Broken Exhaust Manifold Stud
 

I am sorting out a new to me late model A4.
The engine had been sitting in a garage for years, likely around 7 or 8 years.
While still sitting on a pallet under the boat , I pressure tested the block - it checked out.
Drained and replaced the oil. Spun it with a hand crank. All good.
Cranked it with no spark to get oil up and around.
Compression check revealed a stuck valve in #1 cylinder. Some MMO and a few more cranks and all well - compression on all 4 cylinders is spec.

Wired it up and it started on the 2nd crank.
Let it run for a minute and it sounds good with no smoke.
**** I did this with no water and pulled the impellor. I just wanted to get it started.

Fast forward:
I had to move the boat to another yard so the engine is sitting on the cabin sole knowing I have a few things to sort out and parts to switch over.
I have basically stripped all the accessory parts off including the exhaust manifold.
It turns out the center stud is broken and i don't believe it was by me. I used very little force to remove the bolts. The center stud just spun out.
Unfortunately I didn't take a photo of the threads but they look clean and in near new condition.
My thoughts are to pick up a reverse drill bit and easy-out
My questions:
What size bit and easy-out should i use?
Do i need to put sealant on the threads when reinstalling? - the threads are good.
what is the rust on this one port?

If this helps: the reason I pulled the manifold i because the exhaust flange bolt was snapped off. The other appears rusted in fairly well. The manifold itself appears in good condition but I have a new MMI manifold sitting here and will install it.
The next step will be to try and figure out why there is no thermostat in the housing
Thanks all.

Sorry, I'm confused.
Photo shows the manifold studs in place. You say the center stud is broken and that it just spun out? Why do you need a 'reverse drill bit' if the stud is out and the threads look good? DO NOT buy/use EZouts! When one of those breaks off in a drilled hole, you're out of luck - no more options. Perhaps we need a current photo? If the stud is out, you can just reinstall it. If it's broken, you need a new stud (our Host sells them).
Those studs keep coolant in the block and need sealant. I use JBWeld.
Thermostat may have been removed to reduce engine temperature. Leave it out unless you decide later to install it. I ran without one for 15 years!

Sorry for the confusion
The stud is broken. There is about 3/16" threaded into the block
I need to extract the remaining bit and install a new stud
If not an easy-out - then what extractor?

I'd recommend a left hand drill bit, about 1/4 diameter for the 3/8" stud. I bought an assortment of these from mcmaster.com - as I recall, they're even available in cobalt alloy.
I've got several metal cabinets, each with about 2 dozen pull-out plastic drawers. One drawer is just cobalt drills. Left and right are all mixed in, which gets interesting sometimes.
edit: PM me with your address, I'll send you one.

Thanks Al. While I appreciate your generosity, I don't want you to go out of your way.
In return I have a bunch of parts, early and late model.
Respond to my PM with what you need
and I'll see what I have.

Possible good news
 

nyvoyager,

In later late model engines we have seen quite a few cases where what you think is a piece of stud broken off in a manifold stud hole is really nothing more than calcified residue remaining from the end of the stud. One indication of this possibility is if the end of the stud is sort of rounded off instead of showing a clean break. A buildup of calcified crud/residue can usually be cleaned out using a smallish screwdriver (sharpening the tip helps) by gently tapping and turning the blade - sort of like the technique in using a "star" drill in concrete. After cleaning out most of the calcified crud you can use a coarse threaded tap to finish cleaning up the threads. Don

Recently while freshening up an early model A4, I found that virtually all of the studs that went into a water jacket, had been shortened just as Don describes. The material under those studs was easily removed with a small screwdriver, followed by a tap, which revealed that the block threads were still in very good condition.
Happy Holidays, Tom

Well that would be excellent news! I'll have to take another hard look. In the meantime a new stud was ordered.
Don you mentioned later late engines. This appears to be a early late A4.
It has a cast flywheel cover, delco distributor, tstat and oil fill. The head appears to have the old crossover filled in, if that makes sense
Thanks Don and Tom

Manifold studs
 

nyvoyager,

I'm probably guilty of giving too much information. While it's true that most of the examples of this phenomenon that I can remember were from the latest engines (sheet metal flywheel covers), the likelihood of a manifold stud decaying and leaving behind a short plug of calcified deposit depends mostly on the quality of the raw water the boat was operated in and not necessarily on its vintage. Based on your description, you have every reason to hope for good news. Don

Thanks again Don. I won't be able to get to the boat till this next Saturday but will follow-up and confirm. This would be very good news indeed.
And UPS just let me know my parts will arrive in the next day or so. Perfect service from MMI as always

Hopefully you ordered more than one stud. I would expect the other two manifold studs to be in the same condition. While you're there, I'd pull them and have a look.
Should I even mention the head studs? Naah, I won't mention them.

Al: Now that I understand it is likely from corrosion, I think you are right and will seriously consider doing all 3 manifold studs.
The head? I'm not sure I want to venture into it at this time.
I will think about it.

Don, your assessment was spot on.
Corroded end of stud, threads in block are fine.
Thanks and Happy Holidays

Thanks for the feedback
 

This is wonderful news! I suspect that it's too late to ask now, but did you happen to take any photos of the end of the relevant stud to show how its end looked? Studs usually have a very distinctive rounded shape in these cases which a photo might help to prevent someone from attacking with a drill and tap, which can easily make things worse. Don

Yes - I just need to get the photo off my phone and will post it! It is shortened and rounded. Will post in the morning

Photos
 

The stud was from the center of the exhaust manifold.
And just a general picture...about ready to set it on the engine beds

Corroded stud
 

Thanks for the photos. I don't remember what you reported regarding the condition of the hole in the block, but it's not unusual for the threads in the block to survive at the depth where the threads on the stud are corroded away. I'm not sure about this, but it's entirely possible that the stud becomes the sacrificial anode and saves the threads in the block. Don

Don, as well as i can tell the threads in the block are okay. My unscientific method was to chase them with a sharp awl to the end and then a tap to clean them out. They seem okay. Thanks for you help.