[Scarebird]

I am working on an OT motor (L84 5.3) and in the process of helicoiling the exhaust manifold holes tapped them to a size that does not exist (8mm-1.5).

I decided to simply bore out the helicoils to 10mm-1.5 and use larger bolts.

In the process I drilled too deep and hit the water jacket. I am not seeing a way to repair these economically; new units are around $500/each and may be a better notion to simply toss and replace.

Ideas?

[RUDOLFSSON]

-Have the hole welded shut and remachine.

-Replace that particular bolt with a threaded stud and high temp RTV

-Oversized fine threaded OD plug/insert... put in with high temp RTV



Kris.

[1968firebird455]

Mopar exhaust manifold bolts go into the water jacket... I would just stud that hole using a good sealer on the threads.

[mgarblik]

You have many, many options to repair this situation and they will probably all work just fine. You need to decide what you want when the repairs are completed. Do you want to go back to the stock size? If yes, than Time Cert oversize sleeve repair kit may do the trick. They make thick wall sleeves that can possibly take you back to 8mm from 10 mm if that's the goal. If your good with the 10mm size and just worried about the water break. You can seal the bolt with sealer or install a shallow 10mm set screw first with sealer. Then put your exhaust bolt in after. Welding is always an option, but welding porous, thin, oil and coolant impregnated aluminum isn't as easy as it sounds. You just need to choose your repair at this point. IMO, a heli-coil is the last method I would use to fix this particular issue. Even though I like them, having 2 leak paths into water isn't the greatest. Water can travel around the ID and the OD of the coil. Sealer may take care of it. Good luck.

https://www.timesert.com/

["QUICK-SILVER"]

Loctite and pin a bigger bolt in the hole.

Then start over with the size you need.

Clay

[Scarebird]

Some better ideas here.

The Big-Sert seems to be a good one - had I known they existed earlier!

I will find out if the tap is 12mm-1.5, if so a set screw with sealant may plug the bottom of the hole. Also I need to see if the Helicoils come out without too much drama. If they do not it will be grim.

[Scott65]

The heli coils will come out. If you've broken the tang off already, then they'll need to be rolled/pulled out. Which can usually easily be done by lifting the top coil just enough to grab them with needlenose and then pulling/rolling it out of it's threaded hole. Shouldn't be an issue.

[Nobuddy]

If a m10 helicoil has been installed, there isn't enough material left to replace with a m8 Big-Cert. Drill size is 0.406".

[Scarebird]

not quite, that is the drill diameter of the tap - the major diameter is 0.474".

http://www.timesert.com/html/engineeringdataBS.html

[Nobuddy]

Quite. The m10-1.5 helicoil drill or minor diameter is 13/32 or .406 and the wrong pitch. So not enough material left for the Big-Cert tap.

A m10 big-cert could work. But not an m8.

[Bermuda Blue]

If there's enough meat around the hole, drill and tap for a solid external square drive pipe plug (available at mcmaster carr in aluminium). This will seal the hole.

https://www.mcmaster.com/44705K384/

Then clean off the portion of the pipe plug that is protruding from the surface of the head and start fresh.

[Scarebird]

Bermuda - that may work on one hole that is problematic. To seal the hole I will need a set screw and lots of sealant.

Big-Serts work superb, though for what they charge they should! I did the 8mm wrong pitch side first, worked very well.

What did not work well was using a left handed drill to try to fox the Helicoils out.
They did not catch.

[Formulabruce]

Originally Posted by 1968firebird455

Mopar exhaust manifold bolts go into the water jacket... I would just stud that hole using a good sealer on the threads.

I have fixed my 6.0 doing this, and the 8 mm bolts are too small anyway, and suck. If its just one, on the end, they have clamps for that, so plug it and clamp it.
slight bore on manifold and your new 10 mm will be fine as a stud. use COPPER never seize on the nuts

[Scarebird]

Originally Posted by Nobuddy

Quite. The m10-1.5 helicoil drill or minor diameter is 13/32 or .406 and the wrong pitch. So not enough material left for the Big-Cert tap.

A m10 big-cert could work. But not an m8.

Big-Serts for 8mm are 12mm-1.5 - see pic below,

I drilled out the existing 10mm Helicoils without too much drama. The threads are not perfect but usable. I need the shorter 11mm length Sert as the 19mm will not allow the set tool to pass thru the sert.

I will need to hit the local fastener store tomorrow morning for a 12mm-1.5 set screw. If they do not have I can make one from a regular bolt, using a angle grinder to make a slot for a screwdriver.

[FrankieT/A]

Water under the bridge but,

I have done more than my fair share of LS swaps and come across broken exhaust manifold bolts constantly. No drilling, I weld a nut to the remaining bolt no matter how deep. The heat from welding breaks the bond between steel and aluminum and gives a way to grab the remaining piece of bolt. They come right out. I haven't used a reverse drill bit or easy out in over 20 years.

[Scarebird]

I considered that, but Helicoils are essentially just wires and was concerned it would just melt like a piece of rod.

[Scarebird]

Repair complete. Only issue now is if the plug stays watertight. As shown here, I used a piece of welding wire to see how deep the hole is. I marked a swap with the depth so I know how far in to push and swap the threads with sealant. The hex wrench was also marked so the set screw does not go in too far.



While the Big-Sert kit was 4.0, I was not impressed on the info given via email.

I wanted to know ahead of time whether the tap was 12mm-1.5; they got cute with telling me the tap was proprietary.

Horsecrap.

It was simply a tap with their info printed on it. You can do this by simply ordering the refill nut-serts and note what size the external threads are. Get that tap and pilot drill. They do have a nice counterbore tool but a simple countersink tool can do the same thing and be useful for other tasks.

The coil insert tool can simply be a bolt the same size as the insert's inner dimensions, in this case 8mm-1.25

[Nobuddy]

I guess I have been unable to understand what you are doing with the 1.5 pitch. My experience is that all timeserts are synchronous threads. At least the ones I have used were. So the tap for repairing an M8-1.25 also has to be 1.25 pitch.

But glad to hear you have it fixed.

[Scarebird]

Imagine this as a thick walled cylinder. You can have whatever threads you wish inside and out, ie. 3/8-24 on the inside, 1/2-13 on the outside.

Helicoils are just rolled diamond cross section wire that follows the tapped threads so the pitch HAS to match.