Need some help with piston and rebuild

[Jdawg82]

I bought some pistons and cylinders off ebay for my banshee and the bike didnt run right. I tore the bike down and measured the pistons and they measured 66.5 mm. I was told that the bike wasn't running right because the head had to be rechambered to accept the bigger size piston. Also if the pistons are 66.5mm is the bore size of the cylinder .100 over? What size pistons should I order?

[fast87]

if it helps my old cylinders were .020" over, and .50MM's over stock(65MM total), which is 64.50MM...soooo... yours being 65.50MM would make it .040" over, get the measurements for the inside of the bore, then for the outside of the pistons(make sure both cylinders have the same bore, sometimes idiots only do one side, which is bad) and the pistons should be slightly smaller, but i don't know the specs..i do know ring end gap clearace should be at least .004 thousandths(please correct me if i'm wrong), to check this remove one ring, put it in the cylinder as it would normally run, then gently put the piston on top of it to make it square in the bore, you need feeler guages to check the clearances. if that is correct then you most likely have the right pistons, and should start looking at different directions before spending another 160.00 on more pistons..good luck and let us kow how it goes, i just bought a set of cylinders off ebay that are supposedly .020" over with no pistons(i bought new wiseco prolites) so i hope i don't get burned....the best price i can get locally is 180.00 to bore them and the shop has been known to do egg-shaped cylinders and think nothing of it...wish me luck when they get here and i'll do the same for you, be sure to let the seller know what's going on, he might have forgotten to tell you something...

 

~Mark~

[spurdy]

WOW!!! 180 bones to do your jugs? We get them done around here for $40 each cylinder and a top notch job. I guess everything is high on the west end. By the way I think Clymer calls out stock piston @ 64mm, so 66.5mm would be .100" over. Good luck with your bore. If it was me I'de find someone to send them to to get a good job done b4 I'de let someone have them that has been known to f them up. Just not worth the headacke.

 

Later

Edited June 3, 2005 by spurdy

[Jdawg82]

WOW!!! 180 bones to do your jugs?  We get them done around here for $40 each cylinder and a top notch job.  I guess everything is high on the west end.  By the way I think Clymer  calls out stock piston @ 64mm, so 66.5mm would be .100" over.  Good luck with your bore.  If it was me I'de find someone to send them to to get a good job done b4 I'de let someone have them that has been known to f them up.  Just not worth the headacke.

 

Later

376983[/snapback]

 

So if it is .100 over what modifications have to made to the head in order for the pistons to work right?

[spurdy]

So if it is .100 over what modifications have to made to the head in order for the pistons to work right?

376997[/snapback]

I am not 100% sure but I think you can go to .100" over without any mod to the head. Correct me if I am wrong.

 

SP

[Jdawg82]

I am not 100% sure but I think you can go to .100" over without any mod to the head.  Correct me if I am wrong.

 

SP

376998[/snapback]

 

That just what vitos told me so I dont know either. I didnt notice any unusual wear marks on the head or on the tops of the pistons so I should be fine. As long as there are no gouges or imperfections on the inside of my cylinder walls I should be good to go with new pistons correct? I am obviously going to hone them first and I checked to make sure they were within tolerances. What pistons would you reccomend for a ported morted, with toomey t5s and no airbox lid bored .100 over?

[spurdy]

That just what vitos told me so I dont know either.  I didnt notice any unusual wear marks on the head or on the tops of the pistons so I should be fine.  As long as there are no gouges or imperfections on the inside of my cylinder walls I should be good to go with new pistons correct?  I am obviously going to hone them first and I checked to make sure they were within tolerances.  What pistons would you reccomend for a ported morted, with toomey t5s and no airbox lid bored .100 over?

377011[/snapback]

I've always ran Weisco ProLites with no issues. I know there are other sets out there and you can buy Weisco piston that have been modified to be lighter etc. etc....I've stuck with the Pro Lites because I know they are reliable and would be afraid of a lighter piston failing prematurely. I guess it might depend on how much you enjoy wreching.