Time for Rings

[drreese]

I have a 1977 R100S with 62,000 km and it appears it's time for rings. During my pushrod seal replacement I verified the rings being worn past the service limits. I ordered up some new rings and they have arrived. After reviewing the new rings I now realized there's a top side to the two compression rings. I also noticed the the word "top" printed on both of these rings. The lower oiler ring doesn't seem to have a top or bottom side. The packaging of the rings also have illustrations indicating an orientation. During be research and reading I don't remember any reference to orientation of the rings. ( top side ) I'm hoping to get some feedback and tips to help me during the installation of these new rings. Thanks to all that contribute to this amazing forum. There's so much knowledge shared here, it's truly amazing! Ride Safe.

Additional Ring Photos ; http://gallery.me.com/drreese#100267

[mikeb921]

You will appreciate the benefits of new rings after they're properly run in. Make sure you check the end gap (without piston) in the bore. Check it at top, middle, and bottom of stroke to make sure it's within spec.

Good luck,
MB

[20774]

Not sure if this helps, as it's for /2 bikes. I used this diagram to do the top end on my /2.

http://w6rec.com/duane/bmw/piston/ring.JPG

[carockwell]

There is definitely a top and a bottom side to the top rings, sometimes to the second ring, and usually to the third oil control ring unless it is a three piece style expander ring. There are so many rings out there, its hard to say what you have. You should ask the people who sold them what the ring orientation is.

You need to check the piston top ring groove gap to make sure the top ring has not hammered the piston groove too wide. This is easily done with common feeler gauges. Two thous is good, over five thou and you probably need new pistons (unlikely with your mileage).

The piston ring gaps need to be spaced at 120 degree angles in the bore. I believe Oak has formula for which goes where, but it seems to me you would want the oil control ring at 12:00 if it is one piece, or at 3:00 and 9:00 if a three piece with the expander on top at 12:00. Then stagger the top and second rings from there orienting the top ring towards the intake side of the cylinder.

[108625]

Compression rings have a distinct top side because they are slightly tapered on that side. If you look closely at the cross section of the ring, you'll see the bottom is square, while the top is angled downward from it's outer edge to the inner edge. When the piston is on the compression stroke, or the combustion stroke, the rising pressure of the compressing air fuel mixture or combustion gasses pushing against the upper surface of the compression rings and in turn pushes them outward, against the cylinder wall for a tighter seal.
(Many unmarked rings, installed upside down by those who did not know better, have resulted in rebuilt engines that run just as poorly as before they were rebuilt.)
The oil scraper ring (or ring set) needs to do it's job consistently no matter what stroke the piston is on, so both of it's surfaces are the same.

If you think this is fun, wait until you rebuild a Willy's flathead with four rings, or a Yamaha two stroke with one.

[lostboy]

Examine that oil ring closely-it's the same ring BMW sells and there is a top and bottom. The outside edge of the top scraper has a bevel. This bevel faces up.

[carockwell]

Referring to Oak's top end manual:

1. Third oil control ring has bevel on top edge (one piece design)

Facing the left side:

1.Compression ring at 4:30
2. 2 nd ring 10:30
3. Oil ring (3rd ring) 1:30

Facing right side:

1. Compression ring 7:30
2. 2nd ring 1:30
3. Oil ring 10:30

Left and right sides are when sitting on bike, just like port and starboard when you face the bow of a boat.


Oak's top end manual: Priceless

Sorry I did not post this sooner...