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justoneoftheguys wrote:So the condensing chamber is companion to the blocks that have the crankcase vent located at the front?

Maybe I need some help with semantics and definitions. My /7 has the crankcase vent (breather valve?) at the right rear of the starter cavity. The oil mist that comes out moves slightly forward and enters a small well where the oil mist can settle out and drip through a small hole in the bottom of that well. Then the remaining oil mist moves forward through the cavity in the block and then exits up by the starter on the right front of the starter compartment. It then goes into the black hose which routes back to the right carb.

How is that different than what is quoted above?

Kurt in S.A.

Rob's photo shows a "starter housing" who's interior sides are roughly square.
The top of the engine case which will be approximately a horizontal surface, though slightly convex,
and each side rises vertically from that surface.

The post '77 Type 247 will have the right (dipstick) side being the same,
but the the inner left side of the casting will be at @ a 45º angle creating a "chamber"
between it and the exterior vertical cast surface.
The breather valve will be to the rear of this chamber,
and the hose venting the case to the front of that chamber,
the chamber being between these two and filling that side of the interior of the "starter housing".
The venting hose then extends from the vent at the front,
the length of the chamber, and to a fitting in the airbox.
The fitting then distributes the oil to one or both carbs.

An "old school trick" to reduce the amount of high speed-rpm oil blow-by into the carbs
was to "stuff" this chamber with a coarse brass wool
that would, in effect, trap the oil vapor to condense in the chamber
I would not recommend this procedure.

Perhaps this poor photo will help to explain...

The block on the left is the later style with the condensation chamber (1978 R100S)...the block on the right is the earlier style (1975 R90S).

** The breather valve is located in the same place on all the engines...at the rider's right, rear of the starter cavity.

** On the early engines (again, the right block in the picture), the vapors come through the breather valve and immediately exit rearwards to the intake tract. The blue circle is the right side drain hole that has been mentioned previously.

** On the later engines (engine on left), the vapors come through the breather valve...the breather valve has a different style cover that steers the vapors FORWARD...and into the condensation chamber (the yellow circle) where the vapors condense and can drain back into the engine via a tiny hole (the yellow dashed line). The remaining vapors exit out the front of the condensation chamber...through a hose (the red arrow...the hose is missing in the picture) that wraps around the starter and into the intake tract.

** If you go back and look at Rob's photo, you'll see that it is similar to the R90S engine, but the hose exits straight UP as opposed to straight BACK. Rob's is the revised breather system that allows some of the vapors to condense and fall straight back through the breather valve.

Hope that helps...

It looks to me like the condensation chamber system is superior.
Type-248's got ripped off!

I vented mine to atmosphere long ago because I grew weary of oil dripping on my boots from the intake tubes.

Thanks quinner (woof!).

I think that once the engine is fully warmed up (20-25 miles) there will be no more condensing going on in the chamber.

George Ryals wrote:I think that once the engine is fully warmed up (20-25 miles) there will be no more condensing going on in the chamber.

Perhaps, but my casual observation is that the "chambered" system dumps a little less oil into the intake tract(s). I doubt if there is ever any real condensing going on...I believe the vapor remains a vapor. The random bits of splashed oil that might get blown past the breather valve are another story...expecting the drips to return through the breather valve is a dodgy request...tipping them over the edge into a small chamber with a hole has a bit more hope...maybe?

the quinner wrote:

George Ryals wrote:I think that once the engine is fully warmed up (20-25 miles) there will be no more condensing going on in the chamber.

Perhaps, but my casual observation is that the "chambered" system dumps a little less oil into the intake tract(s). I doubt if there is ever any real condensing going on...I believe the vapor remains a vapor. The random bits of splashed oil that might get blown past the breather valve are another story...expecting the drips to return through the breather valve is a dodgy request...tipping them over the edge into a small chamber with a hole has a bit more hope...maybe?

There is no "condensing." The brass wool is catching oil particles in an oil mist, just like the old breather oil caps in the 40's and 50's, not condensing any vapors. Thus, temperature is irrelevant.

Major Softie wrote:There is no "condensing." The brass wool is catching oil particles in an oil mist, just like the old breather oil caps in the 40's and 50's, not condensing any vapors. Thus, temperature is irrelevant.

My thoughts:

The condensing chamber provides a significant distance, surface area, and volume
between the breather valve at the rear (where the oil vapor is blown from the case)
and the hose leading to the carb at the front (where it is expelled from the case)
such that the vapor will have an opportunity to condense and drain back into the case
rather than simply being blown into the carbs.

The brass-wool would theoretically improve this function by acting as a filter
that would "collect" oil from the vapor onto it's surface
where it can then condense, "fall" into the chamber, and drain back into the case.
(However, the addition of a "filter" might alter effective crankcase pressure)

In either case, it does seem to me that condensation, to a greater or lesser degree,
should be initiated by the temperature difference (crankcase vs chamber).

Operating temperature of the engine should not be a significant factor –
but displacement and RPM, given their direct relationship to producing crankcase pressure,
will be most significant.

Consequently, I will also contend that the factory's inclusion of an oil-condensing chamber
was a direct response to the increase of displacement to 988 cc –
and the resulting increase in crankcase pressure #s, esp at high RPM –