help with other quad..

[dirtstalker]

I know this is a warrior forum, which is what I ride, but I have a question about a 400ex that you all may could help with. It's my brothers quad. He was riding today and it ran fine for about a 1/8 mile and then just quit. When we tried to get it started again the starter would turn but the motor didn't sound as if it were turning over. Could feel air coming out of spark plug hole but put a compression tester on it anyway. It never moved the needle as if it had no compression. In neutral it will roll freely for a few feet then feels as if the motor has some compression to it. Any ideas on this? We are thinking maybe broke connecting rod of blown rings? Any advice would be greatly appreciated.

 

[MS_Warrior]

maybe blew a hole in the piston or smoked the rings so its not building any comp?

 

[lbjamm]

Moving it in neutral isn't going to turn the motor. Do a leakdown test and see if the cylinder will hold pressure.

 

[dirtstalker]

That is kind of what I was thinking. Just trying to get a few opinions from different folks on what it might be. Like I said you could feel some air coming from the hole, but it wouldn't read a lick of compression.

 

[MS_Warrior]

That is kind of what I was thinking. Just trying to get a few opinions from different folks on what it might be. Like I said you could feel some air coming from the hole, but it wouldn't read a lick of compression.

well with the plug out and turning it over your going to feel some air but with the comp gauge in there if there is a hole in the piston i wont read it will just force the air into the bottom end and out the crank case breather.

 

[alex456123]

yeah sounds like a hole in the piston.

 

[dirtstalker]

Okay. Thanks guys for all the suggestions. Guess I get to pull it apart and check it out pretty soon. Gotta get the stator put back in my warrior before I start on his though lol. Piston in the 400 is less than a year old, wiseco brand. Any thoughts on why it woulda blowed a hole in it so quick?

 

[rowdy_sohc]

Running lean will cause it to burn a hole

 

[bones]

dropping a valve will put a hole in it fast ... and bending a valve will cause no compression as well

 

[lbjamm]

Do a leakdown before you pull it apart.

 

[Mathius]

Are the 400ex motors non interference? Maybe the cam chain snapped??

 

[dirtstalker]

What is the leakdown test and how do I perform it? Another question about this rig is, before it would start flooding out at times. A buddy told me to change the oil and see if it smelled like gas. It did. He said the fumes coming out of the crank case breather into the air box was causing it to flood out. Reasons why the gas would be getting into the oil?

 

[bones]

rebuild time .. imo !!

 

[Mathius]

What is the leakdown test and how do I perform it? Another question about this rig is, before it would start flooding out at times. A buddy told me to change the oil and see if it smelled like gas. It did. He said the fumes coming out of the crank case breather into the air box was causing it to flood out. Reasons why the gas would be getting into the oil?

If the oil was gas cut, chances are it was the piston or rings? You coulda had a cracked piston, and it just let go....

 

[Gen1Pat]

Flooding when it wasn't running? If it does that it has a carb problem. The fuel needle and seat are either needing replacement, or the float height needs to be adjusted. Constant flooding, and gas getting into the crankcase, and running it as such, can wash out the cylinder walls, and cause compression loss.

 

[lbjamm]

What is the leakdown test and how do I perform it? Another question about this rig is, before it would start flooding out at times. A buddy told me to change the oil and see if it smelled like gas. It did. He said the fumes coming out of the crank case breather into the air box was causing it to flood out. Reasons why the gas would be getting into the oil?

Thread an air hose into the spark plug hole and blow about 100 psi into the cylinder and see where the air escapes. Need to make sure it's at TDC on compression stroke.