BelleauCarl Posted August 19, 2012 Report Share Posted August 19, 2012 I just rebuilt my engine with the help of kevin at hjr. Hjr hardcore mx ported cylinder with fresh bore and hone to 64.5 wisecos. I ride 4 month on that built and now 105 psi on right 120 on left cylinder and got an hard time to kick start. Here some spec pump gaz, 21cc dome, mx hardcore port, +4 timing, air box no lid, castor 927 32:1, 330 main jet, the engine never overheat i got an trail tech and never see over 200f. I ride hard all the 4 month but i was thinking i would be good for more than a year on that built. I made a leak down test before deassembly and 0 psi of leak. Here some picture of piston and dome. Is this an cold seize? Or just normal wear? And top of piston look weird? Jetting issue? I was at 140 psi just after the break in Thanks for your help pointing me to the source of failure Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 19, 2012 Author Report Share Posted August 19, 2012 Everything look ok in the cylinder bore i will get them measured tomorrow. Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
blowit Posted August 19, 2012 Report Share Posted August 19, 2012 Lets take a look at the exhaust side of those pistons. 15lb difference between cylinders is certainly enough to tear down and find out what is wrong. Most likely hung up rings in a piston from overheat. Also need to mark and remove the rings from the pistons, check ring end gap while in bore, and inspect for heavy wear on the exhaust side of them. If they are worn excessively on the exhaust, exhaust gas will start sneaking around the ring and causing this as well as reduce compression induced ring seat thus causing blow by and overheat of the piston. brandon Mull Engineering Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 19, 2012 Author Report Share Posted August 19, 2012 Thanks for the reply brandon! So piston can overheat even if the coolant temp never pass over 200f? For the exhaust side of piston they are like new here some pic The ring move freely in their groove and have no oil built up im gonna look at the end gap, too large end gap will indicate that my ring are worn out? Cylinder wrong bore size? Thanks! Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 19, 2012 Author Report Share Posted August 19, 2012 (edited) What im i looking for end gap? .005? Sent from my SGH-I997 using Tapatalk 2 Edited August 19, 2012 by BelleauCarl Quote Link to comment Share on other sites More sharing options...
blowit Posted August 19, 2012 Report Share Posted August 19, 2012 Yes, if ring end gap is excessive, they are worn out. You would be looking for .004" per inch of bore so .010-.012" optimally. It does not appear your piston skirt have suffered but yes, your pistons can overheat even if coolant temp stays nominal. Just remember that exhaust gasses will easily exceed 1000*F so rinsing that heat down the sides of the piston will cause bad things but pistons and bores would indicate that. I would certainly COMPLETELY mic that engine. Bores for square, size, roundness, and taper, as well as the pistons and rings. That should tell most of the story in what is going on. If this engine pumped up identical numbers when new, you know what it should be. If not, you need to measure the exhaust port height on each cylinder from the top deck of the cylinder to see of they are the same height. Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 20, 2012 Author Report Share Posted August 20, 2012 Yes no problem with static pressure, i was at 140 each side and easy to start, so no problem with the porting job. I just dont understand why compression so low with no major failure and quite low hour on built and with the color of the top of piston i wasnt lean. Can it be some dust passing my air filter? Cause intake side of piston have more wear then exhaust side and i ride in really really fine sand. Even if I clean my filter and oil each ride. Thanks ill go get those cylinder inspected for begining Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 20, 2012 Author Report Share Posted August 20, 2012 I got .065 of end gap so my ring are gone or cylinder is to large i guess? Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
blowit Posted August 20, 2012 Report Share Posted August 20, 2012 I got .065 of end gap so my ring are gone or cylinder is to large i guess? Sent from my SGH-I997 using Tapatalk 2 You will only be guessing until you fully mic the bores and pistons. Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 20, 2012 Author Report Share Posted August 20, 2012 Yes brandon cylinder and piston are at the machin shop right now for inspection thanks for your help Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 20, 2012 Author Report Share Posted August 20, 2012 Piston and cylindre miced, ring are like razor blade and piston worn by sand pass my filter. Do i have to run a a other brand of filter? I run k&n is it good for extra fine sand? Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
ticktock Posted August 20, 2012 Report Share Posted August 20, 2012 Uni filters are awesome for sand. Once oiled throw some outerwears on them and it will trap the sand. You will have to clean them more than KN filters but if you're passing sand it might be worth it. Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 20, 2012 Author Report Share Posted August 20, 2012 Ok so then i will try these for sure, i dont mind to clean them more if it can save my piston and rings! A other question do i need to oil the outwear? Thanks for the advice ticktock! Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
BelleauCarl Posted August 20, 2012 Author Report Share Posted August 20, 2012 If it was your engine guys, did you open up the case to completly clean the shit out of there, its not a big things to deassembly those banshee crank case Thanks for advise Sent from my SGH-I997 using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
ticktock Posted August 20, 2012 Report Share Posted August 20, 2012 It costs 29$ for some good seals, 10$ for a folding washer for the clutch and 10$ for a clutch cover gasket. I would want to check my crank bearings and clean the crank personally. I wouldn't oil the outerwears and you could use pantyhose for outerwears. Foam filters are really good for fine sand alone. Any sponsor carries the stuff, I normally use fast/wildcard Quote Link to comment Share on other sites More sharing options...
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