What year is the Merc Powerhead

[Chris1956]

I purchased a rebuilt powerhead for my 150HP inline six. The "new" powerhead has 12 point, 3/16" connecting rod screws, rather than the bolt and lock nuts on the original powerhead from 1977. I suspect that the rebuilt powerhead may be older in vintage. Also, on the rebuilt powerhead, the 1/4-20 crankcase bolts have captive nuts, versus being tapped into the block. Does anyone know what range of years the rebuilt powerhead is from?

 

[Clams Canino]

Re: What year is the Merc Powerhead

The captive nuts indicate a 1976 or ealier block. Conversely, the connecting rod design you mention is from the 80's - later than your old one.<br /><br />It's not uncommon to "upgrade" and older block with a newer reciprocating assembly, particularly if the old one was just plain worn out in the journal areas.<br /><br />-W

 

[Chris1956]

Re: What year is the Merc Powerhead

Thanks for the info Clams. I didn't expect (narrow thinking on my part), that they would mix and match vintages of parts. <br /><br />As a rule did all the inline fours and sixes have the same design in a given year. That is would I expect to see captive nuts on the crankcase for all 1976 4/6 inline Merc. motors?

 

[Clams Canino]

Re: What year is the Merc Powerhead

The same reciprocating assembly was good from 1968 - 1988 Oh yes, recycling takes place!!<br /><br />I would think the nut issue would follow. All I'm sure of is that the nuts dissapeared as the mid-70's turned into the late 70's. Somewhere between "Rocks" and "Draw the Line" <br /><br />-W