Re: 850 mercury water, leak into cylinder
.... but I'm terrified about even thinking about trying to remove broken bolts from an aluminum casting. Am I over reacting?
I don't know about overreacting, but broken bolts is part of the job... I work on salt water engines (we don't have any fresh water, apart from drinking water
) and there are techniques to deal with struck bolts, and the inevitable broken ones too...
This is what I found works for me. Other people may have other ideas and opinions, that's their deal.
Bolt feels struck. When you back a bolt out of Ali you usually hear it 'crack' off. If it feels like it's turning, by there is no noise, it could be shearing off. STOP! before it breaks. The first thing I do is hit it with a hammer and drift, HARD. The idea here is to shock the bolt free. If I have an engine that has bolts that are obviously going to be stuck, it's an old engine, etc, then I will usually go around all the bolts I want to remove and hammer shock them even before I start trying to remove them. (Sort of tell the engine that I'm serious and it would be far less pain, for both of us, if it just gives up now
).
The next thing I'll do with a stuck bolt is to hit it hard with the oxy torch. One thing about ali when you're heating it.... It will get hotter, get hotter, get hotter, oh dear, it's a puddle on the floor! Unlike steel it doesn't change colour. There is a very subtle sign JUST before it becomes that puddle, the outside gets a slight crazed finish... But by the time you see that, it's already too late.
So, I have a rule. Get in fast, hit it hard, get out fast. So with all that in mind.... I heat the bolts up really fast until it's red.... Then let it cool... The idea behind this one is that the corrosion products holding the bolt in (that white powder) will dry out and release its grip in the bolt.
If that doesn't work... (now is when we will have all those people adding that they use XYZ product and it does ABC.... Well, this is my story, not theirs!) I have tried various penetrating oils and sprays, usually with a very limited degree of success (and for all the naysayers, yes, I did it as per the product instruction...) Ok, bolts still stuck. Then I'm afraid you just have to break the bolt (and hope it breaks under the head, not on the face of the threaded surface), remove the rest of the cover (or whatever you removing) and get them out later...
Ok... bolts broken off, nothing you could do about it.... If there is enough thread protruding to get vice grips on, great.... Give the bolt a few sharp hit with the hammer, heat it up and let it cool, give it a few more hits, then try and unscrew it....
Bolt sheared level with the surface (or so close that you can't get a descent grip with anything)... Nothing to do here except drill and tap. Centre punch it as close to centre as you can... Remember Ali drills easier than stainless, so if the drill is not dead centre you'll end up with an offset hole (not a good look). Now, using a very small drill, drill all the way though... Then gradually open up the hole until you have removed almost all of the bolt material. You should be left with threads around the edge of the hole.... If you got it dead centre you should be able to 'unpeel' the remaining stainless steel out. I usually use a thread repair (Heli-coil or the like) on all hole I've had broken bolts in... And have a good look at the others too.
Good luck
Chris.............
