vibration-at what piont does normal harley engine shaking become cause for concern?
 

I been riding over 20 yrs, and sometimes the everyday things we deal with can get overlooked when changes are slow, at least for me, these types of things tend to get overlooked. my question is concerning my '99 road king, first year of twin cam, I bought it used last year with less than 30 rounds on her, now I'm over 50,000 miles,( not a bad year for putting on miles) Idk if the tensioner has been tended to before I owned it? about a week ago, I noticed a deep rumble like vibration after coming out of a hard right curve, ( high speed, hard turn, low and tight-if you ain't scrapping? you ain't riding) these types of corners are a very common thing when I'm riding, this vibration however, is not...I don't know, and wouldn't think, the curve had anything to do with this change in behavior, it just came on at that very moment and hasn't left since, some 700 miles and still feel it? where do I even start? my drive belt has been tighten since, tires changed, and air ride checked and adjusted... my next step is inspecting the primary chain, shoe, and compensator nut, any other suggestions? I really appreciate and welcome all replies...thanks oh, as to topic title, my engine idle & low speed rubber mount jumpin' seems to be getting more and more, things that never come loose are popping up more lately, I do my maintenance often.

Check those cam tensioners. With or without the vibration, at 50k you definitely need to check. Check motor mount, check swing arm bushings, etc. I'd give the bike a once over and check all at 50k anyhow.

The engine/trans is rubber mounted in the frame and the front one is known to partially fail, which can make the bike vibrate. Quite frankly it is impossible to diagnose problems over the internet, much easier in person! So you have two ways ahead IMHO: 1 visit a local indy to get a diagnosis; 2 start doing some preventative maintenance yourself. Of those #1 should get you closer to a proper solution than #2 will, although you should get there eventually - or strike lucky!

I recommend you replace front and rear mounting rubbers, as well as the swingarm cleveblocks. Buy a factory service manual to learn what is involved, to see if you want to tackle it yourself.