Slight Metallic Whirring sound.WR426 dirtbike Engine

[llamaloui]

Hi all,

This is regarding a 2001 Yamaha WR426F 4 stroke dirtbike.

I've recently noticed a slight mechanical whirring sound coming from my engine. It is not a high pitched metallic shriek. Just a continual squeak that comes around every revolution of the engine.
I'm not sure if it was like that when I bought the bike but I only took notice to it over the last 4 days.
It makes the noise when idling. When I rev the engine, the sound increases frequency. I let go of the throttle, the sound decreases back to the idle level.

The bike is kick start only. I noticed a "rough patch" in the kick starter movement path.
Say it starts at 12 o'clock position. At 6 o'clock, it is a full motion of the kicker. I hold the compression lever in and slowly push the kicker down. Around 9 o'clock, there is about 1-2 cm of "roughness". I can feel a slight scrape, maybe due to rough contact somewhere.

I did an oil change and the rough patch was slightly better afterwards.
I checked the filter and it did not have excessive metal frags in it. Just a small amount on the outside of the filter.

The exhaust is fine, no blue smoke during start-up and operation.
Power is still there, responsive throttle, plenty of acceleration when I need it.
The exhaust makes a gurgling sound accompanied by 2-3 "pops" in close succession when I let go of the throttle after a good hard blast. I don't believe this is backfiring (is it?).


I'm not sure if this is from the timing cams/chain or whether the piston itself is worn.

Any advice from the pros?
Is the bike about to blow up?
Is the timing chain slack or are piston seals worn down?
Or is this just the normal operation sound from this type of bike?

I found a youtube vid about cams/valves for a YZ250F. If I need to do a top end rebuild, can I follow the same instructions for my WR?
Hot Cams Installation Yamaha YZ250F - YouTube

Any advice is much appreciated.



Cheers

[Yakka]

Pretty hard to diagnose over the Internet , my advice take it to a Yamaha dealer and get an opinion. I raced a Yzf 426 and it always had what I describe as a howling sound .

[Falcore]

Got access to a stethoscope?

[filbert]

Got access to a stethoscope?

or a long handled screwdriver that you can put your ear against the handle and narrow down the source of the sound.

[llamaloui]

Hello Thanks for the replies

I did the screwdriver method. Its coming from the top end of the engine. After reading several webpages, forums and watching countless youtube videos, I'm very sure its a loosening timing chain.
I speed up the bike, the whirring sound speeds up with it.

It has an Auto Cam Chain Tensioner (ACCT) with it.

Just wondering if the following method is appropriate:
CRF450 Cam chain tensioner release - YouTube

Its for a CRF450 dirt bike, can it be applied to a Yamaha WR.

Can ACCT's be adjusted while inserted to the engine block? Is it better take the entire tensioner off, readjust it then rescrew it to the engine? Or is the video method OK. It just seems so much simpler rather than pulling everything apart.

Say I follow the method in the video, will the impact from the tensioner springing out rattle the chain causing it to get bumped off or out of sync with some cam teeth?


Cheers

[filbert]

If it's a spring loaded tensioner they do sometimes get stuck and you can just back them off and let them spring into the chain again, I usually do it with the engine stopped, if that doesn't sort it you can usually find a manual tensioner for a reasonable price, these need to be adjusted properly and the lock nut set so that it doesn't come loose mid ride.

How old is the engine? Would the chain have stretched beyond manufacturers tolerances? Try backing off and releasing the spring loaded tensioner a few times or even pull it out and inspect/clean it before you get too carried away.

[llamaloui]

OK thanks filbert. The engine is 2001 year. It runs but theres just that noise. Ill try sorting that out over the weekend.

Also, lets say the chain jumped 1 or 2 teeth while I am riding. What will actually happen? Will I stall and will the bike start up again?

[Falcore]

Some will still run.

I know for a fact that quite a few 1098 came from Ducati out a couple of notches on the belt......

If your suspecting this then get hold of a workshop manual and check the timings. If it's still running then chances are you've done no damage yet. Yet being the operative word.

[robbo85]

The poppig sound isn't backfiring, but air injected into your exhaust to burn unburned fuel & NOx gases to meet emission standards... My xt660 does do it, too. If it annoys you, there apparently are ways to block the air line off. But this will change your emissions.

[filbert]

OK thanks filbert. The engine is 2001 year. It runs but theres just that noise. Ill try sorting that out over the weekend.

Also, lets say the chain jumped 1 or 2 teeth while I am riding. What will actually happen? Will I stall and will the bike start up again?

If the chain jumped teeth it would at best change the power delivery to either more off the line or less off the depending which end jumped, advanced or retarded valve timing basically, at worst bent valves and damage to the piston, you would notice either if it happened.

And per previous posts the popping can be coast enrichment to prevent leaving out mixing with air and flashing off in the hot exhaust or air injection for emissions, sometimes it's an exhaust leak allowing air in for the same result.

[llamaloui]

now to check timing

[Helipos]

The poppig sound isn't backfiring, but air injected into your exhaust to burn unburned fuel & NOx gases to meet emission standards... My xt660 does do it, too. If it annoys you, there apparently are ways to block the air line off. But this will change your emissions.

I very much doubt the 426 will have emission control system on it.