HawkEyes wrote:

Moe wrote: Duly noted. I have a cyl hone somewhere . . . .
I'm not sure if my service manual specs out psi readings, will have to check.
Either way, rings can't be too pricey, as long as the pistons are in decent shape. I'm sure new replacements don't grow on trees.

Joe Poole will have them for you. Ferguson Poole Marine

Yeah I figured I'd be calling him at some point.

Joe! If your reading this I'll probably be buying more parts!

Dang Russ, that was a sad story. What did you do with the motor afterwords?

I had a Mark 58A stop running in the barrel. It was the first start of the year and it ran for about ten seconds. The motor locked up. I pulled it apart to find one of the bearing needles had broken and decided to join in with the piston. It probably dried out from sitting and sucked up to the cylinder. The cylinder and piston were scored beyond repair. I checked other bearings with a 5x and my reading glasses and they were all pitted. At the time I was building a Mark 25 so I checked those bearings and they were pitted as well. Just be glad it hasn't sucked up a needle like mine did, live and learn I guess....

Moe wrote: Duly noted. I have a cyl hone somewhere . . . .
I'm not sure if my service manual specs out psi readings, will have to check.
Either way, rings can't be too pricey, as long as the pistons are in decent shape. I'm sure new replacements don't grow on trees.

Joe Poole will have them for you. Ferguson Poole Marine

Duly noted. I have a cyl hone somewhere . . . .
I'm not sure if my service manual specs out psi readings, will have to check.
Either way, rings can't be too pricey, as long as the pistons are in decent shape. I'm sure new replacements don't grow on trees.

If you have the motor that far apart I would replace the rings. Don't forget to deglaze the cylinders with a hoan before installing the new rings. 100 PSI per cylinder isn't very good. I have seen compression readings as high as 150 PSI on a Mark 58.

I did check the crank for endplay and it was within the manual specs. Any reason I can't reuse the rings or should I replace those while I'm at it? I've got 100 psi even on each cylinder.

Moe wrote: Well I've already had this torn down to basically a short block. The one thing I didn't touch was the bottom end bearings. Lesson learned I guess.

I had to add couple shims to keep everything aligned properly, using a feeler gauge of course.

Well I've already had this torn down to basically a short block. The one thing I didn't touch was the bottom end bearings. Lesson learned I guess.

The good news is no valve train to mess with, the bad news is everything is on lose roller bearings except the top and bottom bearings.
Keep track of the bearings and don't mix them if you can manage it. don't mix the shims in the sides of the piston pins or anything else like that.
If you don't have a manual buy a Mercury Factory service manual, it's worth every penny.
Pay close attention to the water tube.
Expect to break a few bolts, heat is your friend!