Turd Polishing

[Basfis]

1 hour ago, MrGiggles said:

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.

 

Curious if the middle ring is installed the same as the other pistons. It doesn’t look like it was working correctly. 

[fishinwrench]

Wow, that's alot of carbon buildup for an EFI.   That has to be from burnt oil.

Pull the other pistons so you can get a comparison.  

[MrGiggles]

35 minutes ago, fishinwrench said:

Wow, that's alot of carbon buildup for an EFI.   That has to be from burnt oil.

Pull the other pistons so you can get a comparison.  

I'm not sure how long it was ran with a dead/dying hole. I'm sure as it was failing it began to burn more and more oil. 

39 minutes ago, Basfis said:

Curious if the middle ring is installed the same as the other pistons. It doesn’t look like it was working correctly. 

The middle ring is stuck because if how badly the ring lands are eroded.

[Basfis]

8 minutes ago, MrGiggles said:

I'm not sure how long it was ran with a dead/dying hole. I'm sure as it was failing it began to burn more and more oil. 

The middle ring is stuck because if how badly the ring lands are eroded.

If the middle ring is compromised it won’t keep the walls clean. It’s not impossible for it to be upside down from the factory or cracked. It’s job is to keep oil below it. 

[MrGiggles]

22 hours ago, Basfis said:

If the middle ring is compromised it won’t keep the walls clean. It’s not impossible for it to be upside down from the factory or cracked. It’s job is to keep oil below it. 

As far as I can tell it's installed the same as the others. There is no marking or any sort of bevel/chamfer on it.

This is #3. 

[Basfis]

Typically, there is some kind of edge break to aid in scraping the oil back down the wall. I’ve not studied a merc 4stroke ring specifically. The top edge is a backup to the compression ring. 

Are those rings pinned or free to rotate in the groove?

[fishinwrench]

43 minutes ago, Basfis said:

Typically, there is some kind of edge break to aid in scraping the oil back down the wall. I’ve not studied a merc 4stroke ring specifically. The top edge is a backup to the compression ring. 

Are those rings pinned or free to rotate in the groove?

The only function of the oil ring is to hold oil and distribute it around the circumference of the cylinder wall BEHIND the compression rings during the up-stroke.  Cylinders on 4-S outboards only benefit from fresh lubrication on the intake and power stroke.   The compression and exhaust stroke are lubricated only from whatever residual oil is present on the cylinder walls.  

The compression rings are pinned 180° from each other.

[MrGiggles]

9 hours ago, fishinwrench said:

The only function of the oil ring is to hold oil and distribute it around the circumference of the cylinder wall BEHIND the compression rings during the up-stroke.  Cylinders on 4-S outboards only benefit from fresh lubrication on the intake and power stroke.   The compression and exhaust stroke are lubricated only from whatever residual oil is present on the cylinder walls.  

The compression rings are pinned 180° from each other.

I don't think I've ever seen a 4S with pinned rings. I thought it was exclusive to 2 strokes, so the ring gap can't migrate into a port opening, where bad things could happen.

These are not pinned, in my last pic you can see both ring gaps, they're free to rotate. 

[fishinwrench]

1 hour ago, MrGiggles said:

I don't think I've ever seen a 4S with pinned rings. I thought it was exclusive to 2 strokes, so the ring gap can't migrate into a port opening, where bad things could happen.

These are not pinned, in my last pic you can see both ring gaps, they're free to rotate. 

I stand corrected then.  I've never rebuilt a 4-S,  but keeping the ring gaps 180° from each other seems like it would be a smarter design.   

Regardless of whether 2-S or 4-S you still need .005" gap per 1" of bore.   And having those gaps potentially align would be detrimental.....or at least "less than ideal".    No?

[MrGiggles]

33 minutes ago, fishinwrench said:

I stand corrected then.  I've never rebuilt a 4-S,  but keeping the ring gaps 180° from each other seems like it would be a smarter design.   

Regardless of whether 2-S or 4-S you still need .005" gap per 1" of bore.   And having those gaps potentially align would be detrimental.....or at least "less than ideal".    No?

Yep. General rule of thumb on a three ring piston is to clock each ring gap 120* apart when you put them in the block. I saw it mentioned in the service manual for the Merc but I forget what it said.

Im going to run the injectors down to Sho-me speed and have them cleaned and flow tested.