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]

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.

[JOHN COOKSON]

Originally Posted by BobinSF

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