SX150TXRZ Piston Wear Limits Exceeded-Opinions Please?

[cpostis]

Background: Since 2010 when boat bought first had rpm's surging at over 4,000rpm. Found bad O2 sensor, clogged VST filter, and oil pump sync way out of adjustment (adjusted to .04" from .25"), replaced VST filter and O2 sensor. It was estimated the motor had 500 hours on her at that point. Motor run strictly in salt water, religiously flushed with fresh water after each outing. Water pump and thermostats checked/replaced bi-annually. Spark plugs, fuel filters, batteries, and l/u oil checked/replaced annually. Always use non-ethanol 90 and motor is used about 50 hours a year for the 6 years I've owned it. I estimate the total hours to be between 800 and 1,000. Never a problem since initial until now. Motor was idle for about 5 months. This last run while heading towards inlet, and accelerated to about 4,000 rpm after 5 minutes, alarm sounded (overheat) and rpm's dropped. Stopped immediately and checked water stream from telltale. After letting cool, ran slow rpm for a while and tried accelerating again. Alarm (overheat) sounded again after several minutes. Immediately stopped again, let cool and idled back to ramp.
Action/findings: Pulled t-stats and found an excessive amount of mineral/salt deposits around the starboard stat. Decided to pull heads and exhaust cover. To my surprise, they were clogged in several areas with salt/mineral deposits. The block cooling passages were somewhat coated with same deposits in several areas (nowhere near the same as the heads/exhaust cover). Powerhead was stripped and removed. Found the cooling passages at the front of the exhaust guide (the plate the powerhead sits on) filled with deposits/sand. The small orifices at the bottom these bores were totally clogged. Decided to disassemble powerhead and clean/hot dip heads and block. Now the really surprising find, upon inspecting bores, pistons, rings, heads, block, crank; I found all within tolerances and wear limits other than the pistons. The maximum out of spec piston diameter is by 0.0022". The maximum out of spec piston clearance is by 0.0009".
Possible Choices: I'll post piston/bore measurements
1.) Purchase rebuilt powerhead
2.) Complete rebuild with bore and/or hone including new pistons/rings/small, big and main bearings, top and bottom crank bearings.
3.) Same as 2 above, less the big end and crank bearings
4.) Reassemble as is, honing cylinders, possibly replace rings.

[cpostis]

Bore Cylinder 1 Cylinder 3 Cylinder 5 Cylinder 2 Cylinder 4 Cylinder 6
Tolerance 3.543-3.544 3.543-3.544 3.543-3.544 3.543-3.544 3.543-3.544 3.543-3.544
Wear Limit 3.5550 3.5550 3.5550 3.5550 3.5550 3.5550
Measured 3.5435 3.5440 3.5450 3.5440 3.5440 3.5440
Within Spec 0.0115 0.0110 0.0100 0.0110 0.0110 0.0110
Taper Limit 0.0030 0.0030 0.0030 0.0030 0.0030 0.0030
Measured 0.0000 0.0000 0.0005 0.0008 0.0005 0.0005
Within Spec Yes Yes Yes Yes Yes Yes

Notes:

Piston Cylinder 1 Cylinder 3 Cylinder 5 Cylinder 2 Cylinder 4 Cylinder 6
Diameter 3.5372-3.5381 3.5392-3.5400 3.5392-3.5400 3.5392-3.5400 3.5392-3.5400 3.5392-3.5400
Measured 3.5360 3.5372 3.5390 3.5380 3.5376 3.5370
Within Spec -0.0012 -0.0020 -0.0002 -0.0012 -0.0016 -0.0022
Clearance 0.0059-0.0061 0.0039-0.0042 0.0039-0.0042 0.0039-0.0042 0.0039-0.0042 0.0039-0.0042 Limit 0.0080 0.0061 0.0061 0.0061 0.0061 0.0061
Measured 0.0075 0.0068 0.0060 0.0060 0.0064 0.0070
Within Spec 0.0005 -0.0007 0.0001 0.0001 -0.0003 -0.0009

[rodbolt17]

if the crosshatch pattern is still visible and no major verticle scuff marks in the cyl I would not hone them.
when you hone them you will remove .001-.003 from the cyl making piston to wall clearance way out.
would it still work? most likely for a while.
check any scratchs with a penny.
rub a penny acrossed the scratch,if it leaves copper that's bad,if not roll.

if the cross hatch pattern is good I may scrub the cylinders with Bon-Ami.

if the wristpin diameter is still within limits use them.
ALWAYS use new pin clips.

I never reuse a lower bearing.
mains and uppers if the look good can be reused.
make sure each piston,rod and rod cap go back in the same hole.
use new rings.
use new rodbolts.

a trick on installing a new bottom bearing you ask?

pack it in grease,place it on a AL foil sheet.
heat in a toaster oven at about 200*F for 15-20 min.
place the crank on a block so the bottom end is 45* or so higher than the top end.
slide the heated bearing in place and hold it till it cools.
make sure the numbers on the bearing are properly oriented.

a friend uses a fry daddy set on 250*F with cooking oil.
messy but it works.
on a saltwater block that old I would be hesitant to spend the money on boring and new pistons and bearings.

[cpostis]

Thank you Rodbolt. Cross hatch patterns are visible, They appear to be about 33 degrees rather that what I heard should be 45. No major vertical scuff marks. I'll assemble as you suggest.
I use to install bearings on cranks for large refrigeration compressors. I built an oil heater out of a crankcase oil heater element and a small reservoir, It worked great! I'll use that on the lower bearing.
Few questions:
1.) I assume piston for No. 1 cylinder is smaller than others to allow better passage to the O2 sensor. Do I assume correct or otherwise?
2.) All my electrical connectors except for the lighting coil to regulator/rectifier came loose with a nice pop from being clean and lubricated. Other than pulling the release clip outward, is there any trick I am missing to disconnect this?
3.)I guess I should pull the cover off the same regulator/rectifier to see if I have a deposit build up on it in the cooling passages?

Again, thank you for your opinion, I really do appreciate it.

[rodbolt17]

sometimes the connector melts itself together and if you attempt to unplug it with extreme predudice you will destroy it.
I would not remove it unless nessasary.