Aluminum rear mount nuts

I have finally got to installing my engine after two years with it out of the boat. I got it in position, with the rear mount bolts through and just snugged in the nuts but not torqued yet. I checked and played with the alignment and once I had that I commenced to torque the rear mount bolts. The one on the right started to tighten and then immediatly loosened. I could tell it was stripped so I hauled out the bolt, lifted the motor a bit and reached in and grabbed the nut. I was surprised to see that it is aluminum. Why is an aluminum nut used here with a steel bolt instead of a stainless steel nut? Can I use a stainless steel nut? I am thinking that there must be a reason mercruiser went with aluminum but haven't any idea why.

Re: Aluminum rear mount nuts

The reason they are not SS is because they could sieze on the bolt, and that is just really hard to get to to fix. Stick with the proper type of nuts. When they wear out from being tanken off and on too many times, they need replaced.

Re: Aluminum rear mount nuts

Thanks for the advice. I have new aluminum nuts now. Because they are in such a tight spot, I sure wouldn't want the grief of having to deal with seized steel ones.