Blacksmith Posted March 17, 2004 Report Posted March 17, 2004 Hey Guys, Pulled down the topend on my brothers bike tonight because it has dropped about 20 psi on both sides over the past couple of months. Anyway, the bore measures almost perfect, but there is quite a bit of difference between the top and bottom of the piston. If I measure it down on the skirt, it is within the spec in the manual, but it is not within spec at the top. If the measurement at the bottom is the one to use, it looks like we are going to hone and re-ring, if not we will need to bore and buy new pistions. What do you guys think? Also, I might mention that the ring gap on the old rings was over .060. I am pretty sure that ring wear is why the compression has dropped so much. Quote
boonman Posted March 17, 2004 Report Posted March 17, 2004 I usually measure my pistons just below the ring grooves. BUT, this will not correct for wear. The skirt of the piston is what wears. Ican't figure out why there was that much ring gap. ??? Sounds like alot. Is the bore oblonged at all? What are you measuring with? A micrometer, and some snap guages is the proper tool(s) to be using. Hone it, and get a top end kit if they are stock pistons. Go Wiseco!!! Quote
Blacksmith Posted March 17, 2004 Author Report Posted March 17, 2004 I am using snap gauges and a mike to meaure the bore, and just a mike to measure the pistons. The pistons are well in spec on the skirt, but I was not sure if that is where I should measure them or not. As for the ring gap, that is the real question. We have not been in this motor before, but as the bore is stock, I don't see how the rings could be a size too small. I really think that the increased gap is simply a factor of excessive ring wear. However, it is hard to believe that one could end up with that much wear on the rings, and have the bore and pistons measure out as still being perfect. I think that we are going to hone it and install fresh rings. I don't like the idea of installing new pistons in a bore that was not cut to size exactly for them, but I might go that route. Anyone out there ever done it? BTW, thanks Boonman. Quote
svtkid78 Posted March 17, 2004 Report Posted March 17, 2004 you meausure the piston about an inch up from the skirt. if you look inside the piston there should be a line going around that is were to measure. that is where the piston expands the most when hot. then take your biggest cylinder measurement and subtract your biggest piston measurement and that is your clearence. Quote
Lepew Posted March 18, 2004 Report Posted March 18, 2004 What do you guys think? I think unless I was strapped for money I would do a complete top end. Cheap insurance I wouldn't be stranded when I'm having fun. Quote
Nighty Posted March 18, 2004 Report Posted March 18, 2004 So i take it that the cylinder can only be measured in one position which is at the base? Quote
svtkid78 Posted March 18, 2004 Report Posted March 18, 2004 no, the cylonder is measured in 3 different location the bottom the middle and the top. actually 6 cause you measure 3 spots on the x axis and 3 on the y axis. one is to measure taper and one to measure out of round. i think but not sure that x axis is with measurs going with intake and exhaust port and y is measured going with wrist pin. Quote
Nighty Posted March 19, 2004 Report Posted March 19, 2004 What kind of measure tool fits into the cylinder and is that accurate? Quote
Blacksmith Posted March 19, 2004 Author Report Posted March 19, 2004 You use a snap guage inside the cylinder, and then read the size of the snap guage with a mic. A snap guage looks like a "T" with one of the top sections spring loaded and a twist lock on the bottom. I am sure that in the machine world they have another name, and I'd even bet that that name in on the inside of my case, but I have never looked at it. :-) Quote
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