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Just a quick question

Snipe Hunter

I've never seen one. I've heard of aftermarket 4 valve heads. Not saying it's impossible, but I'd say that it would be RARE. If you are observing one, please post a picture.
 
The German Krauser firm offered 4-valve heads for /7 (and maybe /6, I dunno) BMWs in the late 70s up to the mid 80s. I don't know how many were sold, but I remember seeing them occasionally...*very* occasionally, they were not common. One reason may be that the modified motors were not considered sturdy, and didn't live nearly as long as stock BMW motors.
 
Dual overhead cam or "simply" 4 valve heads? When I lived in Chicago I knew someone who had an R100S with what I believe were Krauser heads. The cam stayed in the engine housing but the rocker arms were split to drive two intake and exhaust valves on each side. That was the only bike I've seen in person with that set up but they turn up for sale every once in a great while.

Steve
 
Holy Grail?

Is it possible that O_gur has stumbled on to a pre-war race bike? Daryl Ri would be the guy to ask about that.
 
well it is old! I dont have pics or #'s yet but it is BMW. And it is an airhead boxer. I was just wondering how rare it really is.
 
O_gur said:
for the air head fellows out there.

Exactly how rare is a dual overhead cam air head?

As rare as it gets.

BMW may have produced a factory racer in this configuration, but there has NEVER been a consumer model produced.

NEVER is as rare as it gets, right?

PS: Although Oilheads have cams in their heads, the valves are not below the cam (between the cam and the piston), so technically these aren't overhead cam engines, either.
 
Wow, you sent my brain spinning for a moment there.

I started imagining what would be involved to drive overhead cams from the crank of the typical airhead--say an R100. There's no room to install a cam drive on the front, because of the exhaust pipes. There's no room at the rear because of the intake pipes. The only logical approach would be to install a gear drive from a new gear on the camshaft, driven via a shaft to the cylinder head, to a....

whoaaa. There's no way to convert an airhead to overhead cams, let alone dual overhead cams.

If you're looking at four valves opened by forked rocker arms, it's probably "just" a Krauser. And scuttlebutt is that Krauser heads were a pain in the butt.

On the other hand, lets see a picture. Maybe you do have a one-off BMW experiment.

pmdave
:brow
 
pmdave said:
Wow, you sent my brain spinning for a moment there. I started imagining what would be involved to drive overhead cams from the crank of the typical airhead--say an R100... The only logical approach would be to install a gear drive from a new gear on the camshaft, driven via a shaft to the cylinder head, to a.... whoaaa. There's no way to convert an airhead to overhead cams, let alone dual overhead cams.
You had it correct before the "whoaa." That's how it is done. I have a photo or two of an overhead cam BMW that utilized desmodromic valve gear.

Maybe you do have a one-off BMW experiment.

No one-off experiment. Several BMW race bikes (called "Rennesport") were built with overhead cams, especially the ones that were supercharged (called "Kompressormotor").

I have many photos. I can post a few when I get home.
 
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Hello; Wasn't that overhead cam operated by a tower shaft with bevel gears at each end, similar to the way Ducati do it. I didn't realize that they were desmdronic (with a cam opening and a cam lobe closing the valve)

I have an HP 21 model airplane engine that has an overhead sleeve valve operated by a tower shaft with bevel gears on each end, .21 cu in. displacement.
 
Say 23 Rennsport DOHC engines?

Several privateer versions of likely lesser quality.

Extremely rare but not unicorns.
 
Like this one?
1954_BMW_01.jpg

http://www.motosolvang.com/bike_windows/1954_bmw.html
 
Ohc

Ikchris writes;

"PS: Although Oilheads have cams in their heads, the valves are not below the cam (between the cam and the piston), so technically these aren't overhead cam engines, either."

In the vintage american motorcycle world, OHV motors are referred to as "push-rod" motors as opposed to flatheads. Oilheads have chain driven cams in the heads as opposed to in the block, and no push-rods. The cams rotate above, or "over the top" of the pistons. If the oilhead motor is not a flathead, not a push-rod motor, then I submit that it is right and proper to call it an OHC motor.......with all due respect.
 
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donkey doctor said:
Wasn't that overhead cam operated by a tower shaft with bevel gears at each end, similar to the way Ducati do it. I didn't realize that they were desmdronic...
Rennesport motors are NOT desmodromic. I have a photo or two of a bike with a motor that a guy built by adding some Ducati bevel-head parts. I'll be able to share when I get back to work next week.
 
woodnsteel said:
Ikchris writes;

"PS: Although Oilheads have cams in their heads, the valves are not below the cam (between the cam and the piston), so technically these aren't overhead cam engines, either."

In the vintage american motorcycle world, OHV motors are referred to as "push-rod" motors as opposed to flatheads. Oilheads have chain driven cams in the heads as opposed to in the block, and no push-rods. The cams rotate above, or "over the top" of the pistons. If the oilhead motor is not a flathead, not a push-rod motor, then I submit that it is right and proper to call it an OHC motor.......with all due respect.

Oilheads are more accurately referred to as a "cam in head" motor. Overhead cam would imply that the cams are above the valves, which certainly isn't the case. They're also referred to as a "high cam" motor, but I don't think that's as accurate as "cam in head".

Even though the motor has a cam in the head, there are still little bitty pushrods to activate the rockers.
 
Cancel the "whooaaa!" I guess I was thinking entirely of 70's vintage airheads. And I obviously hadn't been paying enough attention to the Rennsport photos. It appears that lump on top of the cylinder head is for the bevel gear to drive the cams.

The photo raises another question though: "Earles forks". The caption with the Rennsport photo describes the leading link as an "Earles fork". However, in a recent article by Tony Foale in MCN (about front end designs), he noted that BMW never called it's leading link an "Earles". Yes, the BMW leading link front ends were "just like those of" Ernie Earles, but apparently BMW never mentioned that connection in it's literature. Over the years BMW apparently studied various novel suspensions, and then later, very similar BMW designs appeared. Same deal for Saxon, whose front end is very similar to the BMW "Telelever" that came out later.

Foale refers to the 1950s/1960s leading links as "Earles-type".

Anyone know the skinny on this? Did BMW actually purchase the rights to the Earles design, or did they merely pirate the idea? Anyone have any BMW literature that refers to their leading link as an "Earles fork"? I'm not concerned about BMW pirating designs, I'd just like to get the story straight.

pmdave :dunno
 
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