</font><font color="blue" class="small">( from what you said it sounds to me like synthetic would be benifical because of the partial filtration system of the 8N.
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I think it would be quite the opposite. Obviously the oil filtration on that engine is sub-standard. The big selling point of a synthetic oil is extended change time. Looking at both of those concepts, the big way you are getting dirt out of the engine on an N is to change the oil.. the filter doesn't play a huge roll in removing dirt.
Since the oil change itself is the main cleaning function for the engine.. then keeping that same dirty oil in the tractor 2-3 times longer due to the extended drain intervals will be keeping that dirt in the engine longer.. rather than simply getting rid of it at the 'normal' change interval, and then getting fresh clean oil.
Here is the quote I found in the archives. It is from Mobil, and was in answer to a question posted about using their oil in an older tractor engine:
""Mobil does not recommend using synthetic motor oils in pre-1980 applications due to possible gasket and seal incompatability issues""
Soundguy