ATV Florida Forum

This is bothering me a lot. a couple months ago i was riding at croom in the front pit just goofing off. A lot of high rpm low speed stuff...well i was jumping from one bowl to another and my jump started to fall apart so i started going in circles to build it back up. Well after a few revolutions my bike bogged down and died out of no where. I thought it was real odd...then i went to start it and my starter wouldnt turn my engine over!! after about 30 minutes i tryed to start it up again even thought i thought my engine was blown. It cranked a couple times and stopped. I tryed again and it started up. Ever since then i have had this hammering noise while i'm putting a load on the engine. If i rev it in neutral you almost cant even hear it. I checked my valves 3 times to see if they were right and they have been everytime. I dont seem to have any lose in power, MAAAYBE some but nothing crazy. On nice warm days it will fire right up, no problem.

ANY IDEA'S?!?!? I'm clueless. If it were a wrist pin or something it would go away once it was hot...but it NEVER goes away....baaaah

Sounds like you possible need a crankshaft. You can either tear it down now and check it or wait for it to blow up and then buy everything.

NOOOOOO! lol

Why do you say the crank? And i've never diagnosed a bad crank, and aside from looking for cracks or scoring, what should i look for.

Look for a new motor!  ;D

motosport has a stroker crank and top end kit. its only $580.00. good luck.

The only way to find the problem is take the engine a part.

Willlll doooo. Lets hope i can get the parts (and money for the parts, boooo) and get it back together before gatorback.

Thanks for the advice.

mine kinda did the same thing rite by were you were exceot i was in that little patch of woods by the road i was riding and it just turned off, it didnt make the hammering sound or any weird sound but it would sometimes start if i let it sit out in the sun. it turns out i had a  dead battery that was the first think i replaced but the guy sold me a defected one. its probably something simple. good luck

jake

If the motor is coming apart you should tell by having some metal in the oil when you drain it or if you take out the oil filter and cut it open you would have metal in there too. just an idea.

mine has a similar problem from me running with a dead battery that wont hold a charge. I'm pretty sure what happens is under high rpms at wot it needs a battery to give adequate power to the ignition system, thats why the yfzs used to have a problem with the battery's draining at wot ruining baja and stuff like that because it couldn't charge the battery fast enough, anybody remember that? idk but my bike runs bad with no battery it cuts out and backfires when I'm going over the whoops at wot, never did that when i had a good battery and the carb is clean. i also think its ruining my ecm(or whatever its called on an atv) because I'm getting the reverse limiter in neutral sometimes now! anything electronic is something i don't want to worry about fixing but i may have to.

so yea, what im geting at is check your batery before you go and tear down the moter. idk about the funny noises its making tho, you may have to tear it down anyway but check the easy stuff first.

ya i have run with a near dead battery before i know what your talkin about, but i wish it was that easy! haha thanks for the input man.

I had the same thing happen to me, I was about 3 miles out in ONF and a very similar situation,,,,any time I would put the slightest load on the engine it ended up sounding like small explosions with each firing of the cylinder. 

I know I know, that's what happens with an internal combustion engine, but this sounded like it was on the outside of the engine.

I couldn't see anything physically wrong with it, but I loaded up and took it to ATP.

come to find out, it had blown a head gasket.

here the head bolts bite into the metal of the engine gets brittle for certain years of the 400EX and when it heats up they loosen and POP there goes your head gasket.  When the engine cools down you can start it back up and run normally for a few minutes before it starts making noise again.

When it happened to me I was doing some sight-seeing and probably chugging along in 1st or second gear through some tight trails,,,,so probably about the same situation you got into at Croom.

Sorry to say, but if this is the case, you have to replace the engine part where the head bolts tighten to(dunno what the part is called)  if you want, give Mike a call at ATP, he's got the experience with this situation from my 400.

Id@

ps: sorry I didn't see this earlier.

I'm tossin around the idea of just sending my engine to them. But I know they stay busy and I dont want to miss my race on the 29th. I talked about getting my engine re-done a while ago but now i actually have the engine out. I will indeed give mike a call.

I would imagine a blown head gasket would sound very similar to an exhaust leak. But this sounds more like my timing chain is slapping. baaaah i dont know. Thanks for the help Ida  ;D
Hopefully i'll see ya soon up at the Plex, last time i saw you was back in 06 i think when they opened up the new trail system in ONF haha.