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Joined: 3/27/20
Posts: 7
Alternator tensioner bolt sheering off while on trip

We are currently on a crusing trip in the Gulf Islands and the bolt for the alternator tensioner keeps sheering off, this is the second replace in the last two weeks.

Any suggestions on why and quick fix to get through the trip/how to upgrade as the spacer bracket creates a clear weakness for sheer moment? Its a pain to have to drill out bolts and be down for a day each time at a dock!


Cat 36 1984 hul 204

Chachere's picture
Joined: 10/27/10
Posts: 674

It appears from your picture that you have the original alternator bracket, which should have been replaced/upgraded a long time ago. If you go to the "members / important notices" section of the site www.catalina36.org/members/important-notices, the second notice describes the problem www.catalina36.org/members/important-notices/universal-m25-alternator-bracket-upgrade-important describes the problem and has a link to the service bulletin issued back in 1991 by Universal  www.catalina36.org/sites/default/files/legacy/Universal_ServiceBulletin_AlternatorBracket_193.pdf 

Former C36 owner Mainesail has a long write up on the flaws of this set-up and the need to replace it, and details on how: https://pbase.com/mainecruising/universal_alternator_bracket&page=1  .   From my recollection, several owners have posted in these forums about having found this out the hard way, when the bracket failed and took out other essential parts of the engine along the way.

Haro's picture
Joined: 11/7/14
Posts: 280

Since your resources are limited, I would try replacing the spacers with larger diameter pipe. This would provide more stable base. Also the bolt does not apear to be steel bolt.

Maine Sail
Joined: 2/26/10
Posts: 322


I know you're off crusing but PLEASE, PLEASE, PLEASE do not attempt to keep using that alternator bracket. Your next failure could be the timing gear case and when that happens you're going to be looking at a complete new engine or finding a complete spare engine. The last time we had this happen to a customer he wound up with a brand new Beta engine at a cost of nearly 16K!!!!! Those timing gear cases are long ago discontinued, unavaible from Westerbeke, and impossible to find, even used ones are nearly impossible to find. Also, a SS bolt should not be used for an application like that. Grade 5 or 8 steel only. Again, please DO NOT repair this and continue running the motor!!!

That braket was replaced & updated by Westerbeke nearly 30 years ago and you have been lottery winner lucky up until now. Your alternator looks updated and is most likely a higher amperage output than 51A. We saw tons of the original brackets break timing gear covers on the stock 51A alternator and when folks went with a larger alt it was usually a matter of weeks before the timing gear snapped.. Putting a larger alternator on that already horribly designed bracket is an impending death sentence for your timing gear cover.


This is your next failure, if it is not already cracked. https://pbase.com/mainecruising/image/154740185.jpg


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