1972 Mercury 800 piston ??

Gomer50

Chief Petty Officer
Joined
Sep 5, 2009
Messages
507
Due to low compression I would like go ahead and rebuild this motor serial number 3192882.My question is there a difference between low dome pistons and high dome pistons.Or does this only go for the inline 6's not the inline 4's. I was reading somewhere more torque with low dome pistons versa high dome.Thanks
 

Gomer50

Chief Petty Officer
Joined
Sep 5, 2009
Messages
507
Re: 1972 Mercury 800 piston ??

I also would like to hone out the cylinders can someone point out what they would recommend concerning a flex hone (what size and grit)
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: 1972 Mercury 800 piston ??

If your going to rebuild it do it correctly, have cylinders honed with a rigid hone (Sunnen) and check to see if you have wear around transfer ports(90%will). If so bore to the next size up. If you leave taper in cylinder it will have: idling problems,low crankcase pressure, die going in gear(leakdown). Also check the labyrith seals(grooves) on reed blocks ,if edges are not sharp or have a brassy look replace them. You can still get either type piston(high/low) and the low lets you run todays fuel and stock timing where high you need to run a lower timing/increased jetting due to todays fuel. Will will also need to do a bleed mod to the block as restrictors as NLA....see post below.
http://forums.iboats.com/showthread.php?t=288700&highlight=bleed+restrictor
 
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