OK, I bought a used 400EX, which seemed fine. At my first oil change on it, I went from unknown to Mobil 1 20w50 motorcycle oil and a Wix filter.

Afterwards I picked up a loud tap/clack/knock... very singular sounding.
Sounded like a car on a cold morning, but just coming from a single thing.
It would do it on a fresh cold start (summer).
I could make it go away with a throttle blip just the right way.

I tried a lot of things... I went over the valve adjustment, did my best to check the decompressor, tried race fuel, no airbox lid, etc... I tried locating the source with a wooden sounding rod and could locate and hear everything but...

I finally gave up and drained the Mobil 1, thinking maybe it was an oil issue. I replaced it with Valvoline ATV 10w40.

Strangly, I did get surprising results from that. It seemed to go away completely. That went on just a bit and then now, I hear it sometimes at random at startup. I'm puzzled.

I do know for a fact I am running RICH thanks to the guy who did the jetting, and from the looks of the top of the piston it may have been rich quite a while before that work... it's black, probably with carbon I guess.

So.... I plan to work on my carb soon... for one to get it right, and two in order to rule out any sort of weird clatter that may be caused from fuel delivery.

I also want to see what I might be able to do about running something through it to get some carbon out.

Somewhere along the way I also want to pick up whatever I need to check the compression.



I have a few ideas of things it could be, but I'd like to withold those so I don't "lead" anyone into responses. I'd like to get a true idea of what some of you might think the source/cause of this noise is.

Thanks to everyone in advance.

 

It may be piston slap, or loose timing chain, or worn timing chain guides.

 

<div class="FTQUOTE"><begin quote>Originally posted by: Ernie660R

It may be piston slap, or loose timing chain, or worn timing chain guides.</end quote></div>

OK, so you got most of my thoughts right out of the gate, so I'll add one more to that...

Wrist pin








Any other ideas anyone?

 

Wow... I didn't realize it was near this dead in here.

I can hear the cyber crickets chirping I think............................

 

Yep gets that way at times.

 

run some seafoam through it

 

Here... listen to it for yourself...

http://www.youtube.com/watch?v=Ep3pi9K-Fn0

 

sounds like the timing chain to me. easy way to tell is pull the tensioner out and then see if it goes back in. theres a lil screw in the middle u remove and put a small flathead in to retract the plunger, so if u can install the tensioner WITHOUT retracting the plunger ur chain is ready to be replaced. I just changed one in a 400 ex a month ago and it sounded real similar. Its not a hard job but u do have to remove clutch cover clutch and oil pump to change it.

 

<div class="FTQUOTE"><begin quote>Originally posted by: 270quadsportguy

sounds like the timing chain to me. easy way to tell is pull the tensioner out and then see if it goes back in. theres a lil screw in the middle u remove and put a small flathead in to retract the plunger, so if u can install the tensioner WITHOUT retracting the plunger ur chain is ready to be replaced. I just changed one in a 400 ex a month ago and it sounded real similar. Its not a hard job but u do have to remove clutch cover clutch and oil pump to change it.</end quote></div>

Yeah, as you can see there, with my header, it's impossible to get in there and check the plunger. So yesterday I had the carb off going through it and checked the plunger while I had open access from the top.

The plunger is good... but when re-installing it fully extended, it lacks less than a quarter of an inch of going all the way in without any effort.

So I think the noise could be chain clacking from the slack.

The one thing I don't fully understand is why changing to another type of oil really hushed it up a lot. The video is with the Valvoline ATV. With the Mobil 1 V-Twin, it was constant until the engine got hot.... only thing I can think of to explain that is that then engine rotated more freely with the synthetic, causing more slack noise.

The next thing I don't understand is why it goes away after the engine gets hot. Maybe more of the same concept... except then it's a piston up to temp and expanded?


Beats me.


Overall though, I really have a hard time seeing me go in like that, and just do the timing chain.

 

next time use stock honda oil filter, and use honda oil, your not racing obviously keep things stock

make sure you didnt install the oil filter backwards, that would ***** your engine completly, and you might also have put to much oil in

with oil filters there is a rubber gasket on one side, and that faces outwards towards you

read this article

http://www.atvriders.com/articles/oilchange400ex.html