1981 Mercury 7.5 2 stroke

[chrisgt]

A slight leak in a crank seal doesn't usually damage these smaller outboards. The scoring is probably caused by being started up cold and run straight to full throttle without a warmup.

Have you run this thing under load to see how it actually performs??

You can only see a small percentage of the rings, they tend to stick more on the exhaust side, especially if it's a crossflow engine (you can tell if it has a weird shaped piston)

Not all engines came with thermostats in them, it could have been like that from the factory.

 

[Texasmark]

A slight leak in a crank seal doesn't usually damage these smaller outboards. The scoring is probably caused by being started up cold and run straight to full throttle without a warmup.

Have you run this thing under load to see how it actually performs??

You can only see a small percentage of the rings, they tend to stick more on the exhaust side, especially if it's a crossflow engine (you can tell if it has a weird shaped piston)

Not all engines came with thermostats in them, it could have been like that from the factory.

Smaller engines probably so, with only 2 cylinders. On larger engines a thermostat forces cooling water over the top of the top cylinders. Without the stat, they can overheat where there is no cooling water at the top as I read herein and what makes sense. Same thing on a car/truck/tractor engine.....engines that have them are designed for them. Take them out, like in the summer when your equip. overheats, you are doing it a disfavor...find the restriction in the cooling loop, fix it and keep the stat.

 

[Texasmark]

the 7.5 and 9.8 only differed by the carb.

PSI was 120 ish on my 9.8's

run some ring-free thru the motor first to see if the compression comes back

There are skeptics everywhere that condemn snake oil. I maintain all my equipment and have over my 83 year lifetime and that includes cars, PU trucks, OTR trucks, Boats through 125 hp, tractors through 110 HP, all types of 2 and 4 cycle equipment that are required on a farm, and just recently a Kawasaki Prarie 360 that sat for several years with fuel in the carb. Snake oil doesn't have to prove itself to me. The right kind, in the right place, at the right time, with supporting equipment cycling as needed works......no brag, just fact!!!!

 

[racerone]

Issues with these 7.5 / 9.8 HP motors---Poor impeller design.-----They do not have an overheat warning system.-----They do not have overheat shut down.----Engine must be taken apart to replace the lower crankshaft seal.---------Replace crankshaft seals when you have it apart.--Replace upper and lower ball bearings.-----Check reed valves and labyrinth seal--Replace plastic washer at the top of the water tube.