My thoughts (which aren't worth more than you paid for them)...

• Typically, the rings on a BMW are just getting going good at that low mileage. However, that does not prove they are perfect, just that they Should Be in good shape. The only real reason rings might be bad is rust in the bore. But, I believe your model came with a Nikasil bore, making rust fairly close to impossible.

• The best test to perform to get you the most/best insight is a compression test. Make sure all 4 rocker arms have free-play at the adjustment point. Pull both carbs loose from the intake hoses. With both spark plugs OUT, but free to spark against the cylinder heads, let the electric starter run the compression gauge as high as it can go. Typically that will take 3-4 cycles to get 90%, and it may then continue to climb a bit for the next 5-7 beats. You're not looking for a specific compression (except that it should be over 100psi), but one might expect 130psi or higher. What you're really looking for is nearly the same compression on both cylinders. If you've got matched compression, then the engine will run and perform smoothly... which is really what a street rider wants.

Rings run about $55 a set which will add another $100 to your job.New rings will need to be matched to the cylinder diameter and "gaped" accordingly. Placing new o-rings and gaskets on the top end is completely within the competence realm of the owner-rider home mechanic. Gaping new rings is one step higher on the technical totem pole.

Hope this helps.

Much appreciated, Wobbly.

Would a ring set from BMW that is matched to the piston not already have the correct gap?

Would a ring set from BMW that is matched to the piston not already have the correct gap?

Rings are matched to fit the cylinder, not the piston. How would the factory know how large your cylinder has grown in 30K miles ??

Thanks Wobbly. It didn't occur to me that my cylinders ("B" Nikasil) could be out of factory spec at 30k. I have had the cylinders off of my '91 RT with double that mileage and they still looked pristine with perfect cross hatching.

It makes it further confusing that there is only one piston ring part number listed for all R100 models from 1981 to 1995 (Nikasil), and it is listed in the piston , not the cylinder section.

Thanks Wobbly. It didn't occur to me that my cylinders ("B" Nikasil) could be out of factory spec at 30k. I have had the cylinders off of my '91 RT with double that mileage and they still looked pristine with perfect cross hatching.

You have misunderstood. Like Scot, I VERY HIGHLY doubt that your cylinders are out of spec. But you certainly shouldn't trust me.

To understand what I'm talking about you'll need to take off your 2018 glasses and imagine things as they were in 1984. Machining in 1984 did not have zero tolerance as is common to parts made in ultra-modern machining centers. Men still ran the machines, not banks of computers as is common today. So EVERY cylinder had small variations in size.

Plus, suppose the bike was in a small wreck in 1985 and one of the cylinders was replaced. Although the 2 cylinders originally on the bike may have be a "matched pair", the replacement made on a different day by a different machinist certainly would be a different diameter !! This is the type real-world mishap that COULD have happened in 35 years of riding, so we have to allow for the possibility of it.

Finally, what is the relationship between diameter (the bore measurement) and circumference (the spacial habitat of the piston ring) ? It is Pi (3.1416). So whatever variations there are in bore, are multiplied by a factor greater than 3 at the piston ring gap !!

So for multiple reasons the factory NEVER knows what your ring gap is going to be. Therefore, it is incumbent upon the mechanic to check that dimension. Did you follow all that ? This is why I said, "Gaping new rings is one step higher on the technical totem pole."

All the best.

Not to confuse the issue, but if I can get on my soap box for a minute...

Long time readers of my responses may recognize a distrust of most people working in motorcycle shops these days. The reason for this is, if you are smart enough to recognize the geometric relationship between bore and circumference mentioned in the last post, can troubleshoot electronics ignitions, program electronic fuel injections, and master a hundred other engine and gearbox building skills, then you are also smart enough to recognize that you could be making $100K per year as an engineer, instead of making $40K per year as a mechanic. The skill sets are nearly identical !!

So on the rare occasions I visit local shops, I'm not surprised to see tattooed 20-somethings posing as mechanics in place of highly skilled 40-somethings that used to be. Motorcycle dealerships and repair shops are simply not profitable enough any more to support that level of acquired skill. I'm sure it exists somewhere, but it is no longer the norm.

This is one reason why it's so important to follow ABC Cannon #6 and do your own work.