How is this different from other 4 strokes? is it because its a 4-valve. if anybody has any mecanical skill i would like to hear your opinion on this engine. I would also like to hear all benefits and downsides. about the only thing i know about it is what the initials stand for(Radial Four Valve Combustion Chamber) and that it has a little more engine noise than other four strokes.

Jera '00 400ex

 

I have owned 4 of these engines in Honda XR's from XR-250's to my old XR 600R and rebuilt at least 10 of them. R.F.V.C used to be stamped on the head, but they stopped that around 98' or so. These engines display the valves radially instead of parallel, they are in the corners of the combustion chamber and spaced out evenly, resulting in a true "hemi" type engine. The spark plug is also smack dab in the center of all 4 valves resulting in a much better burn. To get the valves at such a odd angle, they use a Sub-rocker arm on each valve. This is the added noise you here because there is almost doubble the valve gear rolling around up there. My XR's never had a problem with pinging that most Hemi engeines do
Joe

 

OH, and my opinion? These are unbreakable engines and run litterly forever..just like any other honda They create great power and run on cheap fuel just fine. The nice thing is that they have berrings on the camshaft that some engines dont like the old 200 series used on the XR 200 and below and the ATC200 models.. They also have a huge automotive style cam chain that will never need replaced Great engines!
Joe

 

With four valves does it fire every stroke or every other?

Jera '00 400ex

 

It's just like a normal four stroke but it has 2 valves running the intake and 2 running the exhaust as opposed to 1 intake and 1 exhaust. It fires every forth stroke.

 

The only differnce between 4 valves and 2 is that 4 allow's more air to get into the engine easyer and having 4 smaller valves allows the engine to rev higher than haveing 2 huge ones. I also sence some confusion on how the cycles work on a 4 stroke compared to a 2 stroke.
4 stroke:
stoke#1: Pistion goes down, intake valve opens, draws air/fuel mix in (intake stroke).
Stroke#2 pistion goes up and compresses air (compresson stroke)
Stroke#3 spark plug fires and becomes the "Powerstroke", pistion goes down
Stroke#4 Pistion goes back up and exahust valve opens letting exahust out (exahust stroke)

2 Stroke:
Stroke#1 pistion goes down on the powerstorke and also lets the exahust out one port while the intake charge is brought in another port at the same time.
Storke#2 pistion goes up for the compresson stroke and draws the new fuel mix into the case of the engine.
there is defently ALOT more to both of these.. but that is the basic's
Joe

 

Good rundown, Joe, both on the Honda engine and on four stroke-cycle and two stroke-cycle engines.

Anyone interested in further 4-stroke/2-stroke info can read "Fantastic Voyage," and "Fantastic Voyage II," accessible from the "Tech Tips" section of the ATV Connection home page.

The Fantastic Voyages provide a thorough and readable account of internal combustion engine operating principles.

Tree Farmer

(I'd appreciate an E-mail and comment from anyone reading these references as a result of this post. Thanks.)

T.F.

 

Can someone explain Yamaha's YZ and what makes it so powerfull?

Thanks,

Dennis

 

The YZ400 engine uses 3 intake valves and 2 exhaust. So instead of 2 valves supplying the air/fuel mixture, it has 3, and there's the normal 2 for exhaust. I don't have a clue how they designed the top end on that thing (camshaft and valve lifters)and how they got it to all work.

 

a friend has the new YZF400.. kinda cool in its own way the 5 valve engine first saw light in a multi cylinder setup in a street bike.. Yamaha just used the same carb and gave it one heck of a hot cam in a single cylinder setup for the YZF.. simply a DOHC with shim type valves