two stroke motor guru's help!

[ex kid]

i just had my blaster ported and polish. the cylinder was bored, we used a Wiseco piston and rings, new wristpin and bearing, new gaskets. the problem is that when i run the quad there is a loud vibration coming from what seems like the cylinder. the head and cylinder are tourqued down correctly and all the plastics and fasteners seem to be tight.

any ideas?
it runs fine and the plug has a nice color(chocolaty brown)

[wilkin250r]

A loud vibration? Did you have any headwork done, or an aftermarket head?

If you increased compression, it could be detonation. Are there any specs of aluminum on your sparkplug?

[ZSK]

I know this sounds wierd but here goes....Do you have an aluminum chassis skidplate? The reason I ask is that my 400 made a sound a lot like what you are describing. I pulled the skidplate off and put some foam in between it and the frame and no more vibration sound.

[ex kid]

Originally posted by wilkin250r
A loud vibration? Did you have any headwork done, or an aftermarket head?

If you increased compression, it could be detonation. Are there any specs of aluminum on your sparkplug?


it is the stock head and there was no headwork, i was thinking detonation... no aluminum on the plug.


i have a chassis skid,but it's not on.

[250rpilot]

you didnt by chance just change from stock to aftermarket pipe at the same time did you? the aftermarket pipes can be pretty thin, and they can enhance the engines natural noises.

also, by vibration, does it sound like a bird chirping really fast? if so, it is most likely your head gasket or base gasket leaking. if it is, pull it apart, spray it with high tack gasket sealer, and slap her on and run it. since your head gasket is copper, i would start there.

if not, i dont know what else to tell ya. im sure beerock does though. he knows everything.

[LS@GtThunder]

There are several things that can cause that noise.

1. If you leave the rubber pieces out of the cylinder (they fit between the fins) after it is bored - it will be noisy. Most companies remove them to bore the cylinder.

2. Excessive piston to wall clearance - most peolple bore the cylinder to large for the Blaster - it is an aircooled cylinder and expands faster and farther then an aircooled cylinder - it needs very tight piston to wall clearance to get good life out of it.

[ex kid]

thanks for the help. i'll look into all of that. any more ideas? keep them coming.

[Rich250RRacer]

Wiseco pistons actually taper more towards the top than a stock piston does, and this will often give you a rattling noise since the piston tends to slap a little bit.

[400exdad]

Is it worse when it is hot or cold? Richening it up would help cool it some... with the porting, where is the jetting at? Did you change it? I would put a big jet in it... make it so it feels like its running on the choke all the time... and work my way down to where it runs good. Leave it jetted like this while you break it in.

Who bored it? Were the reputable? Also, and most importantly. If you built it, did you file the rings to fit like the instructions tell you too. When I rebuilt my first 2 stroke, I was suprised that they weren't pre-filed. If you didn't, it could be the rings binding in the cylinder.

[badass250r]

i just put my top end in the reason it doing it is the rings havent seated yet when they seat the noise should go away if it the noise i tink ur talking about

[beerock]

Originally posted by 250rpilot


if not, i dont know what else to tell ya. im sure beerock does though. he knows everything.

whats your problem man?

I do know one thing, spraying tack gasket sealer on a gasket that is leaking and "slapping" it back together is not the right way to fix the problem.

maybe spray a new gasket and "slap it back together.

Anyhow, it sounds like piston slap, most blasters do it.

Ls@gtthunder is right though, the expansion contraction of the air cooled blaster motor needs a tighter piston to wall clearance. water cooled 2 strokes and four strokes for that matter can run looser clearances.

[250rpilot]

Originally posted by beerock
Anyhow, it sounds like piston slap, most blasters do it.

Ls@gtthunder is right though, the expansion contraction of the air cooled blaster motor needs a tighter piston to wall clearance. water cooled 2 strokes and four strokes for that matter can run looser clearances.


see, you know everything! is there a problem with me saying that?


besides, if it is a NEW copper gasket, that is seeping, there is no harm in taking it off, spraying it, and putting it back on as long as you put it on the same way it came off. most times it it a piece of dirt on the gasket surface that can do this. if the gasket was used, hell no you wouldnt do that.

but i guess you already knew that.:rolleyes: