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I have 21 hours clocked on my rebuild 2012 KTM 150 XC and....I've just realized that my fork and ball are not lined up when I checked my piston last time
So I took it apart today to realign and this is what my piston looked like. The bike runs great down low but had no top end, obviously clear now since the power valve was not opening.
So my questions is. Based on what I have told you and the images attached so I replace the piston and rings?
I saw a bit of marks/scraps on the side of the piston in the one photo but I think that is from me taking the cylinder head off and getting a phone call at the same time
Not having the best of luck today haha
I think the piston looks good, as long as the cylinder is the same, just clean it up and put it together. Slavens racing has a good video on cylinder preparation, should be up on you tube somewhere.
RMDRA lifetime member
2013 350 XCF
2015 450 SXF with Timbersled MHLT
I am not a professional engine builder but a guy who wrenches on my own junk and I would replace the piston/rings.
In the 2nd photo below the locater pin on the bottom of the piston skirt there is some decent wear for 21 hours. Some of that is just the coating, but the lower portion is worn. This is just a observation based upon a photo. It would be interesting to see the top of the piston on the opposite side. The piston has been doing a little rocking. Not major, but some.
How many hours were on the cylinder? Did you have any prep done to the cylinder? Did you go stock size piston or the #2 size piston which is a slightly larger size to compensate for cylinder wear?
If you are in Calgary I would give Skylark a call. I am sure many board members are familar with his work. Have him hone the cylinder, measure the bore and then go from there.
I wouldn't risk redoing a lot more for the sake of a quick hone and new piston/rings.
A compression test will tell you the health of your top end. 180 psi up is good, anything lower I would replace piston/rings. A $20 gauge from crappy tire would do the trick. While your at it check big end bearing clearances just to have piece of mind. On your cylinder check the exhaust port bridges to see if your coating is good, and look for any deep scratches you can feel with your finger nail......take it to skylark for a hone if that is the case.
I've been a big fan of ceramics and dry lube for years, on both my two and four strokes. I'm not sure where in Canada the service is available, so I can't make any recommendations, but there are quite a few places in the US. (I use one in Oklahoma City, since I live about 2 hours from there.)
I'd coat the piston top with ceramic, and both skirts with dry lube - prolly' $30?? Well worth it for the heat transfer barrier from the ceramic, and the dry lube on the skirt improves both piston and cylinder life. I do the combustion chambers as well (and both sets of ports on my thumpers, as well as the valve faces if they're not already coated - although KW valves are usually already coated).
