Piston recommendation. rattle on light throttle

[drumnagorrach]

Took my 4PT top end off this evening ,looks like the little end of the piston is slightly worn ,there is a patch inside the journal top and bottom that is worn clean and front and back have slightly brown coatings . The gudgeon pin is .01mm u/s in the centre ,got an idea all was not well when I could push the pin out with my finger at ambient temp .
Top ring has a 1.2mm gap and is worn on top and bottom faces second has a .5 mm gap ,bore hasn't got a wear ridge but slight scoring can be seen towards the top ,back and front .
I might as well fit a new piston and rings and get it re bored to 1st oversize to take out the scoring ,so where is the best place to buy a decent piston ,and who can be trusted to re bore it ?
Wemoto sell a piston kit for £177 , there are cheaper on e bay ,are they ok ? Do all the Xt 600s have interchangeable pistons ?
The chap I bought the bike off had been told the engine had been rebuilt after Rod Shaw had ridden it to turkey and back ,he was told it was using oil . You would think it would have had new piston and rings ,not so , it looks like the scoring was lightly honed the piston cleaned up ( plenty of scratches on the crown )and the whole lot just put back together with all the original parts ,the wear on the rings didn't happen overnight .
One good thing was the oily carbon on the piston crown came off easily with contact cleaner and scotchbrite .

[xtrider]

I run Wiseco piston in almost everything but Wossener ,CP , and JE will all do the job as will O/S Yamaha if you can find one .

It is amazing how many people will "rebuild" a motor by just cleaning stuff up and some new seals , gaskets and o-rings . Even just putting in new rings and a quick honing isn't that costly but I prefer to always bore and all new piston kit so everything is tight .


I do my own boring , I do have a complete fresh bored & honed cylinder with matching piston kit sitting here on-hand (96mm x 9.5:1 comp ), but I think shipping would cost more than having a local do yours .



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[drumnagorrach]

Thanks for your reply , main question is ,interchangeability, Wiseco don't list a 2002 piston ,just up to 96 ,can I fit one of their pistons ?

[jibber]

http://www.ebay.co.uk/itm/YAMAHA-XT600- ... SwZd1Vdudn

[drumnagorrach]

Thanks jibber.
The one from Greece will do fine, there seems to have been a lot of Xt600 s there ,seems the police used them .

[jibber]

http://www.ebay.co.uk/itm/YAMAHA-XT600- ... SwIWVY-ehA

[xtrider]

Make sure that whoever you have do the cylinder , use the clearance specs from the piston make , not the Yamaha manual , same with the ring endgaps . Those pistons Jibber linked to look like cast so clearances can be a bit tighter and will be a little quieter running . Good enough for a standard rebuild .


BTW the '96 Wiseco pistons will work in the '02 , being a US company we didn't have the newer models so they don't list them .

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[drumnagorrach]

The little end journal in the piston ,has discoloured area highlighted by the arrow . top and bottom of the journal is worn clean ,I think that is showing up ovality and probably the cause of the rattle on neutral throttle . It's been driving me nuts for the last three months ,thing is little end rattles that I have come across have always been synchronized to the piston going up and down ,this has been a bit more random .
When an apprentice engineer and doing the diesel engine module ,we were taught , big ends knock under load ,little ends rattle at the point where the load comes off and mains just growl and vibrate ,but they weren't 600cc singles .
btw , there is an impact mark on the back of the con rod from the countershaft weight hitting it . the mark has a discoloured coating from the oil ,so probably related to the last "rebuild " when the tab washers were butchered and used again .
XTrider, what sort of ring end gap would you use ?

[xtrider]

All the pistons will have a little different end gap specs though .003" to .004" per inch dia of bore is common. The piston kit should come with a paper that has their specs for it plus the piston to cylinder clearance specs.

Check the new wrist pin in the con-rod for slop just to make sure the con-rod isn't worn as well.



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[drumnagorrach]

Just found what could have been causing the light throttle hesitance and subsequent rattle ,well I hope so . The right side carb mounting rubber appears fine but is de laminated from the alloy inner ,I noticed that the rubber coating over the flange flapped a bit when I was blowing it dry, out of the cleaning bath, with the compressed air line . A bit of pulling and the entire rubber coating came off the alloy flange ,oxidisation of the alloy suggests its been like that for some time .
The left side rubber was replaced three months ago but the right had seemed fine .