I have a Blaster that i have been playing with for years. Everyone rides this thing and it goes through hell. Now i want to sell and i have a problem. Friend rebuilt the bike for me. Had a Vito's Forged Piston something like a 67.75mm or something like that and was bored to match. Blew it up and rebuilt again with bore and Wiseco this time. Has a Vito's Fat Bastard pipe, stock carb(not stock jetting), and K&N air filter. After the bike was rebuilt this last time we were trying to get the jetting right and a strange thing happened. Lost compression...head was not torqued down properly and was loosening up. After realizing I pulled the head off and noticed that i could wiggle the piston around in the cylinder. Then i got to wondering if it was possible that he put the wrong piston size in this time? How could it run if it was the wrong size? Should there be this much play or are the rings just bad? Cylinder and piston looks good to me and its only got maybe 20 minutes of run time. I can handle rejetting and all and i know that vito's pipe isnt making things easier on me, but all i want is for this thing to run so i can sell it. I have the manual and all, but this thing was just rebuild and i dont want to go tearing into it with is just being rebuilt. If someone with more experience dealing with tolerances and such could give me an easy way to tell if this thing is done right so i can put the head back on and crank it up to sell it would be greatly appreciated!!!
Buddy's rebuild gone wrong!!
- Thread starter BlasterJ7380
- Start date
you need to have that cylinder measured by a shop. and let us know what jet's ur running and what other mods you have besides the pipe. and you have probably had airleaks and lean jetting that has lead to the first piston failure. sounds like you had the wrong sized piston the second time. it would run with that for a little while if the rings sealed it up enough to have compression. but it would be really bad if you continued to run it. you should always retorque your top end a few times durring break in procedures
The piston being a smaller size wouldn't be the problem if you run oversized rings. I know many people that do this to get less friction from the sides of the piston but the rings have to be oversized. But if you have the equipment do a leak down test while your in your motor. If you don't have a tester but a member on here sells them for cheap and they are very good quality from what I hear. I would check the size of the piston with a caliper and the cylinder size. If the pistons smaller a bigger piston would be safer but oversize rings would be cheaper. But if you dont change the rings before they wear out the piston skirt can smack against the cylinder and blow apart. Hope this info helps buddy. And welcome to the forum man. You'll love it here. =]
get us a piston to cylinder wall measurement, shouldnt be more than .004
if so, it was overbored for the piston size, and to be proper, it'll need rebored and a next size piston in it
ps....to the above post, i've never in over 2 years being on here, ever, heard anyone mention oversized rings as a cure for a worn/overbored cylinder
i think thats only an auto trick, don't think they make them for 2 strokes ????
if so, it was overbored for the piston size, and to be proper, it'll need rebored and a next size piston in it
ps....to the above post, i've never in over 2 years being on here, ever, heard anyone mention oversized rings as a cure for a worn/overbored cylinder
i think thats only an auto trick, don't think they make them for 2 strokes ????
^Really?^ I think it may have been on Ken's site with the mechanic lesson pages that I read about it but maybe it was four strokes? I know you can do it on more engines but the piston can slap and blow the skirt.
i used stock bb piston rings on a .50 over bb piston, opposite of what ur saying but it did work...just wore out fast
Buy a set of feeler guages and check piston to wall clearance .004 wut ur lookin for....
Just imagine that lil piston slapn around in that bigger bore...there's no way to seal for propper compression!! Lucky it ran at all!
Hate to have the bad news but all are rite if ya wanna sell it with it runnin rip it down!!!
Holeshotman has the leak down testers for like 30 bucks....get a compression tester and check that fisrt that will tell ya!!
Just imagine that lil piston slapn around in that bigger bore...there's no way to seal for propper compression!! Lucky it ran at all!
Hate to have the bad news but all are rite if ya wanna sell it with it runnin rip it down!!!
Holeshotman has the leak down testers for like 30 bucks....get a compression tester and check that fisrt that will tell ya!!
I had my cylinder bored recently for oversized piston at a motorcycle shop. when i got it home and put the piston in the bore i was like WTF. the top of the piston would move around in the bore. I called the shop and was like whats up with this. He explained to me that pisons are not perfectly round and they are tapered (smaller at the top more heat up there) because of the diff thickness of the piston expanding diffrently with the heat. So the piston is made out of wack so that when it heats up it will be in wack. So there was what looked like excesive cylinder to piston clearance at the top but sure enough when i turned the piston around and looked at how the skirt part of the piston fit in the cylinder it was nice. So i dont know mabey thats what you are seeing. Guess the only way to know is to take it to a shop and have them check it for you. Peace
All these reply's are great guys thanks. Thats interesting abou the piston being tapered towards the topside ill check it out, because i just cant fathom how this thing was running if it had the wrong size piston in it. I'll be working on it tonight. Can someone tell me how i would get ahold of the guy with the leak down tester??? Im new to this sh*t, but i could def use one, because i would rather tear it down myself this time if it dosnt turn out to be an easy fix.
he said it had alot of play his best bet is to go to the shop and the the right piston there is now way u should have alot of play
This is false. The piston is supposed to rub the walls on the cylinder for support.
If it doesn't it will weiner and slap as it moves up in down, rings arn't gonna keep it centered.
Eventually you will break the skirt or worse.
lol i here u guys we are on here not to fight but to help but to the gut with the piston problem rent one are buy one itsa all on ebay or rockymountianatv.com
