mystery vent...

zsnider said:

how do I check that the flywheel is correct?

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Remove the spark plugs. Put the bike into 3rd or 4th gear. Put a long straw in the open plug hole. Turn the rear wheel in the direction of forward motion. Watch the straw and the OT mark on the flywheel through the timing hole. Also watch the valve action at the same time. When the flywheel is at OT, the straw should have moved the furthest out that it can possibly move. You will also notice that both valves are firmly closed. If none of this matches up, then the flywheel has been installed wrong.

zsnider said:

how likely is it that the magneto rotor moved?

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Not that unlikely. If it wasn't secured to begin with. If the two tapers were not cleaned properly. If one or both tapers were damaged in some way. Could be that it's just been this way for some time.

Although I believe the timing will need to be checked once I get this bike running again I don't think it is why it wont start now.

There is something going on with my compression that was not an issue before I replaced my head gaskets.

After replacing my gaskets and starting the bike easily I went for a perhaps 10 mile ride it stalled when I finished the ride and then the next day It It started for a few cycles stalled out and this is when I noticed the white smoke / vapor coming out of the crankcase pressure relief valve (that is what started this thread). and then it just wouldn't start.

After checking the valve clearance again making sure I am at TDC and trying unsuccessfully to start it I spent some time slowly kicking the engine over and listening. I noticed a squishy, squirty pressure sound about every fourth rotation coming from the bottom of the left cylinder at or at least very close to where the cylinder meats the crankcase. I isolated the sound with a tube. there is also a good bit of oil leaking from somewhere in the same area but I cant pinpoint where it is coming from.

Any Thoughts?
~Z

I've never heard of pressure leaking like that from the point where the cylinders meet the crankcase. On my R69S, there was a thin aluminum gasket between the cylinder and case...it had concentric rings impressed into the gasket. I understand there are slightly thicker gaskets as well as paper ones, depending on year and requirements. The thicker ones can be used to lower the compression ratio.

There's generally not a lot of pressure here, just the pressure that's associated with the changes when the pistons move inward and outward. That's the reason for the breather valve and curved pipe...it helps relieve this build up in pressure when the pistons are traveling toward the crankshaft. At most, I would think that you would get oil seepage, but not air escaping at this joint.

Are the nuts tight that hold the cylinder to the crankcase? These are hard to get at...you need the right box wrench to slip in and over the nut. It's impossible to get a torque wrench on them, so I just gave them as good of a grunt as I could muster, without rounding the heads of the nut.

Try removing the dipstick and repeating your test of turning the engine over. Is the squisky/squirty sound gone now? If so, then you're probably looking at something wrong with the breather, that it's not timing correctly with the moving pistons and your building excess pressure within the crankcase. In the long run, that's not good for the seals and I suppose it could have an effect on the way the engine starts and runs.

What Kurt said. A 14 mm open end wrench modified like this can be a big help in getting the base nuts tight.

<img src="http://www.snafu.org/restore/service/4800-mile/p-20030206-161539.jpg" title="wrench for cylinder base nuts">

I check the base nuts whenever I check the valves. Once in a while I'll find one that is slightly loose.

// marc

sweet! I cant wait to bend a wrench!

There is no visible air or oil seepage. If it is the Breather valve where does that live and how do I access it?

It's on the front of the camshaft...#3 on this diagram...

http://www.realoem.com/bmw/showparts.do?model=0214&mospid=48033&btnr=11_2756&hg=11&fg=30

The front of the engine has to come off....the magneto, points, generator, and timing cover. From the diagram, it looks like it resides on the front side of the camshaft gear. Not sure I have any good pictures, but... This picture shows the backside of the timing chest...not the black ring at the top. This is part of the breather mechanism. You can also see the curved pipe at the bottom. Not sure how the pressure/air is routed to the curved pipe. I think that the air is routed through the tunnel that you can see around the left side of this picture.



Here's the front side of the engine after the timing cover is removed. The camshaft gear is at the top. The breather mechanism seems to be run by this black ring affair as it is nested into the front of the cam gear in the two holes that are visible.



Air from inside the crankcase can get around the main center bearing at the end of the crankshaft...the bearing retainer is open at various spots. As the camshaft gear turns, the two openings on the black ring come by the opening in the tunnel that I mentioned. When the black ring open is on top of the opening to the tunnel (barely visible in the picture), air can escape out the curved pipe.