People spend more time on exhaust flow than intake, I think. I didn't make a PHD study of it, but did come to understand one thing that I think is important. The volume of the intake between the filter and carburetor needs to be at least equal to the volume of the cylinder. More is better, but equal to is minimum for making it go good.

Yeah, Dave, interesting osbervation.

One of the things that was in the article was an analogy with the
Fat straw versus skinny straw. If enough air is between the filter and carburetor so the cylinder can be charged without having to drag it through the filter, it gets a more complete charge. Intake relies entirely on atmospheric pressure to push air in, because of the vacuum from the piston falling. Exhaust has the piston shoving it.
I wish I could reference the article. That's all I've got,man..

Underside.  All good.

another less than ideal photo.

Thanks for taking a look, Dave.  The 2nd ring is more like gunk than corrosion.  

At the top of the cylinder wall, I believe that’s the “carbon ring” that Clymer and others say not to remove or you risk excessive oil consumption.  I could use some educating on that…

I like things clean.  To me, all gunk is bad.  I want to clean it so bad.  But, I guess gunk in the right places acts as a sealant (keeps the oil out of the combustion chamber).

New motor = no gunk, no carbon, get the rings to seat during the break-in period and let the fresh carbon build-up do its sealing job…. Right??..

Rebuilt motor with fresh cylinder bore/hone and a new piston ….  Same thing…

Disassemble, Inspect, no rebuild, reassemble….  If you clean off the carbon ring, won’t it just make a fresh mess in 300-400 miles?  You’d want to take it easy anyway and give it something of a break-in period just like a new motor or rebuild…

I’m really struggling with why you shouldn’t clean up the old carbon mess.  Again, I like clean….  I suppose if I think about it and answer my own question….it has to do with new parts having super tight clearances while used parts are rather worn in.  Too bad it doesn’t work like washing a t-shirt and comes out of the dryer a little snug and you have to wear it a few days in a row to make it comfortable and broken in.  

Thanks Dave!  Appreciate you sharing your thoughts and method.  I’ll trade ya!  Lol.  

Seriously though, I’ve come to the decision to leave “Blue” mostly stock and sell these parts bike parts.  I’ll sell ‘em “reasonably cheap” and hopefully someone with more skill and desire can have some fun with them.

Speaking of over-bores…the cylinder wall already seems thin.  Do people really bore this stock cylinder to 97mm?  Seems like that is getting dangerously thin for the cylinder wall.  Or is there a 97mm sleeve available and a lot of other machine work done to the cylinder to accommodate a larger sleeve?

Looks to me like that motor had a steady diet of dirt.  Those striations above the top ring look like there was all sorts of abrasive material in between the piston and cylinder.

I agree with Dave, the second ring looks like it has a lot of corrosion.  If it were simply "gunk", you would see it on the oil rails (oil control ring) and the top ring (compression ring).  The compression ring is stainless steel with a plasma coating.  The oil rails are also stainless steel and probably have a plasma coating.  The second ring (oil scraper ring) is cast iron.  It corrodes easily.  It was probably sitting in one location for a very long time.  If there is pitting in the cylinder it will be easy to see when you kiss it with the hone.

Note how the entire surface of the oil scraper ring (2nd) is polished, top to bottom.  When the oil scraper is in good condition, only the bottom half will be polished.  That's because the scraper has a trapezoidal cross section.  The trapezoid forms a sharp edge at the bottom of the ring.  That sharp edge allows the scraper to wipe the oil off the cylinder as the piston moves down.  It is easy to install that ring upside down.  When you make that mistake, it becomes an "oil pumper" instead of an "oil scraper".

Thanks Mike!  I sincerely appreciate you taking the time to provide an assessment and give me a good basic education on how to evaluate piston rings.  

So, sitting around doing nothing for a good while is probably the main cause of corrosion on the oil scrapper ring (2nd compression ring)?  Did I understand that correctly?

With the 2nd ring as is, how would engine performance likely be impacted?  Would excess oil consumption be likely?

Regarding the gunk (I’m still thinking carbon) at the top of the cylinder wall above the compression ring, what are you seeing to suggest filthy air/fuel mixture?

Interested in your thoughts.  Thanks!