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Motor help needed. I'm at a loss.

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I've got an 03 that does dual duty as a street legal/track ready supermoto that I also ride in the dirt with a simple wheel swap.

I just had a new top end put in 5 hours before, and my break in consisted of letting it heat up well, and then riding the piss out of it for 20 minutes hard, then going for a longer ride at a mellower pace and then an oil change.

I was in supermoto mode last night at the track and just hammering around the corners. After a ten minute session, I took a break for a few minutes and then went out again. After a few laps, I was coming hot into a corner, banging it from 4th down to first to make the corner. I'd just half-dumped the clutch and had the rear end backed in a few feet, with the wheel tracking smoothly out, but in control, and when I went to fully release the clutch to roll on the gas and get outta there, the bike was suddenly dead. I have many friends on CRFs that also ride exactly like this (banging it down through the gears and spinning up the rear using the same technique).

I pulled off and started kicking it. Dead. It was starting 1st or second time, every time. I kicked it about 60 times probably over the next 20 mins. I checked the gas, and topped it up. still dead. and i mean i was kicking it and it just wouldn't start. i checked the connections on things like the kill switch and they were fine. i pulled the plug out and it looked like my jetting was bang on, although there was a spot of carbon on one side of the spark plug, near the threads on the head of it, that looked a little suspicious. then the kickstarter started binding in one spot and would lock. i then put the bike in gear and rolled it a bit on the tranny to remove the built up pressure, but there was still a sticky spot on the kickstarter's stroke. I pulled the alternator cover off and found a fine metal sludgy paste sticking to the inside of my flywheel magnets. i took off that small round crank cover on the right side of the bike and tried turning the crank, and it would turn (i'm going to try spinning it over later today with out the plug= its just the first half of this happened at the track last night and i haven't had time to dig into it at home yet). i took the cam cover off and without removing the cams, everything seemed OK. the nut that holds the alternator on is still good, and hasn't backed off. does this sound like a bent rod? or a piston that's submurged in my cylinder wall? or a bent valve (although i think if it were a bent valve the kickstarter's stroke would be stiff all the way, not binding in the spot it's in now).

anyway, any thoughts or help would be greatly appreciated. i have had 6 trouble free hours on this top end rebuild before The Problem happened.

Thanks in advance.

Jon

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was the motor done up stock or what did you do aftermarket to it,

and did you ck for spark,

and you should ck compression , with the decompresser hooked up and then loosen it up where it dose not decompress and get that reading also.

it dose not sound good, :applause:

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Yeah, well its a bit more than the spark as it instantly died with no indication or misfiring before. its an internal issue. i'm thinking mangled rod/piston seize/bent valve. and the piston's not really into being moved around right now. i guess i'll start tearing into it and see what happens.

the motor's only mod is the 04 piston that was put in 6 hours ago (for reliability :applause: ).

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Yeah, well its a bit more than the spark as it instantly died with no indication or misfiring before. its

so you didn't check the spark? i would do that just to rule out stator problems. when they fail, they fail suddenly and completely.

i would imagine that an internal problem would do something more dramatic than just die suddenly, but i mostly ride 2 strokes so i dunno.

mw

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Well I just put in a brand new stator on thursday so I know what happens when they fail and their symptoms -- i.e. the bike starts backfiring and shooting flames, and it will kick over and run but when you wind it up it'll not make enough power to spark and then bog down and die at anything over about 1/3 throttle.

And a blown stator doesn't make the kickstarter bind in a spot when the spark plugs out of the motor. It was the very act of my riding that killed it; rev limiter in 4th, clutch in, bang it down to first gear and then feather out the clutch as I begin to turn in on street tires that did it. the thing is, i've got four other buddies on crf450s doing the same things, lap after lap after lap, with many more hours than me doing this, and their motors are fine.

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It was the very act of my riding that killed it; rev limiter in 4th, clutch in, bang it down to first gear and then feather out the clutch as I begin to turn in on street tires that did it.

There you go, over revved it most likely and piston = slap valve :applause:

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Over-revved it? Nope. I'm not doing anything different than just about everyone with a supermoto'd crf450. you can beat on the motor pretty good at high revs and don't have to worry about too much as long as you're on top of the maintenance. I do have a fairly high mileage motor though, and after speaking with the mechanic who "forgot" to mention that my rod was on its way out last week, I've found out with the help of a buddy what went wrong.

Its torn down now. The piston was slightly contacting the cylinder head because the rod and the main bearings were worn. that metal paste i found inside my flywheel was from the rod or bearings, and basically, the bottom line is that i just need a new rod, some seals, and the ol' main bearings. the cylinder is a little worn from it, and the pistons worn front and rear, but other than that, it looks fine. The valves never contacted the cylinder improperly, and that bearing just stuck hard enough to kill any idling of the bike. I know I'm lucky that it didn't go any further and smash the case if I was at high rpms. it was just starting to go and my clutching it in saved it.

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This might be a long shot but ck the spark plug and see if its the rite one for that bike I had a 73 cr250 that if you had the wrong plug it would back kick the kick starter and almost break your ankle, the bike would run but poorly :applause:

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Over-revved it? Nope. I know I'm lucky that it didn't go any further and smash the case if I was at high rpms. it was just starting to go and my clutching it in saved it.

*MENTAL NOTE* replace rod/crank bearing sooner next time :applause:

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Nevermind. I was going to say it was probably a stator problem but then I saw your post about the bearings et al

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