300XS bore scuffing

[mercman867]

Just took my heads of a 60 hour 2017 Mercury 300XS and found lots of vertical scuffes along the entire circumference of all 6 bores. Cylinder 1 and 2 are worse then the others. I have attached pictures of cylinder 2 which is the worst one, but all bores visible vertical lines of which some can be felt with fingertips. Motor was was running fine and within 1.5 mph of when it was brand new. However acceleration has become slightly worse over time. I only ever used the new Merc Racing 2 stroke oil (red color) and motor has never overheated.

What could have caused this?

[Dave Strong]

Reassembled without proper cleaning.

Dave

[mercman867]

Reassembled without proper cleaning.

Dave

It was a brand new motor out of the box

[Cervelo777]

I was concerned about the vertical scoring on my cylinders, so I had compression test and leak down done. All six were 155 or 154 lbs. and leak downs were good. I might suggest you have those tests done just to see what they are. If they are within spec, then I wouldn't worry too much about it. Do you give it a good warm up before putting the hammer down?

[mercman867]

I was concerned about the vertical scoring on my cylinders, so I had compression test and leak down done. All six were 155 or 154 lbs. and leak downs were good. I might suggest you have those tests done just to see what they are. If they are within spec, then I wouldn't worry too much about it. Do you give it a good warm up before putting the hammer down?

Compression was within spec. Could do a leakdown but once the heads are off, I'd rather hone the block and start from new. Break in was done as per manual. These vertical scores can be felt easily with the finger tips.

[XstreamVking]

Could it have not been sent into break-in mode when 1st rigged and sold ? Did your smartcraft ga indicate a break-in mode was initiated? I have seen bore scope vids of my 2005 225 opti with 1800 hrs with almost no scratching. I ran prem plus oil it's entire life.

[mercman867]

Could it have not been sent into break-in mode when 1st rigged and sold ? Did your smartcraft ga indicate a break-in mode was initiated? I have seen bore scope vids of my 2005 225 opti with 1800 hrs with almost no scratching. I ran prem plus oil it's entire life.

I turned on the motor first time myself and showed 120 mins of break in left. Did the break in myself too and i did consume a lot of oil.

Im thinking motor ingested some debris from the plenum. I’m tearing down the powerhead on Friday and will know more.

I’d expect that type of scuffing on all bores to cause some loss of power.

[PanRonnie]

This was optimax oil?

[mercman867]

This was optimax oil?

The mercury racing 2 stroke oil which was recommended for use on the label of the oil tank that came with the motor.

[Motv18]

The hash is all wrong to me which trends me to Dave’s statements

it is a mr300xs so?? Looks rich fouled possible carbon scraping. Mostly it looks out of round leading to flame cutting. But dang that some deep hash probably need merc to see these pics if it truly is nib cause that manufacturers defect level bad bore job.

[Chaz]

Between digital pictures and my old azz eyes, I'm gonna go with :

Poor wall / port prep. If you look at the transfer side that the streaks are on, the radius's in the corner of the port has little chips missing.

The floor of the exhaust port .. it's hard to tell how much chamfer it has. However, the corner has the ever-popular "machine-finished notch" instead of a nice smooth hand-finished rolled edge.



The sleeves are ductal iron and the rings are steel with a chrome face, so your not likely to see much of a witness mark on the ring, but if you look at your port edges real close .. I'm sure you'll find the source of your foreign objects ..

I spend a good 20 minutes on each sleeve before I even think about using it .
You can see the bottom inside corner of this 300xs sleeve where the machine tool
" J-hooked" before going in the next direction.
The good thing is ... it's the narrowest port. It's at the bottom ( OK - that's two ) And all I can / hafta do is chamfer it back to where the ring will never see it ...

On that one there, 867, I would chamfer it correctly by hand. Hit it a few strokes with a set of 220 stones @ light pressure or 280 stones @ med pressure to make sure the hole is round .. and then finish with a nylon brush in reverse rotation to break away any swarf, wash it @ least twice ... New rings and rod bolts... and enjoy your newly blueprinted, sealed up piece ...

[mercman867]

Thanks Chaz, in fact, I inspected all ports and they are very sharp. I nerly cut my finger by rubbing them on the ports. No port prep is visible!

Which are the best aftermarket sleeves I can use for my 300XS?

Between digital pictures and my old azz eyes, I'm gonna go with :

Poor wall / port prep. If you look at the transfer side that the streaks are on, the radius's in the corner of the port has little chips missing.

The floor of the exhaust port .. it's hard to tell how much chamfer it has. However, the corner has the ever-popular "machine-finished notch" instead of a nice smooth hand-finished rolled edge.



The sleeves are ductal iron and the rings are steel with a chrome face, so your not likely to see much of a witness mark on the ring, but if you look at your port edges real close .. I'm sure you'll find the source of your foreign objects ..

I spend a good 20 minutes on each sleeve before I even think about using it .
You can see the bottom inside corner of this 300xs sleeve where the machine tool
" J-hooked" before going in the next direction.
The good thing is ... it's the narrowest port. It's at the bottom ( OK - that's two ) And all I can / hafta do is chamfer it back to where the ring will never see it ...

On that one there, 867, I would chamfer it correctly by hand. Hit it a few strokes with a set of 220 stones @ light pressure or 280 stones @ med pressure to make sure the hole is round .. and then finish with a nylon brush in reverse rotation to break away any swarf, wash it @ least twice ... New rings and rod bolts... and enjoy your newly blueprinted, sealed up piece ...

[Merc 2.5]

U shouldn't need a sleeve , just need fix ones u got then gud hone? Or just send it to Chaz!

[powerabout]

It was a brand new motor out of the box

warranty..

[2jz]

Im thinking samething should b under warranty
I would say too poor prep work before assemble i normally run paper towel with cleaner and check for paper towel catching any parts of sleeve. then address it.

On other note i have not had chance to see 300xs ports but exhaust looks small compaired to 225 pro xs 250 pro xs and 300x ports i have seen