C&C 27 Association Forum

Hugh Morrin

Member

Yanmar 2GM Transmission Slippage; De-glazing KM2-A Clutch Cones

Most C&C 27s are equipped with the Atomic 4 gasoline engine, but some later Mk 3s and Mk 4s were shipped with Yanmar 2GM diesel engines, particularly those that were being delivered to the U.S. The Yanmar engine is paired with a Kanzaki KM2-A transmission bolted on to the back of the engine. My 1981 Mk 3, #894, is so equipped.

There is a well-documented condition (see references below) which results in the transmission slipping and clunking in forward gear. Typical symptoms are that upon shifting into forward, some thrust is realized, but increasing engine RPM does not result in an increase in thrust. Sometimes there is a clunking sound, and then, sometimes, the transmission fully engages and normal thrust is achieved. The problem is not seen in reverse and it is not a cable-adjustment issue. The fix (more on that below) involves removing the transmission from the engine.

My first question for this group is, has anyone disconnected and removed the KM2A transmission from their Yanmar 2GM on a C&C 27, without moving the engine? It appears that there would be enough space, especially if one has a plastic coupling installed, as we do. One could also slide the prop shaft aft. I'm really hoping that we can remove the transmission, without having to move the engine. If anyone has done this, insight and suggestions from your experience would be much appreciated.

For those interested, these posts discuss this issue, commonly referred to as de-glazing the clutch cones:
https://www.cruisersforum.com/forums/f5 … 07948.html
https://www.cruisersforum.com/forums/f5 … Engine.htm:

For anyone undertaking this, the following two YouTube videos created by an S2 85 owner provide invaluable information on the process of disassembling and re-assembling the transmission:
https://youtu.be/UNSW5S8EXus
https://youtu.be/p3eMGM8w0PE

According to the above, the Yanmar 2GMF, 2GM20, 2GM20F, and 1GM series engines all use the same transmission.

The only discussion I found on this forum on this subject is this very dated post, http://www.cc27association.com/f4/viewtopic.php?id=162, but the two replies did not lead the original poster in the right direction.

See photos below.

Last edited by Hugh Morrin (2024-07-24 07:59:10)

---

Hugh Morrin
Blue Zulu, C&C 27 Mk III, #894
Nepean Sailing Club, www.nsc.ca/cc27
President and back-up webmaster, C&C 27 Association