Scored Cylinder help

[dive020]

I have an 86 motor with the long rod and 87-89 piston. The jug is from an 86. The first time I rebuilt the engine I had the cylinder bored and installed a new piston and rings at 10 over. After about 3 months of riding the engine still had decent compression and ran good but I decided to pull the jug to change the rings. When I pulled the jug I found that the exhaust side of the piston had scored the cylinder walls and that the rings on the exhaust side had been worn down to the point that they did not stick out any farther than the piston. They had also seized against the piston. I then took the jug and bored it out again and put a new piston and rings in it again. After a few months of riding I went to check the rings and again I had the same problem. All of the damage seems to be on the exhaust side of the piston.

I don't have any pictures but does anyone have any idea of why this is happening.

Thanks
Shawn

[Honda 250r 001]

JETTING YOUR TOO LEAN.

[1promodfan]

I've heard of guys talking about this same problem. I can't remember exactly what they said was the problem was. Its time for Neil to chime in. I don't think its a jetting issue, but I could be wrong. Oh Neil where are you????

[C-LEIGH RACING]

Was the exhaust port bridge relived after the bore & fit on those new pistons.
If not, then once the engine got real hot, the bridge expanded out & kinda seized the piston in that area.
Happens alot, normaly though from a bore shop that dont do 2 stroke cylinders. They dont know thats suppost to be done.
Neil

[dive020]

I don't know if it was or not, but I would guess not. The scored area is about 1.5 in. wide. If the bridge got into it would it only score in one spot or a whole area?

Thanks for all the help.

[jr4]

dose your piston have two small holes in it in line with the exhaust bridge if not it should to alloe cooling of the bridge

[C-LEIGH RACING]

If the exhaust bridge was not relived, it will bulge out & seize aginst the piston right in the middle. If it did bulge out & you caught it early, most time it will cause a rub streak in the middle on the exhaust side.
Normaly though, it will seize enough to stick the rings down in the piston & then running it more, after that the damage will progress even more.
Have seen it bad enough that the piston would seize on the exhaust & intake sides.
Neil

[chamberlain31c]

exhaust bridge releaved? clearance some of the bridge? so its a little bigger then the bore??

[norcalduner]

Can you post a pic of the piston/s? Trying to figure out the cause of the seizure my bro recently had which might be similar. Thanks.

[dive020]

The piston is a wiseco but I had it ported but I believe that was on the intake side.

How far does the bridge get relieved, or how far should it be past the cylinder bore?

I might be able to get a couple of pictures next weekend but if not it will be some time, maybe a couple of months, before I will be able to get them. I recently relocated to another city but my 250R is still back home.

Thanks again for all of the help