What might of caused this

"This piston is out of a 115 1

"This piston is out of a 115 1981 johnson V4 that came off a boat that i bought, im rebuilding the motor and was curious why the piston did this. And if i should look into why this happend and make sure it doesnt happen to the new pistons when i install them.
if you look at the piston from the top you can see one edge of the dome looks burnt off, and all around the edge of the piston its very rough. Also it looks like there is melted metal flakes like on top of the piston.


If you look at it from one side you can see that the wristpin is recessed a little bit and some of the ring is actually gone. also there a lot of scratches in it.


on this side of the piston it shows the wristpin out to the edge of the piston. there is also a cavity that you can see better from this angle than you can from top that actually goes behind the top ring. I think this is why i was getting 10psi. compression on that cyllinder =).


Anyways i hope someone can fill me in on what i should look for and do before i put this motor back togather, i decided to just bore it .064 over and do all 4 pistons. This piston caused a pretty major scuff so i think i gotta go all the way on the boring =(.
Dave"

" Looks like a mess but has be

" Looks like a mess but has been seen before. Possible cause a,plugged high speed jet not allowing fuel and therefore the correct amount of oil into one cylinder. When rebuilding it is mandatory to check each and every carburetor and check all of the small passages.Also install a tachometer and monitor rpm . If a sudden drop in rpm occurs, then the motor should be checked to find the problem if not you have the results above. Often it seems that people learn the lessons the hard way (through the wallet). Also check timing and full throttle rpm to make sure that the correct prop is on the motor. The prop attaches to the motor but " FITS THE BOAT AND THE LOAD " any used bargain prop may not be a bargain. "

"Dave.... The first picture ap

"Dave.... The first picture appears as a piston that has encountered pre-ignition which is usually caused by a lean mixture (restricted jet), or having the full advance timing set beyond its limit. I've also seen it caused by a ever so slightly failing head gasket that would allow a faint spray of water to enter the cylinder in question which would result in a like case of having a acetelyne torch in there (Really hot!)

The other pictures however, remind me of engines that I have torn down whereas a condition would exist that mechanics usually refer to as "washout". This is usually caused by faulty ignition on that cylinder, or excessive fuel entering the cylinder by some means. Whatever the case, eventually fuel (gas) overcomes the oil mixture due to the fact that it is not burning properly , and the normal 50/1 mixture changes to 60/1, 100/1, 200/1, (impossible to determine). But at any rate, proper lubrication ceases to exist, friction builds, and the aluminum piston is destroyed.

Whatever the cause, thoroughly clean and rebuild the carburetors, and make absolutely sure that the ignition is perfect. The spark on all cylinders should jump a 7/16" gap on all cylinders with a sharp strong blue flame.

Use Champion s/plugs, either QL77JC4 or L77JC4, set at .040 . The "Q" indicates a resistor plug, the "77" is the heat range, the "C" indicates a copper electrode, and the "4" indicates the setting (.040).

The .064 boring job you mention is really pushing the envelope, so to speak. Frankly, myself, I wouldn't consider going over .040 . Anything beyong .040 figure, I'd simply have the cylinder resleeved to standard, but to each his own. I do wish you luck with your overhaul.

Joe"

I have a 40 hp johnson outboa

I have a 40 hp johnson outboard motor
the starter motor doesn't turn the motor fully
my battery is new the conection are good
I tried a battery with a very high cranking power
it didn't work I replaced the starter motor last year
can the exaust be blocked?
or is it the starter motor?