top end q's

[2-strokes-4-life]

i just spoke with my local honda shop and they told me my 125 needs to have a sleeve installed since it has the nicasile bore.they told me once the piston is worn out that it is not a good idea just to install a new one that it must be sleeved.from reading on here i know this is not really the case but i dont have the tools to measure the bore so i dont know.if the bore still has cross hatch marks and looks good with no damage do i just install a new standard size piston?i just received a piston for it from service honda. can i just install this or do i have to measure it and the bore first?also i am alittle low on cash at the moment,is there anyway i can deglaze the bore without having to buy a hone?i've read you can use scotch brite pads.will this work ok and what is the proper way to do it with these?

 

[MX Junkie]

Sounds like someone is trying to make a buck off ya. It's always good to check piston/cylinder clearence when doing a top end (unless you got 20 minutes till your next moto and wanna freshen up the motor). Take to another mechanic and have him take a look at it for a second opinion. But if you say there is no apparent damage and still have the cross hatch, (providing the skirt istill intact) I would just throw it back together with the new top end.

 

[MOTOX888]

you probobly could just install the new piston without honing it it sounds like. but make sure the cross hatch marks are clearly visible and make sure there is no vertical marks in the bore. if your not planning on honing it you can use the scotch brite to take the glazing off...just make sure you move the pad in the direction of the cross hatch marks!! Drop the piston in the bore and wiggle it from side to side to see how much play there is and then refer to your manual to see if the amount of play you have is within service limits. Good luck!!!!

 

[2-strokes-4-life]

thanks for your reply's,the shop also told me that my cr60 cylinder and piston had to much clearance.the thing is,its on a .25 or 1st over piston.i imagine with it being oversize that even new it would be greater than the wear specs in the service manual which i assume is for the standard size.how would i go about measuring an oversize piston?on the 125 i do see a few vertical lines on the cylinder but nothing major.there are no signs of anything like that on the piston itself.can i still just clean it up with the scotch brite pad?

 

[MOTOX888]

as long as when you drag your fingernail over the vertical mark you dont fell it............if you dont, then clean it up with the scotch brite, put her back together and ride. :)

 

[2-strokes-4-life]

MOTOX888 thanks for the info,that will help save some money from not having to have it honed.was still wondering if someone might know how to measure oversize piston's?(read earlier post to see what i'm talking about)i would like to be able to reuse that piston for my 60 if possible

 

[CRguyStan]

To measure the clearance, check the bore of the cylinder with a bore gage and then measure the piston diameter. The difference is normally .001-.003 depending on the engine builder. If you go with .001 you really need to warm up the motor before riding to prevent cold siezures, .003 is about stock for my 03 CR250 and you can barely warm it up and ride with that clearance. Anything over .005 will lessen ring life and may require push starting.
Also remember the piston usually wears more around the skirt, so if the top is fine, the bottom may be out of spec.
Stan

 

[nickyd]

an old school way to check your piston is make sure there is still a taper to it (they are wider at the bottom than at the top)

 

[2-strokes-4-life]

CRguyStan,my dad measured the parts and said my clearances are between .003/.004 based upon what you described in your reply. will this be ok?this is with the bore and the old piston,i will measure the new one when it comes in.just wanted to get an idea of how critical the wear numbers in the manual are. if i am extremely close to the wear limit but not far over can i still run with a new piston as long as i have a smooth bore and the plating still intact?dont know if it matters but my compression befor tear down was 155 psi

 

[2-strokes-4-life]

oh also the bore was measured with a caliper,can that give me a wrong measurement?