STP Oil additive

For about 4 years or more I have had a grinding sound in the rear end.
If the bike is idling, all I need to do is roll forward a few inches and the grinding will go away.
I have spent quite a bit on mechanics and had a dealer rep say he had no idea. I have put maybe 4 thousand miles on it and wondering if when I change my differential oil in the next few days, would adding STP oil additive in a small amount maybe 2% would it help or would it cause other problems.

NO---STP will not hurt anything or fix mechanical problems.

If your bike is idiling then the final drive is not engaged.

I suspect that the noise you hear may be from the bearings in the Driven Pulley. It wouldn't hurt to pull the DP and add some grease to the needle bearing. The roller bearing in the DP is all but impossible to lube, but you might try to fabricate some type of long syringe to inject grease in that bearing. Also check the bearing in the belt case. Though that one tends to whine, not grind. And the whining goes away when the clutch engages. My 2¢

Wynns do a supplement lubricant for bearings and gears in a small tube try that

https://www.ebay.co.uk/itm/Wynns-Lubricant-Supplement-for-Engines/232510931587?hash=item3622bb4283:g:9L0AAOSwPxRZ07X9&frcectupt=true

Jumper. I really like your answer.
I was never intending to fix anything mechanical. I was only hoping to lessen the sound and friction.
I do not understand your "when the clutch engages part Jumper.

Again, I just wanted to say that this is the best, most helpful forum and grateful for all the feel back.

As veteran of some 90,000 miles plus with 2 purchased new SilverWing---I think your noise is associated with belt/clutches.

As you didn't state age//main. history/belt age, miles makes guessing a little hard.

One easy fix, run engine up 15-20 seconds against brakes.....and see what happens to noise. My first Silverwing required this every couple of weeks. Both bikes I always changed belts at makers chart....and of course used OEM belts.

Ride more.

Hi Bud, this in NOT going to be an issue with your differential, given your problem occurs at idle when none of the diff' componants are turning & so it's pointless using oil addatives, they will not cure it.  Most likely scenario's have already been posted by Tim & John

I'm not convinced with oil additives. If there's a noise then there's a problem. Take the rear pulley assembly off and have a look. Check every bearing you can get a finger to for grinding sensations and also check your clutch drum and pads are good. Have a look at the rear drive shaft for scoring or corrosion. You can check the appearance of all this stuff on this forum or on YouTube.

If the problem turns out to be in the final drive then I don't think any amount of additive will cure it, it'll need looking at but even this job is not as scary as might seem.

If you've been getting away with it for four years then it's obviously 'coping'. Have a look....

johnd, The "Clutch" engages at around 2000 rpms which starts you rolling down the road. If you sit at a stop and slowly rev the engine and watch the tach you'll notice that you start moving at around 2000 rpms. it's a centrifugal clutch not like a clutch on a manual transmission.