Hello!

Bought a 5.3 lm7 a while ago and i will be replacing all gaskets and bearings in it, When i took it appart 3 of the header bolts was broken off in one of the heads. Removed 2 by welding a nut on the bolt and they screwd right out. But the third bolt the previos owner have tried to remove by drilling into the bolt that was left, but he havent drilled with a big enough drill to remove the bolt completley. Then he has tried to tap the hole and broken the tap off.. After that he has drilled ANOTHER hole to the side and tapped it. I managed to get both the broken off tap and old bolt out so now im left with 2 holes..
My idea is to fill both holes and re-tap by "solder" or "braze" both holes with pure zink, something i have done before on aluminum with very good results but never on a head.

My question is, Will i warp the head with the heat? or cause any other damage? the zink has a melting point of 780 degrees Fahrenheit.
Btw does anyone know what temp the bolt/flange could reach? so im not filling the holes with zink and then it just melts when i drive

And sorry if the english is bad, not my first language.

 

Why does the spare bolt hole need to be filled?

Can you use an insert on the one you need?

 

Because the threads is very bad in it so i dont want to use it. And its very very close too the normal bolt hole so if i fill one of them i can just fill both

 

Why zinc?

Why not fill them both with aluminum and re-drill & tap the one you need?

Keep it simple.

 

dont have a tig welder, and the soldering/brazing rods for aluminium i can find here have a melting point much lower than zinc so im worried it will melt when i drive.
And zinc works really well for other stuff, sticks really good to the alu and gets hard so i can tap it.
My only concern is if the head will get any damage from the heat

 

I will bet that you never used that zinc on anything thicker than maybe 14 or 16 gauge or .080 metal.

The problem with a thick aluminum casting and brazing it with zinc or anything other than tig welding, the problem is the aluminum needs to get to a temperature that will get the zinc too hot.

The casting will suck heat away from the repair so it needs to be done quick and hot. Doubt zinc will work. Nothing with a torch will work.

 

actually i have used zinc for thicker stuff, IF the head would not be damaged by the heat i would wrap it with insulation. put a small chunk of zinc in the hole and then start to heat it until the zink melts. Then take a needle or something made of stainless steel to scrape the surface to break the oxid layer. then fill it to the top.

Here is a couple of pictures of a repair done with zinc, It not me who have done this but another guy in sweden.

 

Here is the problem

 

If it were mine, I would look up a Time-Sert insert. You can get one oversize and tap the material you have there, put the insert in with some serious epoxy filler, and run an oversize bolt for your header in that one spot. It should hold.

 

Yeah best to just pay somebody to weld that up and machine it back flat. It won't cost much at all and there are people everywhere that can do that, it's really a very common and easy repair.

IMO the whole "zinc" thing is just not a good idea. I know, you're telling us that's the tool you have at your disposal; but that doesn't mean that it's the right thing for everything, much less for this specific thing. Kind of like, if all you know how to use is a hammer, then every problem you come across you start looking for ways to treat like a nail, even if it's really a screw. Concentrate on making an effective repair rather than concentrating on using zinc for this.

I should note also, zinc will suffer extreme electrolysis at the junction with the aluminum, and so will eventually fall out. Not a good repair method to begin with.

 

Thanks everyone!

then i will skip the zinc

either i will Tap both holes, screw in 2 bolts with permanent threadlocker and cut them flush, then drill and tap where i want a hole.

OR

Leave it to someone to weld it. If i do that, would i have to machine it afterwards or will it not cause warpage?

 

Probably will have to be machined, since it will be REAL HARD to fill the holes to where they are EXACTLY even with the surface.

No problem though, you can "machine" it with an angle grinder; fill the holes up to where they're lumps, then just carefully and slowly grind them down until they're level with the rest of that surface. It's not all that critical, given that it's just the exhaust manifold flange, and there are gaskets there to seal any slight irregularities.

 

i mean the surface thats against the deck of the block😛 Its a bit hard to know all the name in english. i have no problem to make the welds flat again😁

 

I'm not seeing how that will be affected by any of this. Since you have the heads off anyway, it wouldn't hurt to have them resurfaced; but this particular repair isn't going to require that, on its own, if the surfaces are OK as they are.

 

perfect! Thats what i needed to know.

i dont see it happen either but as always when i Google everything seems very complicated, almost like when you Google some pain or something and it says you will be dead in an hour 😂😂
but thats why i ask, want to be sure to not warp the head

 

Of course. We don't want to accidentally cause some unexpected problems.

But, this kind of head is large enough and thick and robust enough, that it's unlikely to have that kind of effect. I think you can just repair the one malfunction and not have to worry too much about unintended consequences.

​​​​​​​Hopefully this will be easier.

 

sounds like alot of dicking around for a stock head..looks like it's already off the engine, why not just find another 706/862 head at the local junkyard? you can buy a whole engine for a few hundred bucks, one head can't be much.

 

Well, he is in Sweden...

 

Too much money where i live..

 

This is what I would do if welding isn't an option. You could even run a stepped stud where the timesert is M10x1.5 and it steps down to M8x1.25 for the manifold flange.