'03 YZ450 - Loud clacking/knocking after landing jump

OK, I know I have not posted here much. I promise I have done several days worth of searching on this, and I can't find a discussion about a problem that seems to match these symptoms exactly.

The bike is an '03 YZ450F. I bought it used in 2006. I am a heavy rider (250+) but I don't ride very hard - when I say I landed a jump - I mean what most people here would consider a tiny hop. I basically came up short on a very easy and shallow double (I was probably the only one on the track not clearing it, including the kids on the 65s).

Anyway, right when I landed the bike starting making a loud clacking noise. My first thought was that the mud-flap had become caught against the tire. The bike still seemed to have plenty of power. I jumped again at the next tabletop hoping I might jar it loose. Of course, the noise remained.

I stopped the bike, looked for anything visibly wrong. I couldn't see anything out of place, so I started the bike and gingerly rode back to the pits. This was about 45 seconds.

I am still trying to diagnose the problem. The noise does not stop with the rear wheel - it changes with engine speed, regardless of whether it is in gear or out.

I checked the timing according to the manual, and it was fine - no skipped teeth on the cam gears.

I removed the cams and they appear to be OK, although I have yet to obtain a micrometer to measure the lobes. I did not see any scoring, scratches, gouges, or other obvious signs of problems.

I checked the valve clearances. All were within spec, except for right-side intake valve, which was .20-.23 mm, rather than the specified .10-.15mm.

I ordered the replacement pad to fix that, but I don't see how that clearance issue could a) occur as a result of landing a jump or :excuseme: cause such a loud noise. I am no expert, so if there are good explanations for these, I would love to hear them.

I don't mind going further with disassembling the engine, but I want to have some idea of what I should be looking for before I go any further. This is my first time opening up a 4-stroke engine.

Should I remove the cylinder head and check the valves themselves? Should I be looking at the stator?

Should I fix the valve clearance and put it back together and see if the noise is gone?



Should I fix the valve clearance and put it back together and see if the noise is gone?



That's where I would start.

Do the valve clearances like suggested, and also look on the underside of the engine. I have seen more than one ignition cover break from impacts, just thinking maybe something on the backside of the landing could have pushed it in and possibly hit the flywheel? Just thinking of ideas here. Good luck.

Thanks, guys. I will check again for anything broken. I will fix the valve clearance on the one intake valve, then reassemble and see what happens...

hey i bought my bike not too long... bought as is an 03 yz450f bike makes loud clacking noise somewhat as your describing... not from exhaust not from chain.. all the mechanics ive asked the same question say its just supposed to be nature of the beast.. but in all the starter could but some what stripped causein to slide some what down that could cause it.. it would make the motor seem as if you were kickin it while the bike was runnin

If you came up short and "cased' the jump look at the bottom of the engine for damage of any kind. Carefully look at the clutch cover for any dent or depression....perhaps pull the spark plug and turn the engine over by hand and try to feel for something hitting. ...the clearance in the clutchcover is tight so a small dent in the right place will cause the basket to rub...

is the noise when the bike is in neutral? does it change when the clutch is pulled in?

Also check the kickstarter and make sure a small stone isnt keeping it slightly down. wiggle it and see if it is going to its home position or if the spring feels weak

If all else fails grab a stethascope from the pharmacy and try to isolate where its coming from.

Thanks guys. I didn't bottom out on the landing. I came up WAY short, not on the top of the second peak but just flat in the middle. I also have a heavy-duty skid plate because I do a lot of desert riding over big rocks and stuff, so I don't think I could have broken anything via direct impact. Regardless, I checked pretty closely and I don't see any visible damage. Whatever is making the noise, I think it is inside.

And yes, I am aware that the engine is generally noisy. I've had the bike for years. This is a new noise. It is very obvious that something is wrong. Like I said - imagine if the mudflap was stuck and flapping against the knobs on the rear tire as it rolled. That is what it sounds like. Very loud, very distinct, very wrong.

dude, you already have things apart. find TDC, mark the chain and timing gears with a scratch. pull the jug off and chech the piston, and crank. you might not have to split it open.

Follow up...

I fixed the valve clearance, put it back together, and the sound was still there.

I didn't have the confidence in my abilities to find the problem, so I took it to a local mechanic who I've used before.

The problem turned out to be a tooth broken off of the starter. The tooth apparently got wedged into the clutch gear, and that is where the noise came from.

And, I apparently set the timing incorrectly when I put it back together. This frustrated me, because I followed the instructions in the manual (and advice on this forum) as well as I could, and I still didn't get it right, somehow. Sure looked right to me when I assembled it.

So, I need a new OEM clutch (because aftermarkets don't include the gear that was wrecked) and a new kickstarter mechanism (because the gear that broke cannot be purchased separately, either).

Rings will be replaced and cylinder honed while the top end is off (it already is), so after it's all done, bike will be like new. But it is not going to be cheap.

Thanks for the assistance.

Oh, and save the "you could have saved 1/2 the money by doing it yourself" comments. I couldn't even get the timing right! There's no way I would have gone through all of these repairs and fixed it correctly without the on-site help of someone with some experience. This was beyond my ability level. I wish it were not true, but I have to concede that much.


Thanks for posting with a follow up of the final diagnosis. I appreciate it!! What is your theory as to the chain of events that led up to the starter gear getting broken in there? Possibly the kicker coming out whilts you are in mid air and then upon landing it kicked down enough to engage the gear into the already violently spinning clutch basket? Best of luck and thanks again for the follow up

...Possibly the kicker coming out whilts you are in mid air and then upon landing it kicked down enough to engage the gear into the already violently spinning clutch basket?
The kick starter gear train is always engaged. The ratchet plate on the kick shaft is cammed out of contact when the lever is returned to the top, and nothing will really happen if it engages while running.

The usual cause is some stray object like a gear tooth, screw, or snap ring runs between the gears.

My mechanic suggested what sootgrinder mentioned (the starter catching on my boot in mid-air). I certainly don't remember that happening, but I suppose it is possible that I touched it somehow - maybe with my leg. But I honestly doubt it.

There was nothing else broken, from what the mechanic told me, so I don't think anything got into the gears to break the tooth. My guess is that the simple jarring of the landing impact knocked the gears together at speed, causing a tooth to break. Then the tooth fell into the clutch basket.

I didn't case the jump, but I easily could have bottomed out the suspension in the landing. I'm heavy, and the suspension is probably not set ideally for me, let alone upgraded as it surely should be.

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