I have a set of manifolds from a 1985 225 /6. Two bolts are broken in the cast exhaust manifold. I understand this is not an uncommon problem. What I propose it to drill out the bolts and NOT retap the cast. Instead I would do the following:

1. Use a fully threaded hardened bolt that will fit in the original (now marred) bolt hole.

2. Install the bolt upside down in relation to the carb. In other words the hex head will be under the exhaust manifold.

3. Thread a nut down the bolt to the top side of the exhaust manifold. In essence creating a stud.

4. Install the intake manifold by placing it on the stud and securing with a nut and lock washer.

A couple of questions come to mind:

1. Any reason this won't work?
2. Why would anyone retap the cast iron? If the answer to question one is no.

I have seen this done before, no problems.

Why run the bolt up from the bottom. If you are going to drill it out put the nut at the bottom. You still need something to hold the throttle bracket onto the bottom of the exhaust so it will still look original.

My though is that if I ever need to take them a part again I will only have to remove the top nuts.

I have done this, works fine. I also wonder why anybody would want to tap the cast iron again. The bolts for the fan/spacer/water pump are the correct size and length.

Yep, that's how I've been running mine for the past year as well. And actually, you can probably get away w/ standard grade 5 bolts instead of hardened, so long as you keep an eye on them. I can't see it being a problem for several years. (It hasn't so far.) Btw, good luck finding a bolt w/ a threaded portion long enough to use it inverted like you described... standard bolts will only be threaded on the bottom inch and a half or so. (There's some standard that dictates that.)

Edit: Removed brain fart.

You can also use stainless steel bolts, dabs of anti-seize lubricant, and some brass hex nuts. You should not have to worry about them rusting together again.

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

ever tried tapping cast iron? If you do, try to use a 2 flute spiral tap, they seem to work better. Anti-seize and brass nuts, good advice.