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4/17/2020
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Salem, OR
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Looking for some opinions on my situation. Bought a 2022 ktm 150 with 15.7 hours on it and the bottom rod bearing went out. I bought the bike blown up to rebuild myself but I figured I’d reach out to ktm with such an early failure to see if they could help me out. KTM is paying for the bottom end parts but due to the bottom end going out the piston also needs replaced. The piston that was in it was a 57.94mm so should I replace it with the same size? The cylinder doesn’t look too bad to me but there isn’t much cross-hatching (see pics) I’ve heard both ways on honing these cylinders so what is my best bet? Buy a ball home or scotch Brite pads and scrubbing?
I’d do a light ball hone and run it. Get a B piston.
Can you feel any of those marks with your fingernail? Especially this one in red.
I have the same hours on my 21 I went with an A piston. Around 40 hrs is when you should consider a B possibly. Greatly depends on the cylinder plating wear then. B piston could be to tight and prematurely wear out the plating faster.
The Shop
Can’t feel any of the marks with my fingers. Just get a hone like this one?
Don't hone a plated cylinder it will ruin the plating. Just use a green scotchbrite pad and copy the cross hatch. 45 degree angle to clean up the cylinder.
Ball hones are for old steel liner bores. On plated cylinders the balls can catch the plating edges on the ports openings and causes it to flake off. I've also seen fools hone the plating right off the bore. Remember the plating is really thin.
Ignore the fools who will come on here to challenge me over this. Saying they do it all the time no worries. They are just getting lucky and don't realize they are prematurely wearing out thier cylinders plating faster.
Ball hone it w light oil
Brush hone works fine but go easy. 4 or 5 passes taking about a second each, using honing oil.That will restore cross hatch. No ball hone.
Measure cylinder or have a shop do it, I would assume you would be fine with an A size piston with the amount of hours you have on it, there is only .0008” between an a and b piston, a human hair is about .002 to .003” thou to put that into perspective, it’s pretty minimal, as far as honing a scotch brite would work, as stated before a ball hone would work also but be careful that a ball doesn’t get caught in a port and chip plating, ball hones are ideal for a four stroke cylinder with no port windows, a diamond hone would be the ticket but not the most affordable.
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