Compression in merc 420's
07-21-2003, 05:33 PM
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Compression in merc 420's
What should the cranking compression be in 1989 Merc 420's ? and how many hours of run time before they should be rebuilt ????
07-22-2003, 10:39 AM
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Compression ratio when new is 8.8-1. I would do a leak down and compression test. When the leak down # gets high you need to think about rebuilding or doing a cylinder head rebuild.
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