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Sudden Engine Noise

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Before I take my 2002 520 EXC to a mechanic, I thought I'd check in here.

While out riding yesterday, it suddenly started making a lot of noise from what seems to be the top end, but I'm not positive. Power seemed fine, just the noise, and it came on suddenly. I've checked the valves, and they are OK. I also checked the cam chain tensioner, and it has a few clicks left.

So what next to check? Bike starts up and idles just fine. Just real noisy, and the noise coincides with RPMs. Pulling in the clutch has no effect on the noise.

Odd part is that I adjusted the valves a few weeks ago, and afterwards, noticed the engine was noisy. So I rechecked, and the exhaust were way loose, so I corrected them, and the noise went away - until this last ride. Not sure if that has anything to do with anything.

So what to check next? Or do I just take it in to the shop.

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How many hours on the engine? Is it possible that the valve adjustment nuts are getting loose ?

My buddy just recently had to tear down his 525. The last time he changed his air filter, it was not sitting proper and let in some dust. Chewed the rings and valves real good. Cylinder needs to be recoated too.

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How many hours on the engine? Is it possible that the valve adjustment nuts are getting loose ?

My buddy just recently had to tear down his 525. The last time he changed his air filter, it was not sitting proper and let in some dust. Chewed the rings and valves real good. Cylinder needs to be recoated too.

The valves and adj nuts are fine. The engine has 140 hours since I bought it used, so it could have many many hours on it. I'm changing the oil now to see what may be in the steel filters. As for the air filter, I'm pretty good about sealing the filter with a heavy load of grease.

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Do you know if the cam sprocket has been updated to the new style. The old style had a bolt and nut for the ADC that would fall out. It would usually cause some serious damage when this happens. I would think it would be harder to kick start and the electric start would have a hard time turning the engine over because the auto-decompression would not work correctly.

Also as mentioned, the lock nuts on the tappets have been known to come off.

Could be a cam bearing going out.

I would say you need to pull the valve / cam box off and inspect before more damage is done.

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Do you know if the cam sprocket has been updated to the new style. The old style had a bolt and nut for the ADC that would fall out. It would usually cause some serious damage when this happens. I would think it would be harder to kick start and the electric start would have a hard time turning the engine over because the auto-decompression would not work correctly.

Also as mentioned, the lock nuts on the tappets have been known to come off.

Could be a cam bearing going out.

I would say you need to pull the valve / cam box off and inspect before more damage is done.

The sprocket has been upgraded. I think I may start with the cam and bearing. But would that go out instantly? I'm just confounded that it was an immediate transition to the noise. All the sudden, it was there.

Oh, and I changed my oil, and found some metal shavings in the small screen. Not a lot, but I've never seen them in the screens before. None in the long screen. Is that bad news?

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I have seen two 02 rfs with a broken inner exhaust valve springs. changed in 03 and up with bigger wire diameter heavier springs. I threw away several sets of those I took off customers engines during rebuilds. the fine metal in the bottom filter is probably the thin metal valve seal on the valve stem that the broken spring rubs on it. happened to my wifes 453 and a 400 I rebuilt that the piston hit the valve. destroyed the top end and rod. I have the parts to fix yours as do others but I also have the used/new parts to rebuild the whole engine. I am normally less than 50% of the dealer prices. doc bob

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I have seen two 02 rfs with a broken inner exhaust valve springs. changed in 03 and up with bigger wire diameter heavier springs. I threw away several sets of those I took off customers engines during rebuilds. the fine metal in the bottom filter is probably the thin metal valve seal on the valve stem that the broken spring rubs on it. happened to my wifes 453 and a 400 I rebuilt that the piston hit the valve. destroyed the top end and rod. I have the parts to fix yours as do others but I also have the used/new parts to rebuild the whole engine. I am normally less than 50% of the dealer prices. doc bob

Where are you located, Bob? Also, would that cause the noise to suddenly come about?

Thanks.

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Where are you located, Bob? Also, would that cause the noise to suddenly come about?

Thanks.

bad juju. I am in san juan capistrano. seriously just fatigue. hard to blame ktm for breaking a 7 year old part. bring it down. doc bob

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I'm a new KTM owner (05 450EXC) but my previous bike was a 400 Husaberg which shares the same basic top end design with the KTM. My Hus deveoped top end noise very suddenly and it was due to one of the exhaust cam-follower rollers letting go. The KTM has a milder cam grind and therefore can get by with lighter valve springs so I believe this type of failure is rarer on KTM but it is worth checking, espcially given you don't know the total hours on the engine. It's difficult to check without pulling the valve cover off.

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Hi

Check the right crank nut.

When its loose it makes noise it left hand threades

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Have you checked anything since you noticed the noise?

I would check the valve clearences again- that might tell you something-

then I would check the crank nut.

If neither of those show any symptoms I would take the cam cover off and start inspection of cam bearings guides and rocker assembly and verify all aplicable updates exist.

taken from FAQ (thanks to Dave Hopkins)::worthy:

Chapter 4: Updates

00 bikes should have the water pump impeller changed to a newer one

00-01 bikes should have the cam bearings replaced

00-02 bikes should have the cam sprocket replaced with 03 or newer

00-02 bikes should have the lower cam chain guide replaced with 03 or newer

03-05 450 SX usually need valve guides

All 525SX should have valve springs upgraded.

Any should have the two 6 x 55mm bolts on the cam cover that locate the rocker shaft upgraded to hardened bolts!

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Have you checked anything since you noticed the noise?

I would check the valve clearences again- that might tell you something-

then I would check the crank nut.

If neither of those show any symptoms I would take the cam cover off and start inspection of cam bearings guides and rocker assembly and verify all aplicable updates exist.

taken from FAQ (thanks to Dave Hopkins)::worthy:

Chapter 4: Updates

00 bikes should have the water pump impeller changed to a newer one

00-01 bikes should have the cam bearings replaced

00-02 bikes should have the cam sprocket replaced with 03 or newer

00-02 bikes should have the lower cam chain guide replaced with 03 or newer

03-05 450 SX usually need valve guides

All 525SX should have valve springs upgraded.

Any should have the two 6 x 55mm bolts on the cam cover that locate the rocker shaft upgraded to hardened bolts!

00-02 bikes should have the cam sprocket replaced with 03 or newer

00-02 bikes should have the lower cam chain guide replaced with 03 or newer

^ That also applies to select 03 models. I know because I have one.

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00-02 bikes should have the cam sprocket replaced with 03 or newer

00-02 bikes should have the lower cam chain guide replaced with 03 or newer

^ That also applies to select 03 models. I know because I have one.

Thanks for that. I'm taking it in today. I think it's got to be the cam bearing or bolt that holds the sprocket on. I ran the bike hard one ride when the exhaust valves were too loose (mis-adjustment), and I think that may have led to the failure. I'm not too versed in taking the head off, so I'm leaving that to Factory Wrench in Redondo Beach. I'll update on what it is...

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The decompressor bolt that everyone is talking about is on the top left of the sprocket in this photo

IMG_0223.jpg

Here it is from the back side

IMG_0224.jpg

You should also replace the cam cover bolts, see here:

IMG_0231.jpg

They are prone to breaking, notice the grooving on mine.

IMG_0227.jpg

I am currently in the process of fixing my cam gear before it has broken!

I am not quite sure what I am going to do. I am considering 3 options: TIG welding the bolt & nut in place so it won't come loose, taking it out & reassembling with red loctite and staking the end of the bolt over, or updating to the late 03 piece.

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Well, it was the cam sprocket bolts that were loose, so no major repair.

The confusing part is that I thought I had the updated sprocket, which leads me to the next question: since the bolts were just loose and did not fail, could I have the updated sprocket? It was KTM Santa Monica that claimed to install the updated sprocket, but they're idiots and I don't trust their work.

Was the original 01-02 sprocket victim to loose bolts or failed bolts?

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Well, it was the cam sprocket bolts that were loose, so no major repair.

The confusing part is that I thought I had the updated sprocket, which leads me to the next question: since the bolts were just loose and did not fail, could I have the updated sprocket? It was KTM Santa Monica that claimed to install the updated sprocket, but they're idiots and I don't trust their work.

Was the original 01-02 sprocket victim to loose bolts or failed bolts?

The problem with the bolt on the old style cam sprocket was not the bolts that hold the sprocket on. It was the bolt that went through the sprocket for the ADC. My guess is when they updated the sprocket, it did not get torqued properly or no loctite.

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