Crankshaft burn marks

Doin a top end rebuild due to the dowel coming out and letting piston ring meet the exhaust port and smashing the top of the piston.Anyway with the jug off noticed that when the cranks at tdc you can see two burn marks either side of the conrod on the crank.

Is this normal ?

How do you check to see if your crank is on its way out ?

Dont want to rebuild top if bottom is ify.

The blue color is normal and is part of the heat treatment process. If the color is anything other than a bluish tint then you can proceed to worry.

Check the con rod for any up and down slop and excessive side slop in the big end bearing. If it meets either of those criteria then its time for a rebuild. If you need a rebuild then be sure to check your crank bearings and tranny bearings while you're in there.

Come to think of it they are a bluey/purply colour (darker purple in the middle),They look to uniform to be anything else thinking about it.

Probably being a nervous nelly.

Thanks for your help.

Mine has it as well, on either side of a center pin for the rod. My understanding is that these areas are heated prior to pressing the crank together, leaving the marks. Most every bike/quad/snowmobile/jetski I have been in has these marks.

I found the same marks on mine too. I found it odd but then yanked my crank in every direction without any excessive play.:applause:

It's normal from the process of installing the pin.

277_7701.jpg

What oil are you running there Marco?

BTW looks a wee bit rich.

marko... whats your shoe size?

What oil are you running there Marco?

BTW looks a wee bit rich.

Amsoil Dominator 28:1. My jetting was almost perfect for me at the time, but would be rich for anybody else, since I have a bad habit of revving my bike too much. :)

And see the carbon pattern? The porting was flowing perfectly. :applause:

marko... whats your shoe size

11. Do they look really small in the picture or something? haha

Measures end play and check for play in the bearing and all is fine.

After last weekend blow up dont wanna take any chances with the blue marks.

If others have got blue marks then what the hell.

Markopolo how long has your bike been up and running since the rebuild ?

buemarks on my 2006 yz 250 too but no up and down play so i am going to wait until the next top end rebuild to do the crank.

Markopolo how long has your bike been up and running since the rebuild ?

I put a new top-end in then, and rode it for about 15-20 hours, then I melted the piston, and that took out everything, so I completely rebuilt the entire thing, and it's all broken in a ready to go for next season. :applause:

How did you melt the piston with that jetting?:applause:

How did you melt the piston with that jetting?:applause:

That specific piston didn't melt, but the next identical one did. The track that I practice at is a very wide open track. And if I am coming down a straight and the corner is pretty close, I won't shift like I should, I'll just hold it wide open untill the engine stutters. And the day that I blew it up I was doing 20min long, wide open motos. It was fun, but the bike couldn't take it. Especially with my 240lb self on it.

Yeah, I need to stop doing that...haha

yea my crank stuffers melted on my bike so i would definatly take the crank into consideration, my crank was actually kinda brown too weirdly... that was like in june that happened of last year... its an 03 and was never rebuilt not even top end lol so thats prolly why mine did that but still dont just let things slip

P.S i bought it that way i didnt actually own the bike since new cuz i wouldnt be stupid enough to just not rebuild a bike specially motocross bikes

The blue color is normal and is part of the heat treatment process. If the color is anything other than a bluish tint then you can proceed to worry.

Check the con rod for any up and down slop and excessive side slop in the big end bearing. If it meets either of those criteria then its time for a rebuild. If you need a rebuild then be sure to check your crank bearings and tranny bearings while you're in there.

You said that is it's anything other than blue all is well?

Would this be considered ok?WJsYIAi.jpg

The blue spots at the crank pin are from abruptly heating the crank halfs to allow the lower pin and con rod assembly to be a "slip" fit assembly at the factory.

Blue spots on the lower portion of the rod is bad....

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