Normal break in or damage

[2strokes4life]

I just got this cylinder replated (company did a great job). I installed the top end and have almost got it broke in. Noticed my crank seals were bad. When I took off my pipe, I looked into the exhaust port and this is what I see. I have searched the internet for pictures of normal cylinder break in pictures, but haven't found any. Does this cylinder look normal to you all? It has these vertical lines that appear to just be discolored and not scratched. The piston still looks brand new as it should. It has tons of compression on the kick lever even with the pipe removed. You can hear it forming a perfect seal as the piston moves up and down. Thanks in advance for the help.

 

[_JOE_]

Well, it looks to me like there is a possibility of too little piston to cylinder clearance. Which crank seal is leaking? If it's the left it will lean it out and rob lubrication. If it's the right it will allow some clutch debris to build up on the piston and cylinder. Be sure to check the clearance on the piston while you have it apart.

 

[julien_d]

Yup, that's not normal. Scuffing around the intake ports usually indicates a lean condition like Joe said. Sorry man, that's gotta hurt your feelings.

 

[TRexRacing]

Run your fingernail over the scratches.They shouldn't snag your finernail.You can still see crosshatch through them so you might be OK with running a ballhone through the cylinder to restore the pattern.I would pull the top end and inspect the rings closely if it were mine.A few gaskets are cheap peace of mind.

 

[2strokes4life]

Here's what I found out about the cylinder. You guys tell me if you agree. I sent the company that did the replating the pictures I posted here and asked them for their opinion. I sent them my new Wiseco Pro lite piston when I had the cylinder replated. They matched the piston to the cylinder. They told me today that what I am seeing in the cylinder is known as striping. They said that as long as I have good compression and the engine runs smooth that this will go away when the rings are completely broken in and fully seated. He said it would take a little riding to completely take set. I have only gone through a few heat cycles and a couple short rides. Nothing harsh yet. Both of my crank seals were bad. Here are my thoughts, you guys tell me if they are logical. Even if my left crank seal was causing me to run lean, my right crank seal was pulling clean oil which should have been lubricating the cylinder as well as fouling plugs. I bought this bike used so I didn't know what all was wrong with it. I should have leak tested it before the first start up. It was running pretty smooth on the first couple heat cycles, but started getting worse. Do you think the two bad seals could have cancelled each others damage? Would it have damaged it anyway if I wasn't hard on the gas with that little of run time? Let me know what you all think. I want to have this all figured out before I tear into my 2002 CR 250. Thanks guys. I'm trying to learn all of this.

 

[2strokes4life]

I just thought of one more question after I replied. In my manual it says after the first few heat cycles and short easy rides to pull the top end and check the piston and cylinder. If the piston skirt has any high areas it says to smooth them out. So here's the million dollar question. When you guys/girls rebuild a top end do you actually pull the cylinder back off to check it? Is there a possibility that your cylinders look just like this, but you've never seen it until it is ready for the next top end job. Just wondering. It seems like it could be a possibility.

 

[2bitsamile]

which manual says that? if piston to cylinder clearance is set correctly, and adequate time given for warm up, proper jetting, ... there will be no scuffing of piston, no need to take engine apart. Don't assume cylinder platters set clearance correctly, measure it yourself

definitely not normal. looks like there is a triangular shaped chunk taken out of the cylinder. check to see if the piston ring locating pin has been pushed in. That can happen if the ring is on top the pin as you slide the cylinder over the piston. I install piston into cylinder 1st, then install wrist pin to avoid that potential problem

 

[2strokes4life]

That is not a chunk out of the cylinder. It looks like it in the picture, but there is really not one. That is kind of weird. If the rings weren't in the groove you'd feel it. After I install a new piston in the cylinder I run it up and down slowly with the kicker to see if there are any problems before I button it up. I use the wet rebuild method. I am going to try the dry method on a future rebuild. The manual I use is a Clymer. If you read it, it tells you to break it in with light rides for 10-15 minutes, first in lower gears low rpm's then kill it and let it cool. Then it says ride again in higher gears again 10-15 minutes kill it and cool. Then you are supposed to ride again 10-15 minutes at normal speeds and even wide open for short bursts, but not to ride at the same rpm constantly. After that it says pull the top end and look for high spots on the piston skirt and smooth out if need be. You are supposed to put it back together and ride one more light ride. After that go bananas. I've still got the bike apart waiting on parts to fix the leaking crank seals. That is one thing that sucks about having a 1991. It seems like it takes forever to get the factory parts. I have been waiting 2 weeks already for seals and gaskets.

 

[ws6transam]

It looks like a stripe to me and it also looks like there's crosshatch pattern showing through the discoloration. I doubt it'll be a problem. A soft-sieze will have shown definite galling on the cylinder wall as the aluminum from the piston skirt adheres itself to the cylinder wall. When you pull off the cylinder (as you should very well do, even if it's for peace of mind), inspect the piston skirt. If it shows only polish at the bottom of the skirt, you are good to go. If there are vertical scratches, scuffing, or any roughness that can be felt with your fingertips, it's probably evidence of a mild sieze in which case you will want to reverify bore diameter and piston to cylinder clearance.

 

[julien_d]

It's right around the intake port. Make sure you're not running it too lean. That's the common cause of scuffing around the intake ports. If the compression is good and it sounds good I wouldn't worry too much about it other than checking the jetting real well. My cylinder looks much much worse and still runs pretty darn good. I'll do a replate when I can afford it.

I looked more closely, and I think ws6 is probably right. I can see some crosshatch still through those scuff marks, so it's not as bad as it looks at first glance. Still, I would want to know why!

 

[2strokerfun]

You definitely see the glass half full, which is a noble characteristic. But on your thought of enough oil being pulled in the right crank seal to cancel the lean condition from the leaking left crank seal, uh, no. We all wish this is the way it would work in real life, but it doesn't. Air is easier to pull in than oil and your vacuum is going to pull in air through the left seal more so than oil through the right seal, assuming the seal integrity is weakened exactly the same on both sides. Now we all know both seals probably weren't weakened exactly the same. Maybe in some Utopia the right seal was proportionately worse than the left seal to allow the engine to pull corresponding amounts of oil from right and air from left, well that would bring us to the next point: Lean condition denotes too much air compared to atomized gasoline in your mixture. While it seems the addition of extra oil might mitigate damage, not really. A lean burn is a hotter burn, extra oil or not.
Of course, I'm sometimes wrong.

 

[whenfoxforks-ruled]

If you pull the top end to check it, plan on new gaskets and ring. That is an aluminum piston scraping against a harder surface. Looking in the port is sneaky at best, real trouble can not be seen without pulling the jug and measuring. Did you set the ring gap before assembly? Were the ports beveled, and the bridges relieved? On a side note, who "ported" the cylinder?

 

[2strokes4life]

I agree that the chance of oil cancelling out the air (lean) damage is slim to none. I didn't ride it much at all during the break in cycle. There shouldn't be any damage even if it was lean. The only way it would be lean is the bad seal on the ignition side (dry side). I haven't taken that side apart yet, because I still haven't gotten the parts yet. The jetting is exactly what FMF calls for. The porting must have been done by the previous owner. I didn't measure the clearance after I got the cylinder back from the plater. I sent the piston out with the cylinder. I know what assuming does. I guess I should have checked it. The ports were all beveled and yes the end gap on the rings were good out of the box. I checked them in the cylinder per my manual. Thanks for all of the responses. I appreciate the help. I just rebuilt the top on my 2002 CR 250 over the weekend. It's all stock. It went smooth as silk. I'm ready to start riding and quit working on them so much.

 

[motometal]

i've seen cylinders that looks worse than that, but running fingernail across there is no galling or scratches there. Still, a good idea to take it apart.

Do most people follow the routine of sanding down the high spots? Heck no.

Don't get too obsessed with the break in, even the experts don't agree other than generally don't put it under a heavy load in higher gears at first.

Was it smoking alot?

For jetting, just because FMF says jetting is correct doesn't mean its right for the bike. Err towards the rich side and keep an eye on your plug, plus of course pay attention to how it runs, signs of rich or lean.