Wow - 3 spark plugs. And the valves are diagonal. That's some left of centre thinking.

 

Found the sith it comes from.

http://drmania.free.fr/drmania.htm

 

http://babelfish.yahoo.com/translat...fr=bf-home&trurl=http://drmania.free.fr/drmania.htm&lp=fr_en&btnTrUrl=Translate

 

From what I can tell it is info on the BMR-Suzuki Supermono race bike that used a heavily modified Suzuki DR800 motor with Apfelbeck head and twin crank, hence the interest in the machine from the French Suzuki DR group you linked the images from.

 

http://www.bmr-team.de/

quote:European Season Ended

Our European season ended with a very nice 21yr old German lady named Katja Poensgen winning the championship riding a BMR-Suzuki. She achieved this by winning 4 out of seven races with one second place & 2 DNFs.

The BMR-Suzuki she rode is a very interesting tool. It may have started life as a DR800 motor but that was long ago & far away! It's creator is Rupert Bainzel, and apart from a lot of bottom-end work, the motor features a machined-from-the-solid top end, with an Apfelbeck type of cylinder head where the valves are arranged radially, with exhaust & inlet ports placed diagonally. As you can imagine, this calls for some hairy machining of cams, they are conically ground. It's watercooled and fuel-injected & gives over 90BHP from 741cc at 8000 & peaks at something like 9300rpm. Since this represents a BMEP figure of something in the order of 215psi it is a considerable achievement.

Of course, this didn't happen overnight, it's taken some years to develop it to the present pitch and I know that Rupert won't even think about how much it's cost!

Engine

Based on DR Big Single Cylinder Four-Stroke

Capacity

741cc

Valves

4-Radial

Spark Plugs

3

Camshafts

Twin, Conical, External Belt Driven

Carburation

Downdraught Electronic Fuel-Injection

Power

94bhp @ 8100rpm

Chassis

Aero-Space Quality Tube And Plate Steel Frame

Italian Supermono Championship, wins Constructor Championship and Title, racer M. Lucchiari

 

Wonder if it thumps

 

Damn. As a machinist and tinkerer I aspire to this.

 

stupid question: why two con-rods and counter rotating cranks on a single cylinder?

 

Have to admit I'm curious about the two cranks as well. Love the radial valves. Haven't seen that since Rudges in the 30s.

 

quote:Originally posted by Geeto67

stupid question: why two con-rods and counter rotating cranks on a single cylinder?

They do that on overly large diameter pistons to stop them skewing in the bore.

 

Impressive increase in peak bhp/rpm went from 54bhp/6600rpm, 94bhp/8100rpm.

The early French article hinted at the crank + piston being destroyed by the increase in piston velocity in bench testing. So the skewing must cause the piston the lock in the bore and go boom.

 

I wonder though if a deeper or more robust piston skirt would have solved that. Yes it would have increased reciprocating mass, but maybe not as much rotating mass as twin cranks? Plus that piston looks heavy with two wristpins and the rod mass has to account for something!

It is impressive nevertheless!

 

I would expect the counter rotating cranks to act as a balancer setup as well, eliminating most primary imbalance leaving you with just the up and down from the rods and piston?

 

hoof: honda xr250 and bigger post 84. once even the 200 was RFVC.

twin cranks are ok provided balances and weight are dead accurate to each other. much discrepancy and those big gear couplings will get backlash thatwill have one eat the other then it's cocked piston time. makes more sense than a balanceshaft if done properly.

 

They're not just radial valves - they are opposite each other as well. Never seen that.

 

leaves plenty of room for good diameter tunnel ports.

finally saw my mates espada last week. inlets between cam tunnels miura donk swung 90 degrees. i kissed it's hatch glass.