Does anyone sell a fixture for drilling broken exhaust studs

[Shuie]

Christian, Id be happy to help get #3101911 back on the road . Please put me down for for one exhaust stud drilling fixture and let me know when to send the money.

[A Quiet Boom]

No problem Sherman If you can give me your port diameter I can make on up this weekend. Hopefully JW has this info handy.

[john walker's workshop]

i'll measure the pieces in the morning.

[A Quiet Boom]

Thanks John. I'll get on a prototype right away.

BTW John (North Coast Cab) and Pete. I captured the video at full quality and wasn't happy with the picture quality. I'm recaputring it at a lower quality to see if I get better results. My capture drive is pretty full and I think that's having an effect.

[scottb]

My $.02....I think it should be made of steel simply for durability.

McMaster-Carr sells hardened drill guides.

From idea to prototype in a few days....the Pelican community never ceases to amaze me.

[RoninLB]

Originally posted by scottb

From idea to prototype in a few days....the Pelican community never ceases to amaze me.

ditto.. this is such a cool thread.

[MotoSook]

Put me on the list Christian. I have a set of heads that need some busted studed removed this winter.

[Shuie]

Christian, Im on the road right now and I wont be able to mic the exhaust port until Friday.

Does anyone know the stock exhaust port size for a '72 2.4T?

TIA

[Tim Hancock]

Wow, I guess I should have gotten on-line again last night. It looks like Christian is going to make some of these. Anyway after thinking about this, I decided the following.

1" long externally threaded steel drill "bushings" work just fine and they are easy to swap out to the next size while leaving the fixture attached to the head. The 1" length provides better support to ensure you are drilling straight in. They are compact enough avoid interference with the head fins. Commercial Slip-fixed drill bushings have a large head that would interfere with the head fins.

The bolt type units are nice because if a slight amount of stud is protruding from the head surface, one can back the bushing out to clear this protrusion.

I think the fixture should come with (3) bushings: 1/8" pilot, one sized to remove the center of the bolt just leaving the threads (for the optimist who is hoping to pick the remaining threads out), and one sized for a helicoil tap drill.

These bushings should last multiple times and if a shop were to wear one out they could easily make themselves more in minutes on a lathe.

I like UHMW or nylon removable center disks. I would need exhaust port dimensions for the various heads.

I think $100.00 is a fair price. If Christian has something better or cheaper by all means go for it. I am not going to get rich by making 10 or so drill jigs in a year. If the group wants them though, I will make them.

[RickM]

Instead of utilizing center disks of different diameters could one stepped disk be used? Then it could be machined in one piece.

[Tim Hancock]

The disk acts as a centering pilot, so no I do not see how a stepped disk would work.

[RickM]

Yes, I understand.

If a threaded drill guide was used then the space could be taken up if using a smaller diameter on the stepped disk. Then there would be no chance for rocking.

Just thinking out loud here. Can't hurt to explore a few possibilities.

[john walker's workshop]

the discs need to be a tap fit into the tool as well as into the port. the port of course,needs to be cleaned of carbon in the area of the disc. the discs i've been using are 34.70, 38.65, and 41.60. the ring was a quicky "shim" i made from a weber venturi to go over the larger of the discs so it would fit the SC and carrera ports that are machined out to accept the heat exchanger with the raised ring that goes up into the port. a disc of that size, (41.60) would be better, but i didn't have the bar stock that day. the exposed height of the disc is 4mm.
the tool body is 12.75mm thick, 51mm wide, 87mm long. the angles on the ends are the same on both ends so it can be turned 180° to do either stud. the long angle is 35°, the short angle is 47°. the drill guide is for a 17/64 bit, and has an OD of 12.735 (.502). obviously, the guide needs to be dead center over the broken stud. the drill guide needs to have sufficient interference fit into the body so it doesn't turn if the drill bit starts to bind a bit from particulate matter interference. i wouldn't mind having a steel one, because it would certainly last longer, not that i've had a problem with this one. as far as being an optimist about doing a perfectly centered drill job on the stud, so you just have to pick out the thtreads, it's all in how well the tool is made. i can say that in the 150 or so studs i've drilled with this tool, every one was that way, using the one remaining stud to hold the tool. the only time i had to timesert, was when both studs were broken and i had to eyeball and clamp the tool on, and even then it was 1 for 2. the threads don't generally just pull out, you have to use a pointed pick and a small hammer to work out the leading edge so it can be grabbed with some needlenose pliers, (ground down on their outside so they can reach into the bottom of the hole). then they are twisted out in sections.

[Tim Hancock]

John, that is awsome that you can actually dig those remaining threads out. I never even considered trying when I did mine. I had a Helicoil kit I borrowed from work and never even thought of trying to dig the threads out. You have a 1/2" thick body along with a 1/2" long drill bushing. Are you doing this operation with a hand drill from under the car or do you have the head out and on a drill press? My guess is that you are very skilled at drilling a straight hole if you are doing it by hand with a portable drill. Keeping the drill straight with only 1/2" of bushing
is doable but the average guy may not have the expert "feel" for keeping the drill perfectly straight. I think it would be handy to also have the correct bushing for a Helicoil tap drill also in case. You or I could enlarge the hole after the fact if needed without the guide, but it would be better to use the guide for people who do not have a good feel for drilling relatively straight holes.

I am going try to think of a decent way to make an expanding center pilot that would allow the fixture to be installed then tightened to eliminate play and possibly allow it to be used when both studs are broke after visually aligning.

To anyone reading this: Use a torch on all of your exhaust nuts if they show the slightest signs of being frozen. If heated to red they will come off. Take your time and reheat every turn or so. They will come off and you will not need to worry about any of this. If you do not have an Oxy/Acet setup, borrow or rent one.

[Joeaksa]

Tim,

Spoken like someone who works with aircraft!

I once spent 19 hours drilling out cover screws on a Learjet 35 for an inspection. The idiots before me had stripped the philips heads out when tightening them.

You learn a lot about working with metals when doing this and heat is your friend. So is a reverse twist drill bit!

JoeA

[scottb]

Originally posted by Tim Hancock
I am going try to think of a decent way to make an expanding center pilot that would allow the fixture to be installed then tightened to eliminate play and possibly allow it to be used when both studs are broke after visually aligning.

Can you use a dense rubber bushing? Put a plate on one end, with a welded bolt through it. Run the bolt thround the bushing and through the jig. Tighten a nut on the other end and clamp down on the bushing. As you clamp down, the bushing will expand width-wise in the hole, and get tighter and tighter the more it expands. The only question is whether it will be steady enough, or whether there will be just enough play to cause problems. Maybe something like this should be combined with a nut on the one good stud for stability.

Just a thought....my $.02, FWIW.

[project935]

Put me down for one as well ...
You guys rock. If you need it CAD'd up (probably don't) let me know.

[Tim Hancock]

Scott that would probably work and I can get those ready made, but it would probably not be solid enough to sell to others especially if one is trying to drill the center out of the broken stud leaving only the thread to be pick out later. I thought of quite of few ways as have others. DIY guys can easily make these up themselves, but if someone pays money, it better be as foolproof as possible.

Yeah Joe, it does not take long working on aircraft to get the hang of a drill! Did you then get to drill out a million nut plate rivets with a #40 bit? Or do Lears use rivnuts? I just got my IA rating last year and I do annuals and repairs as a part time business at home at my grass strip. I just got my ratings so I can afford to continue playing with airplanes.

Do you work for a repair station or what?

[john walker's workshop]

the rubber center will not make for an accurate tool. i've used the tool about 50/50 using a hand drill and in a holding fixture in a drill press. a new drill bit is the ticket, maybe a few of them if you have a lot of studs to do. i much prefer the drill press, but with a air drill, doing it in a vise or under the car, it doesn't take very long with a sharp bit. really, you just need the one size drill bushing. after the hole is drilled, it's easy to go oversize with the timesert or helicoil (hate 'em) drill bit if you feel that you have to. it pretty much follows the hole if you can eyeball the drill straight.

[A Quiet Boom]

Thanks for the dimensions etc. I'll work on this at home tonight and give it a try this weekend. Doesn't seem to hard except that I'll have to cut the disks on the lathe by hand. I figure I'll make them from 0.500" steel plate for durability and the disks from cold-roll steel. I'll just buy the inserts from a tool supplier.