90hp/3cyl/96' Merc/Mariner Outboard Noise [video]

[Mr.Austin]

While I wait on a lift eye, I thought I'd reach out to the community with the video below. I've rebuilt 4-cyl, v6, and straight 6's but have not come across a noise like this before and since we're all eager to self diagnose via webMD, I thought it may be worth a shot to lean on your experience and later see just how close anyones diagnosis was

Outboard: 90HP, 3-cyl, Mariner/Mercury
SN: OC282743
Year: 1988-1991 *EDIT* based on part numbers, this range is more accurate

Issues as described by seller: Engine runs very rough
Issues i've found:

• Gas Tank about 1/4 water (DEFINITELY run through engine by previous owner)
• Compression
  • Taken while considering purchase. If I had known condition, i may have shy'd away
  • cyl 1: 110
  • cyl 2: 80
  • cyl 3: 105
• Cyl 2 is the cause of all engine noise

Video: In this video, i'm turning the flywheel with my left hand back and forth about 30 degrees. Again, I've never heard this noise before. My VERY unexperienced thought is that the noise is related to bearings - perhaps crankshaft. I realize the entire powerhead may be toast but I enjoy these projects and will begin to tear into it in the coming week or two to find out.

Anyone want to venture a guess? I'll post another video of tearing into it.

Video of cyl 2:

 

[racerone]

?---Just remove the 20 bolts or so and remove the exhaust cover.-----Easy to see what goes on then.

 

[Faztbullet]

Rebuild time......

 

[Mr.Austin]

Thank ya, Thank ya! I'll get to digging just as soon as the lift eye arrives. Hopefully the previous owner shut it down once the issue arose!

Also, one other question. When finding parts, I see the SN referenced consistently. That said, with my SN (OC282743), does "1996-97 up to OG437999" include 0A#### - 0G#### or does that imply that it's 0G0000000-0G437999?

Simple things like that, I'm not able to find much searching the web. Thank you!

 

[Mr.Austin]

So, found some time to pull it apart. As you'll see, my heart sank over so slightly when I gained access to the crankshaft. Here's a shot of the second rod (middle) --

Appears to me that there was a serious lack of lubrication at one time or another... or all of those times!

Cylinder 1: lubricated
Cylinder 2: no lubrication (pictured above and below)
Cylinder 3: poor lubrication (bearings do spin but stuck within retainer/roller)

Again, here's a second shot of the devastation of cylinder 2

One question related to this and then another:

Oil pump failure
1.) I was told "Oil pump must have gone out" but upon examination, it seems, mechanically speaking, like a rather simple setup. Is the common "failure point" on these a clogged tube, cracked tube (not the case here) or something with the delivery of oil once it's pushed through the pump? I'm very curious how the pump itself goes bad when that's not the case. The following is the oil pump in question : http://www.*****************/newparts...um=MER42959A+2

Top vs. Bottom Guided Rod
2.) I've already purchased and received a replacement crankshaft (existing shaft is damaged). Along with that, I purchased a set of three connecting rods. The rods themselves appear to be in good usable condition. HOWEVER, due to my lack of experience with outboard mechanics, I paid attention to the "compatibility" chart and did not realize that what I purchased were Top-guided rods vs. Bottom-guided rods, which I have.

That said, If I plan to purchase a rebuild kit, could I opt for a top-guided kit and move forward with the top-guided rods? My thoughts are that the differences between the two are compartmentalized within the rod/bearing/piston area, all of which will be replaced upon rebuild but any confirmation would be great!


Thanks in advance for your thoughts from experience! Rebuilding is something I'm familiar with but I've already realized the many, MANY, differences there are within an outboard - all good stuff!

 

[racerone]

Top guided rods will need top guided pistons.

 

[Mr.Austin]

Thanks for confirming! Seems I'd be able to simply opt for the top guided rebuild kit and be all set, given these rods then.

 

[Faztbullet]

Will also need top guided wrist pin bearings/washers.......