Piston pin pitting *picture

25 replies to this topic
  • mxalix258

Posted May 09, 2005 - 05:29 PM


whats wrong with that rod? it looks fine to me, if you guys are refering to the color of it thats the way its sposed to be

  • mkporn

Posted May 09, 2005 - 07:54 PM


Split it and replace the rod, mains, timing chain, piston and rings and wrist pin.... I have seen this many a time. Infact I have done about a dozen cranks because of this..... As for the cylinder, deglaze it with some 1200 grit sand paper or crockus cloth and you will be fine.......

  • ovrrdrive

Posted May 10, 2005 - 12:37 AM


whats wrong with that rod? it looks fine to me, if you guys are refering to the color of it thats the way its sposed to be

I agree. I think all parts that have metal to metal contact should be all grainy and chewed up like that. That way there is less drag and more room for oil to get in. You get higher horsepower that way.

And as for color I also think that looks good. I usually don't replace mine until it gets either teal or fuchsia looking.

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  • YZ250F_Rider

Posted May 10, 2005 - 02:35 AM



  • s3706

Posted May 10, 2005 - 06:41 AM


I am in the process of rebuilding the bottom end on my 2000 426 and you do not need any special tools to get the crank out. After all the bolts and nuts were removed the case halves popped apart with a screw driver. I am shipping the crank to www.lukesracing.com and they will rebuild the crank with a new hot rod kit for about 170 bucks. That is cheaper than going OEM which runs about 350 bucks for a new crank assembly. Lukes racing is also replating my cylinder for 150 bucks. They also do big bore kits. :)

  • grayracer513

Posted May 10, 2005 - 07:29 AM


The rod and pin are bad. It's in an early stage of going to hell altogether, so it doesn't look like much now, but if you run it that way, it will go downhill pretty quickly.

The cylinder is another matter. The shadows from the rings are a concern, but whether they mean the cylinder can't be reused or not depends on whether there is real significant wear there, or just a polishing off of the crosshatching. From the picture, I really can't tell. I would run a bottle brush hone through it, starting the hone at the bottom, and running the hone up the bore, down, and then all the way out the top, taking about two seconds or less total. If the shadows are gone, I'd run it. If any part of either of them remain, the wear is significant enough to worry about.

Another way of measuring the wear present at that or any other particular point in the cylinder fairly accurately without a bore guage is to use a piston ring. put the piston in the cylinder, and the push the ring down against the piston crown. Then push the ring into an area of the cylinder below the lowest point of ring travel and measure the end gap of the ring at that point. The piston will "square up" the ring in the cylinder.

Now, run the ring up into one of the ring shadows, again squaring it with the piston, and measure the gap again. Take measurements with the ring gap in three different places. If the three readings are different, use the largest figure. This will measure differences in the Circumference of the cylinder, so remember to divide any difference you get between the readings taken at the bottom and those taken at the top by 3.14, or they will be exaggerated. For example, if you measure .005" at the bottom, and .007" at the top, the wear that this indicates is .00063", less than one thousandth of an inch.

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