Piston after Piston

BlasterAzores

BlasterAzores

Member
Oct 30, 2008
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Portugal - Azores (ya i know... just go to google
Need sugestions people, im getting tiered of this.
Her´s the deal...

In a period of 5 months this is my 5º piston, this is what im runing:
Auto lube removed, 32:1 fully sintetic oil, Vforce3 reeds, 4º key, Tomey B1 pipe "still stock silencer", wisecon piston, 95 octane gas, stock carb, main jet 290, stock needle half posicion, reed spacer, tors removed, carb cap replaced "no more tors bulky cover".

1st piston melted rings""bad oil racio 25:1""...
2º piston broken exaust skirt "didnt bore the cylinder...
3º piston hole on top ""wrong spark plug, and air leak""...
4º piston melted on top in the exaust side "" damn carb cover o´ring""
5º Piston mounted yesterday, no feedback, still have to retune it and take her for a test run.

Still have a stupid problem i cant solve, when quad comes to a stop the idle stays in hig rev for 5 to 10 seconds and then come to a normal idle.

This thing keeps eating pistons like peanuts, god damn, anyone knows if im forgetting something important on rebuilding the top end.
 
WELLLLL....the 4 degrees may need to be retarded a bit if u are out riding the sh*t ouuta it.. i just toasted some rings with +5 running wot at the dunes for 2 days. exhaust skirt usually breaks because of piston rock/slap. if it stays reved after u let off u need to either adjust ur throttle cable and or idle screw on top of carb. if u are going to build ur own engines then learn from experience....otherwise it can get real expensive. u cant take short cuts or ur wallet and sanity will pay....
 
you are running really lean, obvious by the holes on top of the pistons, and the fact that is stays revved up after you let off the gas
 
do a proper leak down test and be sure you also do a correct plug chop and only then will your issues be revieled
 
FLOTEK said:
do a proper leak down test and be sure you also do a correct plug chop and only then will your issues be revieled
Click to expand...

I´ve done leak tests at home and at 2 diference shops... 0 leaks
The jetting is killing me... runing 290 and i can feel she´s going lean but if try to go up to a 300 main she starts to bog out... tryed diferent needle posisions and diferent needles.
 
blaster biotch said:
WELLLLL....the 4 degrees may need to be retarded a bit if u are out riding the sh*t ouuta it.. i just toasted some rings with +5 running wot at the dunes for 2 days. exhaust skirt usually breaks because of piston rock/slap. if it stays reved after u let off u need to either adjust ur throttle cable and or idle screw on top of carb. if u are going to build ur own engines then learn from experience....otherwise it can get real expensive. u cant take short cuts or ur wallet and sanity will pay....
Click to expand...


Wallet and sanity already paying for it :">
Come to think of it and the quad started to break down after the +4 key, and i ride her WOT like you and for periods of about 4 to 5 hours straight with very litlle stops maybe 10minuts every hour.

Gona take her to a mechanic and chek the timing. Thanks
 
i rode like that a couple years back.... wot for extended periods and very few cool down periods. i broke 2 pistons at the intake skirt and 2 cases. pieces of the pistons got hammered through the case into the trans oil. cool down is important, also don't ride wot too long.
 
First of all, are you doing a propper break in!!!?? sounds like your not. but other than that, seems you have an awnser to each piston problem so why you asking for help when you just need to do things right? also, how much engine experience do you have? do you know for sure your doing a top end rebuild right? your replacing all gaskets when you do? making sure everythings torqued to spec? checking for air leaks? jetted properly?
 
do a plug chop ,not just assuming its close ,run the proper jetting and break it in correctly ,dont use a vitos piston dont use crap premix oil dont run it wide open for extened periods of time
 
the pistons that blew holes are obviously either running rich or have air leaks, could be the pipe, spark plug, carb boot, head, cylinder base....
also, biotch is 100% right about the slap. the piston w/ the broken skirt can be blamed on the fact that you didn't over bore when you replaced your piston. every time you rebuild w/ a new piston you HAVE to bore and hone and go up a size in piston. this is the only way to make sure you don't bust up a piston skirt. at the very least make sure you check tolerance.
also, after you busted the skirts, did you split the cases and clean all the metal bits outta the crank chamber?
 
how old is the bottom end?? worn crank surfaces and worn main bearings can cause airleaks when the motor is running. you have an airleak. are the shops doing compression tests or leakdown tests?? what are the specific results of the tests?? what pressure?? what was the loss and over how long??
 
ok guys, looks like i'm in the market for some of these parts too. My son put straight gas in his, and it busted the intake piston skirt. We have no idea what size the bore may be already, and of course, we're doing all of this on a shoestring budget. So I need to know where to buy a good piston inexpensively, need rings, and I guess we'll get the jug checked and then bored. I had no plans of doing that prior to reading this thread, was gonna stick a new piston in it since the bore is flawless.

I'm also concerned about pieces in the bottom end. We were gonna change the oil, but I'm not real confident about splitting the cases.

So we're wide open for good advice here, as long as it's not "spend a million dollars on unobtanium parts" or stuff like that.

I'm also wonderinig WHERE is a good place to order from, that you guys have had good results with.

Thanks for your help!!
 
just some more info

Is your head milled, what is your compresion at? I've seen some people have a high comp. head run with pump gas and burn it up. it's fast for awhile. Pump gas burns hotter than race gas, so if you are running higher compression it's too much.

When replacing piston you must veryify if jug is ok and have the bore measured by someone with experience to determine the correct piston size.

Proper warm up frist. The piston heats up faster than the jug, Aluminum vs steel heats at different temps. Warm up is to allow the jug to warm up and expand, beacuse the piston will expand first (alum) and if your ride to hard to fast the piston will expand siezing it to the jug.

after a fresh build keep a close eye on the plug color, dont' let it idle to long before checking the plug, it will give you a false reading. Also always wait for the head to cool down some when checking the plug, I've seen it a few times were people pull the plug and when putting it back over tighten it when it's too hot and strip the threads on the head. check the jetting section of forum for proper jetting.
 
Last edited:
Um lasxgames the bike shouldn't idle at all when doing a plug chop. You take the bike into its top gear and pull the clutch and shut off the engine and don't let off the clutch until your stopped. Then pull the plug and check.
Also Ftl900 you deffinately need to split those cases im sure theres metal in the bottom. And like everyones saying you need to pressure test the motor for leaks. Even small leaks can cause the motor to run lean causing it to rev high and in time can cause motor failure.
 
Yes also you dont wana do a plug chop on a completely new plug its harder to take readings from. Use one that has a couple rides on it atleast.
 
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