Battling with broken exhaust bolts - B&S 12.5HP

Hi,
Current project is a 12.5 Flathead Briggs engine for my lawn mower. One of the exhaust bolts has sheared nearly flush with the block and I cannot get it out. I've tired to weld a nut onto the end but no luck.

Anyone got any suggestions other than drilling it out as I don't have the tools or the patience to do that to a high standard.

You could try using a left hand drill bit, I have gotten a few snapped bolts out with them

Thanks! What size do you think would work best for the bolt? It is imperial so I've no idea what size it is but it has a 1/2" head and is the imperial equivalent of M8.

Also try doing what Rich said after you run the engine for a while. Once the block has heated up the bolt might break loose easier.

Run it just long enough for the aluminum to *hopefully* expand slightly around the bolt. Couldn't you just use a threaded pipe fitting instead of the bolt on flange?

Best way to get a busted bolt out is to heat it up, use a propane or a map torch for the heat. Heat the area, nothing fancy, just put it on the bolt that is sticking out. You need to soften the metal probably due to corrosion from dissimilar metals (aluminum/steel) or just jammed in there. Running the engine won't get it hot enough. You need a way to turn it also when it is hot, if enough is sticking out use vice grips, if flush drill a hole down center of bolt very carefully to get an easy out in it or hammer a little star socket in it. Heat it up for a long time to get the heat down in the metal to soften it before turning, when you turn it would take little effort to break it free so heat it up then see if it will turn by a little pressure, if no turn, keep heating till it turns with light pressure.

Either propane or a map torch will not damage or melt the metal so good luck.

Thanks! I'll try that as soon as possible

Be prepared to drill it out. 7/16 drill bit for 3/8 course thread tap.

..and remember a bit of anti-seize will help prevent future issues like this. I use the stuff all the time...

Thanks. I will try to back the bolt out with a left hand drill bit first though.