Super Jet combustion marks on cylinder wall / base gaskets with 1211??

[Pablo]

I'm pulling my cylinder for some honing and new rings to go along with new, lower cc domes. I pulled my cylinder this evening and found some interesting marks around the top deck of the cylinder. If it's normal then I'm a non-perceptive idiot...if they're not normal marks on a cylinder then what's the result of the circumferential, dark, combustion area around the top of the cylinder? I'm assuming it's something to do with how this cylinder was setup with flat top pistons/squish area/and more stuff I know little about (but am learning alot these days). If it's not normal, how best to correct it or is it worth correcting?
#2. Has anyone seen a base gasket and 1211 combined to seal the cylinder to cases? I thought it was always one or the other. Any reason to use both? Do you assume the 1211 changes the deck height of cynder to top of piston stroke?

 

[GIL]

r u referring to the shiny spots above the ex ports? If so-thats where the hone marks have worn down and the cyl wall starts to get a polished effect going on.-normal condition-don't freak out.

 

[Waternut]

Yeah the dark stuff around the exhaust port is normal. The rings are normally compressed into the cylinder and almost perfectly round. When the big exhaust port comes, the rings want to move into it making them slightly out of round so the high wear marks around the port are caused by the rings transitioning back into their normal state. This is why chamfering ports is so critical because otherwise, they'd just snag on the sharp edge and destroy the engine.

The base gasket and the 1211 could just be a result of the previous owner having difficulties sealing the cylinder to the case or they wanted to ensure it would seal to the case. Shouldn't make too much of a difference (0.001"-0.003"). Might lower the cranking compression a couple psi but nothing worth mentioning. Stock base gasket is 0.010" I believe.

 

[SUPERTUNE]

Looks fine, just a oil/carbon coloring at the top of the bores.
Shadowing above the exhaust port are somewhat normal, excessive wear above the exhaust port can be caused by loose piston to wall clearances, port chamfer too sharp, pistons running too hot and over opening of the 'B' pipe top water screw.
No problem with using 1211 on the base gasket, adds insurance from any base leakage.
A new OEM Yamaha base gasket is .023 un-crushed and will loose .002-.003 with crush and end up between .021-.020 thousandths.

 

[Pablo]

r u referring to the shiny spots above the ex ports? If so-thats where the hone marks have worn down and the cyl wall starts to get a polished effect going on.-normal condition-don't freak out.

Yeah, I'm with you boys on the exhaust port markings, but I was getting after the dark ring at the very top of the cylinder wall. I can't remember ever seeing that dark brown, combustion looking ring at the top of any other cylinder I've pulled. The peak piston height in the cylinder is past that brown ring, so I thought it was strange to see the combustion marks below where the piston peaks. Chucky says it's fine, then I'm sure it's fine. Always something new it seems.

 

[SUPERTUNE]

When you put this engine back together with smaller domes, don't run a lot of timing and richen it up some. The dark oil patterns also could be from the brand of oil your running.

 

[Waternut]

The piston comes up past that brown ring but the rings only come to the bottom of that brown ring.

 

[superjetkev]

if your talking about the dark ring around the top of the bores, thats just carbon and the rings dont go quite to the top to scrape it away...for lack of a better term. happens on all engines, big or small. 2 or 4 stroke.