sudden knock/noise happens?

K, so I was trail riding and hitting a couple nice consistent jumps, nothing huge, 2-4 feet air.

So, suddenly, I landed and immediately heard a "knocking"/banging/rattling in the engine. Sounded like something was loose/hammering. Seemed like it may have been slower than piston speed, but just a guess.

I thought it was that the chain had jumped a tooth and the cams were off, and the valves might be hitting. Not so, took cam cover off and cams are in time. So, what now?

Could it be the clutch? The clutch has been stiff and at times harsh, but I just got the bike, so I don't know if this was normal, or if it's in my head. I can say that a friend rode it and couldn't be comfortable with the clutch.

Where do I look?



Trevor there are a few things to check, firstly check the valve clearances, that will tell you if there are any problems there. Secondly run a compression test on it. Might be a good idea to drain the oil and see what that shows.

Good luck

I would pull the clutch cover off and have a look. I would think it is not the engine as something like landing a jump would not effect the motor unless something broke for good. If it still runs good then I would be looking at the drive line and suspension. Check the swing are bearings and the shock linkage. Also make sure the axel bolt is tight!! have had that happen before! Just my two cents..........

Was the noise only noticable upon the landing? If so, I would check your chain (drive chain, not cam chain) tension. A loose chain can, and will slap like hell when landing off jumps, particularly if you're landing 'throttle off'. Good time to check the chain slider on the swingarm too..... :)

Noise happens when sitting still clutch in.......I checked the cams and they are lined up with each other, but didn't check they were lined up at TDC. Is it possible that the chain jumped a tooth on the crank (which would leave the cams lined up to each other but not at tdc)?

What kinda noise can a broken clutch plate or other stuff make?

Thanks for the replies.

What year/model is the bike? Different year YZF's have had clutch and crank keyway issues.....More info' needed.....I doubt you've broken a clutch plate though.

it's a YZ400F 99..........

not a clutch plate, I took them off last night but stopped at that point. have read about different bolts etc in that area that can be loose....what/where are they?

Check the balancer gear drive shaft keyway on the crank. They go bad. The stock key is too small to start with. The only way to truly fix it is to hand fit a key yourself. I did it. Its easy.

K, the washers on the crank behind the primary gear (the one that matches up to the clutch) and the washer on the water pump are bent and ground up. A clutch plate also has a two inch section missing!! I can't find the piece of the clutch or anything else that could have caused the bending. There's a whack of shavings in there to, but I think they're from the washers.

Help me out guys, the parts are in tomorrow, and I'm worried about puting it back together without finding where the pieces are that damaged the washers!!!!



If you don't you putting a grenade back together.

You have to find all the pieces.

Defiantly pull it apart to find those pieces... also look in the strainer on the frame. Never heard of anyone finding stuff in there but this might just be what it was designed for.

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