LiftdT4R Posted March 18, 2007 Report Share Posted March 18, 2007 Ok, this piston is out of my 2001 Banshee, the bike had roughly 50 hours on it, and only made 95 PSI in both cylinders, so I pulled it apart. I bought the bike in 2003, and it only made 115 PSI then, when I bought it, I took out the carbs, cleaned them out, and changed the mains and pilots for FMF pipes. The jetting was correct, 260 mains, 25 pilots for FMF with full airbox. But I guess this is where I'm at. Here's my pistons: I've done 2 top ends on banshees so far, and I've never seen the pistons look like this, with that big blotch in the middle. The other top ends I did had just a light coat of carbon. Anybody tell me what this means? Also, the cylinders still had the cross hatch marks from the hone in them, they were pretty visible actually. On the last 2 top ends I did, I could barely see them. I'm wondering maybe should I just buy new pistons and rings, and not rebore, or should I just bore it. It is on it's stock bore, with 50 hours, so I'm thinking it's probably about time. I didn't measure the bore size yet either, I can't find my bore guage, but I know I should do that too. As usual, thanks guys! :beer: Quote Link to comment Share on other sites More sharing options...
jmd0346 Posted March 18, 2007 Report Share Posted March 18, 2007 Ok, this piston is out of my 2001 Banshee, the bike had roughly 50 hours on it, and only made 95 PSI in both cylinders, so I pulled it apart. I bought the bike in 2003, and it only made 115 PSI then, when I bought it, I took out the carbs, cleaned them out, and changed the mains and pilots for FMF pipes. The jetting was correct, 260 mains, 25 pilots for FMF with full airbox. But I guess this is where I'm at. Here's my pistons: I've done 2 top ends on banshees so far, and I've never seen the pistons look like this, with that big blotch in the middle. The other top ends I did had just a light coat of carbon. Anybody tell me what this means? Also, the cylinders still had the cross hatch marks from the hone in them, they were pretty visible actually. On the last 2 top ends I did, I could barely see them. I'm wondering maybe should I just buy new pistons and rings, and not rebore, or should I just bore it. It is on it's stock bore, with 50 hours, so I'm thinking it's probably about time. I didn't measure the bore size yet either, I can't find my bore guage, but I know I should do that too. As usual, thanks guys! :beer: Something caused that cylinder to go lean and /or detonate. Possibly an air leak? Ive had two do that as well. One turned out to be cracked intake boots. Cant remeber on the other. Quote Link to comment Share on other sites More sharing options...
LiftdT4R Posted March 19, 2007 Author Report Share Posted March 19, 2007 Something caused that cylinder to go lean and /or detonate. Possibly an air leak? Ive had two do that as well. One turned out to be cracked intake boots. Cant remeber on the other. Hmm, interesting, the intake boots looked fine, and the jetting was on spot, although I have no clue what the guy who owned it before me did. Could have been a bad gasket, although I don't know because I threw them away. Are you sure that it's lean though? There's not really any defect in the piston, it's just like crap stuck to it. The few that have leaned out that I've seen have had like pitting almost, and the domes were turned to shit. My domes look fine. Quote Link to comment Share on other sites More sharing options...
jmd0346 Posted March 19, 2007 Report Share Posted March 19, 2007 Hmm. Yeah Its hard to see depth from the pictures. It just looks like to me they had a carbon layer over them then something caused it to burn off. Like I sadi before I had it happen twice like that. I just remembered the second time I broke a ring and pieces of it got on top of the piston and basically beat the carbon off the piston. The more I look at it the more I think it leaned out or detonated for some reason. What reason I dont know. Is that the right side piston? Quote Link to comment Share on other sites More sharing options...
LiftdT4R Posted March 19, 2007 Author Report Share Posted March 19, 2007 Hmm. Yeah Its hard to see depth from the pictures. It just looks like to me they had a carbon layer over them then something caused it to burn off. Like I sadi before I had it happen twice like that. I just remembered the second time I broke a ring and pieces of it got on top of the piston and basically beat the carbon off the piston. The more I look at it the more I think it leaned out or detonated for some reason. What reason I dont know. Is that the right side piston? Yes, this is the right side, but the left side looked identical. I'm gonna do a leakdown test whenever I get this thing back together, I guess I'm gonna rebore it too, 50 hours is a long time for a top end, so even with a rebore, I still think I'll be getting away cheap. I was just surpsied by the piston, and the fact that the cross hatches in the cylinder looked soo damn good, usually I can hardly make them out. Quote Link to comment Share on other sites More sharing options...
jmd0346 Posted March 19, 2007 Report Share Posted March 19, 2007 Well the left piston doesnt look bad. It looks like it should. The fact that you can see bare piston on top of the right piston is what tells me something went wrong. Like I said though its hard to tell with pictures. The reason I asked what saide is because everytime Ive had trouble with mine its the right side. I wonder if its something this engine is prone to or just coinsidence. Quote Link to comment Share on other sites More sharing options...
LiftdT4R Posted March 19, 2007 Author Report Share Posted March 19, 2007 Well the left piston doesnt look bad. It looks like it should. The fact that you can see bare piston on top of the right piston is what tells me something went wrong. Like I said though its hard to tell with pictures. The reason I asked what saide is because everytime Ive had trouble with mine its the right side. I wonder if its something this engine is prone to or just coinsidence. Both pictures are actually of the right piston, but like I said, the left side looks the exact same. About the right side, usually if the right side leans out it is because the choke tube is missing or cracked. I guess this engine did lean out, then, but probably well into the 50 or so hours, and that must have melted the carbon that was on there, like you said about the bare metal. I guess I'll go over all the boots, and everything before I put her back together. Thanks man, :beer: Quote Link to comment Share on other sites More sharing options...
jmd0346 Posted March 19, 2007 Report Share Posted March 19, 2007 LOL! Yeah like I said its hard to tell by those pics. The angle of the top pick makes it look ok but the bottom gives a whole different angle. Good luck with the build. Quote Link to comment Share on other sites More sharing options...
Bansh-eman Posted March 19, 2007 Report Share Posted March 19, 2007 looks like you ran it rich most of the time then like said you went leak and it got hot enough to burn the carbon off the top... Quote Link to comment Share on other sites More sharing options...
LiftdT4R Posted March 19, 2007 Author Report Share Posted March 19, 2007 looks like you ran it rich most of the time then like said you went leak and it got hot enough to burn the carbon off the top... Thanks man, good to know, I looked at the choke tube today, and it was actually cracked through about 1/2 of it's length, and it was a bitch to start in the last few months before I tore it apart, so I think that's probably what happened. Any idea about the cross hatching in the cylinder, like I said, it looks almost new, but only kicks to 95PSI, the last top end I did kicked to 100PSI, and the cross hatching was barely visible. Thanks man. Quote Link to comment Share on other sites More sharing options...
FireHead Posted March 19, 2007 Report Share Posted March 19, 2007 Thanks man, good to know, I looked at the choke tube today, and it was actually cracked through about 1/2 of it's length, and it was a bitch to start in the last few months before I tore it apart, so I think that's probably what happened. Any idea about the cross hatching in the cylinder, like I said, it looks almost new, but only kicks to 95PSI, the last top end I did kicked to 100PSI, and the cross hatching was barely visible. Thanks man. Did you post pictures of your cylinder that I missed? If your cylinders look ok then maybe a new piston and rings will get your compression back up if the cylinder was machined correctly. :thumbsup: Quote Link to comment Share on other sites More sharing options...
Bansh-eman Posted March 19, 2007 Report Share Posted March 19, 2007 if you can still see the cross hatch on the sleeves id be willing to bet your bore is still good... and you went lean and fried your pistons... but without seeing them i cant say for sure.... Quote Link to comment Share on other sites More sharing options...
FireHead Posted March 19, 2007 Report Share Posted March 19, 2007 if you can still see the cross hatch on the sleeves id be willing to bet your bore is still good... and you went lean and fried your pistons... but without seeing them i cant say for sure.... I agree. However, the assumption you have to make is that the cylinders were machined correctly in the fisrt place. :thumbsup: Quote Link to comment Share on other sites More sharing options...
blowit Posted March 19, 2007 Report Share Posted March 19, 2007 I agree. However, the assumption you have to make is that the cylinders were machined correctly in the fisrt place. :thumbsup: I would say those pistons look pretty damn normal. You might putt around in some places or your low end is slightly rich or something but I don't see anything that would indicate a lean condition. No detonation but maybe the pic is not close enough. I would sure be checking tolerances about now, ring gap, bore taper, all things will tell you what is going on. I am thinking you might have a poor port chamfer causing excessive ring wear. The pistons skirts look fine. Mic things and let us know. I am just betting you have a huge number for the ring end gap. We see a bunch of engines with trashed rings at the exhaust because of poor porting and it grinds the ring thin in no time. look under the crown of the piston for color. tan brown is all and good, black or carbon build up is a sign of overheat and may indicate a lean condition. Brandon Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted March 19, 2007 Report Share Posted March 19, 2007 I would say your pistons look normal. Get them measured and if you can I would just say with the stock 64mm bore. What kind of Oil do you run in your Shee? josh Quote Link to comment Share on other sites More sharing options...
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