Re: Intake manifold crack in heat riser

Posted by Rusty O\'Toole On 2010/8/31 18:59:48

I have repaired cracked exhaust manifolds both by brazing and by welding. All worked perfectly, none of the welds failed.

It did not take that long to preheat the metal. Maybe 15 minutes or half an hour. Often the repair was done in a country shop heated by a wood stove, and the most primitive welding equipment. I would put the manifold on the wood stove and build a fence of fire bricks around it and leave it to warm up, then heat up the manifold with the acetylene torch, braze it up, cover with a lid of fire bricks and go away. The cool down did not take that long either, I would leave them for a few hours or overnight and go do something else.

My concern would be that the manifold would eventually burn out again. Of course this would take many years. I would have to look at the job and figure out if it was possible to put a piece of metal on the inside, out of sight, to protect it.

Brazing would be easier and less likely to cause heat stress or warping but would not stand up to as much heat. It is plenty good enough for a normal exhaust manifold but if those burn out spots are caused by some kind of concentrated exhaust pressure like a cutting torch it could be tense.

Another method is to drill out the holes and fit round plugs cut from a scrap exhaust manifold, and braze them in place. This might be better than simply brazing or welding the holes. It depends how bad they are.

There is another excellent method of repair used to fix cracked engine blocks etc.

That is to drill a hole and screw in a pipe plug. Then cut the pipe plug off flush and dress it with a file or grinder. Such a repair can be completely invisible. If you want to be pernickity, sandblasting the repaired area gives it the rough cast iron look.

Long cracks can be repaired with a series of overlapping plugs. This has been a standard repair method for many, many years.

This would completely avoid the problem of welding or brazing and make an even more secure repair. The only question is whether the metal is thick enough.

Now that I think about it the pipe plug method would be the best and easiest way to fix those holes and the longest lasting or most permanent repair. Of course this is just speculation, without actually seeing the job it is impossible to say for sure.