I've had an issue with my 81 R100RT with 79,000 miles on it. There seems to be an excessive amount of oil in the air box and coating the insides of the carbs. I removed the two rebreather covers next to the starter motor. One has the hose going/coming from the air box. The other has the non-return breather valve under it. I can't find a good picture or description of how the valve is installed. Does the curved plate with the thin reed under it go up, or is it installed downwards into the block? I'm thinking this is the possible source of the extra oil in the air box, etc. Attached is a picture of the part.
Thanks for any input
Rick #12173
The reed valve sits on top of the crankcase. When you remove the small cover, you should see the exposed flapper (the "reed"). The reed allows air from the crankcase to exhaust (blow outward) into the hose system that routes this exhausted air to appropriate places.
The reed DOES NOT determine the content of exhausted air. If there is oil, water, or nuts & bolts in that air, then the reed valve is not the problem.
Possible causes:
- Using the wrong grade, weight or type of engine oil could allow the engine to simply throw more oil out the breather system.
- A quick reading of Snowbum will tell you about the liquid recycling well (right next to the breather valve) that can become blocked with trash and cause excessive oil in the breather hose.
- Some Airheads naturally run the engine oil level 1/4" low on the dipstick because the crankshaft simply seems to pick up oil and sling it out. The cure for this is installation of an extended oil pan so that the prescribed volume of oil can be maintained at a physically lower position.
- All Airheads will be forced to suck MORE engine breather air from the breather system if the air filter is dirty and/or clogged. The intake system MUST have air. If it can't receive air through the filter, then it will get it from other sources.... the breather system included.
- The piston rings control the amount of compression chamber "blow-by" that reaches the crankcase... and thus needs to be exhausted to the crankcase breather system. There is always some amount of blow-by, which is why the crankcase even has a "breather system" !! But the volume of blow-by is constantly changing... it starts out high until the rings "seat in", then gets reduced to "normal" levels, and then, due to engine wear as mileage increases, the blow-by also slowly increases. There is also a situation where the rings basically need to be re-seated if the engine sits for long periods or isn't ridden enough. However, having said all that, an Airhead engine with 79,000 miles that has been reasonably ridden and regularly maintained will not need new rings. That's the last thing I'd check.
I say all this to simply point out that there are MANY reasons excess oil could be in the breather hose. And I haven't talked about all the possible sources. But let's correct the idea that the reed valve determines the contents of what is passing through it. NO, the breather valve ONLY determines the direction of flow !
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Yes, the reed goes up, on top of the crankcase. Also, according to Snowbum, the valve is oriented at approximately the 11:00 position (or pointing at the left hand grip).
Down in the bottom of the “well”, just forward of the reed valve, is a small drain hole that allows oil back to the crankcase. Make sure that hole is clear ( I use a pipe cleaner) and the chamber is clean.
Wobbley, Dave,
Sorry for the delay in getting back. I'm also replacing the clutch. The NRV is oriented as you explained Dave. It took some doing to get the valve out so the drain hole could be checked, it was clear.
There is no noticeable oil consumption, < half quart per 2k miles. I do try to keep the oil level mid-level between the level lines (max mim). Just curious as to why there's oil in the airbox and throat of the carbs. rick. 12173
Just curious as to why there's oil in the airbox and throat of the carbs.
• Just curious as to why the 5 or 6 points of investigation I contributed have not been answered.
• Some oil film will always be present in the intake tubes. This whole question hinges on whether the oil really is "excessive".
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Wobbly,
- I used for the past 8 yrs, dino 20w50 Valvoline VR1. Prior to that Castrol 20w50 since owing the bike (42 yrs).
- Checked recycle well, clean, checked drain hole as Dave suggested-open. Making sure the reed valve was correctly aligned under the NRV.
- As stated, i keep the oil level around 3/4 full level, never filling to FULL mark on dip stick.
- Air filter is clean and clear, approx. 15000 miles.
- Last year, while replacing the push rod tube seals, i had the heads cleaned and the cylinders honed. I replaced the rings while reassembling the two cylinders. There has not been any high consumption of oil, not that there was before, no smoke from pipes.
I guess "excessive amount" is a relative term. As we in the colder climes await the warmer riding season, i'll monitor the amount of oil "build up" passing through the carburetors and the airbox once i get back on the road.
Thank you for you input and interest.
redhorse
...and field mice have not built a nest around your starter ?? 🤣
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Is that where those squeaks are coming from?
That's what B-M-W stands for ! Bivouac Mice thru Winter.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Advertisement
