Yz426 piston seized?Please help

First of all Hi for everybody iam new to this forum.My first language is not english so please excuse for spelling mistakes.

So: Yesterday i went for a ride and after 20minutes the bike is just stopped.And it wont start again as the piston stucked.After10minutes the engine starts again without any problem,as soon as the engine getting hot the bike stalls again and the piston wont move anywhere.I checked the oil pressure and its right.oil has been changed 2days ago.Water topped up,i dont know what to do now.

BTW this morning i went for a 2minutes ride and the bike lost some power and it stalls again after 2minutes.

I dont know what to do now.Shall i tear down the top end?

Thanks

Yeah time to tear it apart. Oh and STOP RIDING IT!!! Haha

So it means it needs a complete overhaul?Or just new piston?

So it means it needs a complete overhaul?Or just new piston?

If it keeps seizing you will most likely need a new piston and cylinder repair. You will need to check the connecting rod and bearings as well.

More likely the rod bearing seizing than the piston.

Bad news! i took the cover off and one bolt was totally loose even spinned out(see on picutre)!!also the otherone next to it was a loose.

I tightened back the bolts,and when i was gonna start, it was so hard to kick.

possible just the valves need adjustment?

DSC_2596.jpg

Edited by peter10

Took the head off!Nothing wrong with the piston!

Please check the picture ,that scratch is normal on the wall?

DSC_2609.jpg

Edited by peter10

&%$#@!in goof

Can you feel that scratch with your fingernail? Looks kinda bad.

Can you feel that scratch with your fingernail? Looks kinda bad.

Not at all.its really tiny surface scratches.

Edited by peter10

My main problem was:the engine sometimes very hard to turn over,no Auto Decompression,and feels locked up after stalling.Still dont know whats the problem..

Hmm well I don't think auto decompression would make it stall and seize up. Those loose cam journals aren't good for sure though

Hmm well I don't think auto decompression would make it stall and seize up. Those loose cam journals aren't good for sure though

i think the previous owner didnt retorque those bolts,and the timing off onetooth,but wh on the other cam?why not on thatcamwhich had a loose bolt.Also checkmy other thread i uploadeda pic how the timing wass looked.

Check the cam journals closely they could be damaged. But grayracer513 is correct there, it is most likely the lower rod bearing.

More likely the rod bearing seizing than the piston.

Check the cam journals closely they could be damaged. But grayracer513 is correct there, it is most likely the lower rod bearing.

You guys are right.Just found out sometimes is so hard to move the rod on the crank also there is a burn sign on the crank (see picture)

DSC_2614.jpg

Edited by peter10

Also this is what i foundin the oil filter before oilchange. (check the pic)

DSC_2617.jpg

Maybe its hard to kick BC you don't have a auto decompression cam. Is there another lever on your bike that your not sure what is does. And those pics of the crank from what I understand are normal as is the oil filter.

Edited by four-twenty-sixer

Oil filter doesnt look to bad, I have seen alot worse on running bikes. The blueing on the crank is normal, its part of the manufacturing process. Is the crank hard to rotate?

What year is your bike? I think you need a decompression lever... My yz 01 426 Is similar... These are very high compression engines... So high that when you try to get the piston TDC, you can literally stand on the kickstand and it won't turn through... This is why you need a decomp lever... Especially after it stalls out. After stalling out these things things can be a pain to start...

If it were seized you would have a hard time pulling the calendar off of the piston due to it being stuck.

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