Where can I find 30 over piston and rings for my Tri-Z???

[Racer-X]

So I went to put new piston and rings in my 85 Tri-Z. When I took it apart I noticed that it already had a .010 over piston in it. Also the sidewalls looked a little scratchy so I wanted to have it bored out so I could get it back to running 100%. The guy at the machine shop said it would be best to do 30 over because 20 over might not be quite enough. So now I have a fresh jug that's .030 over or 68.75mm instead of the stock 68mm. My problem is I can only find the stock 68 size and the 2nd overbore 68.5 size. Where the heck can I find a 3rd overbore size piston and rings? I looked on Google, eBay, Rocky Mountain ATV, ect..... Everybody has 68mm and 68.5mm but nobody seems to have 68.75mm? Am I not using the correct numbers or terms? Can anybody help a brother out on this one?

[Hunting Chip]

I found an old 3wheelerworld discussion on this...242237
Try this...Search 515p3...I found this site...
http://www.powersportsnetwork.com/enthusiasts/catalog_item_detail.asp?catalog=1475&levelcode=10322&product=144325&cattype=&ProductCategoryCode=

[Hunting Chip]

I guess that's only helping confirm the part number. I can't find where it's available yet either.

[350for350]

I'd be careful of that machine shop if I was you. It sounds to me like your cylinder was "bored out and ready to go". The piston manufacturer always sends clearance specs with their pistons. How does this person know what your clearance is if you don't even have a piston to be measured?

[yaegerb]

X2......next time buy the next size piston first then have the shop bore to that piston.

[John Tice]

Any shop who doesn’t preorder a piston needs to be replaced. How in the heck could your cylinder be bored without a piston; these little cylinders only need a +.0015” skirt clearance.
Wiesco pistons are sized in .5mm steps; I never bore a cylinder without a piston in my hands. Since your cylinder is a 4 stroke? It could have very well have been honed to the next size. I only purchase Wiesco pistons direct from the factory in order to check on the stock on hand.
If you send me your cylinder I’ll bore or hone your cylinder FREE if you order a piston from me? Check out my site, we are always looking for people who are interested in the trade.

John Tice
503-593-2908 Alternate 541-595-0310
www.smallenginemachineworks.com & www.nwsleeve.com
Turning Custom Cylinder Sleeves Since 1971
http://forums.everything2stroke.com/threads/49513-How-It-s-Done-Projects-around-the-Shop.com

;)

[Racer-X]

Well he just measured what it was and compared that to the stock 68mm. Also he had some banshee heads and what not there but it's not a motorycle based shop by any means. But anyway. I found that wiseco website shows one that's for 69mm. So I'm going to double check this out to be 100% sure and just have them bore it out one more time to 69mm. At least if this works out it, I think it will technically be 255cc's instead of 248cc's. I couldn't really find an 85 yz250 jug to see if maybe that would work either. So it's either this or I find a whole other jug the surely will need work and be 1 of 4 for sale on the planet hahaha. But FYI don't ever bore your Z 30 over.

[yaegerb]

69mm is actually a 1mm overbore on a z. Dem walls gonna be thin plus it's your last bore. Maybe consider a sleeve for more life?

[barnett468]

Well, it looks like Yamaha did not even offer a 3rd over for the tri z . I would call Wiseco like Hunting Chip suggested and ask them if they have one since they didn't list the size along with the part numbers.

FROM THE 1985 TRI Z PARTS FICHE

https://www.cmsnl.com/yamaha-ytz250n-1985_model9122/partslist/A-06.html#results



PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR

[barnett468]

Ok, I decided to not be lazy and I looked it up . The last number of the Wiseco part number is the size in inches.

515PS = STD
515P1 = .010" or .25 mm
515P2 = .020" or .50 mm
515P3 = .020" or .75 mm
515P4 = .040" or 1.0 mm

In your case, you need a 515P3.



PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR