Posted by Peter Kennedy on 4/16/2025 to
These photos of the Yanmar Common Rail marine diesel 4JH57 are to help determine the correct alternator replacement. In this engine the output terminal of the stock alternator is very close to the engine block. The engine takes a dual foot mount alternator where the two feet are 3.15" apart. It already comes with K6 pulleys but the alignment of the pulley is a bit different so when selecting a Balmar alternator we get the CR variant which comes with a special pulley to match the alignment.
In the front view below you can see the 6 groove belt and you can also see that the adjustment arm has a dogleg.
I don't know if the idler pulley you see is standard on this engine or not.
For an engine like this the Balmar XT-CR-170-K6 Alternator for Yanmar Common Rail comes set up to fit right in, and comes with a special pulley 61-0050 that has the necessary spacing.
Below is a rear view of the Balmar XT-CR-170-K6 alternator with an arrow showing the position of the output stud. You can see that it will end up outboard of the engine,
It is also possible to fit a Balmar 250 amp alternator on this engine. The correct model would be the Balmar XT-CR-250-K6 Alternator for Yanmar Common Rail. You will need to get a longer belt and a longer adjustment arm. You will have to source the belt yourself but the adjustment arm would be the Balmar UBB2 Dogleg adjustment arm with Belt Buddy Tensioner
Peter Kennedy has been in business since 1991 designing, installing and servicing marine electrical systems. The purpose of this blog is to offer support to both professional installers and do-it-yourself boat owners who wish to undertake this work themselves.
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