98 R1100GS motor rattle at light load

Hello, my 98 R1100GS has a slight rattle at idle and light load that seems to be worse when it gets warm. The bike has 54K miles and I just upgraded the cam chain tensioner in hopes it would go away. I know diagnosing motor sounds over the internet is almost humorous but I was just wondering if maybe this was common. For reference, my 99 R1100GS with 81K miles does not make this sound so that is what got me wondering since obviously they all don't do this. It is not in the head as I know what the cam chain sounds like, it seems deeper in the motor and is not consistent. Almost sounds like a marble rolling around. Maybe the front timing chain? It has done this for the 4K miles I have owned it and I thought maybe it was just a BMW thing, but then I got the other 1100 and didn't hear it and got me wondering. I'm not real worried but I can;t help but wonder what it could be. Thanks

Hello, my 98 R1100GS has a slight rattle at idle and light load that seems to be worse when it gets warm. The bike has 54K miles and I just upgraded the cam chain tensioner in hopes it would go away. I know diagnosing motor sounds over the internet is almost humorous but I was just wondering if maybe this was common. For reference, my 99 R1100GS with 81K miles does not make this sound so that is what got me wondering since obviously they all don't do this. It is not in the head as I know what the cam chain sounds like, it seems deeper in the motor and is not consistent. Almost sounds like a marble rolling around. Maybe the front timing chain? It has done this for the 4K miles I have owned it and I thought maybe it was just a BMW thing, but then I got the other 1100 and didn't hear it and got me wondering. I'm not real worried but I can;t help but wonder what it could be. Thanks

Morning SmokinRZ

That type of internal noise is very difficult to find even when working standing over the bike.

The noise that you describe is consistent with a front accessory drive chain rattle, or even a R/H side cam chain rattle.

The good news is that a number of the BMW Boxers do make a similar rattle & you never hear of any actual failures.

I guess if you can use a mechanics stethoscope, or piece of hose to your ear, to locate the exact point of rattle inside the engine then we can help you solve it. But without knowing the point of origin we are guessing at ghosts.

If it were my bike I would try my best to locate the noise's location inside the engine then work from there. If that is not possible then start by shimming the R/H cam chain tensioner spring to see if that effects or eliminates the rattle (caution: don't shim to the point of spring coil bind when in use)

Then, at next valve adjust, use a strong light to look at & inspect both cam chain guides on each side to look for excessive wear or broken guide tips.

If the above doesn't work then either live with the noise or pull the engine front off & carefully inspect the front chain for stretch, look (very carefully) for chain contact with the engine case, & replace the front tensioner parts. (sometimes even all that won't eliminate the rattle).

The noise probably isn't a big deal UNLESS it starts getting worse. If it keeps getting worse then you will probably have to find it & address it.

Thanks DR. I just had a friend listen to it that chased a similar rattle on a R1150 GS. He replaced the front accessory drive chain and tensioner parts to no avail and he said this sounds similar. I'm not going to worry about it now unless it gets worse.

Quick question: What octane fuel are you using? It could be detonation causing pinging from running low octane or possibly high compression from carbon buildup causing the pinging..

You might also check Rocker Endplay next time you adjust valves.

Instructions here (you'll have to register and be signed in to download):

http://advrider.com/index.php?resources/orepad.42/

At light load, I would consider a rattle at the throttle bodies. Could be not in sync, or a worn shaft. Worn shaft and bushing would need somewhat high mileage.

Thanks to everyone everyone for the replies. As usual, I think DR has the diagnosis. My 1150 buddy thought it was similar to his accessory drive chain noise also. I run 92 octane at 500 feet above sea level, plus it doesn't sound like pre-detonation. I've heard bad throttle bodies and you can play with the cable wheels and get them to stop or change pitch and mine are fine. At this point I'm not going to worry unless it gets worse.

And I will check the Rocker Endplay next time I do a valve check. Thanks for the link James. Got it downloaded.

And I will check the Rocker Endplay next time I do a valve check. Thanks for the link James. Got it downloaded.

Afternoon SmokinRZ

Rocker arm end-play rattle is more at low RPM & idle, by the time you get to part throttle & higher RPM's the valve action is so fast that the rocker arm doesn't have time to slide or click.

If you adjust your rocker arm end play be careful as you can't get a feeler gauge around the back side so that could be the tight spot. If you reduce the rocker arm end play to the point that it starts sticking when hot (gets lazy) then you can hang a valve just long enough to have a piston kiss it. (do not set to minimum end play using a feeler gauge).

Personally I use a dial indicator to set rocker arm end play as that shows ACTUAL rocker arm movement regardless of any hidden tight spots.