How to prevent ring snag and cylinder scoring?

[noah9988]

I've been having trouble with cylinder scoring. I just put a new top end on because the one I was using was scored up bad, but still ran. This time I made a point to chamfer the ports and the piston window, skirt, and wrist pin holes. I ran it for maybe 20 minutes when I heard a pinging or popping when it revved up a bit. I was riding it easy when I felt something "let go" in the engine and it died. Surprisingly it started back up but I just peddled home. When I took the head off I saw two score marks over the transfer ports. I've had this happen before and I was mad because I specifically tried to prevent this from happening. It didn't seem that bad though. When I took the cylinder off... well the rings where snagging bad and the top end is trashed.

I am 100% aware that I could have (and probably did) cause this problem... I'm just wondering what I did wrong and how to do it the right way. Btw, there was no damage to the exhaust port surprisingly.

 

[mony0_3]

You must have some metal shaving in the engine that needs to be removed.

 

[noah9988]

You must have some metal shaving in the engine that needs to be removed.

I doubt it. I washed it out with soapy water and a toothbrush and then sprayed it down with brake clean.

 

[DieselTech]

I've been having trouble with cylinder scoring. I just put a new top end on because the one I was using was scored up bad, but still ran. This time I made a point to chamfer the ports and the piston window, skirt, and wrist pin holes. I ran it for maybe 20 minutes when I heard a pinging or popping when it revved up a bit. I was riding it easy when I felt something "let go" in the engine and it died. Surprisingly it started back up but I just peddled home. When I took the head off I saw two score marks over the transfer ports. I've had this happen before and I was mad because I specifically tried to prevent this from happening. It didn't seem that bad though. When I took the cylinder off... well the rings where snagging bad and the top end is trashed.

I am 100% aware that I could have (and probably did) cause this problem... I'm just wondering what I did wrong and how to do it the right way. Btw, there was no damage to the exhaust port surprisingly.

To me it looks like something went thru the engine. Is both locator pins for the piston rings still in piston? Was both wrist pin clips still there & intact when disassembled? When I chamfer the edge of the ports I just use 400 grit zirconium sandpaper & do it by hand. More of a polish than a chamfer i would say.

 

[Nickt919]

To me it looks like something went thru the engine. Is both locator pins for the piston rings still in piston? Was both wrist pin clips still there & intact when disassembled? When I chamfer the edge of the ports I just use 400 grit zirconium sandpaper & do it by hand. More of a polish than a chamfer i would say.

I just went thru this. My damage wasn't nearly as bad though. At first I thought a ring grabbed my exhaust port because there was a lot of the port edge chipped away. As it turned out one of the ring guide pins came out and screwed me up. Look close for something missing as DT is suggesting.

 

[noah9988]

To me it looks like something went thru the engine. Is both locator pins for the piston rings still in piston? Was both wrist pin clips still there & intact when disassembled? When I chamfer the edge of the ports I just use 400 grit zirconium sandpaper & do it by hand. More of a polish than a chamfer i would say.

Both clips were fine. I'm not sure about the locator pins, I'm at work and I'll take a look when I can. I chamfered the ports slightly and then used sandpaper and did it by hand. I didn't smooth the edges of the rings so maybe they were sharp?

 

[Karl Snarl]

I've been having trouble with cylinder scoring. I just put a new top end on because the one I was using was scored up bad, but still ran. This time I made a point to chamfer the ports and the piston window, skirt, and wrist pin holes. I ran it for maybe 20 minutes when I heard a pinging or popping when it revved up a bit. I was riding it easy when I felt something "let go" in the engine and it died. Surprisingly it started back up but I just peddled home. When I took the head off I saw two score marks over the transfer ports. I've had this happen before and I was mad because I specifically tried to prevent this from happening. It didn't seem that bad though. When I took the cylinder off... well the rings where snagging bad and the top end is trashed.

I am 100% aware that I could have (and probably did) cause this problem... I'm just wondering what I did wrong and how to do it the right way. Btw, there was no damage to the exhaust port surprisingly.

Looks like some needles from a bearing went through.

 

[noah9988]

Looks like some needles from a bearing went through.

I'm going to check to see if anything is in the bottom end.

 

[noah9988]

Found the culprit... That isn't from a failure, when I took off the old top end I thought I might have dropped a clip in the engine. I forgot about it and you know the rest...

I was surprised to see my crank and crank bearings turn brown... that means it got hot, right?

 

[Karl Snarl]

Found the culprit... That isn't from a failure, when I took off the old top end I thought I might have dropped a clip in the engine. I forgot about it and you know the rest...
View attachment 175885View attachment 175886
I was surprised to see my crank and crank bearings turn brown... that means it got hot, right?

Rainbow means you got hot. Brown is ok, blue, gold, rainbow equals hot. Black ehhhh some blow by.