pittss1c Posted October 7, 2009 Report Share Posted October 7, 2009 Has anyone ever measured their piston after it has been used? I just had a cylinder failure that looks a lot like the ring caught the exhaust port. For fun, I measured the cylinder and piston... then called the piston manufacture to find out the sizes of a new one. The jug is dead on at .060 over (1.5 mm)and the piston has 1.5 marked on the top....sounds good! But when I measure the piston, (10 mm above the base) it is ~1.25 over. Actually, I had the piston manufacturer measure a new +1.5 piston and it seemed all the dimensions of the piston I have (also marked 1.50) were about .25 smaller than a new one. Do pistons change sizes this much, or do you think the guy who put the engine together got bad pistons? I realize that this is still an indication of a bad engine builder. Amazing that the skirt didn't break first! I can actually move the piston around in the cylinder noticeably in the non-failed cylinder. I am assuming now that this is the cause of the ring getting caught, not due to incorrect chamfering. Quote Link to comment Share on other sites More sharing options...
uwenr Posted October 7, 2009 Report Share Posted October 7, 2009 Your best bet is to take it to a shop and get it bored and have them tell you what they bored it to. I wouldnt buy anything but wiseco pistons. If you are at 65.5 (1.5 over stock 64) have them bore it to 66 and get a set of wiseco pistons. Banshee stock cylinders only go to 66.5 you are getting close to the end. http://www.wiseco.com/ProductSearch.aspx the last 4 digits are the size Quote Link to comment Share on other sites More sharing options...
racer Posted October 7, 2009 Report Share Posted October 7, 2009 Your best bet is to take it to a shop and get it bored and have them tell you what they bored it to. Ass backards. Measure the bore, determine amount of material to be removed, then order pistons. When pistons arrive mic them, and bore accordingly. Much tighter tolerances can be held this way, but it takes a little more time. Quote Link to comment Share on other sites More sharing options...
pittss1c Posted October 7, 2009 Author Report Share Posted October 7, 2009 The deformations in the bore are not very sharp, so it looks like I can measure them relatively accurately at ~.127mm, so that means you would have to bore a little over .25mm to get it round. I hope this means that a bore from +1.5 to +2.0 should be a piece of cake... Now I just need to pick a shop. I see FAST advertises here. Are they the best solution? Quote Link to comment Share on other sites More sharing options...
blowit Posted October 7, 2009 Report Share Posted October 7, 2009 Ass backards. Measure the bore, determine amount of material to be removed, then order pistons. When pistons arrive mic them, and bore accordingly. Much tighter tolerances can be held this way, but it takes a little more time. Correct.. Boring the holes before having the pistons in hand is asking for a problem. Holding proper tolerance here will make a large difference in engine life... B Quote Link to comment Share on other sites More sharing options...
pittss1c Posted October 7, 2009 Author Report Share Posted October 7, 2009 I'm guessing that is why I ended up with a trashed engine. Looks like the guy I bought it from bored it to 65.5 and put +1.5 pistons in it, but the pistons are much smaller... .28 mm clearance instead of .05mm. My plan is to send it to a shop that knows WTF they are doing, and have them shipped back bored/honed with the pistons in it ready to go. It might cost a few bucks more, but less then the ~$400 (absolute best case) I have to put out cause the last guy was an idiot. Quote Link to comment Share on other sites More sharing options...
racer Posted October 7, 2009 Report Share Posted October 7, 2009 .. .28 mm clearance instead of .05mm. Yikes. Quote Link to comment Share on other sites More sharing options...
racer Posted October 7, 2009 Report Share Posted October 7, 2009 Boring the holes before having the pistons in hand is asking for a problem. Holding proper tolerance here will make a large difference in engine life... Ya, shaft priority 'n shit. Quote Link to comment Share on other sites More sharing options...
pittss1c Posted October 7, 2009 Author Report Share Posted October 7, 2009 I know...right? My piston from 10mm up from the bottom is 2.569 inches and my cylinder is 2.580 (my calipers are in inches) which is .011 clearance or .011*25.4=.2794mm. It is almost as if this was a +1.25 piston that was stamped 1.50. Quote Link to comment Share on other sites More sharing options...
crustydemon Posted October 7, 2009 Report Share Posted October 7, 2009 I know...right? My piston from 10mm up from the bottom is 2.569 inches and my cylinder is 2.580 (my calipers are in inches) which is .011 clearance or .011*25.4=.2794mm. It is almost as if this was a +1.25 piston that was stamped 1.50. First off dont measure with a caliper. Use a mic and a snap gauge or dial bore gauge. Quote Link to comment Share on other sites More sharing options...
racer Posted October 7, 2009 Report Share Posted October 7, 2009 First off dont measure with a caliper. Use a mic and a snap gauge or dial bore gauge. Not many people have, or even know of, snap gauges. Besides- he's not boring, just giving some data. Pitts, I guess that's possible. What are you going to do about this situation? Quote Link to comment Share on other sites More sharing options...
pittss1c Posted October 7, 2009 Author Report Share Posted October 7, 2009 I am using snap gauges for the bore, but calipers to read the snap gauges. I could go get a caliper for the piston/snap gauge reader (harbor freight right down the road), but it is either great coincidence that I get consistent reading of the bore that exactly match what would be expected, or this method is accurate. What am I going to do? Well, I'm not going to ride at the banshee HQ badlands ride this weekend. Second, I am going to solicit feedback about where I should send my juggs. If they can be bored to 66 successfully, I will have that done concurrently with the piston purchase. It will be mostly bolt on and ready to go. Also, since I need new domes, I might drop them down 1 size. It was conservative compression to start with (130 PSI)... Might try to get closer to 150. My fear is, I have found a couple of errors with the engine now (shift star screw came out, and some torque errors). I fear that the rebuild that occurred right before I bought it was done by a hillbilly. I am tempted to tear the whole engine apart and check everything over the winter. Quote Link to comment Share on other sites More sharing options...
racer Posted October 8, 2009 Report Share Posted October 8, 2009 I am tempted to tear the whole engine apart and check everything over the winter. Not a bad idea. I used to do mine every winter, not so much anymore. Quote Link to comment Share on other sites More sharing options...
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