Air pulse system on airheads

[ksdcr]

Does anyone know what the years, that BMW installed the Pulse Air emissions plumbing on airheads?

 

[barryg]

Maybe ‘81 till the end of airhead production.

 

[20774]

Snowbum says the "1980" on forward, so likely before the Sep 1981 '81 models. His article on the pulse-air system is here:

https://bmwmotorcycletech.info/pulseair.htm

 

[ksdcr]

Snowbum says the "1980" on forward, so likely before the Sep 1981 '81 models. His article on the pulse-air system is here:

https://bmwmotorcycletech.info/pulseair.htm

So all the way up through the mid 90’s last variations, like the Mystic, RT and R100?

 

[20774]

So all the way up through the mid 90’s last variations, like the Mystic, RT and R100?

Apparently. Snowbum mentions making custom parts for his own 1995 R100RT when he dealt with the system.

 

[stevenrankin]

80

I just saw an ad for a R100RT 1980 for sale and in the pictures there is the pipes for the pulse system. St

 

[kinterridge]

1980 forward W/ BING CV carbs per Snowbum. Euro Moto Electric shows the delete kit as 1980 thru 1996.

 

[lkchris]

Engines from this era were tuned pretty lean ... fuel/air mixture wise ... but the possibility remained that unburned fuel could enter the exhaust.

The purpose of this system was to introduce oxygen rich air into the exhaust stream, thereby causing spontaneous combustion of that unburned fuel.

There is no performance degradation created by this system, but it does get the exhaust system and probably exhaust valves a bit hotter.

German fuel injected vehicles of the era have a system called "secondary air" that accomplishes the same thing, although the air is blown into the exhaust with an electric fan. The injection is well controlled enough that this system only runs for ~ 30 seconds following a cold start ... when the engine is provided a rich mixture to keep it running until it warms up. After that, O2 sensors keep the mixture correct.

PS It's my feeling that BMW got the jetting wrong on 81-84 R80 engines. In any event, my '84 R80G/S was jetted pretty rich. One time a couple of us running R100RS did a ride with another on an '83 R80RT ... which was on reserve way before we were. Of course that engine was running 1000rpm faster at same speed/same transmission gear, too.

 

[mneblett]

but it does get the exhaust system and probably exhaust valves a bit hotter.

+1. The hotter exhaust valves was the reason I removed/blocked off the pulse air system in all my airheads (last one I took off was on a '94 Mystik). The combination of BMW's valve seat material change when unleaded fuel became mandatory* and the additional heat from the immediately adjacent fuel burn at the exhaust port resulted in accelerated valve recession. Removing the pulse air plumbing and rejetting away from EPA-mandated terribly lean Bings made for better running.

* I can never remember the exact year the new valve seats came in. I remember BMW making a big deal of the new plasma-sprayed Nikasil cylinder liners when they came in in 1981, but I'm not sure whether the new valve seat material came in '80 or '81. There's getting to be too few memory cells left ...

 

[20774]

I don't know specifically but it was for the 1981 models with the change to the valves. I presume then any bikes built September 1980-on. The issue as written by Oak was that the valve seats were made of tool steel which didn't transfer heat very well. The heat then was retained in the valve face. The valve face tuliped or warped more than recessing, but the result was the same. Oak used terms for valve recession prior to the 1981 models but for the 1981-1984 model years, he used the term valve face plastic deformation. For 1985, BMW finally got the metallurgy right.

 

[mneblett]

I don't know specifically but it was for the 1981 models with the change to the valves. I presume then any bikes built September 1980-on. The issue as written by Oak was that the valve seats were made of tool steel which didn't transfer heat very well. The heat then was retained in the valve face. The valve face tuliped or warped more than recessing, but the result was the same. Oak used terms for valve recession prior to the 1981 models but for the 1981-1984 model years, he used the term valve face plastic deformation. For 1985, BMW finally got the metallurgy right.

When in doubt, ask this man!

 

[20774]

For those that want to follow along, find Oak's write up in the March 2002 Airmail!

 

[lkchris]

* I can never remember the exact year the new valve seats came in. I remember BMW making a big deal of the new plasma-sprayed Nikasil cylinder liners when they came in in 1981, but I'm not sure whether the new valve seat material came in '80 or '81. There's getting to be too few memory cells left ...

The valve seat change didn't happen until the late 1980s and corresponded with the end of 40 mm carbs and large valve heads on R100s ... at least in USA. Valve seat angle was changed as well as valve seat material.

 

[20774]

The valve seats were changed for the 1985 models. The 1981-1984 had the valve issues.

 

[jackskelly34]

Burnt valves?
Really?
Anyone want to explain exactly how the Pulse Air System works?
I’ve asked this question for 40 years and have never heard it correctly explained.
Even the Rubber Chicken Racing dude couldn’t answer the question correctly.

 

[20774]

Kent seemed to have a good explanation above. Snowbum has a lengthy explanation on his website. Tell us what Tom Cutter told you. Seems like he should also know what it's all about.

 

[pglaves]

"The solution to pollution is dilution." Add air into the exhaust, downstream from the exhaust valve, and the amount of any pollutant measured at the tailpipe in parts-per-million will be lower even though that which came out of the exhaust port at the engine remains the same. Voila! Take that regulators!

 

[lkchris]

Photo of ruined exhaust valve from my "84 R100RS ... compared to intake valve on left. That knife edge would soon fail, causing valve to retract far enough for keepers to separate and then valve to hit piston.

 

[oldcamper]

Photo of ruined exhaust valve from my "84 R100RS ... compared to intake valve on left. That knife edge would soon fail, causing valve to retract far enough for keepers to separate and then valve to hit piston.

View attachment 96342

How many miles were on the bike?

 

[lkchris]

How many miles were on the bike?

If I recall correctly, around 60K. Photo is from 2002