Well, I eventually got my bike running for the first time since buying it:) but it sounded bad:( It ran fairly well but lots of piston slap. Took it apart and the bore and piston is trashed. So, my question is, what's the biggest oversize I can go to??
It's got a Weisco .080 oversize piston which is 2mm over already and the bore measures 87.1mm.
Some pics.

I think i've found the answer looking through old posts. It's bad news! Biggest oversize I can find is +1.5. Weisco used to sell a +2 which isn't available any more and it's what I have anyway.
It's looking like another cylinder. Any advice appreciated.

Enduronut (Dave Sigle) bored a jug 1.5 over and sold me a Wisco piston, after I seized my 4th over. You might contact him.

Nick

Engineering type stuff isn't really my bag (if indeed anything is!) and I wouldn't even consider questioning your conclusion over the state of the barrel and piston. All I would say is that there have been a number of posts here stating that it is usual for Wiseco pistons to be noisy when the engine is cold. Something to do with clearances when re-bored. But as I say, most people know more than me on this!

Alan

YZ490 starts at 87mm & goes to 89 in wiseco or probably 88mm in genuine piston kits. Need to consider pin size & gudgeon height etc but might be worth chasing up. I have a 4th over 465 kit on trademe but i'd guess that's only 86mm but i think in theory i could have bored my 465 to 490 so i could measure this piston [where did i hide it lol] so far as pin size & other things if ya want as will relate to a 490 kit.
www.trademe.co.nz/Browse/Listing.aspx?id=2257839629

Check here also
wossnerpistons.com/
Call them,sometimes have stuff unlisted

Thanks for the advice everybody, much apreciated.

After all the research it has to be a replacement cylinder. There's no option for any piston sizes bigger than +2mm (8th over)

RT325, that all sounds a bit deep for me (port timing, jetting etc) but I apreciate the pointer.

Maybe LA Sleeve has your 400 sleeve still, they have sleeves for days! But, not mine! Your's is newer than my ol 73 gyt cylinder with a +2mm as well. Mine is usable (barely). Your's looks pretty hashed! a conversation paperweight maybe? Unless someone here has one try LA Sleeve, EBay may get you one like I got, usable, but not 2nd over as advertised. (it was stamped that, but that was 1.5mm ago)!

I wish there were somewhere that had piston specs, I mean real specs like compression heights (pin location), skirt & "window" specs, rod lengths, etc. A trick we used in 2.4 911 motors (for racing ,time trials or hot street) was to use 2.2 pistons as w/longer rod of 2.4 pin height in 2.2 yeilded 10.5 compression in a smog de tuned 8.2 of 2.4. (bore the same) This infromation in vehicle "tech books", pin heights, skirts, cam profiles, etc. baisically they are blueprints. Anyone have this type info? With stuff getting scarce, it'd be nice if some other part could be used.

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