Look at the nickel sized wear pattern in the cylinder.
The photo actually looks a little worse than reality. The dark line makes it look like its really deep but its only about .001-.002 off the surrounding area.
Has anyone seen something like this before, and if so is it going to spell trouble for my re-boring?
My concern is that it might go deeper than surface and that boring it out won't remove it all. I guess if its that bad it will show up on the Magnaflux.
It could be a casting flaw. If boring it out doesn't clean it up you can sleeve the cylinder. Blaine Motor Supply in Dallas bored out my block, did a good job, and were quite reasonable but that was several years back. Your main bearing cap looks good, how are your rod journals? Maybe you can rebuild your engine without re-babbitting.
I have seen such stains in cyl. walls before. What caused it, is a question. The way I have dealt with it is, feel the smoothness of the cyl. walls, mic to see if the bore needs boring. If all is good and rust pitting is at a minimum or at all, I run a cyl. hone to deglaze it and smooth and take out minor surface flaws. Have yet to have any problem any.
I have seen such stains in cyl. walls before. What caused it, is a question. The way I have dealt with it is, feel the smoothness of the cyl. walls, mic to see if the bore needs boring. If all is good and rust pitting is at a minimum or at all, I run a cyl. hone to deglaze it and smooth and take out minor surface flaws. Have yet to have any problem.
Can't tell much by the picture. How far down from the top is it? It may be where the piston pin was parked when the cylinder was full of water/coolant. If it's below ring travel, I wouldn't worry about it. (Unless it's a crack.)
I think the rod journals will be OK. They were still on spec at 1.248 by calipers but I'm confirming with micrometer tomorrow.
The babbitt is pretty decent, but there was excessive end play so I'll have to re-babitt the rear main for that.
And I'm taking the block to Blaine's next week for bake and peen cleaning, which I think will remove all the babbitt anyway.
For better or worse, I've committed to putting everything back to factory tightness. I'm making a learning experience out of it. Education is expensive, LOL!
Ken, yes its hard to get a good pic of it. Its about an inch and a half from the bottom of the cylinder. I think its deeper than where the wrist pin gets to at BDC. The oil ring travels across it though. Its only on one side, and there is about a .001 to .002 depression to it.
Richard, My 27 block and eyebrow stains going into the water jackets. some castings are a little porous and gases pass thru and leave carbon. Its far enough down that the cylinder pressure is very low at that point and should not be a problem. The rings will pass over it. Look at 2 strokes with the ports in the cylinder and the rings go by them. Scott
As the thrust is only on the rear cap you can build up that without re doing the rest of the cap. A good shop could just hot tank up to the babbitt and use Evaporust in the cooling chamber for the rust.
Looks to me like the piston pin came loose and scraped the cylinder wall.
Could it have been that the rod was crooked and when the piston got all the way down and the crankshaft started to push up, that the rod moved very quickly toward the front of the engine and that the end of the wrist pin hit the cylinder wall with a thud in that spot? If so you need to re pour and straighten your rod.
I see cylinders in the back ground. Are we talking about the main bearing or the cylinders?
We're talking about cylinder #1. Ted just asked about the bearings so I added a comment there.
Sorry I know its hard to see in the pic, but you can see a nickel sized feature. The center of the feature is 1-1/2" from the bottom of the cylinder.
The center of the wrist pin on CI piston goes to about 1" above the bottom of the cylinder at BDC, so I was wrong, the wrist pin did travel past the point where we see the wear feature. And remarkably, the feature is exactly the size of a wrist pin. But I cannot imagine the wrist pin could wear it so perfectly while it was in motion. Also, the wrist pin cannot exit the piston unless the keeper groove is worn away completely and it had not. Everything was in good nick in the pistons/rods except for some very slight wrist pin wear. The pin bushings were correct and still recessed 1/32".
Anyway, Ted is right, worst-case I can sleeve it. It may just have to be a mystery as to the cause. I'm rebuilding the whole lot, so whatever it was will be fixed. And Ted may be right about a casting flaw.
Let me know if I can see it in person. The photo is not too good.
I have run marks like that on several engines (including much more modern higher speed engines). If the bore is decent everywhere else? A simple honing of the cylinder should be fine. My first thought looking at it when I first glanced at the picture was "slightly bent rod and wrist pin hitting", like Norman K suggested.
Remember, the piston travel is NOT a constant speed. The crankshaft TURNS at a constant speed. The middle of each stroke is VERY fast, while the top and bottom of each stroke is very slow with extremely rapid acceleration and deceleration between the middle of the strokes and full stops at each end. A slight bend in the rod WILL cause the rod to kick slightly in the offended direction, which could cause the wrist pin for some tiny fraction of a second to tap the cylinder wall. I have seen the result of this before, and suspect that is the case here.
Did you have this engine running before? It probably had a minor knock for some time that nobody knew the cause of, and maybe even ignored. Personally, I have run some marginal steel timing gears. They knocked. I ignored them because I knew it was a harmless noise.
Look around the area for breakage of the casting, you probably won't find any, but it should be done all over with any engine anyway. I have been unpleasantly surprised a few time, and glad I didn't find out the worse way later. If you are planning to have the cylinders bored up a size anyway, it should be fine!
Drive carefully, and enjoy, W2
I was just thinking when I read this all. Couldn't be that the mark is just a default during the casting and it is in the engine since it was first made. If this is so the mark is there for about a 100 years.
What size are the pistons???
If they are standard I should not worry about it.
Sounds like the Babbitt in the block is good. The end play and thrust is a function of the rear main cap. You can get a re-babbited rear main cap or build up the thrust with some Babbitt and a 250 or 300 watt soldering iron. If you re-Babbitt you should get the crankshaft magnafluxed before you do anything to the block.
If the crank is good and Babbitt in the block is good I would not re-Babbitt, just fix the thrust in the rear main cap. It makes no sense to me to wreck good Babbitt by baking and peening.
I would take a hard look at the wrist pin and piston that travels on that side. Anything on the other side of the bore?
RE: main bearings: I too, agree with Ted, IF the Babbitt and crank are good, leave well-enough alone. "If it ain't broke, don't fix it!" you can clean out the water jackets pretty well without hot-tanking the block. Yes, it involves some effort and getting dirty, so it's not as neat as dropping it off somewhere and picking it up clean--but you are saving yourself finding a good Babbitt shop, and (if he/she is good) waiting in line for your block's turn and then paying for the work!
Just to answer a few of the questions...
There was no obvious knock when I heard the engine run (7 years ago! Ive slept since then!)
The pistons were standard cast iron. I just finished measuring everything today and found an average piston clearance of .009. Pretty loose.
There is no mark on the opposite side of the bore. Its just this one spot.
I'll save the crank and babbitt discussions for a later thread. Ive learned more about the crankshaft today.
I took a good close look today at the wrist pin travel. At maximum lateral pin travel, the upper connecting rod boss stops against the pin bushing boss, and at that point the pin is still inside the piston. (The pin cannot continue to move outward after the rod boss contacts the pin bushing boss because the set screw prevents any relative movement between the rod boss and wrist pin). But as many of you are suggesting perhaps the piston itself was slapping hard at that spot and it was the outline of the pin bushing boss that made the wear pattern in the photo.
I will be getting the block Magnafluxed next week, so if this little wear spot is deeper than a minor surface irritation, I guess it will show up then.