Broken tap stuck in cylinder head

Well, I hate to admit this, but I've done a number on my cylinder head.
While looking for the source of the cylinder head gasket leak that I recently posted about, I took off the valve cover about 3 times. The last time, I stripped the threads for one of the the valve cover bolts (lower rear, LH side). No problem, just pop in a helicoil while working on the cylinder head gasket.

I followed the instructions, installed one helicoil, but it wasn't near long enough. The instructions with the kit I bought said to install a second one if the first one wasn't long enough. This seemed to work, but it took a lot of effort to seat the valve cover bolt, and it leaked oil from this bolt when I test rode it.

I let it sit over the weekend, and decided to run a tap down the hole just to clean up the threads. I selected the correct tap (M6 x 1.00) and hand threaded it about halfway down the hole, where it started to bind up. Then I put the handle on it turned it about 1/4 of a turn, and the tap broke off in the hole.

Now what? If it was a bolt, I'd try to drill a hole and use an easy-out. I'm pretty sure this tap was so hard that I won't be able to drill a hole in it. Anyone have experience with this. I sure don't want to pull the head off again it I don't have to.

ouch...

I don't know how deep it broke off... if you can get on it with needle nose you might unscrew it... if not, then a trip to the machine shop or dealer is your option...

If you warm the spot with a heat gun you might find it loosens the tap a bit...

get a dremel grinder get a carbide burr cover all but hole you will be grinding so you dont get metal chips in the motor go into the flutes of the tap so you dont hit the threads it will take awhile and you might need a few burrs but you should be able to get it out with out much problem hope it helps

Go to a machine supply house and get a tap extractor set for that size tap.
Do it right, so you don't have to pull your head.

460

Tap removal

As you have already discovered, taps are hardened. If a bolt twists off in a hole, it usually gives way flush with the surface. When a tap breaks, it is a shattering and rarely is more or less event where a tap extractor will work, as the end is jagged. There is also another problem...When a tap breaks it is from being overstressed, so is likely to be really hard to "unscrew" with any means. I have no idea how much a head would cost for your bike, but if I were you I would remove the head and take it to a machine shop where the tap can be removed by an electrical discharge machine so further damage will not be done in an attempt to do it yourself.

In many cities, particularly where there is a large manufacturing base, there will most likely be a shop that is exclusively devoted to drill and tap removal. This will be the best choice over a job shop. Many tool and die shops have numerous jobs for the EDM lined up and the setup is or can be complicated for most of them. This means the line moves slowly. A drill and tap removal shop works with a much faster turn around time. Even if no shop exists in your area, a web search will find many across the country where you can ship your head.

Thanks, copandengr and jetboat.
I think the tap extractor sounds like the way to go. The tap is pretty well shattered. I am in Detroit, so we have all kinds of machine shops. I've not heard of a tap & drill removal place, but there is probably one in town.

A new head is about $650. Used at Beemer Boneyard, they are in the $200 range, but of course, they have none in stock for my head right now. So at least I know what the top end cost will be. It appears that BMW changed head part numbers several times over the years. Attached is picture of my cylinder head with casting numbers visible. I see 10, 05 and 93 clearly on the head. I'm not sure if there are other ID numbers on the head.

All the mechanical efforts are good, but if none are successful, take the head off and find someone that does EDM work. A lot of machine shops have this equipment for when a CNC breaks off a tap in a part, and rather than scrap the part they burn out the tap and save it.

Being a tool & die maker edm (electrical discharge machine) is the way to go here.The tap more then likely broke because you put in 2 helicoils one on top of the other.Not a good thing to do because of slide thread pitch offset.Helicoils are made of very hard stainless steel that a regular tap has a hard time cutting.Once threaded into the pitch offset the tap broke.You can try a tap extractor.Most of them have 2 prongs that need to match the tap flutes.Hopefully your tap was 2 fluted.What a PIA job that turned into.Never double up on helicoils! Good luck.

I knew there was a reason I use my ordinary tap set so gingerly! Have always lived in fear" of getting one stuck or broken so am very very cautious. Sorry you got bit.

Good luck with repair and thanks to you guys for the education on what to do if I ever bust one flush. Wasn't aware (though I probably should have been) that EDM removal is commonly available.

In general, assuming you have conventional taps, next time buy a gun tap that has the flutes arranged to kick the chip out ahead of the tap. Then finish with a bottoming tap if you can't go through.

Use sulfur oil or similar (such as anti seize) as a tap lubricant.

Good rainy-day education today guys. Thanks.

nrpetersen said:

In general, assuming you have conventional taps, next time buy a gun tap that has the flutes arranged to kick the chip out ahead of the tap. Then finish with a bottoming tap if you can't go through.

Use sulfur oil or similar (such as anti seize) as a tap lubricant.

Click to expand...

you should read my column and just forget using a tap in trying to straighten out the threads.A carbide tap would be the only thing that would touch this material ( heli-coil).And then in doing so would ruin the threads in the lower heli-coil.

41107 said:

you should read my column and just forget using a tap in trying to straighten out the threads.A carbide tap would be the only thing that would touch this material ( heli-coil).And then in doing so would ruin the threads in the lower heli-coil.

Click to expand...

I agree & maybe my earlier post was misleading. I've never seen two helicoils used together, and helicoils are hopelessly hard to cut with any tap. EDM it out.

Never follow instructions....

Petersen and all,

I have learned my lesson now, but quoting from the instructions on the Helicoil package, "Add additional insert for increased length applications." So much for following instructions.

I found a few local EDM shops, but they aren't really set up for small jobs. I decided to stop by the dealer, which is near my office (Detroit BMW, reputable mechanic Don). He said he's ground out taps before.

I'm pretty sure the set-up charge for one EDM job would be more than the cost of a replacement cylinder head (~$200). So, I'm leaning towards taking it to Don because he knows what the bike needs to be like when it's done. Also, I can leave the cylinder head on and avoid buying another head gasket ($65).

This job has been a PIA. I've never had anything like this, and I've been wrenching on all my stuff for a long time. This is the first time I've had to admit defeat and take the vehicle to the dealer.

I have used 2 helicoils before no problem, my bet is when you inserted the tap it started to screw the lower one in further, where the external thread started to taper, this just squeezed everything tight and bound it up.

As far as EDM, again find someone with CNC's. The one we had at a former job, was real simple, set the part straight in the edm fluid, and position it under the electrode, and turn it on. It looked like a miniature drill press, and it just fed the electrode in slowly as it burned the tap out. Set up was 5 minutes tops. But if your mechanic has the tools to grind it out, that is good too.

P.S. They are few and far between, but engine repair/performance shops sometimes have the simple EDM's too. If you don't know any, stop by the local farm tractor store, they still rebuild mid 20th century motors.

I helped a customer out a couple of years back who sheared off a hardened pin in a refrigeration compressor. I took it to a local shop who EDM'd the pin out while we waited for 25 bucks and for other motorcycle examples over the years, I've never paid more than $50.

Tap is out

I should have posted earlier. The tap was removed by the BMW dealer. I paid more than $50, though.
They did a good job on that, but they messed up my idle. I had mentioned that the bike idled at low speed (~900 RPM). The mechanic said that he could raise it, which he did, but now the bike dies as it first drops to idle at every stoplight. I guess I'll have to get into that when my work lets up a bit.

James,you said the first heli coil was not long enough? The insert only has to be about 1 to 2 times the diameter long.You install the coil just below the surface and break off the tang with a punch and hammer.If you put in 2 coils you will not get them to line up right and the bolt will cross thread and get tight,when you get the broken tap out pull out the coils you put in and install 1 coil just below the surface and break off tang and insert the bolt. I can tell you how to get the old coils out if you need.

Tim

Lowrider Tim, I put two Heli Coils in and would love to know how to remove them. If I remember correctly I used a locktite product to secure them.

Thnaks,
Mark

P.S. I did so because the instructions on the package said to.

Mark, The locktite makes it a little harder but not impossible---I would soak the hole with acetone blow it out after about 5 mins. and soak it again and leave it as you take an awl or some sharp tool to pry back the first thread of the coil till you can grab it with a small needle nose,don't pull sraight up and out but try to twist it as you pull up. Then try the deeper one the same way. Install one coil just below the surface of head,say one thread below. Let me know how you do.


Tim