My buddy just finished rebuilding his top end on his 250r. He had the cylinder bored and honed and put in a new wiesco piston. The reason he had it bored was because the top piston ring must have hit the port and broke causing scoring. So he put it together and rode it only a couple times. He immediately noticed that it wasn't idling properly (kept stalling). Then he was riding it and it made a horrible noise so he shut it off. I towed him back and he pulled the top end off. The same thing happened again. The piston ring must have hit the port again. The ring was all broken off in the exact same spot. What could be the problem? Why would the ring be catching on the port? How can he correct this? I have some pictures of it if it helps. He's pretty frustrated right now. thanks for any input.

 

Have the port windows been chamfered. The edge of the port has to be chamfered some or the rings will wear fast as the sharp edge scrapes the oil off.

Any billy-bob bobby-bob home port jobs???

Has the cylinder sleeve cracked???

Some pix will ALWAYS help, email below:

 

I have also heard of people installing the piston backwards. The ring tips will then protrude into the exhaust port.

 

heh, arrow out the exhaust port always.


Backcountry seems like he enjoys seeing Billybobthortonbackwoods portjobs.

 

<< installing the piston backwards >>



The first thing I checked for was direction of the arrow. The piston was installed correctly. No porting done what-so-ever and no cracks in sleeve. I'll try to get the pictures up asap.

 

have you checked the chamfers on the ports? if they're non existant, it would explain the problem.

 

I've seen total absolute hack jobs from Billy-Bob Bobby-Bob types, and I've seen actual good well planned and executed work too...Just sometimes ppl think that more is better...&quot;Well I dun wy-dend my exhost til it touched them thar transfir ports, shoot, I dont know why them pisstun rings stik out in the exhost port&quot; Then I've seen &quot;My analysis and action plan was that I raised my exh 1.5 mm, and widened it to a maximum of 70% of bore size, I reshaped and aimed the main transfers more to the center, with a flat roove to be more biased to top end power, I however, did have the boost port open 2 degrees prior to main and aux transfer to help with the loop scavenging at lower RPM's&quot;

You see all types...

Any pix yet???

 

I have the pics, but there is too much glare from the flash. Too hard to see any details. I'll have to retake the pictures.

Backcountry, are you the same backcountry who used to post on offroad.com's board a couple years ago? Just curious.

 

Backcountry have you been able to access the Macdizzy bulletin board lately? I have not been able to and wondered if others were having problems. Machwon.

 

I was going to put this topic on macdizzy's board, but I couldn't get on it either. [img]i/expressions/face-icon-small-sad.gif[/img]