Why???

[Facinus]

Ok so last fall I bought a 2002 blaster, ran great for a few days, then died. Rebuilt the top end, worked great for 30min then died again.. same problem. Piston scarring up on the exhaust side. So i let it sit over the winter because i didnt have a garage. Just got moved into my new house with a garage :^)

Anyway, i put the kit in and noticed something. The piston hugs the forward wall. Why? And how do i fix? Here's a pic so u can see what i mean

http://i40.tinypic.com/25k0ojp.png

 

[stephen12091985]

are you getting it bored out when u switch pistons?

 

[stephen12091985]

and are you rubbing 2 stroke oil in the cylinder and piston when u put them in?

 

[Facinus]

I honed it. And I put oil in and just worked it up and down, but forgot to put it on the walls before actually putting the piston in

 

[stephen12091985]

I honed it. And I put oil in and just worked it up and down, but forgot to put it on the walls before actually putting the piston in

that could be why and ur cylinder could be out of round

 

[brandoz28]

yup^^^ take her to the machine shop and get it bored and put in a new piston

 

[phragle]

whats the piston to wall clearance?? it should only be 3 thousandths of an inch or so.

Thats 0.003 inches. a human hair is 0.0393700787 inches. If your eyballing clearances one tenth the thickeness of a human hair, therrein lies your problem.

 

[2_Smoked]

Where i got my cylinder bored and honed the guy explained something to me. He told me the the constant rubbing up and down of the piston against the cylinder wall actually makes it bigger, so if you are not getting the boring out and just honing you are removing more material thus making the clearance way out of spec. Take it to the machine shop, let them tell you what size piston to order. Btw, that last 30 minutes it ran....I bet it smoked like crazy

 

[Brute71]

hows the crown of the piston look?

 

[nd jat]

I'd guess you got a piston thats for the stock bore, Instead of getting the next over sized piston that you should of got for it.

 

[brandoz28]

I'd guess you got a piston thats for the stock bore, Instead of getting the next over sized piston that you should of got for it.

he didn't have it bored

 

[nd jat]

He didn't specify if it was or wasn't. But if the cylinder is scored, more often then not you bore it over.

 

[brandoz28]

I honed it. And I put oil in and just worked it up and down, but forgot to put it on the walls before actually putting the piston in

actually he did^^^lol

 

[xJust_Causex]

ya but he bought it use and it could have been bored over before, did you measure the cylinder before you orderd a piston or did you just assume?

 

[Brute71]

if the bore is correct, then its probably just the rings pushing the piston that way since they open up on the intake side.

 

[nd jat]

ya but he bought it use and it could have been bored over before, did you measure the cylinder before you orderd a piston or did you just assume?

I just thought that if he could notice gap differance from front to back that the piston he had was a size or two smaller than needed. Plus honing a cylinder a couple of times is enough to need a new sized piston for proper clearance, But still should of had it bored to keep the cylinder in specs. :-[

 

[brandoz28]

I just thought that if he could notice gap differance from front to back that the piston he had was a size or two smaller than needed. Plus honing a cylinder a couple of times is enough to need a new sized piston for proper clearance, But still should of had it bored to keep the cylinder in specs. :-[

i agree, and this time it should be bored out. take it to the machine shop and have them do it for you, and tell you what size piston you need

 

[musselman]

It's probably a good idea to find out why it went down in the first place. Jetting to lean, no oil, air leak somewhere. You should definitely find the root cause or it will happen again.

 

[Facinus]

that could be why and ur cylinder could be out of round

yup^^^ take her to the machine shop and get it bored and put in a new piston

Ok cool

whats the piston to wall clearance?? it should only be 3 thousandths of an inch or so.

Thats 0.003 inches. a human hair is 0.0393700787 inches. If your eyballing clearances one tenth the thickeness of a human hair, therrein lies your problem.

Well then my piston is too small

Where i got my cylinder bored and honed the guy explained something to me. He told me the the constant rubbing up and down of the piston against the cylinder wall actually makes it bigger, so if you are not getting the boring out and just honing you are removing more material thus making the clearance way out of spec. Take it to the machine shop, let them tell you what size piston to order. Btw, that last 30 minutes it ran....I bet it smoked like crazy

Actually it ran great, was just going down the road and lost compression and died. Had to push it home lol.

hows the crown of the piston look?

It's a brand new piston, however both the old ones were scarred in the exact same places, the exhaust side. Which is the side thats noticeably closer to the wall

I'd guess you got a piston thats for the stock bore, Instead of getting the next over sized piston that you should of got for it.

ya but he bought it use and it could have been bored over before, did you measure the cylinder before you orderd a piston or did you just assume?

The first time it died I had it measured at 67mm. But this time i accidentally ordered 68mm (which didnt fit) and then exchanged for 67. If I exchange again the people at denniskirk are gonna be like wdf this guy is an idiot lol

 

[shortboxbs]

actually he did^^^lol

he honed it, but i doubt it was bored or the shop would have done that for him. sounds like he used a drill honer and just got rid of the scars, then reringed and let her fly.
and if it meassured out at 67, did you get a 67.25 or get another 67 even?