While looking for a part number I found this hairline crack on the piston skirt, I don't feel so bad now she didn't fire up this spring.

I noticed one of the intake tracts was noticably dirtier than the other.

This could be one of the reasons, the rubber is losing it's bond on the flat part of the aluminum intake manifold, I could also feel movement on the round section which leads into the cylinder.

I think the carbs open at different throttle openings so the port which has the closed carb ('till you open it up) has a vacuum created in it, this could be pulling oil down the valve stem.
What are the valves like for play in the guides, if they're worn you're not going to get a better opportunity to replace, or have guide liners fitted(these are supposed to be the bees knees if you believe the blurb!)

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I wouldn't be too worried about that rubber down there at the cylinder mount bolt. It should only be a problem if it is loose up around the clamp ring. Of course if you have some gasket goo then stick it back down.

gixxer.rob: That's exactly what's happening, I'll clean it up and seal it with silicone, about a third of the rubber on the round barrel section has come loose and I can feel it's gritty inside.

*Touring Ted*: Absolutely Ted, I'm just glad I didn't get it running or it might have been a really expensive repair !

oothef: The valves do have some play but I don't have the tools to check if there in or out of spec, I'll have to wait and see what the machinists find. thats the first I've heard of "guide liners" I'll look into those.

I can't say for sure if the condition of these carbs is after 60.000km or less, I was told the bike went in for carb work but the extent of it may have only been to pop the float bowl off.
Cylinder head side of the carbs.

Loads of carbon and cylinder sludge has been splashing into the carbs due to the tight intake valves not sealing, this shot is the diaphragm carb.

Same cylinder side of the carbs but this shot is the throttle valve on the regular carb.

One of reasons to do your own repairs, I was told when I bought the bike in 2008 it had recently gone to a shop for carb work, instead of replacing the float bowl seal they used some kind of glop that hardened like cement and ruined the rubber seal.


Top of diaphragm was pretty much spotless.

The underside of the diaphragm is only filtered by a course inline foam filter that works great for keeping the humming birds out, not so much the gritty fine stuff.




Lots of crud found in the regular carb top chamber, I'm sure some of this stuff finds it's way down the throttle valve and into the intake tract.

None of my manuals list this as anything more than a "Diaphragm Set" this is the top spring side, not sure if thats fuel or cleaning solvent.

And where the diaphragm sits, would really like to know the proper name for this valve.

And the underside of the diaphragm that pushes on the brass pin.

hi did you get your bore and piston measured? ( i dont know if you could with the split in the piston ) im interested in knowing if this is a bore / piston or valve problem or both thanks steve

No Steve the piston/bore was never properly measured since I didn't have a 4" micrometer on hand, the piston did move back and forth in the cylinder, the rings were much worse than the piston, they were excessively worn and sticking, since we discovered the piston was cracked the machinist didn't bother taking measurments, he pretty much just looked at it and said "1st over" I'd say it was a combination of the rings and the valves, the valves were tight and later when I did a solvent seal test all four leaked, also the exhaust valve guides are shot.

She's finished and running like a champ ! Thanks to all my fellow XT'ers who helped with this build.


Motorsports Forum. - Top end rebuild

I'm sure you understand the piston MUST be replaced now !!

Ted

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Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.