Turd Polishing

[fishinwrench]

9 hours ago, MrGiggles said:

 

Go ahead and get it outta your system, Wrench

Well looky there....a lower unit and a Tilt/trim pump.

Right on. 👍  

😉

[MrGiggles]

7 hours ago, fishinwrench said:

Well looky there....a lower unit and a Tilt/trim pump.

Right on. 👍  

😉

It was cheap enough that I could put those on Ebay and make a little. 

Any idea what torched #4?

[Big Mike]

you have been busy😀

[fishinwrench]

5 hours ago, MrGiggles said:

It was cheap enough that I could put those on Ebay and make a little. 

Any idea what torched #4?

The amount of coking (burnt oil deposits) on the top of the piston indicates that it was not from lack of lubrication.   

If there is coking inside the BOTTOM of the piston then the cause can be labeled as "over-heated combustion chamber". 

Typically failure from overheat occurs on the top 2 cylinders (because heat rises) but I've seen plenty of cases where lower cylinders succumb to overheat first.....for reasons unknown. 

On a 4-stroke your compression readings may very well be skewed by leaky valve seats.  

[MrGiggles]

15 minutes ago, fishinwrench said:

The amount of coking (burnt oil deposits) on the top of the piston indicates that it was not from lack of lubrication.   

If there is coking inside the BOTTOM of the piston then the cause can be labeled as "over-heated combustion chamber". 

Typically failure from overheat occurs on the top 2 cylinders (because heat rises) but I've seen plenty of cases where lower cylinders succumb to overheat first.....for reasons unknown.

I'll know more when I get the powerhead laying on the table and the piston out. 

I'm sure Mercury's software has an injector contribution test function that would allow you to check them (by energizing them for a few milliseconds and measuring the drop in fuel pressure), but about all I could do is rig them up on the motor and see how they spray. I pulled #4 out of the rail and there isn't anything obviously wrong with it.

Leakdown test showed all of the leakage going into the crankcase, not through the valves.

[fishinwrench]

Pre-ignition is a result of overheat.  Ultra-hot (glowing) bits of carbon on the top of the piston are acting like spark plugs. 

Cylinder scoring on a 4-S can be from contaminated oil (fuel in the oil).  

[fishinwrench]

You can effectively test the injectors with a 9v battery and compressed air. 

[fshndoug]

Put your tongue on that thing and I will check your compression

[MrGiggles]

I was going to get the flywheel off and get the rest of it pulled apart, but my puller is too small. I was tempted to get after it shadetree style, but don't really want to add a new flywheel to the parts bill.

[MrGiggles]

Took a little time after work today and pulled the powerhead. 

The bearings in the bottom look perfect. Got a couple photos of #4 after I pulled it out.