top end rebuild

[mxpimp2000]

im about to install a new piston kit on my yfz450 for my first time doing it myself but it was rebuilt jan.09 and im just wantin to put a higher comp piston and fresh up the motor.

im wondering will i have to get my cylinder honed or anything or can i just pull of the cylinder and piston and the new one go right on and slap it back together?? i know what to look for as far as wear on the cylinder but as long as there arent any marks at TDC or any scratches i should be fine correct?

also ive heard u can install rings right out of the box and dont have to gap them ive never done it on my previous 2 stroke bikes so wat is the reasoning

[440exhondaman99]

as long as there is no marks or deep scratchs in the cylinder then you can just drop it down in and put it together as is.... you could hone it but if its only 1 year off of rebuild and the oil was changed when it was sapose to then that cylinder has to be perfectly fine.. i doubt you will have to gap the rings but i would check them just for the hell of it... its not hard and dont take any time.. you normaly only got to gap the rings when you take cylinder and have it bored to the 100% perfect exact fit to the piston... but you should be good to go with out any boring or honing if the bike has been taken care of... just get that timing right thats the hardest part of doing a topend the rest is cake

[mxpimp2000]

yeh i change my oil after every race if not every race its changed every other race and if i change it every race ill run the same filter until next change since the oil comes out same color as it goes in. as long as its TDC when i pull it apart timing should be easy but my luck it wont be easy

[440exhondaman99]

Originally posted by mxpimp2000
yeh i change my oil after every race if not every race its changed every other race and if i change it every race ill run the same filter until next change since the oil comes out same color as it goes in. as long as its TDC when i pull it apart timing should be easy but my luck it wont be easy


im not real shure how to time that bike but yes starting at TDC is a start i know that much... but yea i wouldnt wory about having to hone or needing bored it sounds like the cylinder will look like new when you pull it apart... ive ran the nastyest junk oil in my old motor all summer and only changed it 3 times and it was road everyday.. when it needed oil id dump what kind of oil i had in it and didnt care because i had my good motor sittin on the bench ready to drop in... once i gave up on waiting for it to blow up from beating it every day i just changed my motors and i tore that one apart and i looked at the cylinder and it looked bran new still i was highly shocked that it could ever look that good... the piston looked great and its now being reused also... but anyways as long as you get your timming marks right you wont have a problem and the onlything you will need is a gasket kit wich you already knew im shure...

[aDviSol2y]

I would hone it. just for piece of mind. it takes just minutes, so why not?

[rt20ps]

You should always hone the cylinder and you should always check ring end gaps. I don't care how many times you got lucky in the past...

[aDviSol2y]

Originally posted by rt20ps
You should always hone the cylinder and you should always check ring end gaps. I don't care how many times you got lucky in the past...

x2

[mxpimp2000]

Originally posted by aDviSol2y
I would hone it. just for piece of mind. it takes just minutes, so why not?

what does honing do? i never understood it and thought it would remove the nickelsil coating if honed

also i have a old stock cyliner can i gap my rings using it? that way i can go ahead and do it before i pull my motor apart

[440exhondaman99]

Originally posted by mxpimp2000
what does honing do? i never understood it and thought it would remove the nickelsil coating if honed

also i have a old stock cyliner can i gap my rings using it? that way i can go ahead and do it before i pull my motor apart


no i would ring gap them to the cylinder your using just to be 100% on the money

[mxpimp2000]

well i called my local race shop today and its gonna run me $10 for hone and thats if it needs it because the guy that builds the motors said it may not need re honed if its still in good shape with cross hatching

[440exhondaman99]

Originally posted by mxpimp2000
well i called my local race shop today and its gonna run me $10 for hone and thats if it needs it because the guy that builds the motors said it may not need re honed if its still in good shape with cross hatching


yea tear it down and if you can see the cross hatchings then put it back together... when you first fire it up... warm it up dont realy rev on it much just get it up to tempiture and then shut it off and let it completly cool.... that setts the rings better... but once its cooled completly then run it for a lil while to brake it in then go like hell like its maid too

[mxpimp2000]

as soon as i get up the nerve to try it im gonna tear into it which is gonna be scary buildn a 4stroke for my first time. ive watched many vids and read a ton of articles and how to's plus i have the manual if i get stuck

[440exhondaman99]

Originally posted by mxpimp2000
as soon as i get up the nerve to try it im gonna tear into it which is gonna be scary buildn a 4stroke for my first time. ive watched many vids and read a ton of articles and how to's plus i have the manual if i get stuck


man it cant to be hard... i did my budys preditor 500 it was my first top end... i didnt have **** but a motor that was in peices... i didnt get to tear it apart even so i could have an idea... just wach how it comes apart... i did my 400ex with out any no how about a week ago and i got it back together no problems at all... main thing just make shure you know wich cam is intake and wich is exhuast...