'98 YZ400F engine noise

EdLennon

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#1
Hi all,

First of all, I want to say thanks for the input I received last week. You guys were spot on with regard to my bike sputtering and popping. I had a little bit of crud build up in the carb. I took it apart, cleaned the whole thing with carb cleaner and blew air thru all the jets. The thing now behaves like normal.

Well, almost...hence my plea for help once again.

When I finished putting around the yard tonight, I happened to hear a faint "jingle" type noise coming from the engine. I can't seem to figure out just exactly WHERE it's coming from, but it's there and it's bugging me. I don't exactly know what to do or what to look at first, so any advice you guys can dish out, I'm willing to try. Could the chain tensioner need to be adjusted?

Also, there is a black breather tube coming down the left side of the frame that appears to begin at the top of the engine (maybe some sort of PCV valve or something?). Well, I have owned this bike since new in '98 and never noticed puffs of air coming out that tube, but that is what seemed to be happening tonight. Is that normal? I don't have anyone near me that owns one that I could check out.

Thanks once again for your advice,
Ed Lennon
 

Humai

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#2
Ed, the YZ400 is quite a noisy engine and I'm surprised to hear that a faint jingle could be heard amongst the clatter-clatter of the valves and cams, the rat-tat-tat of the small end clearance, the whirring of the cam chain, the tap-tap-tap of the piston slap and the staccato mechanical cacaphony of the lash in the balance shaft and primary drive gears.

Since you suspect the cam chain and it is easy to inspect, start there. Cam chain noise will sound worst at idle and is not power related.

Does the noise decrease when you put your open palm against the clutch cover? Lots of noise is emitted from this point normally.

The breather hose you describe allows the crankcase air displaced by the piston to breathe in and out as the piston goes up and down. It is perfectly normal to observe not only air being sucked and blown through it when the engine is idling but the odd drop of oil may escape too.
 
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EdLennon

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#3
Humai,

Thanks for the reply!

I have never adjusted the cam chain tensioner, so is there a "proper" way to do it? I don't wanna screw anything up if I can help it.

I didn't notice any decrease in noise when I pushed against any parts of the motor (pipe guard, ignition cover, clutch cover).

Ed
 

holeshot

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#4
The cam chain tensioner on YZF is not adjustable. It's an spring loaded tensioner that automatically applies the proper tension.
 
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#6
The levers are known to rattle and jingle quite a bit at idle as they start to wear. Also, if the header is loose it jingles, try putting your foot on the header pipe when you here the noise. Its easy to leave this loose when your changing your oil filter. Also check the heat shield on the header pipe to see if its loose. My levers jingle someting fierce. Im thinking of removing them and putting heat shrink on the end and punch the bolt hole out or someting.
 

MARK IT

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#7
I notice after 2-3 laps at the track mine a 99 starts wistling when i lug it. Felt like it was running hot but wasnt, the bike is Race Tech all the way.
 

EdLennon

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#9
Pardon my ignorance, but how do you check it out. Do you have to pull the whole engine apart? I'm not sure how to check it.

Thanks,
Ed
 
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#10
Originally posted by EdLennon
Pardon my ignorance, but how do you check it out. Do you have to pull the whole engine apart? I'm not sure how to check it.

Thanks,
Ed
To my knowledge there is no service limit on the cam chain, having said that I did replace mine on both my YZFs when I replaced the piston/rings. This was at about 100 hours, at which point my '01 still looked as good as new but I already had the parts...

My thinking was at roughly $34 it made good financial sense to just replace it.

To do so you would need to remove the head cover and cam caps, just as you would if replacing valve shims. You also need to remove the flywheel and (probably) both chain guides, the rear guide bolts to the cases behind the flywheel...

Then you just remove the old chain and drop in the new one.

To ensure that the tensioner is working properly just disengage it with the head cover off and make sure it is putting good tension on the chain, making it taut between the cam wheels, when you release it.

Hope this helps.