SM2K Yanmar RPM

Mark Hayden

We have a SM2K with an Autoprop. We have been getting somewhat dark exhaust from our engine so we've had a Yanmar serviceman look at it. The Yanmar 4JH3-TE engine is rated at 3800 RPM. When testing the boat on calm water (clean hull, clean prop...), we could got 3100 max RPM, similar to when I purchased the boat. Referring to the maintenance log, the original owner got 3250 max RPM when he tested it around the time of purchase from Amel.

The Yanmar guy I am working with tells me this RPM is an indication the engine is overloaded and is a likely cause for the exhaust. He went further and says that Yanmar would not warranty the engine in this application, given the load, gearing ratio, propeller combination prevents it from reaching the spec'd RPM. The implication being it is a flawed design, which I find hard to believe.

I contacted Amel several months ago about this and didn't get a response. Has anyone been told this before? Is there an explanation for the design?

Thanks in advance,


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