1986 45 Mariner noise in motor and then shut down

"I have a 1986 45 HP Mariner t

"I have a 1986 45 HP Mariner that has a problem. S/N A948990 4 cyl. Compression in all 4 cylinders is between 102 and 115. Now the problem.
We were going across the lake full throttle for about ¼ mile when we heard a loud noise in the engine and it quite running. It sounded like a rod, or something in the motor, broke. I restarted the motor and it ran crappy so we stopped and fished for about ½ hour. I restarted the motor and it ran great again. We started home and got about ¼ mile and it made the same noise and quite. I restarted it again and it ran crappy again but got us home. I haven’t taken it apart yet. Nothing seems to be loose or damaged that I can see.
Any ideas?"

"Stephen, if those are your co

"Stephen, if those are your compression numbers "after" this episode, maybe pull the flywheel and have a look underneath just to see if anything let go (including the flywheel key).

Make sure the magnets are still intact and stuck on properly and that everything else is anchored where it should be..."

"did it overheat and try to se

"did it overheat and try to seize, has it had a waterpump and thermostat lately?"

"Graham,
Thanks for the quick

"Graham,
Thanks for the quick response. I'll take the flywheel off after work today and check it out.
JB,
I have never replaced the waterpump or thermostat in this motor. There was water coming out of the pee hole and it was warm but not hot."

"Grahm,
I took the flywheel o

"Grahm,
I took the flywheel off and everything looks good. There is no flywheel key, just 8 1/4-20 bolts. I'm thinking I should start it with a garden hose and let it run for a while and see if the waterpump is still working good. Per JB's suggestion."

"Yes Stephen, JB and I often a

"Yes Stephen, JB and I often approach issues differently (and even agree once in a while) - so yes, definately follow his suggestion.

However, on the hose DO NOT rev it up - the hose can not supply enough water to cool for more than idle speed.

If you can put it in a barrel (even a garbage can will work) you can throttle it up a bit and see if you can determine the source of the noise that you heard (assuming that it is pumping water normally)..."

"I have an barrel that I can u

"I have an barrel that I can use to run the motor at a higher RPM. I will do it the first part of next week becauce my better half has plans for me this weekend. Till then, thanks.
Steve"

"You say there is " no fly

"You say there is " no flywheel key " only 8 bolts!Sorry to say that you did not remove the entire flywheel, you left the hub on the crankshaft.Some models had a key between the hub and the crank and some were splined.Have you drained / inspected lower unit oil???"

"not-a-student,
You are right

"not-a-student,
You are right. I just checked the magnets. There didn't appear to be anything wrong up there so I didn't take off the hub.
I didn't check the lower unit oil. I will do that after work today.
Thanks for the help
Steve"

"before you run it again, pull

"before you run it again, pull the plugs and see if one might be smashed or have any aluminum deposits, you'll know the bad one if its there"

"The plugs look fine.
I pulle

"The plugs look fine.
I pulled the lower unit plug and it didn't look fine. The magnet looked hairy. There was quite a bit of steel shavings on it. Looks like I will be taking that apart next week. I'll let you know what I find.
Thanks agian Steve"