I'm experiencing some top end engine knocking on my 97 GS500 with 21k miles.  The knocking only occurs under acceleration and seems to get worse as I accelerate.  I can hear the knocking, but it is quieter, if I rev the engine in neutral with the bike on the center stand.  So far I have checked the following:

1.  Cam chain tensioner - removed it from the engine and verified that the spring-loaded arm is moving smoothly and the spring is not broken.  I wound the coil spring tighter (as Srinath suggested in other posts) but the noise is still there.

2.  Removed the valve cover and turned the engine over by hand to see if the cam chain went loose at any time.  I pressed on the chain section between the cam gears during this test.  There were some parts of the rotation that had the chain slightly tighter, but the chain never lost tension.

3.  Verified oil level is correct.

4.  Chain is not rubbing against center stand.

5.  Had two bolts missing where the exhaust attaches to the cylinder head due to the previous owner snapping bolts off in the cylinders (thanks buddy!  ).  Drilled and re-tapped holes, there are now 4 bolts holding the exhaust to the cylinder.

6.  Checked stator, no magnets are missing or loose.

7.  Spark plugs are tan-colored.

8.  87 octane fuel in tank.

My last idea is to install an APE manual cam chain tensioner.  My thinking is that the cam chain is looser than the automatic cam chain tensioner can compensate for.

I'm running out of ideas, please help GS guru's!   

What are your valve clearances?

Quote from: bergj1986 on June 21, 2012, 07:02:18 PM
5.  Had two bolts missing where the exhaust attaches to the cylinder head due to the previous owner snapping bolts off in the heads (thanks buddy!  )

Does this mean you've been running with only 1 exhaust header attached? Possible it could have damaged the exhaust valve and your hearing a byproduct of that.

Can you have someone rev the engine while you listen? Could it be coming from the bottom?
I had noise. Thought it was cam shaft noise.
until.....
it got REALLY REALLY BAD and  the engine got REALLY HOT.
It was the bearing on the engine crankshaft counterbalance. Symptoms are kind of what you describe. Sitting on the bike I thought it was from the top. Had I known better, I would have listened for the noise while someone else was on the bike. I might have found it came from the lower front. The counter balance was banging the inside of the case due to a worn bearing. When the bearing completely went - well, it REALLY banged the inside of the case. (See thread on "Junior's Demise").

adidasguy, what did you have to do to replace the crankshaft counter-balancer bearings? Where are these located?

Dizzledan, the bike was not run with one exhaust header attached.  The exhaust headers should be attached to the cylinders with (2) bolts for each side, a total of (4) bolts.  The previous owner snapped off one bolt per header so each header was attached with one bolt instead of two.  After I drilled out the broken bolts, retapped the hole, and installed new bolts, the the exhaust note did not change.

Quote from: bergj1986 on June 24, 2012, 09:33:18 PM
adidasguy, what did you have to do to replace the crankshaft counter-balancer bearings? Where are these located?

Couple guys from the GS500 Club came over and we built a new engine from parts of 4 engines. Defective engine: case is probably toast because where the bearing went - well, it wasn't there anymore so the case got ground down in the 4 miles to get home. By that time, anyway, the lower case was probably junk.

Here is where it is:


With the washer and bolt off:


This video shows it clunking. And you get the idea of the sound.
http://www.youtube.com/watch?v=Atq4nKfh7kg&list=PLD69FF46ABA0D8D4B&index=4&feature=plpp_video

Thanks!

When your counter balancer bearing was shot, did your engine knock at idle or did it only knock when under load?  I think if mine is defective, I will source a replacement engine.

The banging varied. Before complete failure, it would come and go depending on rpm and load. It is a counter balancer, so it has a mind of its own.
After total failure, it was constant.

If you haven't had a total failure like I had, you can replace it. You would need to crack the case to insure all the oil ports are clean. A clogged one will make that bearing eventually fail from lack of lubrication.

Check the oil for metal dust and chips. Drain a little or suck a little out and pour through a filter. A black pig mat works or a blue shop towel. Dark color makes metal show up easier.
Though metal in the oil would indicate a problem exists somewhere - could be other than the counter balance bearing.

The interesting thing on this type of failure is the engine still ran and idled fine. Still had power. Since the counter balance is somewhat a non-critical part, then engine was still running great. But it was so noisy it must have freaked out people as I rode home.

If I had to vote, I'd say check the counter balancer bearing as well.  These motorcycles seem to be suseptible to this failure.

Yep - and I wonder how long it took for it to get this bad: