Oversized pistons??

[xwhatsit]

That's crazy money. I trust you've been scouring eBay for Wiseco stuff? Being a dirt bike I'm sure they'd have something, possibly higher compression versions if you're that way inclined as well.

EDIT: No cigar. Rare model? Not common in Merika?

[FilthyLuka]

Update to that above, the main bearings are clear of the rust - the water in the crank didn't reach them so that's the good news.
The bad news is the local Yamaha shop just quoted me $300 for a first oversize piston and rings, too much for this boy.
Anyone know any alternative sources of pistons & rings?

Wiseco

That will be all

[FilthyLuka]

Okay, attached is a page from the wiseco catalog. Doesn't have xt550, but you might be able to bore it out for a xt600 piston? You'd need to ask someone with experience in this field, motu maybe? If the bottom ends are the same you could drop in a xt660 chrome plated cylinder ($210NZD from wiseco), but then again i have no experience with this kinda bike so you would need to do some research on compatibility and such

You can order them straight from wiseco too

it translates to $205 NZD for a high compression XT600 piston kit.

[Ixion]

PM Motu on Advrider. He reasearched EVERYTHING there is to know about pistons and cranks for the four valve Yammy singles. I *think* you can bore it to 600 and fit an XT600. But Motu will know.

[Wired1]

Thanks guys, I'll scour ebay for wiseco, the 550 is rather rare so I might need to look for a 600 kit or throw the whole lot in the bin. The 600 pistons are 95mm and mine is 92mm so I doubt that there is 3mm spare bore in there.

I will also try to clean up my bore and see how it goes. A local bike head told me to try an emery flail to remove the rust, apparently it dosn't damage the bore and the rust expands out so removing it shouldn't result in lost material. He also reckoned that a light rust is beneficial as it improves oil retention in the bore! I'll bet some of you have an opinion on that too!

And I'll PM Motu just incase he has a source of cheap pistons or can point me in the right direction. If anyone else has a useful website saved for Yamaha or Wiseco pistons then let me know. Cheers.

[FilthyLuka]

Thanks guys, I'll scour ebay for wiseco, the 550 is rather rare so I might need to look for a 600 kit or throw the whole lot in the bin. The 600 pistons are 95mm and mine is 92mm so I doubt that there is 3mm spare bore in there.

from the look of those photo's i reckon you could bore out 3mm, you could always measure up the width of the cylinder wall and see if its possible to bore out that much.

If the top ends are the same between the xt600 and xt550 then it would be a pretty nifty upgrade to just throw on a xt600 top end...

[Motu]

What is the standard bore size?

[Wired1]

What is the standard bore size?

Standard is 92mm x 84mm stroke. I had a look at the bore and it looks like there could be enough meat to go to 95mm.
I also tried the emery flail idea and it did indeed clean off the worst of the rust lumps and leaves it relatively smooth. It makes me wonder if new rings and a drop of kero might sort it out?

[Motu]

Get it honed at a reconditioners,then if it looks OK get them to do a wear check on it.All XT's from 500 to 660 have the 84mm stroke.So it should go to 95mm which is standard for a 595cc.....but you may need a sleeve and bore the barrel to suit.The 550 was the first of the 4 valve motor,so I'm not sure what is interchangable with the 600's.