Piston/Cylinder Wear Question (with pics)

[gascadia]

First I'm new to dirt biking and also gasgas, and I have to say this forum is amazing! I've already learned so much here, and I've only been reading for a few weeks.

Anyway, I bought a 2013 xc200R about a month ago, and I simply love it. I'm the 3rd owner, so I've been going through everything to make sure it's all in good shape maintenance-wise. The previous owner used to race and had a few other bikes, all in excellent shape. So of course it was super clean, and came with records indicating the suspension was revalved, and has the RB carb divider plate and circuit mods w/CEK needle and jetting. It also has the larger power valve cover from checkpoint offroad. The thing starts easily, runs great and makes plenty of power.

The guy I bought it from said he did the top end, all fluids and wheel bearings at 146 hours, but he reset the hour meter, so I have to take his word for it. Looked like a brand new hour meter with 8 hours on it at the time of purchase, and after a few test rides is now up to 16. After the last ride I pulled the pipe to inspect the piston, and wanted to get some opinions on wear from you guys who've worn and replaced many a piston.

Since this is my first bike I don't know much about reading early signs of wear, but I see more blow-by than I expected, and some small nicks, scratches & slight wear on the skirt. The cylinder still has crosshatching and the piston still has grooves from manufacturing.

Here are some photos of what I'm talking about.

Cylinder with crosshatch:



Rings:



Blow-by:



Middle of skirt:



Bottom of skirt:



My main concern is the amount of blow-by for only 16 hours, and the little nicks along the skirt. Any thoughts on what might have caused this? Dirt making its way in through the intake perhaps? If this blow-by and wear is excessive for only 16 hours, I wonder if he might have put an A piston in this B cylinder. That could explain the blow-by. If others think this is not normal, I will pull the cylinder and measure everything. I'm looking at ordering a wossner "b" kit to have on hand for when the time comes (hopefully it's not now).

Thanks in advance!
Tristan

 

[Gasser Nate]

The blow by may have been caused from not properly de glazing the cylinder at the last top end. The scratches are correctly stated by you as being from dirt being passed by the filter. To my trained eye I don?t believe that piston only has 16 hours on it.
I would hope if the guy raced it he has replaced pistons earlier than 146 hours. But these gasser motors are strong and will still run well way past scheduled maintenance.
I like to replace piston and rings on new to me bikes so I know where I am at.
Gives you a chance to check the rod for play and to also check the plastic crank spacers as they commonly come loose on that model. I have replaced about 10 sets.

 

[gascadia]

Thanks for the advice Nate! I suspected it had more hours than I was told. It seemed strange that he reset or replaced the hour meter for just a top end build. Ah, craigslist..... Perhaps he did replace it recently and just wasn't clean enough during the install and/or slacked on filter maintenance. He wasn't the original owner and only had it for a few years. So I'm guessing he replaced the piston once during that time. But either way I don't like the look of the wear, so I'll go ahead and order the piston kit.

I assume I could run this piston a while longer without damaging the cylinder, but what do you think? I can't feel the scratches with a fingernail. I have a growing list of things to do this winter, but want to get some more riding in before snowboarding season starts and my local trails close for the winter. I would guess maybe 10 hours or so of our Western Wa. tight woods. Not too aggressive. I suppose I could just monitor it every couple rides too.

My list already includes swing arm, linkage and wheel bearings which are fairly toasted, but I cleaned and greased them up to get me by for now. I'm also going to install silicone coolant tubes & aluminum impeller, rotors and pads, repack the silencer, and add a bunch of protection & guards to the bike. Maybe fork oil too for peace of mind. It would be rather convenient to do everything all at once. Plus, if I do have to address any bottom end issues I'd have the rest of the winter to do it without missing out on too much fun.

Cheers!

 

[Gasser Nate]

Yeah that top end will be fine for a while. It is definitely not on its last legs or anything.
I have a good silica ball hone that is awesome for deburring and deglazing. Brings the cylinder up like new.

 

[5valve]

What you have is OK.

What I have is non solvable and is calling probably for new cylinder/piston set.

What you see in pics has happened 4 times in a row over a span of 7 riding hrs. New piston and diamond hone every time. Bottom end currently doing 2nd time, conrod included.
Piston to cyl clearance 0.08mm.

Piston in pic has done 3hrs.

The actual cylinder lines in picture were created in newly honed cylinder in 5 minutes of idling only. No dirt, everything clean, completely stock jetting, to exclude any lean condition. Black plug.

Total engine hrs 72. I have never came upon such a problematic bike. Managed to accumulate 7 riding hrs since february and constant repairing in between.

Bike kind of works normally, but at constant gassing or in tech terrain, heat arises, engine vent constantly on, due to heated water. Sth is griding. Thermostat removed, waterpump ALU impeler, cases and cooling system pressure tested OK.
No pinging, no heat pitting on squish band or piston faces.

Have no clue what is going on....

 

[blitz11]

What kind of piston / cylinder clearance do you have? have you measured that? Ring end gap? I am curious about those.

 

[Neil E.]

I agree that ring end gap wpould be suspect. Are there a batch of "A" pistons with "C" rings out there?