I'm sure the info is here somewhere, but I can't locate it so I'll just ask.  How often should I check the valve lash on my 1985 K100RS? They was adjusted 22K miles ago when I first bought the bike.  I'm about to set off on a fairly long ride this week.  Do I need to find a valve cover gasket and be prepared to adjust the valves, or are they likely to be stable for -- eons?  
I should add she's running very well, but I have no sense of what tightening valve clearances on a K-bike feels like. My old airhead tells me when she needs attention, but the K-bike is a whole different beast.

The best demonstration of valve clearance adjustment is Chris Harris' K100 Valve Clearance Check youtube video.

The exhaust valves are more prone to clearance tightening than are the intake valves..

Go for it. On your bike a simple jo and you should be able to re-use the seal as there's not a lot of pressure on it. Careful of the torque of the cover bolts! The seal gets pressurized with the rubber bobbins around the head bolts; the bolts themselves bottom out and need minimum torque. You have a manual of course.

It's interesting that you raise the question of a manual.  I own a Haynes manual.  Try as I may, I cannot find the specs for the valve clearances anywhere in that publication.  There are paragraphs on many aspects of checking and adjusting the valves, but the only specs. I have come across are those mentioned in the YouTube video by Chris Harris.  He says min./max values are 15mm-20mm and 25mm-30mm for the intake and exhaust, respectively.  Now I know that if it's on the internet, it MUST be true,   but I still would be more comfortable if I had some verification of those specs.
Mr. Harris also says that if the valve clearances are found to be loose one should not do anything about it.  Loose is okay by him.  Hummmm.  I find that to be troublesome advice. There is typically a range of valve lash that is thought to be acceptable. Tight burns valves, loose changes valve timing and theoretically can reduce performance.

Loose will affect performance but should not do damage so no real urgency. Tight will do damage if not attended to.

My copy of the Haynes manual has a "Routine Maintenance" section which starts on p.26. At the very top under the heading 'Specifications/Engine', you'll find the valve clearances stated about 3 or 4 lines down.

I agree. Wise to be cautious. I'm reminded of the Perato Principle which can be loosly applied here to say... "80% of the internet is bullsh*t". In reality that percentage is probably a lot higher. No worries with Chris Harris' YouTube channel tho. He is a well respected 'one-handed' mechanic amongst Beemer DIYers...

Thanks for leading me to the specs in the Haynes manual, Kaptain.  Somehow I never expected that under routine maintenance.  My mistake.  Well, I did have a look at the valves.  It was not a happy time.  The three cylinders I checked all were tight, so I buttoned it up and rode to a shop where someone who can swap the shims could make it right. I'm really glad I did look at them, as I'm about to log many miles on that K100RS.  A blown engine on the lonesome highway would surely ruin my tour.  
Truth to tell, I am surprised to see they closed up in 20K miles.  Honestly, that is something my Airhead couldn't typically do!

"No worries with Chris Harris' YouTube channel...." 

I take it you missed his video on sussing a problem with the forks on an R65 (?).  Chris and his trusty sidekick demo stripping the fork assembly.  They invert it in a vice and remove the fixing bolt on the slider to release that from the fork tube itself.  The oil promptly spills out, runs down the fork tube and onto the floor.  

That does not inspire confidence in his mechanical experience. 

I've no idea why the above few lines are in boldface font.  I've tried to correct that, without success.

Kaptain Holister wrote:My copy of the Haynes manual has a "Routine Maintenance" section which starts on p.26. At the very top under the heading 'Specifications/Engine', you'll find the valve clearances stated about 3 or 4 lines down.

I've also been caught out by Haynes Routine Maintenance section having the data I was looking for. 
(I have 3 Haynes manuals, 2 came with  bikes and one a gift from an ex K owner. You'd think one of them would have had a Clymer for variety!)

Sometimes if you look carefully enough, the relevant section does say somewhere in the fine print to look in the routine maintenance section. Not always, though.

Everything I've done so far, I've found anything I needed in the Haynes manual, but often a pain to find the actual place where the info is. 

Bill

Those wayward specs caught me out too back when I was first looking.

Brickrider2... which clearances were tight? I'm guessing exhaust?? and which pots?
Have you been getting any exhaust popping or backfires?

Experiences from members here tell us that shop mechanics don't know what they're doing with a K and they're expensive. Its an easy job to do yourself and the shim removal tools are easy to come by.

Brickrider 2 - are you sure the clearances are tight?

I checked mine on the '85 K100RS recently - writing them down as I went. Before I got to the end of the exercise I realized that what I had initially thought was a 'tight' reading was simply a case of me not flexing my feeler gauge sufficiently (old hands will correctly identify me as a complete novice in this respect!). I found that I obtained more easily repeatable readings by putting my eye in the plane of the feeler gauge to ensure I had it correctly flexed, then sliding the gauge for and aft (at right angles to the longitudinal axis of the blade)
made for more consistent results. In the end they were all ok

I'm with the Kaptain - rather stuff it up and learn something than have the potential of a professional stuff it up and leave you in the dark

I'm certainly on board with the notion of servicing my motorcycles myself.  I've done that for decades with airheads and Italian motorcycles. I need to find a source for the special tools for the K-bike, then future valve service will be in my hands.  
My check of the valves yesterday showed every valve was tight.  The exhausts were a no-go at .25mm and the intakes were a no-go at .15mm. The latter felt fairly loose with the .10mm blade, so my guess is that they are at about .12mm.  This last minute revelation had put me in a bad situation, given my planned departure in a couple days for an extended ride.  I hastily put the cover on and took the bike to our local shop. 
Reflecting on the bike's history while in my hands, I suspect that the valves were set too tight by a "pro" mechanic when first I bought the machine. I'm confident no damage has been done and at present she runs exceedingly well.  Maybe that would continue during the expected 2K miles I'll ride in the next week or so, but I feel uncomfortable setting off knowing the engine needs attention. Better to err on the side of caution. 
The K-bike head is designed is such a way that seems to call for a feeler gauge that has the leaves bent at roughly a 45 degree angle.  I think an accurate check may be easier using that design.  However, I note that in the Chris Harris video discussed earlier he's using the Wurth single leaves with plastic tabs.  What's the collective wisdom there?  Is one design clearly superior?

Shim removal tools can be had from a few places. They're all roughly around the same price.
Info for Kenneth Lively US
Motorworks UK
Motorbins UK
Motorworks have the shims but you could probably order those from somewhere in the US. 29mm/flat is what you need.

I agree with Rawdon that it can be difficult to get a 'definitive' feeler gauge reading and if you're simply using a method to determine whether a gap is just either 'in' or 'out' of spec, its easy to make a wrong assessment imo because the feeler not sliding in could just mean, as Rawdon points out, that its slightly off angle. The only way to determine for sure is to actually measure the gap. 

As for the style of feeler.... I just use flat ones. But I do admit at times its fiddly to get it to slide in behind the cam.

I use a very simple spreadsheet to calculate the required shim sizes. Makes it easier with no mistakes.

Cheers

The Wurth feeler gauges are available as a set for oilhead and airhead from Beemer Boneyard.  Or you could do what I did, which was to buy a cheap metric feeler gauge set from Sears, separate out the ones I wanted and wrapped some wooden handles around them.  The handles were easy - just square wood with a saw kerf partway down, insert the feeler gauge and glue / clamp in place.  The ones I used were brass and they work fine for a "GO" / "NO-GO" measurement.

I just use a set of feeler gauges and so long as you have 10 fingers on each hand and universal knuckles it all works well