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Top end failure.

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Hello, this is my first post.

I have a 1998 Kx250 and went for the first ride of the year last weekend. After about an hour I noticed a rattling noise from the engine then on a hill climb on way home it quit. When kicking it over, there was a clunk noise now.

 

Ended up removing cylinder and found damaged piston, cylinder and head. It looks like the wrist pin bearing failed and caused this? But being the first 2 stroke I've had fail (haven't ridden since high school) I'm not totally sure where to go next. Is the crank going to have to be replaced since it looks like some metal was down there and was dented into the crank? Is this bearing failure something normal? I bought this bike 2yrs ago and was told "the engine was recently rebuilt". The cylinder looked way cleaner than the rest of the engine and the connecting rod has HOT RODS on it. Anyway here are the pictures. 20170404_173812.jpg

20170404_173736.jpg20170404_173750.jpg20170404_173825.jpg

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Dang that sucks. To play it safe i would either get a new crank or have that one rebuilt. The main bearings will most likely need to be replaced as well. How bad is the cylinder? How much damage to the head?

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42 minutes ago, GasMixer44 said:

Dang that sucks. To play it safe i would either get a new crank or have that one rebuilt. The main bearings will most likely need to be replaced as well. How bad is the cylinder? How much damage to the head?

Cylinder has a pretty bad scratch in it, try to get better picture tomorrow. The head has some marks like the top of the piston. I'll get a picture of that too, as that reminds me I wanted to see what  people think of the head, and if it is fixable. Either way I'll split the cases and clean out any metal in there and replace any/all bearings if need be. There is nowhere that will rebuild a crank near here. So only choice is bottom end kit with crank I suppose. Is a cylinder always able to be replated? Or only if the scratch is so deep? 

20170403_212908.jpg

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It really depends on how deep it is. As far as numbers, i have no idea. You might be able to get away with getting the biggest piston you can for that size bore if it can be replated. If it cant be replated then maybe go bigger bore or a sleeve of possible

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9 minutes ago, GasMixer44 said:

It really depends on how deep it is. As far as numbers, i have no idea. You might be able to get away with getting the biggest piston you can for that size bore if it can be replated. If it cant be replated then maybe go bigger bore or a sleeve of possible

Nah, they can replate any cylinder to oem spec, doesn't matter how deep the scratch is... Don't need a bigger piston...

 

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Small end bearing came apart and the rest was done by debris.  Replating to standard size would be no issue for that cylinder.  Under no circumstances would a resleeve be an acceptable option.

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IMO sending the crank out to be rebuilt by someone like ken o connor or eric gorr or the slew of other reputable places is better then just buying a whole new crank.  You know for sure they are truing the cranks to high standards, and a crank rebuild is cheap like under $100 labor.

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IMO sending the crank out to be rebuilt by someone like ken o connor or eric gorr or the slew of other reputable places is better then just buying a whole new crank.  You know for sure they are truing the cranks to high standards, and a crank rebuild is cheap like under $100 labor.


I'd send out the crank but being in Canada shipping to most of those places with the dollar change I'd be cheaper to get a hot rods bottom end kit for $400.

Here is a picture of the head. 20170406_075658.jpg20170406_075647.jpg1491490880715.jpeg

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Cylinder scratches can be welded up, machined, and then replated. I'd do a full bottom end if I were you.
 
 


Thanx, I've been watching a bunch of your videos already. Haha.
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11 minutes ago, Nam_acillatem said:

I'd send out the crank but being in Canada shipping to most of those places with the dollar change I'd be cheaper to get a hot rods bottom end kit for $400.

 

Given that it's a hot rod crank, there is no sense of rebuilding it. It would be best to find a stock crank and have it rebuilt with pro x or wossner rod. I'd recommend ken o connor racing for crank rebuilds.

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Id do bottom and top, fix cyl ofcourse.  clean powervalve, and some new reeds. :thumbsup: That is a very good bike use to race one back then. :ride: favorite kx 

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Another example of when buying a used bike, take everything the seller says and assume the opposite.

 

"The valves are good, I just checked them."  ----good means they are there

"New bottom end" ---new means we rode it for at least a year...

"jetted for 6000'."  ----jetted for 6000' is exactly the same as sea level, apparently.

 

"ready for the dunes" ----if you are taking it there for a burial.  

 

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