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Discussion Starter #1
There is a production 4 stroke bike with almost no engine braking at all, without a slip clutch.
Who made it, what's it called and how did they manage to do this?

Aris
 

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Discussion Starter #4
Andy said:
Hi Aris,

Is it the 1998 Yamaha YZ400F...

Here is a quote:

"The 400F also has almost non-existent engine braking. The light flywheel and short stroke combine to let the YZ400F freewheel almost as much as a two-stroke"

Source: http://www.motorcycle.com/mo/mcyam/yz400f.html

Andy
Hi Andy,

No it's not the YZ400F, but you 're very close ;)
This bike behaves LIKE a 2 stroke, not almost.

Titomike, it's not a scooter. Nothing to do with scooter variable transmission etc.

Aris
 

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Discussion Starter #6
Hi guys, I'm back from 2 weeks holidays in Greece!
It was great and the weather was perfect.

Here is a clue for th trivia...
It's a new MX bike. I think I gave it away now..

Aris
 

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Discussion Starter #10
RCjohn said:


:D

How about the new Honda CR450F? :p
You got it!! :) I was expecting you to find it after the last answer, it's a Honda after all!

Now you must say how it works :D

Aris
 

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ariszr7 said:


You got it!! :) I was expecting you to find it after the last answer, it's a Honda after all!

Now you must say how it works :D

Aris
Damn man, do I have to tell you everything? :rolleyes: :p

I actually have no idea... they put oil in the gas. :D
 

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Discussion Starter #13
Andy said:
Hi Aris,

It has a real short stroke and skirtless light weight piston.

Andy

Hi Andy,
You re right about that, but there is something more in the design of that engine, which is a very simple idea and it works!
It's crazy if you think about it, and that's why I though it would make a great trivia.

Aris
 

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Does it have anything to do with the auto-decompressor for hot-starts?

I'd like to find the answer to this - My buddy just bought one of these and he thinks he's a technical genius. I'd like to quiz him about a feature on his own bike.:p :D
 

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Discussion Starter #15
Hysyde said:
Does it have anything to do with the auto-decompressor for hot-starts?

I'd like to find the answer to this - My buddy just bought one of these and he thinks he's a technical genius. I'd like to quiz him about a feature on his own bike.:p :D
Hysyde,

It doesn't have anything to do with the decompressor. The decompressor is a really nice design on this bike and the hot start system works fine as I hear (unlike the YZ400), but the answer is in another design aspect of the motor.

Even if you don't find it, someone else will, or I'll give it away finally. You'll impress your friend anyway :D

Aris
 

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Hi Aris,

Here is what I found.

The oiling system could best be described as "semi-wet sump." It isolates the crankshaft in its own chamber, with one opening in the bottom of the case blocked by a one-way reed valve. The oil is pumped in through the crank center and excess is blown out by piston pressure on the down stroke, in effect creating a negatively pressurized crankcase. This aids in reducing compression braking, as well. The centercase-enclosed oil pump also sends oil up a cylinder stud to the cam, where it lubricates the vitals on top before falling down the camchain tunnel, past the ignition rotor and into a small sump to be collected. Total motor oil capacity is 700cc, and it is completely isolated from the tranny fluid.

Source: http://www.cycleworld.com/xp6/CycleWorld/features/1101_honda_motorcross.xml

Andy
 

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Discussion Starter #17
Andy said:
Hi Aris,

Here is what I found.

The oiling system could best be described as "semi-wet sump." It isolates the crankshaft in its own chamber, with one opening in the bottom of the case blocked by a one-way reed valve. The oil is pumped in through the crank center and excess is blown out by piston pressure on the down stroke, in effect creating a negatively pressurized crankcase. This aids in reducing compression braking, as well. The centercase-enclosed oil pump also sends oil up a cylinder stud to the cam, where it lubricates the vitals on top before falling down the camchain tunnel, past the ignition rotor and into a small sump to be collected. Total motor oil capacity is 700cc, and it is completely isolated from the tranny fluid.

Source: http://www.cycleworld.com/xp6/CycleWorld/features/1101_honda_motorcross.xml

Andy
Hi Andy,

You are absolutely right about the lubrication system and it's a briliant idea from Honda that should be followed, but it's not what makes the engine feel like a 2 stroke with closed throttle.

The answer lies in a geometrical characteristic of the main components o fthe engine...

Aris
 

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Discussion Starter #18
I tried to find the answer on the net, but couldn't :confused:

It's not in the specs anywhere, I read about it in a detailed technical presentation about the CRF in a Greek magazine.

I think I'll have to give you the answer, because it's not fair if nobody can find it...:(

What do you think guys?

Aris
 
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