I messed up - Manifold Stud Repair

[cfergu22]

I had to remove the manifold and get a new one. The original Manifold was completely corroded and rusted away. When I removed it, the stud closest to the transmission pulled out.

The threads were shot in the block, a regular 3/8ths stud just spun freely.

So I cleaned up the hole with a drill bit, and tapped it for a 7/16ths repair stud. I tried to do it free hand because I had so much better access with the manifold removed.

Unfortunately I must have had the tap a little crooked when making the new threads. The repair stud is about 3/16ths off in alignment at the end. I can't slide the new manifold on.

I removed the stud before the JB weld setup so now I have to figure out how to get a stud in there that'll line up correctly. As far as I can tell, I have 2 choices...

1) put the manifold on, use it as a guide, and try to re tap the hole. I'm not sure if this will work, because there's already threads in there. Will there be enough material for the new threads to hold? Then I would just JB weld the repair stud in and let it setup before I torque down.

2) Put the manifold on as a guide and drill the hole out a little more to put a Helicoil in there for the repair stud. Seal the Helicoil and stud with JB weld.


Any tips or suggestions would be appreciated. I would much prefer option 1, but I don't have much experience with this and don't want to mess things up without getting some guidance.

[Al Schober]

I haven't done either, but I think I'd go with option #1. If that fails, you can always try option #2.
As I understand it, the stud isn't off in position - just angle. I'd retap for the repair stud being careful to keep the tap perpendicular to the face. I did do a heli-coil for a head stud and rigged a guide to keep the tap straight.
Some JB weld on install and it should be fine. I think I'd use the manifold to keep the repair stud straight while the JB sets up.

[joe_db]

I hate to be depressing, but down this road lies a lot of grief because those studs go into water jackets and leaks are not always obvious. Water can migrate into the manifold and cause all kinds of slow acting destruction. This in the end was what ruined one of my engines
So....the real repair requires the engine out of the boat and at a machine shop.

The *I need to fix this now and cheap* repair may involve the manifold. If you are SURE the stud is in good and water-tight, I would be very tempted to drill out the manifold just enough to get it on there.

[cfergu22]

Thanks for the replies...

I'm trying to avoid modifying the brand new manifold, just out of principle. Although it's definitely on the table to avoid removing the engine.

My current plan is to use the old manifold as a guide and try to re tap the hole. Just like in Moyer's instructions for the repair stud (what I should have done the first time) Then see if I can get the stud in there solid and straight, loaded up with JB Weld.

If that works, great. If not, I'll use the old manifold as a guide and try the repair bushing.

I know i'm opening myself up to leak problems, but judging by the rust damage on the old manifold, that stud was probably leaking for a very long time.

If all that doesn't work then I'll have to pull the engine and take it to a machine shop for a professional fix. I'm just really trying to avoid that because every time I have to remove something from the engine, it causes a waterfall of problems.


Any advice to getting the stud hole as clean as can be to accept the JB Weld?

[Dave Neptune]

If you have access to a drill press do this. Ream or drill the manifold very careful so it stays flat for a good straight hole and only this hole. Then mount the manifold "perfectly in place" with the other two studs. Now tap by getting the tap started in an existing thread and tap "dry" no oil or lube if you wish to use the JB. The quality of the threads will depend on how thick the block still is there.

If there is little quality thread perhaps going to a 7/16" helicoil may do you well.

Dave Neptune

[joe_db]

If you have access to a drill press do this. Ream or drill the manifold very careful so it stays flat for a good straight hole and only this hole. Then mount the manifold "perfectly in place" with the other two studs. Now tap by getting the tap started in an existing thread and tap "dry" no oil or lube if you wish to use the JB. The quality of the threads will depend on how thick the block still is there.

If there is little quality thread perhaps going to a 7/16" helicoil may do you well.

Dave Neptune

If he drills the manifold bolt hole 3/16" then it will go on anyway without tapping the block again.
I tried all these repairs at one time and they all failed eventually. I would really think twice about doing it again. YMMV, maybe my block was just rotten.
What happened was water would seep into the exhaust and then rot out the "dry" part of the exhaust that wasn't really dry and also get back into the engine and rot that too.

[Dave Neptune]

Joe, JB Weld inside the block is only a "patch" as it will eventually allow water or oil to get through cracks from the stresses it was not designed for. Studs IMHO should always be bedded in a non hardening sealer and never an RTV type.

The helicoil would be a better "fix" if all goes well centering and aligning.

Opening the hole in the manifold may just get to a very thin spot or even an air pocket. Also threads work well to hold but at an angle one side can work against the other so the entire thread is not holding just one side.

Dave Neptune

[cfergu22]

Dave, what sealer would you advise in a situation like mine. Where you might need to fill a little more of an area than perfect threads?

[Dave Neptune]

If the threads felt OK I would use Permatex Aviation grade and if there loose I'd go with the Permatex #2. Both available in good parts houses. This will work only if the threads have enough integrity to hold the torque loads themselves.

I would also set the manifold gasket wet so sealing with a bit less torque on the studs is possible. Here I'd use the Av grade.

About how many threads do you think you will have in the block?

Dave Neptune

[cfergu22]

I'm not really sure about how many threads.

I have it threaded really well for the new repair stud, the threads are just crooked. I'm hoping that using the manifold as a guide just helps me sort of clean up those threads and make them straight. I'm sure it won't be as strong as if I did it correct the first time.

The real question is, can a hole be threaded twice, at a slightly different angle.

[joe_db]

I cannot imagine how you could re-tap a hole with the same thread size at a new angle and not make a mess out of it.
If it were me I would drill the manifold a tiny bit vs. making a mess out of the block. The *correct* repair is drilling a bigger hole and using a repair stud that has threads one size bigger.
So if you think you can drill and tap for this repair stud with the engine in place, that would be the best way to do this.

https://moyermarine.com/product/drill-tap-kit-716-for-installation-of-repair-studs-oblk_06_446/

[cfergu22]

Just wanted to post a follow up to all this.

So I had already drilled and tapped for the repair stud, that's what was crooked.

I ended up deciding to try to re tap it straight. I used the old manifold as a guide, to hold that tap straight. I used a lot of sealant, let it sit for 24 hours, then pressure tested the block. It held up, so I reinstalled the manifold, and besides some exhaust issues that i needed to fix, it worked really well. I only torqued that stud down to 20 foot lbs.

One issue I ran into was that the manifold was to thick to use for the whole tapping process, so I started the tap, got as far as I could, then slid the manifold off and got 2 more turns on the tap.

I know tapping the hole again was risky, but because I had already used a repair stud my only other option was to drill out even further for a bushing or helicoil.

My thought was to try making the threads straight, and if it leaked I'd pull it off again and drill it out for the helicoil. I was happy that it seemed really solid once it was in there.


I really wish I had used the manifold as a guide to begin with and just dealt with the lack of access. But everything's a learning process.

[sastanley]

I would have tried your approach first as well...You had nothing to lose at that point.
Glad it worked out. Goop that bad boy up with #2 or #3 (Av grade) Permatex!

I can't remember which one, but #1 or #2 Permatex actually hardens up pretty well and would be a bit more flexible than JB Weld, and may hold the cooling water back for some time. One or the other dries/hardens, the other stays sticky.#1 & #2 are in a tube.. #3 is in a jar with a brush..I use it on gaskets, and it is more liquid than the other two. Dave or Don would be able to tell us if #3 cures up and stiffens enough for this application.