93 Force 70hp piston/ring project

[bacon13]

My first post after educating myself on this site. I purchased my first boat with the force motor that wasn't running. Compression test showed good on cyl #1 and low on #2 and #3. I took head off and found this on those cylinders.

 

[bacon13]

I took intake off and was able to pull the #2 cyl which ate a ring. There is some scratching of wall as seen in photo above.
#3 obviously also ate a ring. There is damage to a reed also.

More to come.

 

[jerryjerry05]

You sure you want to spend a bunch of $$ on this?
The 70 Force wasn't the best design.
The single carb feeding 3 pistons was a trouble spot.


You'll need a machine shop that can bore the holes.

All the parts you need can be bought on the net.

You'll need pistons and rings. Wiseco is usually what I use.
The OEM need special tools to put the wrist pin into the piston.

If the exhaust cover doesn't need to come off?? don't remove it as they can be a B to reseal.

Gat a bore scope for your phone.
Use it to inspect the exhaust.

 

[bacon13]

What would the factory bore dia be it it hasn't already been overbored?

 

[jerryjerry05]

If it had been bored out previously??
The pistons would be marked with the over size on the crown of the piston.

I don't have the spec on the standard bore.
Someone with a manual might add that info.

From the pic: I see a spring keeper holding the wrist pin in.
That's called a style 2 piston.
Style one is a pressed in wrist pin.

The OEM is NLA for any size piston.
You'll need an aftermarket.
I use Wisco.
Make sure you get the complete setip as wisco rings won't fit anything but Wisco.