pistons rocking in cylinders

[shee rips]

i just tested my compression today before i tore the motor down and i got 100 and 105 psi on one guage and 95 psi on both sides with the other guage.

It ran great, it took 5 or 6 kicks to start it cold but after that it always. started first kick. you stroker guys are goin to laugh at this but it went pretty good too.

i got the head off and everything looks good. i noticed that i can rock the pistons back and forth a little. there is no crosshatching visible in the cylinders so could that be causing it? I'm goin to put some new wisecos in it anyway so would those fix the problem, that is if its even an issue. I know there is supposed to be some clearance there, just not sure how much.

 

also i plan on shaving the head .020 but it looks like the piston could hit the head. I'm 99.9 % sure that this is the first time the bike has been apart. I didnt check the squish before i took it apart but it should be fine i think.

thanks in advance for any help :beer:

[swrbansheeboy]

i'm just guessing your engine is all stock but your compression is still low, not dangerously low but still low. as long as you dont find any major problems when you pull the jugs your new pistons should take care of the excess slop in your pistons. find a good machine shop to take em to and they will get it handled for you. as far as what the clearances should be it depends on if your running cast or forged pistons and if it's an air cooled or water cooled bike. i think banshee's with wiseco pistons usualy run .003 clearance but dont quote me on it...

[locogato11283]

how old is that topend? id consider boring and moving up a size in the piston.. sounds like you need a rebuild to me. 100 psi is way low. you really need to be up around 150..

[shee rips]

i think its the original top end. its an 03 but im not sure how many hours it has. it has the original front tires and they are almost smooth if that gives you an idea of how many hours it has. Im gonna rebiuld it anyway, I was just wondering if new pistons would fix the little bit of play in there.

or maybe im just makin a big deal of nothing here :shrug:

[blowit]

i think its the original top end. its an 03 but im not sure how many hours it has. it has the original front tires and they are almost smooth if that gives you an idea of how many hours it has. Im gonna rebiuld it anyway, I was just wondering if new pistons would fix the little bit of play in there.

or maybe im just makin a big deal of nothing here :shrug:

 

 

I would bet the pistons are done and need replaced. You need to search the site for some threads about checking bores. As I have mentioned, you have to start with simple math. Measure it! If you do not have the tools to do this, have a shop do it. FYI, most shops will insist that you just bore it because they do not want to spec the bore and want your money. We like our motors to last so we only bore when it is really needed. As long as the bore is not oval or out of round by more than .0005, it will be fine. As far as clearance goes, .003 is what you are looking for.

 

Motors will wear the pistons first so new pistons will close down the tolerance for sure. Measure and see.

 

 

Brandon

[shee rips]

yeaa 100 posts :biggrin:

anyway i just got out the feeler guages and when i push the piston over to one side i can get the corner of .009 in there so from what i understand that is too much but new pistons should fix that i think.

also are you supposed to see crosshatching because i cant see any in either cylinder?

[blowit]

yeaa 100 posts :biggrin:

anyway i just got out the feeler guages and when i push the piston over to one side i can get the corner of .009 in there so from what i understand that is too much but new pistons should fix that i think.

also are you supposed to see crosshatching because i cant see any in either cylinder?

 

 

Yes, that is a sign you might have some cylinder wear but maybe minimal. You will want to ball hone and re-hatch the cylinders before you put the new pistons in. The life of the engine depends on those scratches.

 

 

 

Brandon

[locogato11283]

if the engine is original from 03 just do it right and have it bored to the next size and new pistons.. by just replacing the pistons you are really half assing it, esp on cylinders that are 4 years old..

[blowit]

if the engine is original from 03 just do it right and have it bored to the next size and new pistons.. by just replacing the pistons you are really half assing it, esp on cylinders that are 4 years old..

 

 

Why is that half ass? If the hole is the right size, use it. Age or time does not constitute boring. The more you bore out, the more prone they are to liner warp.

 

Brandon

[LiftdT4R]

you really need to be up around 150..

150? On a stock engine? 130 is probably more like it, I think thats the highest Ive ever seen after I rebuilt it and thats at sea level. But yeah, 100 is way low, and if you can't see any crosshatching you probably need a bore and hone. Just my .02.

[ClimbAnyHill]

130 is stock but you can get up to 150.. Big difference & you would like the response.

Not sure if a shaved head would get you the result but a cool head will.

Maybe you dont' have the right pistons in there??

[locogato11283]

150? On a stock engine? 130 is probably more like it, I think thats the highest Ive ever seen after I rebuilt it and thats at sea level. But yeah, 100 is way low, and if you can't see any crosshatching you probably need a bore and hone. Just my .02.

 

elevation will play a part in the compression.. i dont know exactly what a stock banshee compression is, but i know he needs more than 95 or 100 pounds.. hes prolly lucky it will even start.

 

blowit, if he cant see the cross hatching anymore id say that combined with his 95 pounds of compression would more than likely require it to be bored. i suppose if it mic's out right he could get away with just having it honed. either way something needs done with the cylinders.. but it sounds like the tolerances arent even right for just new pistons and rings.

[FireHead]

Yes, that is a sign you might have some cylinder wear but maybe minimal. You will want to ball hone and re-hatch the cylinders before you put the new pistons in. The life of the engine depends on those scratches.

Brandon

 

Word. :geek:

 

I don't know if the tolerance of the bores is set right for the pistons either................. :ermm:

[shee rips]

I am at maybe 300 feet above sea level here. As far as i know it hasnt been apart until now. i still have the cylinders on there and that .009 is with the old pistons. I measured it by pushing the piston to one side and put the feeler guage on the other side. Im not sure if thats the correct way or is it supposed to be .003 all the way around?

ya and i didnt think 100 psi would be enough either and thats all i ever got on my dirtbike before and after a rebuild so i think both of the compression testers i tried are probaby not working right :shrug: ill see if i can get ahold of an expensive one here

i also got the head shaved .020 yesterday :biggrin:

thanks for the help guys

[IRONDOG]

Piston clearance is not measured at the top of the piston- it's normal to have more clearance at the top because the pistons are made that way. They are "cam ground" smaller at the top to allow for more expansion in that area as the piston heats up. The thicker top area of a piston will expand more than the thinner skirt area.

I bore cylinders every day and I can guarantee you yours will need to be bored- you have wear at the exhaust port area that you cannot see as well as wear on the back of the cylinder around the intake ports. If you run a rigid hone through them this will be evident, you will see lots of low worn areas that will be untouched by the hone. Don't use a ball hone (dingleberry hone) those are for lawnmowers.