9.9/15/18 vs the 15/20 four stroke Tohathu/Nissan/Mercury engines

km1125

Chief Petty Officer
Joined
Aug 10, 2016
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496
Are there any similarities or exchangeable parts on the 9.9/15/18 4S engines vs the current 4S 15/20? I understand the 15/20 have a slightly larger displacement (328 vs 351) than the older ones. The cowling and the lower unit look very similar, if not exact, but I've never seen them side-by-side. I would imagine much of the internal (crank, cam, pistons) might be different but what about the rest? Where the 15/20 whole new engines, or just a displacement tweak on the 9.9/15/18?
 
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