Oil in cylinders

[Shades]

Hi i am in the middle of getting my '76 R100RS sorted out and I also have another thread going about pushrod rattle.
But it uses oil, most noticeable on the left cylinder, when its cold it smokes a lot from the left side and when hot it only smokes on hard acceleration. I know smoke on cold start is normal when the bike is left on its side stand but i always park it on the center stand.
The compression is good on both cylinders and runs great. I have had the heads apart and found everything in good shape. So I will change the oil rings. But I got worried when I saw how much oil there is in the cylinders, there are twice as much in the left cylinder as in the right, does this mean there must be something else wrong ? This is my first boxer engine, so maybe I'm just not used to be able to see how much oil there is able to get by worn oil rings.

Oh and the bores looks good with good cross hatching. The piston reads 94.22 so it is first oversize, the left side oil ring is a one piece type and the right side has a spring inside. So my guess is the right side has been changed.

[Wobbly]

It's wild ! And it sounds as if it's not the top end's fault. Not all top end oil comes from rings and guides. Some ideas you might check...

• The level of the oil in the engine may simply be too high. I wonder if you have the correct dip stick ? There are multiple dipsticks for the 247 engine, all different lengths.

• Is your air filter new ? Clogged air filters make the carbs suck oil-laden air from the engine breather that would not otherwise be drawn in.

• Is your breather disc nicked or cracked ? 1976 used a round phenolic disc that often suffered damage. You can replace it with the newer all-metal "reed valve" type.

• Is your breather oil return well clogged ? Just in front of the breather disc is a depression that collects oil mist and returns it to the engine via a small hole at the bottom of the "well". If the well is full of oil, then the oil return hole may be clogged. When that happens, the engine burns lots of oil.

Check those ideas out.

[Zombie Master]

Good stuff Wobbly!

[Shades]

Thank you Wobbly! I have the dipstick that came with the bike, I can tell it once was the same blue color as the brake calipers which makes me think it's the original. By the dipstick the oil level has never been above max. Will look into the different lengths.
The air filter is new, I have yet to check the breather ! I have been busy at work but the reed valve is in the shopping cart with new rings. Will check the well.
I plan on changing the oil rings, they come in sets with compression rings. Should I change the compression rings as well when I am in there ?

[barryh]

I get a little oil in my left cylinder but nothing like as much as your left cylinder photo or even as much as your right cylinder.

One thing I've been meaning to try and never got around to, is simply to route the breather to the exterior on a temporary basis. Depending on the results that might eliminate the breather as a source of oil.

[Wobbly]

I plan on changing the oil rings, they come in sets with compression rings. Should I change the compression rings as well when I am in there ?

As a motorcycle engine builder (about 35 engines in 2016) I really can't see the rings passing that much oil. It has to be coming down the intake. There must be evidence of it in the plastic tubes. But, I've been wrong before !

My suggested order...

1) Rings are really expensive. I wouldn't buy them until you've had a chance to look under those 2 small covers just to the right of the starter motor. That's like a 30 minute job to get in. The old breather valves give so much trouble, you might want to add the newer reed valve regardless... making it the last time ever.

2) I can't see anything saved by adding one ring. Not with the expense of all new gaskets, push rod tube seals, and o-rings for the top end. Then the trouble of cyl honing and head torquing. And if you did hold them back, where/how would you keep them so that they wouldn't be a ball of rust in 2025 when you finally need them again ? Buy them to hold them just doesn't make sense.

[Wobbly]

One thing I've been meaning to try and never got around to, is simply to route the breather to the exterior on a temporary basis. Depending on the results that might eliminate the breather as a source of oil.

We are thinking the same thing. That is suspiciously too much oil for a simple ring issue, unless the pistons are submerged !

However if you think about it, by the time you take off the starter cover and route a new hose to mask the symptom, you would be done faster to simply take off the 5 screws and 2 breather covers and directly attack the cause.

I hate band-aids; I greatly prefer cures.

[robert]

The cylinders and pistons need to be pulled and inspected.
You may find some interesting things there, cylinder bore distortion,
excess clearance, broken or very worn rings. Some 1000cc cylinders
don't do well with O/S boring.

[Shades]

I appreciate advice from people who has done this longer than I have been alive!
I will take the covers off the starter and air filter later today. But one thing I am not sure I understand is how it can be more in the left side than right side when the line from the breather is directed to the right side intake. But yes, I did find oil in the intakes the first time at had it apart (it actual startet smoking after I assembled it, I took it apart because of a weird noise and was afraid it was a bearing) and thought it was the heads since compression readings are equal and reads 145psi but the heads have been done a couple of years ago before I got the bike and everything looks good! That's why I thought rings when it started smoking. But yes, I can see that would not leave oil in the intake.

Man I wish I could say "sorry, have to leave early because my new bike is sick" and figure this thing out. There not much "good weather" left in Denmark.

[Shades]

Forgot to say I checked the rings in the bore and the end gap measured as new. Could the cylinder be distorted but still have good compression?

I am starting to feel silly, I can see in my own picture of the intake that there is oil in the rubber mount ....! So yes the oil must be from the intake. But why would it almost stop smoking when hot ?