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Looks fine other than you were burning oil. Just please do not post this on the 400ex 450r forum on facebook. . . Those guys will bash the crap out of you there.
 

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Was it smoking? yes burning oil is not so good. . .
Why did you tear it down?
 

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I'm just as curious about the cylinder walls . . . .

Rick
 
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I see some chips missing on the piston rim, so?? that might bother me, as if that metal came off running and got down inside, it could have the sides all messed up
, Like mac said, need to see the sides of piston and walls of cylinder to be a better guess here?
 

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you cant go by just look. measure your piston to bore clearance, is the bore out of round? how do the rings look? cant tell by the pictures how the oil rings are doing.

how does the other side of the piston look? any dark coloring, if so that top end has been overheated, almost guaranteeing your cylinder is out of round.

get that cylinder and piston off, take it to a competent machinist. you'll be glad you did in the long run.

BTW, I would strongly recommend valve stem seals at bare minimum while your in there.
 

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Discussion Starter · #11 ·
you cant go by just look. measure your piston to bore clearance, is the bore out of round? how do the rings look? cant tell by the pictures how the oil rings are doing.

how does the other side of the piston look? any dark coloring, if so that top end has been overheated, almost guaranteeing your cylinder is out of round.

get that cylinder and piston off, take it to a competent machinist. you'll be glad you did in the long run.

BTW, I would strongly recommend valve stem seals at bare minimum while your in there.
Why valve stem seals? Are mine bad? Piston looks good, no dark coloring. How do you measure piston to bore? The rings look fine
 

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My best suggestion for you at this point is to download the service manual for your machine and read the engine repair section...from there you will have a better understanding of what we are referring to here.
 

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Hard to tell in the pics but it looks like some of that scoring on the cylinder wall is fairly deep? I don't really like those chips in the top of the piston either but I've run worse...like manny said it is worth measuring it now that it's off the machine, if your really in doubt buy an oversize piston and rings for it, it's not going to hurt anything and at least you'll be confident that the motor is at 100%....
 

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Does my piston look ok? Do i need to replace it???

The motor ticks but chain and valves and tensioner are fine
Just because the tensioner and chain feel fine dosnt mean they are. I would bet that chain is stretched and thats why your hearing a tick. When the chain gets to a point where the tensioner cant keep tension on the chain anymore it will tick. Pop a crf450 timing chain in and never stretch another one again. And that piston looks exactly like the 5 sitting on my work bench. Stock 400ex piston. Weird thing is the chips missing at the top. And what looks kinda like crosshatching in the cylinder still. Almost looks like someone tried to just hone and re-ring it and didnt use a normal ball hone or something. Kinda weird. Could be the camera playing tricks with the eye though. I would take everything you have to a competent machinist and have them inspect everything. The reason you change valve seals also is because your right there, they are cheap, and worth every penny.
 
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