new topend

[blasterguy15]

ok so my blaster recentley blew up and this is the third time in two years and every time its a piston skirt the first two were the intake sides and this time it was the exhaust side and u could see that the intake side was going to break because the right side of it had a big crack that u could see so idk whats wrong but the crank has no up and down play and minnimal side to side play so for now i just got a 50thousands piston and gonna have the cylinder rebored and maybe send my flywheel and jug to flotek what do u guys think
I:I

 

[sporty982000]

well id be looking at those inner cases for a crack.

did you do leak down tests each time afer the rebuild ?

you might have a crank/rod out of spec.

or you ride hard.

you using weisco pistons ?

 

[Awk08]

sounds like you were just throwing new pistons into well worn cylinders ?
did you measure the cylinder to piston clearence ?
if it is beyond the service limit, it leads to piston slap, the leading cause of broken skirts
what made the decision to go 50 thou over ?

that cylinder needs to go to a reputable shop, and they will tell you what size overbore piston to get, then bore that cylinder for that exact piston.

 

[Reaper26]

my friend has a 04 that did the same thing, it broke the skirt and cases twice, i rebuilt it and put a new crank in it, and had ir bored .020 over, the reason it was breaking the skirt is the cylinder was wore, causing the piston to flop back and forth, and check the cases to make sure they arent broke or just have a hairline crack. just have it bore out and it should be fine.

 

[blasterguy15]

sporty i do ride very hard and my dad tells me i dont have to do a leak down test so im just trying to make him happy but no im not using wiseco because that was the first one i put in there and it broke in 2 monthhs

awk every time it broke i had it rebored and thats what i was thinking was piston slap

and reaper i checked the cases there fine and im just gonna have it rebored and run it

 

[Blaaster]

sporty i do ride very hard and my dad tells me i dont have to do a leak down test so im just trying to make him happy but no im not using wiseco because that was the first one i put in there and it broke in 2 monthhs

awk every time it broke i had it rebored and thats what i was thinking was piston slap

and reaper i checked the cases there fine and im just gonna have it rebored and run it

You tell your Dad that he is so very wrong. I am possibly older than he and I know better.

A leak down test is needed after every rebuild and every time you mess with the intake after the carby.

You should do a leak test at least twice a season.

You show me a man who does not own a leak down tester and I will show you a man with empty pockets.

 

[sporty982000]

sporty i do ride very hard and my dad tells me i dont have to do a leak down test so im just trying to make him happy but no im not using wiseco because that was the first one i put in there and it broke in 2 monthhs

awk every time it broke i had it rebored and thats what i was thinking was piston slap

and reaper i checked the cases there fine and im just gonna have it rebored and run it

I prefer not to get into a debate of sorts. And im sure you just passing on what pops said.

this will help explain things to you and you can share with you're father.

Yamaha blasters are one. A two cycle motor.

the blaster motor, is known after a few years, to have the crank shaft seals fail. (meaning they let air in or out.

the blaster motor, is a air vaccum motor. the air pressure from the stroke of the piston, pulls the air and fuel from the carb and reed cage. If you have a air leak somewhere. it will prevent the proper fuel and air mixture being pulled into the carb.

Causing it to run lean and blow up !!

thats the simple info on it.

Air leaks can happen from bad seals, bad gaskets, connections and fitting at the carb. ect.

So a air leak, will kill a 2 cycle motor, the blaster motor 4 sure.

You mention top end rebuilds, but nothing about new crank seals or ect. If you have a also a crack in the inner cases, it needs fixed.

I leak down tester is a must !

And weisco is about the best piston out there, compared to the cheaper ones.

I bet more than likely you have a crack or damaged case.

there is 2 ways to see this.

1- take a flash light and look into the rod and crank and rotate the rod and crank. while doing this. look inside in the middle, this is where the two case halves come together. you will be able to see that area on the back upper side.

this is common area where damage happens from a broken piston.

its not a true check, but its something.

I recommend, new crank seals and gaskets and splitting the cases and looking at the inner case for damage.

Do it right and you wont have to go thru this again anytime soon.

here is a few pictures of what I mean of inner case damage.

CRACKED, see below

gotta do one of these.

Sporty

 

[sporty982000]

a seal on flywheel side, crank seal. bad. here is pic

 

[sporty982000]

Also, got pictures of your cylinder, do you know what chamfer is ? did the shop who bored your jug, know to do it ? if not, that to, can wreck a piston.

can you post some pictures,

Sporty

 

[Blaaster]

You have dropped 2 skirts and not done a leakdown test, Tsk, Tsk, Tsk.

 

[*Quad*King*1986]

leak down test a very important as stated above^^^^ you can grab one off a member here that makes them, im sure you can go on ebay just make sure its the right kind, and you could even possibly get one at the local repair shop etc, or if your really feeling crrazy just build one yourself! the bottom line is you gotta do the test or else your never going to pin point or even figure out what the problem is and your going to keep dumping hard earned money & all of your spare time into it just to have it blow up again a month or two later

 

[blasterguy15]

thanks u guys make alot of sense but i just sent it to be bored and im gonna do my own port job get jets do a plug chop and either build or buy a leak down tester and make some air shrouds and put a atc 250r rear shock but from what i could see there was no cracks in the cases but before i put it together ill check it again