YZF350 Posted October 2, 2009 Report Share Posted October 2, 2009 Hi, Does anyone know where I can get help (manual etc) to change out stock pistons? Also, what are the factory oem pistions size (is it 64mm)? I need to change both pistions--compressions is reading between 35-50 on both cyclinders. Thanks sguys, Chris Quote Link to comment Share on other sites More sharing options...
lt250rfd Posted October 2, 2009 Report Share Posted October 2, 2009 check the pinned section of this forum has a manual download. if not get a clymers book. Quote Link to comment Share on other sites More sharing options...
kodie Posted October 2, 2009 Report Share Posted October 2, 2009 Your compression is reading at 35-50? You more than likely need more than just pistons you will need a bore/hone job also. Once your compression starts to drop below 90 that is when I go up in bore. What you do is take the head off make sure you drain your radiator fluid. After the head is off you take off the 4 nuts (per cylinder) that hold the cylinders on and then pop the cylinders off sliding the piston and crank rod out from the bottom of the cylinder. Then take the circlip out that holds the piston to the crank rod and slide out the pin and the piston should come off. Do the same for the other side. Also if your cylinders aren't ported, now would be a good time to think about doing it since you got it apart the site sponsers do great port work. Do a forum search there are more companies out there that do great work as well. If your compression is seriously down to 35-50's you will see a big difference in how she runs. It couldn't have been running too good with that low compression. I'm pretty sure with stock head your compression should be around 120 or 130 I can't remember some one correct me if I'm wrong. Let us know how it goes. Quote Link to comment Share on other sites More sharing options...
Idontknowwhy Posted October 2, 2009 Report Share Posted October 2, 2009 (edited) Get a clymers manual first off, best investment you can get... I figure you didnt hold throttle wide open while kicking, so it won't climb as far as it should..but i may be wrong..does tester have same length threads as plugs? And before taking jugs off make sure you drain the coolant out of the jugs like a 10mm bolt on the side of each ..if not when you pull it off the deck all that coolant will run in the bottom end Edit: kodie you out of cambridge?? I'm out by st. clairsville ever go out pogues? Edited October 2, 2009 by Idontknowwhy Quote Link to comment Share on other sites More sharing options...
YZF350 Posted October 2, 2009 Author Report Share Posted October 2, 2009 This may be crazy but Im still learing abit. So when I checked the compression I took out one plug and inserted the tested by screwing it in--kept the other plug in. Then I kicked the bike hard and it read 35-50. The only way the bike starts if I jump it in 2nd gear--pushing it or pulling it with a vehicle and barely wants to start....but can get it running..... Quote Link to comment Share on other sites More sharing options...
Idontknowwhy Posted October 2, 2009 Report Share Posted October 2, 2009 Did you hold throttle wide open when kicking til needle stops on gauge? Quote Link to comment Share on other sites More sharing options...
YZF350 Posted October 2, 2009 Author Report Share Posted October 2, 2009 Did you hold throttle wide open when kicking til needle stops on gauge? Ok, just took off the motor and took head off. Are the piston rings suppose to spin freely? The pistions have a good bit of carbon on them. Is this normal? The needle bearings look like they are in good condition. What you think? Chris Quote Link to comment Share on other sites More sharing options...
kodie Posted October 2, 2009 Report Share Posted October 2, 2009 Ok, just took off the motor and took head off. Are the piston rings suppose to spin freely? The pistions have a good bit of carbon on them. Is this normal? The needle bearings look like they are in good condition. What you think? Chris I'm willing to bet you will need a bore/hone job and some new pistons. If your only reading 35-50 on the tester. Yes your pistons are normal are the juggs still on it or off? Edit: kodie you out of cambridge?? I'm out by st. clairsville ever go out pogues? Hell ya cambridge st clairsville is only like 40 miles away... I've enver heard of pogues wheres it at? I went to like the past 8 powerline parks you ever go there? Quote Link to comment Share on other sites More sharing options...
robert.b.west Posted October 2, 2009 Report Share Posted October 2, 2009 Did you kick it more than once? you want to hold wide open throttle and kick multiple times until the compression does not raise any more when you kick it. Quote Link to comment Share on other sites More sharing options...
YZF350 Posted October 3, 2009 Author Report Share Posted October 3, 2009 yeah, I kicked it about ten times on each cylinder testing it to make sure it wans't a bad reading. I just broken down and bought a clymers manual online 30 bones. How will I know if I need to hone out the cylinder? And yes, the jugs are still on. I really just want to keep the bike stock b/c I don't know that much and scared I am gonna fuck something up, you know? Quote Link to comment Share on other sites More sharing options...
kodie Posted October 3, 2009 Report Share Posted October 3, 2009 well the low compression is a sign that you need to go up in pistons with a bore and hone job it happens to everyone eventually your cylinders just wear down and need freshend up with bore/hone and some new pistons. are your cylinders scared or scratched? Quote Link to comment Share on other sites More sharing options...
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