cylinder score picture

[fitethesystom]

Here is a picture of my cylinder before I took it to the machine shop, what do you guys think caused these? Sorry, the photo quality is terrible... it's like that mainly at the top and some mid-way down. The shop says it's lack of lubrication, what do you guys think?

mike...

[fitethesystom]

I also forgot to mention that the bore was not worn out (85mm)other than these scratches, it's not out of round, and the cylinder taper is fine.

[key4202003]

my guess is sand or dirt build up, in the dirty air filter, making its way into the combustion chamber

[fitethesystom]

That's what I was thinking too...

[Rico]

Very common for a 400ex. A new piston or sleeve is needed about every 3 years, no matter where you ride, how good you take care of your motor and intake, it's just common.

[GOTFEAR]

HEAT HEAT HEAT. im just guising the marks are on the ex side. fix it and run kendal 20-50 oil and lucas oil mix the two 50 50 it works good and stops cam wear. the only thing diferent is warm the motor up longer. it takes about a 1/2 hp to run this oil set up but wort it

[fitethesystom]

My bore will be finished and my part's will be in at the end of next week if all goes well. I cleaned the ends of the valves off, now i'm going to remove them and install new Valve seals and clean it up real good. Anyone else doing a rebuild right now that has any tips? Oh, I have a quick question. Does anyone know if I should buy Full DMC Alien 2 pipe exhaust for $100.00? The old owner want's to know if I want it. Cheers!

Mike

[fitethesystom]

...And thanks for replying!

[alaskin 450R]

dude you dont need a new sleeve, just get your cylinder honed, it will clean all that s**t up. i just honed and bored my friends truck engine.

[Rico]

Originally posted by alaskin 450R
dude you dont need a new sleeve, just get your cylinder honed, it will clean all that s**t up. i just honed and bored my friends truck engine.

:huh

[xsr71x]

Originally posted by fitethesystom
My bore will be finished and my part's will be in at the end of next week if all goes well. I cleaned the ends of the valves off, now i'm going to remove them and install new Valve seals and clean it up real good. Anyone else doing a rebuild right now that has any tips? Oh, I have a quick question. Does anyone know if I should buy Full DMC Alien 2 pipe exhaust for $100.00? The old owner want's to know if I want it. Cheers!

Mike
I'm in the middle of a twisted crank, FUBAR piston, cylinder, possible bad valves etc.:D

[GOTFEAR]

hone that cylinder it will be fine as long as you can rub your finger nail acrose the scratches and dont grab

[fitethesystom]

Too late. It's been sent away to get bored and I've already ordered the oversized piston kit. Assembly begins soon I hope.