New Piston Rings in Cylinders, Small scratches

[WinnipegBoatMan]

So I'm just getting my pistons back into the powerhead of my '85 Mariner/Mercury Inline 6.. I've got all new rings, the cylinders have been honed and cleaned out. All the rings are aligned, and cylinder and pistons are all oiled up, and i've got the pistons in the cylinders. As i'm checking the rings inside the cylinder, thru the exhaust port, and intake port, to make sure i didn't break any rings (Which I just did on cyl#5), i've looked at the inner cyclinder wall and I'm noticeing that there are a lot of scratches on the cylinder!! What the heck?!
I've even pulled out one of the pistons after i installed it, thinking there was a fogeign object trapped inside the rings, but nothing! But its odd, because if you look down the cylinder, from above you don;t see any scraches, but from the exahuse/intake ports you do?! I don't hear any thing binding, and the piston is moving freely? What is this? Will this continue scracthing and ruin my newly rebuild powerhead?? or will this go away?!
Here is the link for my progress so far on my Mariner! If you have any input it would be great!! THANKS!
http://forums.iboats.com/showthread.php?t=366059&page=2

 

[bryanwess2000]

Re: New Piston Rings in Cylinders, Small scratches

I'd wait for someone else to comment but what your seeing is probably normal
This is metal on metal contact with the bore being the softer metal. I would
expect some light scratching. My bores showed marks after measuring them.
Now if it's enough to catch your finger nail on I'd worry.

 

[WinnipegBoatMan]

Re: New Piston Rings in Cylinders, Small scratches

After I did notice the scratches, I did pull out one of the pistons, and i did manage to get my hand into the bore to feel around, and i didn't notice anything too serious to catch my finger nail

 

[arsenalpsu]

Re: New Piston Rings in Cylinders, Small scratches

Those are from metal on metal contact of either a high spot on your ring or cylinder. What you DON?T want to see are scratches on your piston skirt. Do your cylinders have that "scratched" look from being honed or are they smooth as a baby's butt? The scratched look/pattern should be what's in your cylinders which helps hold the oil, along with the groves on your piston which create a microscopic thin layer so there is no "real" contact between your piston skirt and the cylinder. All this being said there is no way for both rings and cylinder to be 10000% perfect that is why there is a break in period for any new or rebuilt engine. The small imperfections in the rings & cylinders slowly "mend" together so you have smooth motions and less friction after breakin.

 

[WinnipegBoatMan]

Re: New Piston Rings in Cylinders, Small scratches

I do see the honed pattern, and all cylinders have been honed, and before i installed the pistons to the cylinders, i did check for high spots and nicks on the piston skirt, and have removed the nicks.. But i still see small vertical scratches, possibly from the new piston rings? Could possibly the Ring end Gap cause this? Because on the piston that has the worst looking scrathes, the ring end gap is in that area..

The good news is that I did get a wood toothpick in the exhaust port to feel the scrathes, and it never caught on anything.. so am I just going nuts?

 

[bryanwess2000]

Re: New Piston Rings in Cylinders, Small scratches

What arsenalpsu is talking about is the bores and rings not being perfectly
concentric( perfectly round). The rings have to scratch the bores to seat.
They actually shear off the peaks left from honing to form a near perfect
seal. You have to use your finger nail to be able to estimate surface finish.
As long as you can't catch your finger nail on the outside edge of ring gap
you should be ok. Your just being overly concerned. The surface finish of
your bores looks something like this WWWWWWWWWWW with peaks and
valleys and the rings chop off part of the peaks and an oil film fills in the
valleys and your piston skirts slide over this film.

 

[arsenalpsu]

Re: New Piston Rings in Cylinders, Small scratches

That's what i was going for- as long as all the new scratches are on the cylinders, not the pistons you're ok.

Hopefulley your piston skirts of your old/reused pistons aren't too bad- and there should be no new scraches on them, if there is that could indicate an issue.

 

[WinnipegBoatMan]

Re: New Piston Rings in Cylinders, Small scratches

OK! I pulled the whole crank apart this morning to finally get to the bottom of this crap! I found out that its the ring end gap that is causeing the marks on the cylinder walls. Now this is where i am confused, visually you can see them, but when I get my fingernail on the mark, I don't feel anything. Could I have caught it in time?
Now here is the real question, why would the ring end gap cause this? High spot on end gaps? And what Can I do to fix this problem? file with microfile? Also someone had asked if the gap was the correnct measurement? Well my Merc book doesn't tell me anything about the gap size?

PLEASE HELP! Thanks!

 

[WinnipegBoatMan]

Re: New Piston Rings in Cylinders, Small scratches

Any idea's?

 

[jyenney]

Re: New Piston Rings in Cylinders, Small scratches

Your cylinders will be fine. Like the guys said, so long as it doesn't catch your finger nail, there will be no issues. I've rebuilt plenty of motors, and it happens to alot of cylinders, when I'm rolling the motor over to install another piston, I see light scratches on the cylinder that I've just installed the piston in.

 

[turbinedoctor]

Re: New Piston Rings in Cylinders, Small scratches

Just by the nature of the end of the ring moving up and down there will be what appears to be a scratch. It could just be the line between wear and no wear. I dont know if that does justice for what I am trying to say?

 

[sschefer]

Re: New Piston Rings in Cylinders, Small scratches

When you size the rings so that the gap is between .018-.025 there is often a sharp edge left on the ring. That edge needs to be chamfered away using a small honing stone. If you do that you won't have the scratches or at least they won't be as noticible.

As a side note: Even when the end gap is correct without filing, you should dress the ring ends. Factory fresh rings also have sharp edges.

 

[WinnipegBoatMan]

Re: New Piston Rings in Cylinders, Small scratches

Thanks GUYS!! I'll get everything in order!

 

[daveswaves]

Re: New Piston Rings in Cylinders, Small scratches

OK! I pulled the whole crank apart this morning to finally get to the bottom of this crap! I found out that its the ring end gap that is causeing the marks on the cylinder walls. Now this is where i am confused, visually you can see them, but when I get my fingernail on the mark, I don't feel anything. Could I have caught it in time?
Now here is the real question, why would the ring end gap cause this? High spot on end gaps? And what Can I do to fix this problem? file with microfile? Also someone had asked if the gap was the correnct measurement? Well my Merc book doesn't tell me anything about the gap size?

PLEASE HELP! Thanks!

That somebody else was me in your other thread, glad you pulled it back apart to check. Sounds like you are OK, typically the ring end gap on a piston ring is .005 per inch of cylinder diameter. So in your case it will be 2.875 times. oo5 or just under 15 thou. 15 thou will be fine.

 

[sschefer]

Re: New Piston Rings in Cylinders, Small scratches

Revised, wasn't awake this morning --

I'm not tryig to upstage anyone here but, the upper ring is .004 x cylinder diameter and the lower ring is .005 x cylinder diameter. This difference helps to reduce ring flutter on the top ring. However, you can only use these figures reliably when you're working on a fresh bore and using a torque plate. Ring butt and scuffing can occur if you do this on a worn cylinder.

Normally, rings are gapped at about 1" from the top of the cylinder but if the cylinder is worn then you want to gap more closely to the bottom most portion of vertical ring travel in the cylinder.

Merc's recommended end gap is huge and will result in lost horsepower but it may be necessary because of the large side clearances required by these engines. I've asked for some clarification on that from other sources.