Turd Polishing

[rps]

At some point you ask Wrench to find you an old, but serviceable Evinrude?

[fishinwrench]

5 hours ago, MrGiggles said:

A leaking lower crank seal makes sense, with symptoms I have.

A leaky crankshaft seal shouldn't effect cylinder performance.   You have sealing rings on the crankshaft that seperate the vacuum and compression of each individual cylinder. 

 

Here is an example from a 200 Evinrude that I have torn down presently.   As you can see, the sealing ring is above the lower crank bearing and lower seal(s).

Did you do a cylinder drop test, and spark plug inspection to determine that the lower cyl. was indeed weak, before tearing it down?

If the crankshaft seals were subjected to 130+psi of compression.... they'd blow out every time the motor was started.  They are only designed to hold 12-15psi.

[fishinwrench]

Post a few pics (all sides and the top & bottom) of that bottom piston.  I can do an analysis of it right here, I think.

[MrGiggles]

40 minutes ago, fishinwrench said:

Post a few pics (all sides and the top & bottom) of that bottom piston.  I can do an analysis of it right here, I think.

There are two sealing rings between cylinders, but none on either end of the crankshaft.

In this diagram, #18 and #22 are the sealing rings, #25 is the main lower crank seal, and #26 are the smaller crank seals that ride against the driveshaft. 

The lower plug has always been cleaner than the rest, and often wet. 

The pistons are unremarkable, aside from the bottom one being a little cleaner around the edges. My best theory on that is it was eating a little water, which is also likely what led to the demise of the lower crank bearing.

 

[MrGiggles]

The plugs. Far right is the bottom cylinder. These only had 2 trips on them.

[MrGiggles]

1 hour ago, rps said:

At some point you ask Wrench to find you an old, but serviceable Evinrude?

About all I ever see on the market is those old V4s. Probably good motors but they're a little archaic. 

Seems like 60-90hp motors are tougher to find. See a lot of 35-50s and 115+.

[fishinwrench]

Wow.   What I see is a very low hours motor.  Lot's of very short trips at low RPM.  

So it looks like bushings #22 & #25 are what seal off the upper and lower crankcase on that one, instead of having c-shaft sealing rings. 

By design that powerhead is always gonna be a little weak on Cylinder #3 because the crankcase volume is greater there.   If there's enough clearance you could actually stuff the #3 reed cage to partially make up for it.    Do you see the difference in the configuration between cyl #1 and cyl #3 ?   (sealing bushing is BELOW the bearing on #1....but ALSO BELOW on cyl #3).   I assume there is a bleed hose nipple that feeds lubricant to the upper bearing ( there would have to be).....Whereas the lower bearing relies solely on residual unburned crankcase leftovers to lubricate it.   

A bit of wonky engineering if you ask me. 🙄 Definitely not a blueprinted powerhead. 

[MrGiggles]

15 minutes ago, fishinwrench said:

Wow.   What I see is a very low hours motor.  Lot's of very short trips at low RPM.  

So it looks like bushings #22 & #25 are what seal off the upper and lower crankcase on that one, instead of having c-shaft sealing rings. 

By design that powerhead is always gonna be a little weak on Cylinder #3 because the crankcase volume is greater there.   If there's enough clearance you could actually stuff the #3 reed cage to partially make up for it.    Do you see the difference in the configuration between cyl #1 and cyl #3 ?   (sealing bushing is BELOW the bearing on #1....but ALSO BELOW on cyl #3).   I assume there is a bleed hose nipple that feeds lubricant to the upper bearing ( there would have to be).....Whereas the lower bearing relies solely on residual unburned crankcase leftovers to lubricate it.   

A bit of wonky engineering if you ask me. 🙄 Definitely not a blueprinted powerhead. 

The hour meter on the original boat was just under 300, but I have no clue if it worked.

The bores and all the bearings are excellent, aside from the lower main, and it really isn't all that bad, just a little rough and noisy.

Is the missing carbon on the top of #3 piston typical of what you see on a cylinder that is eating a little water?

The top of that diagram is cut off, the upper crank seal is just like the lower, residing in the mag plate, on top of the bearing.

It does have the oil bleeder hose like you said.

With the powerhead on the work bench, I think I could rig this up and pressure test the crankcase just like you would a chainsaw.

[fishinwrench]

25 minutes ago, MrGiggles said:

 

The top of that diagram is cut off, the upper crank seal is just like the lower, residing in the mag plate, on top of the bearing

Ahh.....I just realized that.   😅 Ok.

 

25 minutes ago, MrGiggles said:

 

Is the missing carbon on the top of #3 piston typical of what you see on a cylinder that is eating a little water?

If the clean spot lines up with the exhaust port....then yes.  That one looks a little "steam cleaned" all the way around (more like a head gasket leak).

But your bottom cylinder is always going to be the coolest running cylinder, so it's hard to say on that one.    A bad exhaust cover gasket, or a microscopic crack in the block on the exhaust side can allow a bit of water to be sucked into the cylinder also.

[MrGiggles]

13 minutes ago, fishinwrench said:

Ahh.....I just realized that.   😅 Ok.

 

If the clean spot lines up with the exhaust port....then yes.  That one looks a little "steam cleaned" all the way around (more like a head gasket leak).

But your bottom cylinder is always going to be the coolest running cylinder, so it's hard to say on that one.    A bad exhaust cover gasket, or a microscopic crack in the block on the exhaust side can allow a bit of water to be sucked into the cylinder also.

I replaced the head gasket a few months ago, it appeared to have been a leaking a little bit externally.

To answer your other question, when I pulled the #3 plug wire, it ran no different. 

Spark on that cylinder is great, compression is 120# on all three, and I have swapped the middle and lower carbs fixing another issue.