Join Date: Apr 2008
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Re: motor mounts
On the Yanmar 2GM the stiffness the forward and aft engine mounts differ. The differing rigidty is designed to allow the engine to wobble rather freely at low speed. The wobbling decreases as the RPM"s go up.
I've been able to replace the front mounts without disconnecting the the shaft from the transmission but I don't know if you can replace the rear mounts without disconnecting the the shaft.
In a couple of instances, upon inspection I have found that the nuts have vibrated off the bolts fastening the mounts to the bunks. Replacement with ny-loc nuts has eliminated this problem.
When you pull the bolts fastening the mounts to the bunks, you should inspect closely for fretting particularly the neck of the bolts. Look for a pitted surface and fine 'red' iron oxide dust that look like cocoa powder. The dust particles are much harder than the steel bolt, so abrasive wear is inevitable if the iron oxide dust is present; however, particulates are not required to initiate fret. Fretting decreases fatigue strength of the bolts and can result in fretting fatigue, whereby fatigue cracks can initiate in the fretting zone. If in doubt, replace the bolt.