125-200cc WR165 Piston damage assesment

Hi guys.

My WR165 started sounding a little rough after 25-28 hours, so I took the top end off to have look.

This is what I found:
https://www.dropbox.com/s/m67rzun7bmo3kfs/2013-11-19 20.04.12.jpg
https://www.dropbox.com/s/j306c4sfqzigcq5/2013-11-19 20.03.49.jpg
https://www.dropbox.com/s/4tu39cfrz2b0g88/2013-11-19 20.03.29.jpg

There are a small amount of marks on the head, and the top edge of the cylinder is roughed up/chipped.

Do you have any ideas as to what could be wrong?

My own guesses are:
1. Running lean
2. Leaking coolant into the cylinder
3. Too thin base gasket

Thanks in advance for your insights

When you say the motor was sounding rough, can you describe what you were hearing? And what's the condition of your head O rings?

If your O rings are good then I would suggest your piston looks like it has suffered some detonation damage. Possible causes of detonation being too low an octane fuel or jetting too lean\air leak into the crank case.

Or simply crappy fuel

I don't know where you are located?
The Aussies and the rest of Asia all have to modify the heads to adapt to the fuel conditions

mine was also detonating a (crackling sound above a certain rpm ) like something is breaking and snapping inside the cylinder it stopped me from pulling the throttle more open when hearing that.
after the modified head no issue anymore
the bite is out of the power delivery but still an impressive delivery
yet I am confident it last

Robert-Jan

That is exactly what happened with my 165 - I would describe it as hearing a high-pitched rustling/tinkling sound at a certain RPM. Turned out to be poor fuel. I have the modified low comp head too now, and no more issues.

Thanks for your inputs.

I'm located in Denmark, and we traditionally have quite good fuel quality. I have been running primarily on 95 (RON) with a 2% premix of mainly Castrol POWER-1 Racing (full synth).

The sound, was just simply more pronounced "explosions", and sometimes it gave quite a rattle, under closed throttle/high rpm conditions.

The inner o-ring in the head was a bit flat, but I didn't look into it while disassembling the engine. I will have a closer look and take some pictures when I get to the workshop.

I don't quite get why it should be running lean, but still have all those brown/black deposits on the top of the piston, normally I associate gray color with lean. But I'm not really strong in the world of 2 stroke

Detonation erosion. That is pretty extreme, especially since it sounds like it eroded the cylinder, too. 95 RON fuel is no better than our 91 R+M/2 fuel or 91 "pump octane". You need higher-octane racefuel, or a milder head cut. Make sure your ignition timing is correct at the stator plate.

I've never seen too-lean cause that kind of detonation damage, though it could certainly compound an already borderline state of tune. I'd say no to coolant in the cylinder, but severe detonation usually does trash the inner o-ring. Too thin of a basegasket could do it, very similar to a too-aggressive head, resulting in too-tight squish and higher cylinder pressures from the lower exhaust port. I see no lubrication damage.

What basegasket did you use and what was the new kicking compression?

I have already sent Emilio a couple of PM's on dealing with the head. Hopefully he will get back to me so we can reduce his compression for his fuel.

Assuming I sell my 449 I'm going to buy a used 125/144 or 165. This will be my first 2 stroke.

I don't understand the consequences of running pump gas vs race gas in a 2 stroke and how head mods help one situation or the other.

I am a recreational trail rider that doesn't push things too hard. Will this issue effect my bike much? I guess I should ask the previous bike owner what gas he ran? What if its race gas but I plan on running pump gas?

I searched this a little so excuse me if I'm asking a repeated question.

Thanks
Mike

Thanks Kelly. Think I get it.

What was the squish on this motor?

I can't tell you which basegasket was used, or what the squish was, since I didn't install the kit myself.

Here are some high detail pictures of the piston, top and cylinder.

Note the chipping of the Nikasil on the top of the cylinder

Hi Emil,

I think you would be taking a chance on the lining continuing to flake off if you continue to run it like that. I would ship it back to me and I will take care of the problems.

Walt