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02_yz426f

02 yz426 top end rebuild

31 posts in this topic

I have a 02 yz426f I've had for a couple years an have decided to rebuild the top end had the jug resleeved with wisco sleeve an new wisco piston an rings an used wisco gaskets didn't seal up an was getting coolent in the oil now I've used cosmetic gaskets an still not seeling up any help would be much appreciated

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First off, I cannot recommend that the cylinder in any YZF should ever be sleeved.  If in need of that much repair, they should be repaired and re-plated with Nikasil as they originally were, or bored oversized as a big bore kit and re-plated.   Sleeves can cause a whole set of problems all their own, including head gasket sealing issues.

 

Secondly, I have to agree with the OEM only sentiment. 

 

As to coolant, there are three places where a gasket or seal failure will allow coolant to invade the oil supply:  The head gasket, the base gasket (at the front where the water passage from the crankcase is), and the right side crankcase cover (the passage behind the water pump).  The point of entry may also be a crack in the head, cylinder, crankcase (within the coolant passage from pump to base), or the right side cover.

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I bought the bike used an raced it a few times an never had any problems what so ever until I went to ride it one day an no longer had to use the compression release an talk about hard to start b4 that no issues an now I'm at this point an its definitely the head that's not sealing after a lil coolent was seeping from the middle of head an jug

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Probably the shitty cometic gaskets. I had my fun with them and had to take everything back apart and used oem gaskets and everything's good.

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No I torqued to 25 fp I couldn't find my book a it 25 on some form online but I found my book last night an it says 32 fp but I'm going to go ahead an order a set of oem gaskets

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Well actually it's going to take longer seeing as you have to pull the cams to torque the other two down, 

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Yeah but since it got coolent in the gaskets wouldnt I have to tear it all the way back down pull the jug an every thing back off to clean it back up or do you think it would seal just torquing the head bolts

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To be honest i did everything correctly with the right torque specs and it still leaked on the right of the head gasket. Not sure where yours is leaking but i don't think all of that work is worth the 45 bucks for new oem head and base gaskets just to have to go back and do it again. I'd just get the new gaskets and be done with it.

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Ok so I ordered the new gaskets put the bike all back together step by step bike sealed up great an was ripping around the yard a little bit when all of a sudden everything went to a screeching halt so I pushed it back into the garage and pulled the cover off to find out that my center intake valve head busted the bucket and the Valve came apart including a broke timing chain what causes this to happen

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Wow. Are you sure the cam timing was right? Any chance you revved it way too high? It can be hard to tell what happened first... if the cam chain breaks you can have piston/valve contact that damages the valve/bucket, or if you have piston/valve contact for some other reason it can break the cam chain.

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The point of failure was probably the cam chain, which would allow the valves to be out of sync with the rest of the engine and hit the piston, jamming the valve into the cam and thereby breaking the lifter.

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