Sorry to hear that it's all gone pear-shaped.
I know hindsight is a wonderful tool....
For anyone else finding this thread with similar problems, or just trying to remove small SS bolts from aluminium castings, here's how it's done.
First some information regarding the materials you're dealing with.
Stainless steel. Very low shear strength. Breaking bolts off is very easy, easier than mild steel.
Aluminium. low melting point, about 660C (1220F).
Aluminium Oxide. Very high melting point, about 2,000C (4,000F), and forms naturally on the outside of bare aluminium with exposure to air.
When you heat aluminium, the outer oxide layer keeps you from seeing that the aluminium has melted well before the oxide has shown any sign of melting. Once the oxide layer reaches 2,000 degrees and melts, the aluminium below it is already melted and causes the puddle on the floor and a big hole in your casting. So, heating aluminium is fraught with problems. Doesn't mean we can't do it. It just means we need to be careful.
Now, what causes the bolts to seize is the salt interacting with the aluminium and creating that white paste you'll see. It swells up, 'grabs' the bolt and locks it in place.
When confronted with SS bolts in an aluminium casting, always assume it will be seize, and deal with it as such. Put the spanner or socket on the bolt and attempt to turn loosen it. If it goes 'crack' and starts moving without too much force, great, you win. If it feels like it is starting to turn, but you haven't hear that 'crack', STOP, you're shearing it off! The threads are locked and you are screwing the head off. Before you break it a few options are still open. My first method of attack it to try and 'jar' it free. A few solid raps with a hammer and drift, or even the hammer directly on the bolt head. Sometimes that will shake the corrosion products free enough for the bolt to be unscrewed. If that doesn't work, method 2, the 'hot spanner'.... The rule I work to here is 'go in hard, get out fast'. Turn the flame up on the oxy torch and hit the head of the bolt directly. DO NOT heat the aluminium, the heat will conduct down the bolt well enough. Heat the bolt up until it is red hot and glowing nicely. Shouldn't take more than about 20 or 30 seconds. This dries out that white paste holding the bolt in and turns it to a white powder. The loss of the water is what gives the bolt a little extra room to move. Once you have done that, LET IT COOL... While the bolt is still hot, it will shear even quicker. Once it cools, give it a few hits, for good measure
... And try and unscrew it again. Again, feel it and listen for the 'crack'...
If a bolt does start turning but 'goes tight' then, and only then, turn it back. If it doesn't move initially, DON'T try and turn it backwards (tighten). All that will do is break it off faster by increasing the shear force at the head/shank junction. (yes, I know some of you have done that and succeeded. You got lucky, or the bolt was mild steel, not stainless.)
When all that fails you may be left with no other option but to shear it off and deal with the broken bolt. If you can, before shearing it off, centre punch and drill the bolt exactly in the centre. It's much easier to get a centre on the head than the broken shank. If the hole is even slightly off centre, the drill will move off and as aluminium is softer than SS, getting it back to centre again is very difficult. Personally, I don't like 'easi-outs', they break off more often than not, and removing a hardened piece of easy-out is beyond most peoples' capacity, mine included. I prefer to drill the bolt to the tapping size and just re-tap the hole with the remnants of the old bolt there. Most of the time, the old bolt will come out when very little of it is left anyway.
I also don't like dealing with stuck bolts in awkward spots, the ones at the bottom of the head cover in this case. I would just pull the powerhead off, put it on a stand on the bench and work with easy access. That would also give the opportunity to do the exhaust cover and powerhead gasket replacements at the same time.
I hope this helps anyone else facing the same problem.
Chris.......
