Oil heads/airheads

[jphillips138845]

I have been riding a 92 100GS for the past 16 years which I assumed was an airhead. When I started thinking about it I do not know the difference between an airhead and a oilhead. I assumed it was something to do with the cooling or lubrication of the valves.

 

[acejones]

Cooling and lubrication.

Don't tell him about hexheads

 

[BUBBAZANETTI]

well, there's hundreds if not thousands of differences, but the main ones are:

engine is cooled by recirculated oil from the sump, fed through small passageways to the heads

valves are actuated by a chain driven cam in the head, not push rods like the airhead

4 valves per head instead of two

fuel injection instead of a carbureator

significant hp increase, (between 25 and 40 or so depending on the model, considering the late 1000cc airheads were 60hp machines)

displacement difference (1100 or 1150 vs the 1000cc of your GS)

many other design, structure changes, but those are the big engine changes.

 

[pglaves]

The "Oilheads" have two oil pump chambers on the same shaft. One provides low volume high pressure for lubrication - as is normal. The other pumps high volume low pressure oil into cooling passages in the heads past the combustion chamber and the exhaust valves. Thus the moniker, Oilhead.

In cooling effectiveness this puts them somewhere between a typical air cooled engine and a water cooled (like most cars) engine. They still don't like to run at idle, stopped in still air for any length of time, and don't do as well at staying cooled as a water cooled engine in paddle-foot or stop 'n go traffic.

They still need airflow past the cylinders and through the oil cooler(s) to keep the engine cool. Oilhead police bikes are generally equipped with fans on the oil coolers like fans at radiators on water cooled bikes and cars.

 

[Rev_Eddie]

The Oilhead engine is a cam-in-head design.
It has pushrods.

 

[BUBBAZANETTI]

The Oilhead engine is a cam-in-head design.
It has pushrods.

yep, i was trying to indicate the difference in cam position and the relative length of the rocker arm, srry if i confused.

 

[osbornk]

significant hp increase, (between 25 and 40 or so depending on the model, considering the late 1000cc airheads were 60hp machines)

displacement difference (1100 or 1150 vs the 1000cc of your GS)

True of SOME oilheads. My oilhead doesn't as much horsepower than many 1000cc airheads but does have more torque. My oilhead also has a 1200 engine. It is the misunderstood R1200CLC or R1200C.

 

[jphillips138845]

Thanks for the info, I did not realize such a vast difference, even within the oilheads.

 

[19991100RT]

Thinking out loud

Would there be any gain (translates to "peace of mind") in fitting the Oilhead with a cooling fan on a thermostat? My American Classic has one and it does give me peace of mind when stopped dead in trafic hearing the fan kick in. May Paul might have a thought or two. I'm thinking a 12 volt computer cooling fan kind of thingy mounted to the Oil Cooler.

 

[lkchris]

"Airhead" describes every BMW two-cylinder (and one cylinder) engine made up to the 1995 intro of the what's called the oilhead.

The oil circulation of the oilhead engine serves to provide much the same noise dampening that the water jacket of a water cooled engine provides--noise reduction is the main reason for the change, but of course the better cooling helps pave the way for better horsepower, too.

The oilhead manual says it's good for 30 minutes of idling, but I wouldn't press it. Remember, rpms = heat, so keep them at idle when stopped. This probably applies even to the oilhead unless it has the oil cooler fan.

The "american classic" has a fan because it needs one. For the BMW oilhead, mostly just police need one because they need to keep their motors running to support warning lights, radios, etc. Everyday riders can switch the bike off.

Remember also, that this is the era of synthetic motor oil--which is much more tolerant of heat.