Likely causes of top piston failure

[YN2(SS)]

I don't have a problem with my motor, 1980 Mercury 70, but I keep hearing about top piston failures, especially in inline 6 cylinder motors. What are the main culprits for this? Poor cooling? Mixture too lean? Too little oil in gas? All responses welcome.

 

[flyingscott]

All of the above will trash a cylinder. On mercury motors regardless I change the waterpump every 2 yrs they are the main culprit for wrecking the top cylinders.

 

[racerone]

Agreed , most folks just do not understand the importance of maintaining the cooling system.--------Poppit valves / impellers must be looked at regularly.-----And those 3 cylinder Mercury motors did have a history of issues with the top cylinder.

 

[YN2(SS)]

Whats the best gas /oil ratio for this motor using TC-3 oil?

 

[flyingscott]

50-1

 

[YN2(SS)]

Adjust it as rich as I can without fouling the plugs?

 

[merc850]

The high speed is fixed all you can adjust is the low speed which only affects mixture up to 1600 rpm or so. TCW-3 for outboards and I use Amsoil synthetic 'cause it's excellent.