jspeeddemon

I have taken apart many Mercury marine engines and I don't see any great diffeences between them and an automotive motor. I mentioned in my first post the main three differences I have known of in disassembling a marine motor. You can't get any better than a Dart BigM or Merlin III block for a start and that is certainly heads and tails better than a Gen 6 502 or a 496 block. Add a couple thousandths more piston to wall clearance to say 6.5 or 7.0, some Inconel exhaust valves which are a whopping $30.00 a piece from Ferrea or Competition products, big deal. Buy a 114 LSA or 112 LSA cam, and you have a great start to a marine motor that will live long. Add brass water jackets to the intake if you plan on going in salt water. Now go on Ebay and start adding all that up and it does not justify the motorspeak price because it's marine. I get tired of hearing how a fellow boater gets it stuck to them because it was a marine motor. Furthermore most marine motors that last a long time a relatively low performance say 500 HP or less. That doesn't strain the parts hard enough to tear it up. 600 HP stresses the rods and crank more, then 700HP even more. When you crank up the power, there is a lot more carb tuning especially, that needs to be done, that seems to be the number one mistake. I haven't torn up a bottom end piece in years, mainly because I use the very best rods I can afford, that is the heart and soul of the motor. The rod bolts take a serious beating.

formula31

Wrist pin clearances. Typically .0007 should be upped to .001 on marine hp. Marine oil pan too.

carney

Clearances, Play the major rule. I have to add I bought a pair of 454 create motors and put blowers on them .Five years later they still run strong. But what I thought was different ,when I took the intakes off to put the blower intake on and change the cams, the motor came from GM with brass soft plugs and mr43t spark plugs. All I could think is that the boat builders did not buy enough motors from gm and they were selling them over the counter. ???????????

zz572

i have a 30 spectre cat put 2-572s changed valve covers and oil pans painted blocks orange and flywheels ,never changed anything inside except little springs on distrubuters to keep timing from bouncing 60 hrs no problems none! totally recomend, these moters are high performance period!

zz572

oh the best part ,boat runs 118 mph yea baby! would like to hear from others.just remember to change OIL TO MANUFACTURES RECOMMENDATION 20/50 w racing oil!

KAAMA

Valve guide clearances too.