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Old 11-15-2012, 01:58 PM   #16
Houseoffubar
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Places like Mega Cycle will grind custom cams to the customers spec, to accomplish things like this.

Years ago, I realized my GSXR1100 had to cylinders at TDC, at a time, and a wasted spark (like most every other inline 4) I thought it would be fun to have the cams ground so the bike would fire two cylinders at once. This way I could have "twin cylinder bike" just for fun, and the confused reaction to the sound of it.
I decided it would be hard on the crank, etc. having two power pulses at a time, so abandoned the idea.
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Old 11-15-2012, 02:15 PM   #17
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Quote:
Originally Posted by Houseoffubar View Post
Years ago, I realized my GSXR1100 had to cylinders at TDC, at a time, and a wasted spark (like most every other inline 4) I thought it would be fun to have the cams ground so the bike would fire two cylinders at once. This way I could have "twin cylinder bike" just for fun, and the confused reaction to the sound of it.
I decided it would be hard on the crank, etc. having two power pulses at a time, so abandoned the idea.
That's called a "big bang" engine. It was a semi-common thing to do with brit twins for dirt track racers. Some of ducati's desmosedici V4 factory racers had big bang engines that basically acted like a v twin. I'm sure somebody's done it with an inline 4. Someone needs to make a big bang airhead. All you'd need is a cam. Who's gonna do it? It'd be a 1000cc thumper. Talk about a tractor! I can't imagine it would last long, but oh what a ride.
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Airhead Wrangler screwed with this post 11-15-2012 at 11:29 PM
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Old 11-15-2012, 09:02 PM   #18
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Massive Thread Degradation

All well & good but the initial post is an article about BMW building BOBSLEDS for Team USA.
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Old 11-15-2012, 10:06 PM   #19
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Originally Posted by Airhead Wrangler View Post
That's called a "big bang" engine. It was a semi-common thing to do with brit twins for dirt track racers. Some of ducati's desmosedici V4 factory racers had big bang engines that basically acted like a v twin. I'm sure somebody's done it with an inline 4. Someone needs to make a big bang airhead. All you'd need is a cam. Who's gonna do it? It'd be a 1000cc thumper. Talk about a tractor! I can't imagine it would last long, but owe what a ride.
Yamaha R1 had the Big Bang motor a few years back, which had 2 cylinders firing at the same time much like a twin. It might even be still current. Have a flatter sound of the engine.

On the Airhead Aero motors, they cams are reground with the lobes reground to suits the reversed heads.

You can buy them out of the UK.
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Old 11-16-2012, 01:08 AM   #20
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All well & good but the initial post is an article about BMW building BOBSLEDS for Team USA.
Ozmoses, no offence, but The other discussion is far more interesting...
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It's just better when there's twins involved....
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Old 11-16-2012, 01:42 AM   #21
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Ozmoses, no offence, but The other discussion is far more interesting...
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Old 11-16-2012, 09:13 PM   #22
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Originally Posted by Airhead Wrangler View Post
Chris, what's your take on how they did this? They must be using a left head on the right side and vise versa, but they would've had to grind a custom cam to make this work, right?
What if it's timed to run counter clockwise (from the front). Would that work with reversed heads, pistons and a stock cam?
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Old 11-16-2012, 09:26 PM   #23
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Originally Posted by mattcfish View Post
What if it's timed to run counter clockwise (from the front). Would that work with reversed heads, pistons and a stock cam?
I was thinking about that too, but you'd need to find a way to move the timing chain tensioner to the other side as well as modify the oil pump so it doesn't pump oil in the wrong direction. In a motorcycle application there's also the issue that you'd be spinning your wheel in the wrong direction also. It'd probably be easier to make a cam than overcome all the rest of that.
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Old 11-17-2012, 01:52 PM   #24
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I was wondering about the oil pump too, but with it's rotary design, it doesn't seem like it would matter which way it was spinning. Maybe I'm wrong there. Seems like a simple adapter could be made to reverse the chain tensioner. Maybe this would have an application for mounting an airhead motor and 5 speed tranny on a "backward drive" Ural.
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Old 11-17-2012, 02:07 PM   #25
Houseoffubar
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So much easier with a two stroke!
I had a Bultaco Trials bike that would run backwards all the time. Just lug it a bit with the clutch at idle, and it would kick right around, and run like a dream. Threw me over the bars a couple times
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