welding a broken head bolt - aluminium head

[Franknstein]

Hi All
See my attached pics.
I removed a cylinder head from my 328i BMW the other day and one of the head bolts snapped. The block is aluminium and the head bolts steel. It snapped a couple of mm below the surface of the deck.

My plan is to weld a nut to it then try extract... if that method does not work, then I can grind flat and try and easy out etc..

I was after some advice welding this, even to ask if it can be done, as I am concerned I will melt the aluminium.

My thought was to take the top half of the broken head bolt, and machine it hollow, with a wall thickness of a couple mm, then chop it down to about 5mm tall. Then drop this little hollow cylinder piece into the hole sitting on top of the broken stud section, then fill it with weld... now it will sit proud of the head by a couple mm...
then drop a washer and m10 or larger nut on top and fill with weld again...

The theory is the little hollow cylinder should protect the threads from the arc.

See my diagram. Blue is my hollow cylinder I will make from the other section of the head bolt, the pink is the weld, and the grey a washer.

I have a stick welder which I have welded a lot of stuff with. But I actually bought a GYS smartmig about a month back, but havent tried it yet! Should I try this with the stick or mig?

Any suggestions/thoughts/warnings appreciated.
thanks

 

[dobbslc]

Have a search as there was a thread here a while ago about exactly the same thing.
You can get a special arc rod for what you're thinking of doing that forms a slag barrier around the weld pool to protect the head.
Once you've got it hot it should come out much easier.

 

[gordon stephenson]

I would not go the easy out route, they just don't work.. Instead i drill down the centre, check with the good studs as to how much is left in the head, drill almost right through just a bit smaller than the thread root diameter. than grind the end of a chisel or allen key to a quare with sharp corners. hammer this down the drilled hole to broach the hole and make it a good fit on your tool, then screw out, if yo have not drilled right through the stud give it a good hammering with the broach to help loosen the threads,

 

[Woody.v8]

Have a search as there was a thread here a while ago about exactly the same thing.
You can get a special arc rod for what you're thinking of doing that forms a slag barrier around the weld pool to protect the head.
Once you've got it hot it should come out much easier.

Here you go
http://www.mig-welding.co.uk/forum/...ylinder-head-bolt-with-5mm-sticking-up.58532/

 

[steveo3002]

ive done a few similar jobs on alloy heads , washer over the hole and weld on high heat , then weld a nut to that

ive not had it damage /melt the alloy on what ive done , but then im no expert just a tinkerer in a shed

easy outs wont work for you...it will snap and make things 100x worse

 

[BrokenBiker]

i have done this on an exhaust stud but used tig. worked fine, i just put a few blobs on the stud the rested a nut over the blob and filled it with weld, let it cool a bit and wind it out

 

[Digger6135]

Put the head back on, fixing it with a couple of bolts, then using damaged bolt hole as a guide select a drill that will just fit through the head, then proceed to drill, this will centre the hole in the damage bolt,
select another drill that will remove most of the metal without damaging the threads in the block, if you could find a left hand drill of the right diameter the chances are that the bolt will come loose and unwind itself out of the block, while you are drilling it out.

Digger6135

 

[AndyStobbs]

Are the bolts tapped direct into the block, or do they sit into a ladder type arrangement such as on a Rover K series?

 

[mike os]

with it below i would think weld a washer then a nut?

 

[wyn]

If you have a bit of time, start soaking it in some sort of fluid to help free it up a bit before getting on with drilling or welding.

 

[gordon stephenson]

Never tried it but the Yanks on another forum recon that warm the seized part and run melted candle grease into it.

 

[BrokenBiker]

Never tried it but the Yanks on another forum recon that warm the seized part and run melted candle grease into it.

I've tried it...just makes a mess and makes it harder to keep the drill straight when trying to start it off to drill it out

 

[Kent]

Done this sort of thing lots
No problems melting the ali arc damage from a cack handed mistake is the only risk I can see. Ali takes more heat than most when it's localised
The heat applied in welding will actually break things free easier than you might expect - never fails to surprise me anyhow
Few months back I got a very seized front pin screw out of an old boxlock shotgun
It had been soaked in kerosene the works ( actually left it in a tank of it for a week) tig welded a little bit of bright bar to it and it felt like it was half way unscrewed - I assure you it was anything but tried just about every trick in the book before I welded it out

 

[gordon stephenson]

BB, accurate drilling needs either a guide or at the very least a decent centre pop mark to prevent the drill wandering, and start off with a smaller drill.

 

[T0rnado69]

and before you start, cover the water and oil ways with tape

 

[Franknstein]

Wow. Overwhelmed by all the responses. Thanks all.

So, last night I built a blu-tack dam around the hole, and sprayed a pool of PlusGas in there. It will be soaking for about a week, as I will only get time to tackle it the weekend after next. PlusGas it appears is simple kerosene.

My next plan is to fab a (300mm long) 25 x 5 steel flat bar with a 40mm long offcut of solid round-bar (32mm diameter) welded to the centre. Then a hole either side of the flatbar corresponding to the head-bolt holes either side of the offending one.

I've bought a set of titanium coated HSS left hand thread bits, 3,4,5,6,7,8mm... and will drill the centre of the round bar on my drill press at 3mm, then bolt to head and drill offending headbolt at 3mm, remove and go to drill press and move up to 5mm, back to head... rinse and repeat till about 8mm. This little tool should work as a really nice drill guide - provided I get it 100% accurate to the centre of the broken bolt. Lots of plusgas sprayed whilst drilling and taking it slow.

If I am lucky it will come out with the left-hand bit, if not, at least there is no chance of the drill driving the bolt further down and putting pressure on the weak aluminium threads.

If the LH bits don't remove it... then I will mig-weld all the way down from the bottom of the now hollow bolt right to the top, and weld a nut on top.... with all the heat it should come out.

If that fails, grind flat, drill out, and helicoil or timesert - hoping it wont get to this stage, not really thought through plan C!!!

I'll send updates and pics on how it goes.

Oh and thanks for finding the link to the other thread on this subject - I read it with great interest.

 

[Windy Miller]

... and will drill the centre of the round bar on my drill press at 3mm, then bolt to head and drill offending headbolt at 3mm, remove and go to drill press and move up to 5mm, back to head... rinse and repeat till about 8mm. This little tool should work as a really nice drill guide - provided I get it 100% accurate...

Have you thought about how to get it 100% accurate with your drill press? Gonna be tricky!

Are you in SE London? If so, pop the 32mm bar over to me and I'll drill you the first hole on the lathe - it will work out more accurate than on the drill press

 

[Kent]

A note on working with welding small parts and blanking up things you don't want a blob of spatter or the arc wandering to plasticine is very useful
Never tried bluetack because I always have plasticine in for this and similar

 

[Jim Davey]

Extraction electrodes FTW.

 

[Woody.v8]

http://acronyms.thefreedictionary.com/FTW
Erm im confused?