Identifying weird engine knocking/rattle

[yves_dj]

Hello to the fellow gs500 riders. Being that this is my first post on this forum, it has helped me a lot with my bike so I'd liked to express my gratitude to the community of this forum. I've done lots of work to my gs, and this couldn't be true if this forum didn't exist. Having said that, I now came across a problem which worries me a lot.

Video link:
https://www.youtube.com/watch?v=acr8gw95FDY
I think it's obvious to hear throughout the video.

Description of the sound:
It seems to come from the crankcase. I used a long hex key as a stethoscope and I'm pretty sure it originates from there. It's a loud rattling sound.

First occurrence of the sound:
A while back, I rode my bike back from work. It seemed to die when in low revs. One cylinder wasn't firing anymore below around 4k revs, so I was pretty sure it was a carburation issue. I began the work to rectify this problem, but some stuff happend so the bike sat still for 2 months. The valve cover was off for that period (as I decided to check that as well, I was 12k kms behind on that service) and the carbs were pulled out as well. I finally was able to rebuild the carbs and check the valve clearance, the bike fired up and all was well. I rode it for 300 km and the sound appeared in that time and it got progressively worse.

State of the bike at this moment:
I thought I'd change the oil, filter and sparkplugs to see what that did, as it had been sitting exposed for a while. When that was done, I started the bike with choke and now it just wants to die. It climbs to 3k revs, makes horrible sounds and drops in revs (on choke) overtime. I turned the choke of and it fires for a while below 1k, and dies.

Few remarks:
Bike is from 2004.
The carbs weren't all too dirty, but maybe one of the jets were clogged. While disassembling the carbs, I noticed that the pilot screws had no washer and o-ring, soooo maybe it's turning out of spec? I will be checking the amount of turns at some point.
Carbs are not checked for synchronization at this time, I didn't touch the screw but the carbs were separated during overhaul. (fuel t-piece broke when removing hose)
Intake boots were not replaced.
Valve clearance check resulted in 1 shim changed (clearance went from 0.03 to 0.08). The others where at 0.04mm.
Bike has been in 2 low speed, low slide crashes resulting to oil leaks from the crank case lids (no crash bars), this has been fixed a while ago.

I searched around for a while and thought maybe it was the cam walk, but holding the hex key on the valve cover proved to me that the sound didn't come from there. (at least I think it doesn't)
Could somebody take a listen to this and guide me into the right direction? I couldn't stand parting with this bike as I did a lot of work to it. Or even making it blow up

Thanks in advance
Yve's

[herennow]

Very hard to tell form phone videos. All the base is gone.

It does not sound like my cam walk. It does not sound like main bearing rumble. cams chains are more slushy sounding.

I'm thinking a tappet noise or else a misfiring problem, listen to whats coming out of your exhausts.  An old trick for misfires is to hold a piece of cloth (bandana if you live in the US, handkerchief if you live in the UK) so its taught  over the end of the exhaust, you will see it move very regularly if all is good.
If misfiring you will see it move irregularly. Also listen for leaks around the exhaust headers. You should remove and inspect those bolts every year.

[yves_dj]

Thanks for the great tip herennow, I'll be trying that out today.
I did loose some bottom end grunt so I might just have a leak somewhere.
The headers should be good as it has been to the dealer a few months ago, and they found a leak there. So I'm suspecting the boots between carbs and engine, or boots from the airbox side, as they did look like crap
Will be syncing my carbs as well.
I'll post an update ones they are replaced.

[herennow]

If it went to the dealer all bets are off.... They can break anything those guys...