Ozzy87 Posted May 7, 2007 Report Share Posted May 7, 2007 Alright, I think my bike is just getting a little tired or something, im running 19cc domes and pulling 165 psi per cylinder which i believe is good at around 1800 ft. over sea level. before I put the engine together 2 winters ago I measured the cylinder to piston clearence to be right at the edge of whats recomended possibly even a thousandth or 2 over. could this be my problem? But im still pulling 165 a cylinder. Any input helps, thanks Quote Link to comment Share on other sites More sharing options...
chronicwatson Posted May 7, 2007 Report Share Posted May 7, 2007 Alright, I think my bike is just getting a little tired or something, im running 19cc domes and pulling 165 psi per cylinder which i believe is good at around 1800 ft. over sea level. before I put the engine together 2 winters ago I measured the cylinder to piston clearence to be right at the edge of whats recomended possibly even a thousandth or 2 over. could this be my problem? But im still pulling 165 a cylinder. Any input helps, thanks Ya if i was you i would put a new top end in it just to be safe. Quote Link to comment Share on other sites More sharing options...
Ozzy87 Posted May 7, 2007 Author Report Share Posted May 7, 2007 boring and two new pistons is a pretty expensive way "just to be safe" I dont want to have to do this unless I know it's going to make a noticable difference. Because it runs alright now just doesn't seem to have all the power it should with my mods. and this was about the only reason I could think of (because I went through absolutley everything else at this point) where it would not be doing what it should. Thanks for the input, anyone else with ideas? Quote Link to comment Share on other sites More sharing options...
blowit Posted May 7, 2007 Report Share Posted May 7, 2007 (edited) boring and two new pistons is a pretty expensive way "just to be safe" I dont want to have to do this unless I know it's going to make a noticable difference. Because it runs alright now just doesn't seem to have all the power it should with my mods. and this was about the only reason I could think of (because I went through absolutley everything else at this point) where it would not be doing what it should. Thanks for the input, anyone else with ideas? Well, you mic'd your pistons before and they were .002 out of spec, you ran them some more, and want you know if you should do a top end? The answer is YEP. Your compression test will not tell you squat about piston skirt clearance. Yes, you can have an engine totally worn out and still make good on a comp tester. Take it apart. By the way, boring is NOT always needed. We see this a bunch when people cannot measure a bore (even a technician) correctly, so they bore to the next size. Unless there is a problem with the bore (taper, oval, surface damage, etc), you generally can ball hone it and put it back to bed with new pumpers. Brandon Edited May 7, 2007 by blowit Quote Link to comment Share on other sites More sharing options...
Ozzy87 Posted May 8, 2007 Author Report Share Posted May 8, 2007 im 60 over right now so your saying i could just hone it out if everything measures out good and drop in some 70 over pistons? Quote Link to comment Share on other sites More sharing options...
blowit Posted May 8, 2007 Report Share Posted May 8, 2007 im 60 over right now so your saying i could just hone it out if everything measures out good and drop in some 70 over pistons? NO NO, guess when I said honing, I should have said deglazing and crosshatching. You would not size the bore with the ball hone, only clean it up. You would install fresh .060 over pistons. You are running Al on Cast Fe sleeves so the pistons will wear first. Simply measure it. I am wanting to put my foot in my mouth about now because if you don't understand how to properly mic a bore and piston, you can get yourself in trouble. Trust me, most machine shops don't even do it right. We actually have an excel worksheet to do our numbers for taper and oval and compare to piston data. Not hard at all but has to be measured correctly. Please just measure the bore at top, mid, and bottom on the X and Y axis and post the numbers and I will help you. Brandon Quote Link to comment Share on other sites More sharing options...
bradellingon Posted May 8, 2007 Report Share Posted May 8, 2007 well i need top end i my bike has 124pis with 19cc head at 480 feet saelevel (ohio) haw can you tell if it needs a bore or just new piston and rings Quote Link to comment Share on other sites More sharing options...
blowit Posted May 9, 2007 Report Share Posted May 9, 2007 well i need top end i my bike has 124pis with 19cc head at 480 feet saelevel (ohio) haw can you tell if it needs a bore or just new piston and rings Measurements and inspection of bore. If the bore "looks" perfect, then proceed to measure the bore comparing only to the size of piston you have. IE, 64.50mm and so on. Your piston will never measure the bore size, you must go from the numbers on the top. Most Wiseco pistons will hold a .0002" tolerance. example, pistons says 64.75mm, you measure your bore and have .0005 of taper and .0000 oval and bore measures 64.74mm, you can just add pistons and be back to brand new again. Keep in mind, you NEED to know what you are doing when inspecting and adjusting bores. It may be smarter for some to just have this service performed. Brandon Quote Link to comment Share on other sites More sharing options...
Ozzy87 Posted May 9, 2007 Author Report Share Posted May 9, 2007 ok so your saying I could just hone it and put in new 60 over pistons if the bore measures out good? But that doesnt make sense to me if im already at the limit on my wear tolerances. Id be taking out more cylinder material by honing hence making the piston to cylinder clearence even sloppier at 60 over. Thats why I was wondering if boring and going to 70 over pistons would wake my engine up and give it the power it should have. But like I said before im pulling 165 with 19 cc domes at around 1800 ft (eastern-northeastern wisconsin) So I would think if Im still getting a good seal at the rings I should be good and have problems elsewhere? Or does the piston to cylinder clearence have that big of an effect? Quote Link to comment Share on other sites More sharing options...
blowit Posted May 9, 2007 Report Share Posted May 9, 2007 ok so your saying I could just hone it and put in new 60 over pistons if the bore measures out good? But that doesnt make sense to me if im already at the limit on my wear tolerances. Id be taking out more cylinder material by honing hence making the piston to cylinder clearence even sloppier at 60 over. Thats why I was wondering if boring and going to 70 over pistons would wake my engine up and give it the power it should have. But like I said before im pulling 165 with 19 cc domes at around 1800 ft (eastern-northeastern wisconsin) So I would think if Im still getting a good seal at the rings I should be good and have problems elsewhere? Or does the piston to cylinder clearence have that big of an effect? Yep, it does. When you say your out of tolerance, what is out of tolerance? What does your bore measure? what does your piston measure? what should the piston and bore measure? These are all questions you will have to answer to know if you can drop in 60 overs. ball honing "might" remove .0002 on a good day so that is not much. Yes, your entire piston is a timing component on a two stroke. The whole piston needs to stay in spec. I mentioned piston slap earlier, or you can ride it until it breaks a skirt and then rebuild it. I cannot verify the condition of the engine so what I say is just advise at best. Have someone measure it if you don;t have the tools. Brandon Quote Link to comment Share on other sites More sharing options...
Ozzy87 Posted May 10, 2007 Author Report Share Posted May 10, 2007 So right now the best option im looking at is boring a size bigger and putting in new pistons. That way my piston to cylinder clearence should be within spec. I should also get a healty boost in power if my cylinder to piston clearence is back within tolerances, correct? Quote Link to comment Share on other sites More sharing options...
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