must be a lot of other tap breakers out there.

89 S4


Tap Removal Update at 1 AM:

Based on some encouragement from Marc and Jim at DEVEK who have some experience with just what I'm up against, I bought 4 packs of Dremel 7150.
This is a 2 pack of diamond bits: a tapered point plus a ball bit. OSH had them for $5.49. The befuddling thing is the apparently identical single tapered point is $14.99. Anyway, 7150 is realtively speaking a deal.

I have the flutes almost completely clear. The hard part of this is that unless I lay on the motor and hang my head into the space between the radiator and block, I can't get a clear view. I resorted to a vanity mirror laid at an angle against the radiator. This helps a lot to see the damage I am doing.

If I had a tap extractor I think it would come out now. I will keep plugging away until I free it. I have the tap removal service as a back up. It would have been fun to see how they handle it, but if things progress I will call them and cancel the visit. Also, I was off-base on the hole depth. All the holes around the pump are at least 17MM deep, so the 9.4MM TimeSert will not be a problem. I don't need a bottom tap either. The bolts only have 9MM of thread exposed, so everything should be fine for inserting once I get the tap out.

Anyway, I am surprised how common this problem is and not just with novice tappers like me.

From Marc at DEVEK - when faced with a stuck WP bolt that doesn't give easily when you attempt to remove it, before you break it give the bolt head a hard hit in the middle with a centerpunch. This will often break the threads free. Wish I had seen that soemwhere in the 928 Tips. Had I tried that and had it worked my TB/WP would have been finished in no time.

From Jim at DEVEK - use soft (Sears) taps rather than hard tungsten carbide taps. Sounds reasonable considering the block is aluminum, and if it breaks, removal isn't such a bear.

89 S4


> Something you might consider is removal of the radiator for more room.
> It's already drained, and only requires the removal of the oil cooler hoses (and trany cooler hoses if so equipped) and will provide you with some additional wiggle room so to speak.
> Jay
> 87 S4 Auto

This is a good suggestion. If I lift the front end I can sit on the ground inside the engine compartment and be eye level with the problem with plenty of room for drilling. I still have the final drilling to do tonight. Inserts are at hand ready to be installed following the most careful drilling and tapping.

To those who have BTDT, this must seem like a lot of fussing over a silly little tap, but I would have preferred a less eventful first-time TB/WP.
Barring broken taps, the job is a good do-it-yourselfer with only a few head scratchers the first time (getting all the accessories off, getting the TB by the wiring harness). Other than having to use a floor jack to lift my 18" long 3/4 inch drive and force the crank nut loose and dealing with cam gear replacement (careful not to change cam timing) there are few issues.

89 S4



Here is a link to a page I wrote some time ago. I hope it helps.


Actually in reading it over it looks like it won't work for your problem.

If the block was steel then you use a punch to fracture the remaining part of the tap. I would not try this on aluminum. Yet the principle is the same. If you can get a Dremel bit inside the hold beside the flutes on the tap you might be able to remove some of the threads in the aluminum and release the tap. It would take a little time but you would not have to remove that much to loosen the tap. The same approach could be done with a drill but it again is going to take some skill and luck not to break a drill off and make the problem worse.

Dan the Pod Guy
Portia's Parts