Cylinder scratch - broken piston ring?

[Petri]

The #3 cylinder of my 2005 ABS FJR (euro model) has low pressure (exhaust valve leaking), so I removed the cylinder head.

I found, besides what appears to be a bad valve, a small vertical scratch in the cylinder bore forward side. Otherwise the cylinders look immaculate (the honing marks are still visible - after 94000 km). The scratch can be felt when sliding a finger over it. Not so very clearly or easily, but nevertheless.

It does not look like anything might have broken off from the valves that might have caused the scratch. I really do not like the idea of having to open the engine more to replace broken piston ring(s) and maybe the piston itself.

Is there any way to check it without opening, or any chance the scratch might be from something else? Picture below:

 

[eflyguy]

Why was the valve leaking? I don't think a scratch like that would cause significantly lower pressure.

 

[Canadian FJR]

Curious if you were burning any oil.

Canadian FJR

 

[Geezer]

Can you feel the edges of that scratch by scraping your finger nail across it? From the picture it looks like the hatch marks from the honing are not completely scratched off across the mark so I think it is very minor. Maybe it was always there or maybe some small bit of debris got into the combustion chamber at some point. Based on the color I would guess that the nikasil plating has not been penetrated.

I have never had a broken ring, but I would expect if the scratch was caused by the edge of a broken ring the scratch would continue all the way down below the top of the piston to the lowest point of the travel of the ring.

 

[Fred W]

I bet the "scratch", which looks like two parallel scratches from here, is at the point where one of the rings meets itself. I doubt that is causing any loss of compression. I'd fix the valve that's leaking, put the head back on and test it again.

Before you took the head off you could have done a wet compression test to see if the scratch or rings are the reason for the loss of compression, but now that you have the head off it's too much work to get it back on to do that test. The head bolts are all single use, and you'd need to replace them twice.

OTOH maybe you could get the head back on well enough for the wet compression test with the old stretched out bolts. Just do not torque them to spec as they will break.

 

[Petri]

I could just very barely notice the scratch with finger nail, I think. And not for the full visible length of the scratch(s).


We did leakage test on a cold engine before (dry) and could easily tell the exhaust side was leaking (blocked one exhaust pipe and could feel air coming out from the other). We listened through the oil cap too but could not be sure whether we heard abnormally high air flow there, compared to other cylinders.

Here's a picture of all valves. Guess which is the bad one? Haven't taken them off yet.

 

[Constant Mesh]

Don't the rings typically move about a bit (rotate) on the pistons?

You may have experienced a slowly occurring valve guide / oil seal issue which KO-ed the valve.

 

[Viper Pilot]

That 'scratch' mark is nothing more then a slight visual imperfection of the cylinder wall plating. The honing marks are still there and crossing that imperfection area with out any wear. As Fred mentioned, after you fix the head problem reassemble using the old bolts with just a snug tightening to allow youi do do a 'wet' leak down test. I bet you find that the #4 cyl. is just fine and with leak down reading similar to the other 3 cylinders. Then disassemble and using new head bolts reassemble and torque to spec. and you should be good to go.

 

[Mihalis fjr]

From the picture of the head,the one valve up and left as it shows in the photo in cylinder 3,looks that it has a very different color.I don't know if something goes wrong with this valve...Looks from the color like she has burnt.Perhaps caused due a very tight gap between this valve and the camshaft,but not very sure.My thought..

 

[eflyguy]

That 'scratch' mark is nothing more then a slight visual imperfection of the cylinder wall plating. The honing marks are still there and crossing that imperfection area with out any wear.

This.. if you look at the full-size pic on Flickr, you can see another similar, but smaller and less pronounced, mark about an inch to the left..