125-200cc WR 125 piston pitting

Hi!

I have a WR125 from 1996 that I've had for a few years but not ridden that much at all. When I got the bike I had a new Wössner piston installed and it does not have excessive hours on it to this date.

Now to the problem: The bike has been smoking a lot (I think forever but it feels like it's been getting worse) so I took of the head to see that the gaskets weren't busted and caused cooler liquid to enter the combustion chamber. What I saw when I took the head off was not a pretty sight though. Both the top of the piston and the inside of the cylinder head shows quite heavy pitting. The cylinder looks and feels smooth and fine but I guess the pitting on the piston and head is a bad sign?

How would you suggest I solve this matter? I am really not keen on splitting the engine at this point, is there some way of avoiding a total rebuild?

Please see attached pictures to see what I mean. (Please note that the spark plug has been cleaned up in the picture, it was all black)



Best,
Anton

Okay, so a quick update:

Given that this bike rarely gets used and I'm really an amateur, I decided to try to salvage the cylinder head and aim for only replacing the piston. Please let me know if there are any danger involved in using this pitted head or if I only risk losing some performance. I attached a picture of how the inside if the head looks now. I only sanded down the sharp edges on the pitting to not remove too much material (risk of lowering the compression?).

Also, how do I know which dimension piston I should order? The piston i have in there now is the standard diameter (55.95), could I just go one dimension up to the 55.96 assuming that there has been some wear or is it crucial to get the bike to a shop to get it properly measured?



Thanks!
Anton

this motor ingested something. maybe a piece of the ring or the big end bearing cage is coming apart. you wont know until you take it apart. chec for a hole in your air cleaner element also.

Ok, thanks for the reply!

Do you think I'll be good using that cylinder head or is it now useless?

Don't fall for the old "I hardly ride so it'll be ok" trick. Your motor doesn't know or care how much you ride it only knows what IT needs, they're selfish like that. If you only ride occasionally you don't want a breakdown ruining it!!
I agree totally with wrx. My sons rm piston and head looked identical to yours thanks to a failed big end bearing. Time for a complete strip down Anton.
A machine shop or motorcycle workshop should be able to advise the best option to redress the head.

yeah man shes rooted. looks like mates 300exc when it let go(think it was little end roller bearing pins that did all the damage)

yep sumpin got sucked in there hopefully it came from outside and the bottom end is ok

It looks like the bearing cages on the con rod bearings are starting to fail, or it sucked something in. My guess would be rod bearings as the 95-6models had a habit of doing just that.
Mine was worse than that. Rod kits are hard to find for the 1995-6 125's also.

I would think that reusing this head is not so much a problem.

make sure that you find out that the rest of your engine is OK

you might consider to do some lathe work on the head 0.8 mm following the shape of the dome and 0.8 mm of the cylinder connection surfaces yet it would probably not a game changer of running it as is now

Robert-Jan

Not much issue running the head like that, take high spots off as localised heating can occur but you wont notice any difference.
Take the cylinder off and remove the piston this is very easy and no need for a shop just yet.
Now look at your small end and rings fingers crossed you chiped a bit off one of them or the small ends gone.
Pull the con rod up push it down and wiggle it forward and back all the time have your hand on crank to stop any movment if its tight and you can feel no movment awesome next check its freely rotating no graunching etc if thats all good (doubtful) clean it out and get piston away you go.
Any debris or graunchy or movment your looking at new rod kit strip bottom end etc
Good luck oh and the big cost in shops with bikes is labour so get the engine out ya self and do asmuch as you can yourself.