XR650L: "RFVC" - What does it mean?

On the top of the cylinder head - on the outside are the letters : "RFVC" on both sides - What does it stand for :) ? Thanks.................

Honda says, "Radial Four Valve Combustion", but I have heard mechanics say "Really F***ed Valve Chamber"

Radial Four Valve Chamber

The valves on the heads of the XR250,400,600,650L are all tilted in towards the center of the piston. The benefit is that the valves can be bigger, therefore allowing more air to pass. The additional benefit of the design is in how many rocker arms there are to each valve - 2. Very little stress on the cam. The valves, the rockers and the cam should conceivably last forever, provided that there is adequate lubrication.

Drawback: It's complex... Heavy.. lots of heavy moving parts. Lots of reciprocating mass that requires heavy valve springs to push against their mass. The valve cover has all of the rocker arms integrated into it. The valve cover on an xr600 has more metal and is 100lbs heavier than the entire engine on a CRF450 :)

and the design is essentially the same as when Honda inroduced it in 1972 with the XL250 Motosport, 4 valve head, hemispherical combustion chamber, rocker arm for each valve. Cams are better now and ride in bearings vice plain aluminum bushings on th head. Valves and guides are harder and made of better material - simply technology - materials and engineering is better now but still resides on the basic design of the Honda overhead cam motor with a 4 valve head.

Radial Four Valve Chamber

The valves on the heads of the XR250,400,600,650L are all tilted in towards the center of the piston. The benefit is that the valves can be bigger, therefore allowing more air to pass. The additional benefit of the design is in how many rocker arms there are to each valve - 2. Very little stress on the cam. The valves, the rockers and the cam should conceivably last forever, provided that there is adequate lubrication.

Drawback: It's complex... Heavy.. lots of heavy moving parts. Lots of reciprocating mass that requires heavy valve springs to push against their mass. The valve cover has all of the rocker arms integrated into it. The valve cover on an xr600 has more metal and is 100lbs heavier than the entire engine on a CRF450 :naughty:

 

 

Great info! 

Here are some visuals of the radial configuration.  

 

I'm not sure why they didn't use two overhead cams.  I guess this design is lighter, more compact, and is able to deal with the incline of the valves more easily and reliably.  

 

I can't really say anything bad about the design.  The ones in the pictures have been running since '98 and look great on the first tear down.

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Edited by hollerhead

I wonder if the OP checked this thread a decade later?

 

While we're at it, the XR200R (1984-1985), XR250L, XR350R, XL350R, XR500R, GB500, XL600R and NX650 have been left out, as far a U.S. models. I may have missed some, but the point is that one poster tried to be smart about it and left a whole lot out, which a little real RFVC knowledge coupled with a quick internet search would have revealed.

 

Honda used a pent-roof design on earlier engines, like the XR500R, but for whatever reason, went to the RFVC. The XR600R was a big-time, wining desert bike of the era, so it obviously worked during the time. They've moved past that and many bikes today use a pent-roof design, but that doesn't mean RFVC isn't any good, it just fell aside. With the way things change and more is learned about internal combustion engines, it may return.

So not Really Fast, Very Cool:rolleyes:

Great! Thanks for the info hollerhead and onederer.

 

Last fall I was in the market for a reliable, durable and affordable dual sport bike that I could ride all over the western US (mostly on dirt) and transform to my needs once I got know the bike. So far the xr650l exceeds expectations and for $6200 new I'm feeling like I made the right choice. Plus all of the knowledge about

the bike in this thread and many other threads around are priceless.

So not Really Fast, Very Cool:rolleyes:

 

This engine can be made into a fire breathing beast and it will be a FAST reliable beast with a long lifespan. 

Great! Thanks for the info hollerhead and onederer.

 

 

I did forget to differentiate between the non-RFVC XR500R and the RFVC XR500R. The early 1980's were a transition year from the older engines to the newereven keeping the model designation at lot of the time. It can get as confusing as Harley's model letter designations.

 

Anyway, the XR650L is still a very good value and quite capable for off road use. Take care of it with regular maintenance and you'll get good service out of it.

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Edited by treelinerider

Love the RFVC on the xr650l. I ride to really remote places and EFI introduces another point of failure as does liquid cooling.

 

And you don't think having 8 rocker arms for one cylinder adds failure points?!   :thumbsdn:

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