Help! Did I blow up my engine?

[wrk24wheel]

This past weekend, my wife was riding her 300ex when somehow the oil drain plug managed to fall out. She said the quad stopped and would not restart. After letting it cool down she started it again and rode another 1/2 mile, then it died again. At this point we noticed oil dripping from the engine. The plug was gone! I towed it back and cleaned everything up and filled the crankcase with oil. At the same time, I tore down and cleaned the carb, because the dynojet main jet also managed to vibrate loose.

After getting everything back together, it fired right up. However, it is acting like the carb is not set right. It will idle great and start up better than it ever has in the past. Dead cold, it will start in a split second. After letting it warm up though, it bogs down between 1/4 and 2/3 throttle. You can gently give it throttle to get it to rev up, but then it makes a loud noise like metal vibrating against metal at about 3/4 throttle.

I cannot tell if the noise is comming from the motor or from something else. I tore the carb apart again tonight and everything was put back together correctly. However, it still acts like there is something wrong with the carb. The only thing that I have not been able to check is the spark plug. The plug wrench that came with the bike was the wrong size. I am going to buy one tomorrow. I really don't think there is going to be anything wrong with the plug though.

I have checked the oil pressure and it looks good. Could she have burned up the crank bearings? Or do these bikes always make a funny sound at full throttle? I am used to loud bikes I ride a KTM.

Any help would be appreciated. The motor only had 16 hours on it. I hate to think that it is blown up.

[dork]

could be the bottom end, but you really need to check the rocker arms and cam. they are very sensitive to proper lubrication and if they run dry the rockers will come apart and contaminate the engine. just pull the valve adjuster covers and look in. if they're shot you'll have alot of play too. the crank runs on caged ball bearings and the rod on rollers, so they can tolerate a bit of dry running. might be wrist pin noise too.

[underpowered]

i used to ride a 300EX and when i bought it was doin somthin similar. It tured out the oil filter had been put in backwards by the prior owner whiched caused little or no oil to get to the top end. it junked the rocker arms and cam but other than that the motor was fine.

[wrk24wheel]

I know it not the filter or the rockers. I pulled both covers before I even fired it up for the first time again to lube them. I poured quite a bit of oil in there to begin with. They are very tight right now, however, I am getting the plug wrench today so I can check the valve clearance. It is not at TDC right now and there is absolutely no play in either rocker.

There was also plenty of oil up there after running the motor for about 20 minutes already. The new oil still looks good. As for the gallon of oil that I ran through it before fireing it up again also looked good.

I just wish I could get the thing to run right so I could figure out if the bottom end is going or not. Could the engine being bad cause the bogging like that? Or do I just still have carb issues? I have checked both boots for air leaks and the carb is on their nice and tight and set in there the way it should be. I am running out of ideas on that end.

[Aceman]

Why don't you compression test it and see if she fried the rings? It will never run right if it has low compression.

[Jonesy]

there is absolutely no play in either rocker.

This may be part of your problem. There should be a little play in the rocker if the valves are adjusted corectly, if they are too tight it will be low on compression and not run right.

[wrk24wheel]

I got the plug out and checked the valves and they were fine. The intake was a little off, but not by that much. I was unable to test the compression, because my tester only supports 14mm and 18mm threads. It still continues to backfire through the carb and stall when jabbing the throttle.

[Warrioreater400ex]

This is gonna sound really dumb, but im just trying to cover all of the bases here, first off the throttle part sounds like it isnt jetted right, and the noise.... it cant hurt to check the bolts holding the heat shield on the exhast pipe. Mine were kinda loose on my 400 and it didnt make much noise until 3/4 thottle, and its so close to the engine it was seriously hard to tell it was coming from it... hey its worth a shot. not trying to insult you with such a petty thing, i just know sometimes we overlook obvious things.... at least i know i do

[wrk24wheel]

I have already checked the basic stuff. The sound is definetly coming from inside the head. I did a leak down test tonight and only lost 5%, well within tolerances. Now I am more confused then ever what might be wrong.

The only thing that I can think of is the camshaft bearings. Isn't that about the only thing that could make noise in the head and not affect a leak down test?

I guess it could also be the crank bearing, but the sound really sounds like it is coming from the valves.

[Aceman]

The way your telling it, sounds like you need to start tearing your engine apart. I would at least take the rocker cover off and have a look at everything. The lobes on your cam might be bad or your rockers could be worn, you just need to take a look.

[wrk24wheel]

Just a quick follow up and thank you to those who helped out.

The answer to my question, is YES I DID BLOW UP MY ENGINE!

I pulled the top end and the cam is completely burnt along with the rocker arms. The piston is shot below the rings and I have a feeling the tranny is shot too. Needless to say, I just purchased a brand new crate motor for it. Figured it was cheaper and easier then rebuilding this one.

[DiRTdiGGr660]

that thing must have been makin some SERIOUS noise while she was ridin it bone dry:eek2: