Yanmar GH/HM alternator saddle mount concern

May 20, 2015
Pearson 39-2 33 Annapolis
I have a Yanmar 3HM35F - alternator question is the same as 2 and 3 GM and maybe even later engines. This is the stock hitachi alternator

The boat is pretty new to me and the alternator locked up a few weeks ago. I replaced the belt and it seemed to be working fine, but I noticed that the foot bolt going through the saddle was tight in the alternator, but not that tight in the engine mount, allowing for some play, and contributing significantly to an alignment issue. Today, I disassembled to inspect and upon reassembly, the alternator locked up again. I am tightening down on the foot bolt to eliminate the play, even though it doesn't help much with alignment.
Help - have I broken the alternator by doing this?
If so, what am I missing -some different washers, etc. on the foot bolt?

The foot bolt is 8 mm which matches the parts diagram.

Video attached is a few second of how much play there is before mounting bolt on foot and arm are tightened down.


Apr 22, 2011
Hunter 27 Pecan Grove, Oriental, NC
To eliminate the play, place a shim to fill the space between the engine mount and the alternator mount. What do you mean when you say the alternator locks up?