QuestionMr. Shively,
I have a 2005 Kaw Kx250, which I purchased used and have no information regarding its prior use or maintance. I runs great, but I decided to take the top end apart to get an idea of its condition. The piston had moderate wear and the rings looked new (perhaps the prior owner re-rung the original piston). I plan to install new piston and rings, however; my question is how do I prep the cylinder? It shows no damage, but small "scratches" throughout, which are undetectable when you run your fingernail over them. They look almost less pronounced than the usual cross hatches on a new cylinder, but are not in as consistent a pattern. There does not appear to be any glazing or burnt oil residue. The factory manual says not to hone the cylinder do to its plating. My local shop says to hit it with a ball hone to de glaze it and put some cross hatching in it so the new rings will seat better, and claim that the ball hone won't damage the plating. Other sources say a scotchbrite pad by hand is the best way to clean it out and put a little texture in it. What it correct? Thanks very much for any response. My email address is Cossairt76@yahoo.com.
Thanks,
Joe Cossairt
Cossairt76@yahoo.com
AnswerHi Joe,
Sorry for the delay. I've tried replying several times over the past two days. AllExpert's servers must have be down.
My experience with Nikasil coatings is to simply deglaze the cylinders. Review the following intel. I'll send the complete article to your email.
Respectfully,
Mark Shively
Honing Hard Materials
In recent years, Nikasil coatings have provided a challenge for engine builders. Nikasil is a hard coating of nickel and silicon carbide about .0025½ to .003½ thick that is applied to cylinder bores to improve wear resistance.
Invented by the German firm Mahle, Nikasil was originally developed for the Mercedes Wankel rotary engine. It has been used by BMW and Porsche in some of their engines, and is also used in many chain saw engines, some motorcycle and marine engines, and even many NASCAR Winston Cup engines.
Goodson's Jensen says PERs have had success honing Nikasil treated cylinders with diamond. But for smaller shops that have only portable honing equipment, you can't exert enough pressure with diamond to hone Nikasil. The best advice here is to use #220 silicone carbine and just do a couple of strokes to deglaze the cylinder.
If a cylinder has to be bored to oversize, cut it out with a boring bar and then hone in the usual manner to achieve the desired dimensions and finish.
All that most shops do is slightly roughen Nikasil cylinders. "You don't really remove much material. The Winston Cup shops are running some of these motors five races before they redo the cylinders. The Nikasil coating really extends ring life and cuts down on ring wear."
