My recent project quad is an '86 YFM225 Moto-4. Finally managed to scape up the extra cash to order rings, gaskets and oil...I wanted to see this thing fire up last night but I ran into a problem.
I looked on the yamaha site I ordered the set from and there are two sets available, the one I had (standard) and what I'm assuming are oversized (.50)?
I have never had an issue with measly rings before, and I'm desperate to get this thing running so I can troubleshoot some carb issues.

Here's the deal:
-The rings I have are standard OEM rings
-All but the top/compression ring fit perfectly
-Compression ring starts to fit, but won't fully seat

I've cleaned the grooves and inspected the piston...there seems to be burrs and thin spots preventing the rings from seating. Is is ok to maybe file down these spots until the ring seats? Do I need to be more "aggressive" and maybe tap these rings until they seat...this is my first small engine rebuild...I'm used to Cummins, Detroit and CAT, I feel like I might obliterate this piston if I even look at it wrong. In other words, I'm a bit on edge. I don't want to buy a new piston or rings :/

 

Ok, disregard the past post. I have a new problem...the piston its self. It's a damn good looking piston to be stock from '86...and I can't seem to find any info on what exactly this piston is (make, size...) It has stamped onto the top:

-XC
-B0013
-4675MO7150
Can anyone help identify this...the rings are absolutely correct for the model and OEM piston, but I need to know what rings to buy for this gem.

 

There are service limits on the ring grove and ring clearance. Or sounds like you have no clearance at all. Your best bet is to replace the piston also. You don't want to put this back together only to have a ring seize and maybe ruin a cylinder over a 80 dollar piston. But if you want to chance it you maybe able to take a emery board for fingernails and sand the ring grove on the piston until the ring moves freely in it

 

Ok after some research I cam up with this, which really confuses me.

-Part number is equal to a Wiseco 250cc .020 over-sized piston
-XC is an indicator on specific rings to be used with Wiseco pistons
-The other stamped number B00I3 gives no results, what does this number signify?

Long story short this explains my problem, but I still don't understand how a 225cc quad is running a 250cc piston. Is this possible? If so what do I need to do?

 

Sounds like someone either had bored the cylinder out as far as possible on using a 225 piston and decided to try a 250 piston and rings. If the cylinder liner looks pretty thin this could be the case. Best to have the cylinder bore measured against what the std bore should be and the maximum allowed over bore.Cylinder may be bored too much. OPT

 

Cylinder Bore: 71.5mm
OEM Bore Spec: 70mm

Piston Diam: 71.4mm
OEM Piston Diam: 70mm

My measurements weren't 100% accurate to the finest measurement due to the tools I have, but is a roughly 1.5mm difference enough to equal a 225-250cc difference?

I'm completely lost, I've done this before countless times but with prior knowledge of exactly what has been done and needed. This is more complex than I imagined

 

Ok, scratch the whole thread...crunched the numbers and everything adds up correct and the bore/piston was done correctly. After playing with Google a bit more I found the exact rings I need for the bore/piston. Thought I was going crazy, assumed everything was for a 225cc engine, turned out the actual displacement was 230 and uses a piston .020 oversized typically used in a 250cc....but everything adds up correctly.