Can I replace a Yanmar YSE8, 8 hp with a Yanmar GM 20F, 18hp on my 1978 Irwin 10/4 without difficulty? What would be the problems if there were any?
Dan Dickison responds:
Thanks for your question. The short answer is no, but let me qualify that. You can certainly do this, but you need to keep in mind that replacing an auxiliary inboard engine on a sailboat ranks right up there as one of the most difficult, involved, and time-consuming tasks that a boat owner can saddle him or herself with. To do this, you'll first need to line up the motor mounts on the new engine with those that exist in the boat. If they don't line up, you'll have to add new mounts to the boat, which means grinding and glassing in an area that's probably not particularly accessible. Of course you'll have to take a template from the new engine to figure out just where the new mounts need to be installed.
Then you'll have to make sure that the alignment of the prop shaft is similar enough to that of the old engine so that the prop will fit through the shaft log with relative ease. This is perhaps the most important consideration for the job. To be sure that these two engines are compatible in this way, check with your Yanmar dealer or Yanmar representative.
Then you'll have to deal with rewiring and realigning the fuel line, the cooling intake hose, and the exhaust lines. It doesn't take much imagination to realize that this is a pretty involved project. Plan on it occupying at least several full several days of your time. Sue Holt and Larry Hamilton, two of SailNet's most active contributors did this same project (albeit not with the same kind of engines) and they said it basically took them a week, and they had help from professional boat yard staff. Have a look at the article that they wrote for SailNet about this project and you'll get a taste of what you're in for. Here's a link to that piece: Replacing the Diesel Engine.