View Full Version : Yanmar KM4A Gearbox problem

03-24-2010, 05:55 AM
Gearbox operates normally for a while but then "clunks" into forward gear the longer I use the engine the louder the "clunking"
201 hours. 4JH4E Engine. 5 years old.HELP
Jim Allan.

03-29-2010, 04:36 PM
Hi Jim,
It sounds as if you might not have a gear problem, but a dampner problem. The dampner transfers power from the engine to the gear and is much less expensive. It uses common springs to dampen the klunk when changing direction of the prop shaft. Aside from the dampner make sure the shaft is secure in the coupler and the prop tight on the shaft.

03-29-2010, 04:42 PM
It sounds like your gear is ok, but you have something else loose such as the engine damper. The damper transfers the power from the engine to the gear via a set of springs that can become loose. This can cause a klunk when shifting form forward to reverse. Also make sure prop is tight and the shaft is well secured in the coupler. We may have a KM4H gear if it is the problem.