Re: Mercruiser 140 exhaust manifold questions
Petrey10, I'm going to tell you a story about my own interaction with this forum. At the end of last year's boating season, I planned to winterize my boat--something I had never done before. I read the advice of the more curmudgeonly contributors and was less than satisfied. They wanted me to spend a lot of time and money and I was sure there was an easier way.
After a lot of searching and re-posting, I found someone who verified my suspicions--there was an easier way. I didn't have to winterize at all, since the Mercruiser 140 had a self-draining block! Hooray!
One solid freeze, several hundred dollars in parts and twenty or so hours in labor later, I'm left wondering why I didn't listen to the curmudgeons here.
Cast iron is difficult to weld. Doing so correctly is expensive and time-consuming. Welding cracks in a manifold correctly would be much more trouble than simply replacing the manifold. Welding them incorrectly will cause more problems than it solves.
The answer to your question is that cracks in the manifold can cause water to flow into the exhaust outlets and into the valve ports, causing a variety of problems that are far more expensive to fix than a cracked manifold. You can switch over to the Mercarb, but there's a good chance that the ports won't line up, as there were many changes in the heads over the years. Chances are also pretty good that the parts motor you're looking at has its own problems--perhaps its own cracked manifold. If you're certain about the fit and the condition, it might be a good idea. However, you need to remember that manifolds are an expendable part, and it's normal to have to replace them at regular intervals. That's just part of normal boat maintenance.
