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What kind of motor are we talking about here (I don't recall it being mentioned). The drainback hole for the breather in the cavity towards the front of the motor wasn't present in the /5 generation if I remember correctly.

Also ... the bulletin cited is for the Nikasil barreled engines - and even for those I've certainly never experienced a breakin so bad that it would really aggravate the venting system.

I still suspect the RMS.

John Falconer wrote:What kind of motor are we talking about here (I don't recall it being mentioned). The drainback hole for the breather in the cavity towards the front of the motor wasn't present in the /5 generation if I remember correctly.

Also ... the bulletin cited is for the Nikasil barreled engines - and even for those I've certainly never experienced a breakin so bad that it would really aggravate the venting system.

I still suspect the RMS.

In the first post, the OP said it's original '77...metal crush washer on dipstick and drain hole in breather system.

The bulletin is dated 1990, but the point that ring break-in is an extended process still applies. By re-honing, the break-in process was essentially re-set...~300 miles into it and there's oil getting blown out of the dipstick. I'm simply suggesting that the description is a perfect recipe for "too much" blow-by during the combustion process. AND...clearly the dipstick is not sealing like it should...

My advice was based on 1) taking care of the obvious (the dipstick is not sealing like it should...fifty cent solution and maybe a change in technique (using the pliers to tighten it))...2) checking something that isn't likely, but is free and easy (the drain hole)...and 3) having some patience and allowing the rings to seat and settle before jumping too any expensive or time-consuming conclusions. That's all.

Nothing wrong with doing the obvious, but, before I'd do anything serious, including the re-hone that is already done, I'd do a leakdown and make sure that it's really a compression leakage issue. I know, I can't imagine what else it would be, but better to know than to chase shadows. Once you're sure, then you can apply the patience technique and see if it clears up with more miles.

"AND...use the pliers in the toolkit to tighten and loosen the dipstick (as per BMW)...the metal dipstick washer can and does seal well if done according to Herr Hoyle."

I wish to know how many of you are tightening your dipstick with pliers? We need to count you.

How many of you have ever heard this suggestion?

I wish to read this advice in any official BMW literature.

How come the rest of the entire series of BMW didn't leak at the dipstick when they weren't tightened up with pliers? Was that just luck?

Mine has an o-ring.
No pliers.

Thanks for all the input. It was bugging me to no end, so last night I pulled the jugs. On the left side the ring gaps were all aligned & there was obviously a good bit of oil ahead of the piston, some pooled below the intake valve. Plug was oil fouled of course.
On the right side, the ring gaps remained evenly distributed.
As for the cylinder bore, not knowing what grit hone was used, it really seems way too light as the walls look faintly "scratched" and are quite smooth- these are iron liners. I'll make a phone call about this later today to gather more info. I almost feel I could give these more tooth by hand with 40 grit sandpaper than they have currently...


John Falconer- why do you suspect RMS?

I suspect the RMS because the partial vacuum created in these motors by the one-way action of the breather valve is actually quite significant when all is working properly. In my experience the part that most often prevents the intended vacuum is the RMS - and when it is leaking the engine often makes a "honking" sound at low RPMs.

lrz wrote:Thanks for all the input. It was bugging me to no end, so last night I pulled the jugs. On the left side the ring gaps were all aligned & there was obviously a good bit of oil ahead of the piston, some pooled below the intake valve. Plug was oil fouled of course.
On the right side, the ring gaps remained evenly distributed.
As for the cylinder bore, not knowing what grit hone was used, it really seems way too light as the walls look faintly "scratched" and are quite smooth- these are iron liners. I'll make a phone call about this later today to gather more info. I almost feel I could give these more tooth by hand with 40 grit sandpaper than they have currently...


John Falconer- why do you suspect RMS?

Ring gaps are not pinned in place, so it is normal for the rings to migrate out of the original location at assembly time. It would be very unusual for a piston with gaps offset to be found in line upon disassembly later, but it is possible.

If you wish to stagger them, then ignore the usual advice of 120 degrees and use 180 degrees, as that is what would require the gas to travel the most to get into the crankcase.

Whatever you do, don't use a ring compressor to install the cylinders. The cylinders come with a ring compressor chamfer machined in the base.

That is just general advice, as like John F. I too think you have an issue with the rear main seal. In my/our experience over pressure in the crankcase is caused by the faulty RMS at least 90% of the time. I would start there.

While we are on the subject of rings, I seem to recall reading somewhere that piston rings will rotate as fast as one RPM when the engine is at full speed.

Is that true, or did I just make that up? Perhaps it was valves.

Duane-it was actually on your site several years ago I read about spacing ring gaps! Certainly having them aligned is not good, though. No ring compressor-just thumb nails.

I do have a RMS still in the bag from replacing the oil pump o-ring as the RMS was not leaking and looked to be fairly recent at the time. I don't mind doing it as time allows, but was curious why it would seem to be the culprit beforehand. There is no associated "honk" sound or oil on the shelf at present.

One thing I will say, I totally dislike removing the starter from these bikes. I say this in reference to accessing the breather valve. The fiber disc on there I replaced not too many miles ago.

Now, some of you wont like this but in the interest of full disclosure I submit the following: my OCD tendencies sometimes cannot be subverted & I need to streamline garage storage space asap so I did, in fact, use 36 grit paper by hand to "crosshatch" earlier this a.m.
Ultimately, I don't think it can hurt-famous last words.
The fellow w/the ball hone offered that it probably was a bit undersized for this bore diameter but since it was a favor, he did what he could. I simply didn't check as my buddy had the barrels on by the time I arrived-his thing is Brit bikes, btw.

So, it's reassembled & I'm about to start it up, then into winter storage...