Port Timing

[oldcollector]

Doe’s anyone know the intake and exhaust port timing for the standard Mercury Mark 20H? I am in need of the dimensions. The diameter of the cutting tool, The distances from the inner dome to the upper edge of holes,and to the lower edge. Any info would be much appreciated. Darryl

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seakaye12, neps989

[A Hoskins]

From the book “How to Modify Your Mercury Outboard” by the late Harry Brinkman, the intakes should open 112 degrees ATDC, the intakes should close 248 degrees ATDC, the exhaust should open 98 degrees ATDC and the exhaust should close 262 degrees ATDC. Harry says +/- 1 degree is fine. All this also applies to the Mark 55H. I didn’t find anything else specifically for the Mark 20H. Guess you’re gonna have to find/make yourself a degree wheel and figure the distances out yourself. Good luck.

"Fox News" isn't.

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opposedtwin

[howard-pickerell]

Look at the APBA stock speck sheet for the class B MK20H and it gives you the measurements from the block base gasket . This will make it much easier for you to do your work

[Author]

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