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Help: I seized my 04 up yesterday in the WORCS race, decatur, tx

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3rd lap and the bike/motor made a loud PSSSSSSST and it was dead instantly. White smoke or steam maybe out of the exhaust pipe/can.

I haven't torn into it yet so I'm not sure what I'll find.

The motor is locked up. No movement in the kickstarter at all.

Any ideas as to what went wrong would be greatly appreciated.

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Obviously something "stuck" in the cylinder or crankcase that won't allow it to turn over. Sounds as if a water channel was breached causing the sizzle and steam.

Were you running the stock bore?

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Yes, the only thing motor related that isn't stock are the stainless valves.

Does this mean a new jug?

Some were thinking a valve may have let go. I don't know too much about these 4 strokes, all I have done internally is the valves about a year ago.

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It (sadly) may mean a lot of new stuff or you may get lucky. I stuck my yami 450 a year or so ago and got away w/ only bending valves (on the top end) - no damage to the head. I also had to replace the rod and piston (obviously). I went 3mm over on the bore so I was able to reuse the cylinder.

Who only knows where the water (if it is water) is coming from, but that will need to be dealt with too. If the water problem is due to the cylinder, that won't be so bad 'cause you may need a new cylinder anyway.

I know this sounds mean, but you're about to learn about 4-strokes just like I did - you'll spend some $ getting out of this one, but you will gain a great education if you do the work yourself - or at least some of it.

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Not mean at all. I fully anticipate spending time and money on this deal. Expensive education, but aren't they all?

It was time for a new top end anyway.

So I'll need a top end, probably valves?, possibly a cylinder?, and possibly a rod kit? all gaskets etc...

Am I forgetting anything?

Thanks for the info.

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If you're comfortable doing the work, break into it and and take a look. Like I said, you may get lucky and not need valves or any head work. If the piston is stuck, you'll more than likely need a new cylinder. I don't know about the Hondas, but my yami rod bent when my piston jambed. I just got a whole new crank assembly.

You'll probably need to get into the case if for nothing else than to inspect for scrap metal and clean.

Yeah... gaskets out the wazoo too.

Don't forget about www.servicehonda.com - ton's cheaper than the dealer for OEM stuff.

Here are some of the biggies:

Crank/rod: 13000-MEB-671 CRANKSHAFT $199.58

Piston: 13101-MEN-670 PISTON $61.05 ('04)

Cylinder: 12100-MEN-670 CYLINDER $168.70

Head: 12200-MEB-770 CYLINDER HEAD $207.77

In valves: 14711-MEB-670 VALVE, IN. $51.96 (each)

Ex valves: 14721-MEB-670 VALVE, EX. $30.59 (each)

Again, you may not need some of these, but it's worth considering.

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The steam was an indication of water entering the combustion chamber, probably a head gasket. Seizing well that is another story, could be many things, valves bent or broken, cylinder scored and piston seized. You wont necessarily need a new jug, but it will need new nickasil. You wont know until you open it up. Good Luck. 😢

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your rod will be seized to your crank, the coating will be cooked off your piston and you will have scoring on the exhaust side of your cylinder.

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1/2 of the right intake and exhaust valves were sitting on top of a rather ugly piston. The bottom of the head is beaten up, but the cylinder looks good. The rod and bottom end look and feel good without splitting the cases. The valve stems were still being held by their keepers.

Any thoughts as to what may have caused this? Was it maybe just a valve failure and the broken valve just killed one of the other valves? I have 10 months on these stainless intake valves. Maybe 50-60 hrs.

Any input would be appreciated...

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Everything below the top of the piston looks like I think it should. The piston was within 1/2" of the top of the cylinder. The ring is still there. I looked at the wrist pin to see if I could figure out how to get the piston out. Without getting my manual out I could not. It looked as I guess I would expect it to. What are you thinking the wrist pin would look like?

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It sounds as if the rod/piston connection may be good. That's doesn't mean the rod is still good, only that they (piston & rod) didn't separate.

You'll have a circlip on each side of the piston that holds the pin in. Remove one of them (or both if you want) and pull the pin out. You may need to tap the pin out using the handle of a screwdriver or a piston puller if you have one.

What was the cylinder like? Any apparent holes? Any signs of shrapnel below the piston i.e. in the case?

It's begining to sound like it's a head issue. The valves getting "tapped" could have easily brought the head up enough (if not torqued down properly) to spill (and cook) water.

Mechanical energy is funny stuff though. If the action is from the top of the piston upward, at least your problem may be isolated in that area. Searching for metal scraps deep in the motor sucks. When my yami went, it wasn't pretty down low.

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Make sure you check your cam to see if the gear flange spun on the shaft. When my cam chain tensioner failed the cam chain jumped the gear teeth letting the valves hit the piston. Bent both my intakes and when it jammed up it spun the cam flange. Cam lobe timing was off about 20 degrees and it drove me absolutely nuts when I put it back together not realizing the flange had spun. Had to put in a new cam.

Hard to say what triggered your explosion. But if both the left valves are ok it would seem to rule out a cam timing problem. However I'd replace (or modify) your CCT while you are at it.

Did it grenade at high, mid, or low rpms? Valve springs all still good? No broken ones? I'd check them for proper tension before reusing them.

Hard to believe a SS valve came apart for no reason. I'd first suspect contact with the piston.

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All springs appear to be good. None broken. I have ordered a piston kit (wiseco 12.5:1), head (backordered), cam chain, cam chain tensioner, head gasket, cylinder gasket, resleeve of the cylinder to match new piston.

CCT= Cam Chain Tensioner?

It let go at mid rpms. It was definitely not an overrev situation.

Thanks for all your input and help!

Those in the know think it was due to the cam chain/tensioner being older, worn/stretched. Does this sound remotely feasible? My guru said he has read where the cam chain should be replaced with the top end.

Thoughts?

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Hey guys just because the valves were steel does not mean they wont break with out contact .i have a customer a big shop in NY that has had 2 crf 450 fail ex valves the heads poped off since the poor valve is operating @ temperatures of 1400 degrees this is the one that usally fails first .a couple of years ago the HD 883s that were being raced on the dirt tracks needed to have the valves replaced every week end to prevent failure .i had ferea make some valves from there hi tech alloy with a 2500 degree operating temp, and started using bronze seats that pulled heat from the valve along with heavyer springs and brought the failure rates to 0 almost every one out there is using them now . It would be a good idea to put a new crank in that 450 also or @ least check it for rod bend with a pin and a set of paralells have a pin made that fits your rod small end ,and slip it through the rod with paper strips between the paralells and the pin ,load the pin by turning the crank there should be even pressure while trying to pull the paper stips rotate the crank in the other direction and repeat this will tell you if theres any twist in the rod .

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If the cam timing got out of whack both the left and right sides intakes (or exhausts) would both show some damage. RHC probably has the right diagnosis. He knows more than I about motors thats for sure.

Ok, so it happened at mid RPMs. What was happenening at the throttle? Was it a high load situation like a sand wash or something? That would support the high heat/ weakened valve theory.

BTW, when my cam chain jumped because of the bad CCT (you got the acronym figured right) it happened when I chopped the throttle after a jump take off that required high rpms in 2nd gear.

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The motor was under pretty substantial load. Sand section slight uphill. Probably 3/4 throttle consistant. There was no drastic throttle movement within the last 30 seconds of it's life. Just smooth roll on to boom.

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You might want to go a little richer on the main jet to reduce the combustion temps a after you get it back together.

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