250-500cc My piston change (2004 WR 250)

I recently bought my -04 WR250. It has 12000km on the clock, and the previous owner never did a piston change. He claims he has taken good care of the bike with frequent oil and air filter replacement. He also claimed it wasn't driven very hard.

I took the whole engine out of the bike, to be able to clean everything properly, and to bring the engine inside my house. So here it is on the table:



This is what I have done so far:

Top off:


Cylinder looks fine to me. I can't feel any wear inside the cylinder wall.




Also removed the left Power Valve-cover and 3 of the 4 cylinder nuts.



Now for my questions:
Does it normally get this "messy" behind the PV-covers?
The last nut is inside the PV housing. What shall I remove to gain access to the last nut? The circlip and the axle below? Anyone have any tips for me?

Thanks,

"First-time-changing-piston-on-a-2-stroke-since-moped-age-Harald"

Cylinder looks like it got a little hot on the exhaust side as I see some siezure marks. Loose piston or improper warm up possibly

Remove the PV link arm (I think its an 8mm nut), push it out of the way and then you can access the last cylinder nut. You should use a crows foot adapter to retorque it to spec. And yes, powervalves are dirty and yours looks normal to me.

Dont forget to check the ring gap before assembly.
Good luck. Post up if you need any further help.

Thanks for your input. Will those seizure marks become a problem? Weaken the coating perhaps?
I have now removed the 8mm nut and arm, but the axle is still a problem. I can fit my spanner, but have no space to turn it around. Tried pulling out the axle, but did not dare to apply much force. Can it be pulled out? If not, I guess I'll need to find some other tools...

Edit:
Nevermind that last question. Seems obvious I can not pull it out:



What kind of tool do you recommend for the job? I can't fit a pipe on there, and my spanners open end will slip and destroy the nut if I use force. (Closed end will not fit.)

Harald, I cut the end off of a broken 1/2" extension and welded it about in the center of an open end wrench of the proper size, 14mm I think but can't remember for sure, any way, then I could get into it to all of them to loosen them as well as torque them on re-assembly hope this helps.

Dave

Take a 14mm box end wrench and make it thinner with a bench grinder. It will then fit on the nut. You will only get about a quarter turn, but it works.

Funny you should mention that, because that is what I tried last night.

Thanks for the suggestions to the both of you.

Here is the piston and cylinder. Exhaust-side:



And intake-side on the following two pix:




The cylinder intake side has a few marks. Not deep. Can barely feel them with my finger. Hope it is okay to reuse this as it is. Will bring it to my mechanic friend, along with my new Wiseco piston to measure clearance, ring end gap and so on according to the repair manual. I don't have the tools for this myself.

Seems I have a E-cylinder.

Would you bother to repack this? Or just put it back together? The material seems fine, allthough at bit messy from the oil.

If your fingernail gets caught at all in the cylinder you need to either hone it or plate it...period. That being said, if that is the original cylinder and piston and was truthfully ridden that long...Amazing.

Might as well repack it you have it open now anyway, looks pretty good though, as long as its not wet should be fine.

.......

Thanks for your comments/advices.

Cylinder is now delivered to a local workshop for inspection and perhaps a light honing. The guy at the workship immidiately said .... "It has had a seizure. Perhaps due to lean mixture while driving on the road."

Sparkplug was all black, by the way.

I will repack the silencer, since it is kinda wet with unburnt oil.

12,000kms is that for real

I think so. Previous owner said he never changed the piston. He was the second owner, and bought the bike when it was two years old.
I can't know for sure that the odometer is correct, as it is the kind that resets itself when it runs out of battery. Hence it has to be set manually when you replace the battery.
I got the bike for a fair price, and was willing to take the risk involved.

Just wondering ...

Did you check the compression before you tore it down?

Why did you choose a Wiseco piston?

No, I did not do a compression check.

I chose the Wiseco after reading numerous threads on this forum and Thumpertalk, where I found positive reviews and comments. And I got the Wiseco kit for the same price that the original costs over here.