Broken Manifold Studs

[BobinSF]

While attempting to remove a threaded plug from the top of the exhaust mixing elbow, I felt something give way; I had broken all three of the studs holding the manifold to the block. The looked very rusted.
My path to repair seems to be the following:
1. Remove the manifold, after unbolting the carburetor and disconnecting the water inlet and outlet hoses and the tube from the bottom of the carburetor to the intake manifold.
2. Try to remove the three stud stubs from the block with the stud remover tool.
3. Failing in the above, drill out the stud stubs, tap and place three repair bushings in the block.
4. With new manifold studs and manifold gasket, replace the manifold and reconnect disconnects from #1.
My A4 is very tight in my Tartan 27. If #2 fails, it probably means removing the engine to do #3. All this definitely pushes my skill level, so having the boatyard repower with a Moyer rebuilt A4, or going electric, looks tempting. Any advice would be most appreciated.

[Al Schober]

Bobin,
I'd be curious as to where the studs broke? At the base of the nuts, at the block, or elsewhere? The possibility exists that the studs failed because the block and studs corroded from inside - studs corroding in preference to the block (high nickel). Hopefully you'll find that the studs corroded and the block is OK.
Your plan sounds good except you're going to have to disconnect the exhaust.
Once you can see the side of the block, check the wall thickness in way of the studs (corrosion). Hopefully it will be 1/4" (or more) - 3/16 or less is not enough metal to hold new studs and heroic measures will be needed (inserts/bushings).
Hope this helps..

[sastanley]

Bob,
Hang on...we need pictures. I understand your access is tight. I found a bad manifold stud (that had already been "oversized" with a Moyer oversized stud by the P.O. I learned from other members of the forum)...I was able to replace it with another oversized stud..the block held strong, the stud went bad. I simply cleaned up the threads, and with advice from Ken in the Moyer parts dept. used JB Weld to seal up the threads and I have been a happy camper for several years now.

Pictures help, A LOT! like this one..this was the block after I got the bad stud out. Ken, and all the forum members assured me it would hold (and it has!) The manifold studs enter into the water jacket, and they like to rust away.



Take some pics and let's go fix it!

[BobinSF]

Thanks, Al and 'sastanley', for your helpful responses.

I disconnected the water inlet hose so now have about an inch between the block and the manifold; still not enough for useful photos. The three studs broke off within where they thread into the engine block. At two of them, the 'inside' half of the stud is still there; on one, I can probe all the way through the threaded hole. Next step is to remove the manifold for a closer look; probably drilling out and tappingfor the 1/2" to 3/8" threaded inserts is needed.

[Don Moyer]

Failed manifold studs

Bob, can you post a photo of the failed end of your studs? I don't want to give you false hope, but it would be very unusual for a part of a stud to break off halfway into a threaded hole - let alone all three. All manifold studs, and all but one head stud, enter a water jacket; and what we have seen happen several times over the years, is that some studs didn't hold up very well and they literally became something like sacrificial anodes. The result was that as the end of the stud corroded away, it left behind a hard calcified deposit that can give the impression that part of a stud broke off and got left behind. When this happens, you can take a small screwdriver and use it as a "star" drill, turning it as you gently tap through the calcified deposit and then chase the threads with a 3/8" coarse tap. Don

[BobinSF]

Here are 3 photos: the manifold studs (actually bolts); and the holes for them in the block. On the hole to the left, the wider recessed area is about 1/16" deep.

[joe_db]

If you can, I would remove the engine to work on that.
I have been in that situation and the repairs I could do in place needed repairs of their own soon enough

[JOHN COOKSON]

All this definitely pushes my skill level, so having the boatyard repower with a Moyer rebuilt A4, or going electric, looks tempting. Any advice would be most appreciated.

A couple of observations that will help you to decide whether to work on the current engine or replace it: A compression check; and also do you remember what the oil pressure was engine warmed up at cruise throttle setting?

TRUE GRIT

[romantic comedy]

If you can, I would remove the engine to work on that.
I have been in that situation and the repairs I could do in place needed repairs of their own soon enough

It may be possible to just move the engine. Move it somewhere in the cabin where it can be more accessible, if possible.

But there is never a substitute for working on an engine on a bench in a shop!

[sastanley]

It looks to me like the hard work is on the manifold..I think you will find what Don suggests above...gunky leftovers of bolts in the holes in the block. I'd poke around in those holes with a pick and then get the 3/8" tap on that bad boy (or "thread chaser" if you have a set..I think they do less damage to the block than a tap when you trying to simply clean up an existing threaded hole)

I bet if you can get the gasket off the manifold, the nasty old bolts will come out. I am trying to figure out what was holding the manifold to the block..probably the rust!

Both halves of those mating surfaces do need some cleaning up though.

[joe_db]

How is your time vs. money meter calibrated?
If several thousand dollars was fine with my wife, I would be very tempted to get the Moyer short block and get it all over with.
If the money side is tight, this might actually be an easy repair if nothing else is wrong. The amount of corrosion I see there gives me pause ....

[BobinSF]

Happily, I was able to chase the manifold stud threads in the block to what seems their full depth, about 1/2 inch. The threads seem to be in good shape. So it appears that I can buy new studs, gaskets, etc., from MM and pursue the repair.

Concurrently, I want to remove much rust from the manifold, block,, head, etc. It seems that a needle scaler is the way to go. I will carefully try it on the machined surfaces between the manifold and the head to see if it mars the surfaces.

The inside of the mixing elbow (pic) is full of rust. Getting it loose from the manifold looks impossible. Another Forum reply said that soaking his in muriatic acid for a month worked.

I thank all of you for your advice on the broken manifold studs.

[Al Schober]

Bobin,
Removing the mixing elbow from the manifold is a piece of cake - a recip saw with a carbide blade will do it in about 30 sec. This will leave half of the nipple in each part - also removable using the same tool. Each half gets two saw cuts on the inside about 1/4 inch apart - try not to get into the female threads. Knock out the pieces between the cuts, then collapse what's left of the nipples.

[BobinSF]

Removing the mixing elbow from the manifold is a piece of cake - a recip saw....

Al Schober, your method worked just fine; thank you.

Needle scaling is proceeding well, and I am able to do it on the machined manifold-to-block surfaces without marring them.

[joe_db]

Do not forget:
Water can and will follow the studs into the manifold and get water into the cylinders (intake side) and/or feed water into the exhaust, which may back up into the cylinders and WILL rust out the riser where you would think it was dry.
Found that out the hard way
Do a good job sealing the new studs!