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Old 05-26-2015, 10:54 AM   #1
amockalypsenow OP
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Porting: unshrouding valves?

Howdy friends,

I'm giving my xr650r some new valves and a fresh valve job.

While I have the head off I plan to take out some roughness in the ports. I don't want to bore it out at all, I want to keep the velocity up and the bottom end happening. I plan to just clean it up.

I am wondering if I should unshroud the valves?


Also curious about whether or not to mess with the valve guide boss/bowl or whatever you call it.

Give your thoughts please!

Thanks!

Cameron

:-)
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Old 05-26-2015, 11:31 AM   #2
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See if someone local to you has a "flow bench".
This helps measure air flow when cleaning up the rough castings on the intake an exhaust ports.
I'm not familiar with the valve shrouding you speak of.
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Old 05-26-2015, 11:59 AM   #3
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A valve is "shrouded" when there is a wall next to the open valve. The valve may be open, but the wall next to it blocks the flow.

How much clearance do you have between the edge of the valve and the shrouding near the valves? How much valve lift do you have?

I'm willing to bet that there is plenty of clearance and you don't need to mess with it. taking metal out of the combustion chamber lowers compression. And I like that quench band around the edge of the chamber.

I can see that there was some factory machine marks that would be unshrouding the valves (I see best in the lower valves in the picture). At best I would just blend those machine lines into the casting. But not even think of touching anything that is on the deck of the head.
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Old 05-26-2015, 12:10 PM   #4
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How expensive, hard to find are those heads? Personally if you don't know what you're doing I'd leave it alone or have a pro do it. It's not going to make a noticeable seat of the pants difference. It's real easy to screw up a perfectly good head. I've gotten away with it on some heads with no gain for the street and I have also ruined a 650 Bonnie head. :(
Oh and sorry I also have no idea what "unshrouding the valves" means.
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Old 05-26-2015, 12:54 PM   #5
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Experience XR350 head

Long ago:

I had a XR350 valve break and damage the head - new head from Honda was out of price range so I took a dremel and smoothed the damaged head from the broken valve. Worked saved $$$

You have a clean head designed by Honda Engineering Leave it alone spent time on putting it back together correctly.


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Old 05-26-2015, 04:16 PM   #6
amockalypsenow OP
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Thanks broncobowsher for the informed reply.

To the other people that don't have experience with this yet feel qualified to be negative and lame: buzz off!

I tig weld, machine, and wrench quite competently; and I have experience port matching and smoothing out heads. I'm perfectly capable of not fucking up my ports thank you very much. I'm looking for actual experience with these, or similar, heads.

Anybody experienced with something to add, I'm keen to learn.

Thanks.

Cam.
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Old 05-26-2015, 07:58 PM   #7
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Quote:
Originally Posted by amockalypsenow View Post
Thanks broncobowsher for the informed reply.

To the other people that don't have experience with this yet feel qualified to be negative and lame: buzz off!

I tig weld, machine, and wrench quite competently; and I have experience port matching and smoothing out heads. I'm perfectly capable of not fucking up my ports thank you very much. I'm looking for actual experience with these, or similar, heads.

Anybody experienced with something to add, I'm keen to learn.

Thanks.

Cam.
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Old 05-26-2015, 09:23 PM   #8
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You might want to search around here for some of the threads where Cyclewizard had done some extensive mods to the RFVC heads, even going so far as converting them to a pent roof.

I've always been overly cautious of removing to much meat from around the valve guides for heat transfer, but I've only dealt with air cooled engines.
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Old 05-26-2015, 09:44 PM   #9
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http://www.advrider.com/forums/showthread.php?t=97875
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Old 05-26-2015, 09:49 PM   #10
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Some good info in these responses. I would be wary of unshrouding those valves at all. The ledges around the chamber are carefully engineered to provide "quench" area while the piston is at TDC. The quench creates turbulence which helps to reduce detonation. Those walls also help with the "tumble" motion of the intake charge that is so important for torque in these four-valve engines.

If you were working on a 1960's small-block Chevy, there would be lots of opportunity to pick up meaningful results with a die grinder. This cylinder head is already highly developed, so it would take a maximum professional effort to get much more out of it. I'm talking five-axis CNC porting, which is big $$$.

I'd button it back up with good parts and enjoy!
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Old 05-27-2015, 12:21 AM   #11
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Check out the moto tune website

http://{\rtf1\ansi\ansicpg1252 {\fonttbl\f0\fnil\fcharset0 .HelveticaNeueInterface-Regular;} {\colortbl;\red255\green255\blue255;\red0\green0\b lue0;\red255\green255\blue255;} \deftab720 \pard\pardeftab720\sl480\partightenfactor0 \f0\fs32 \cf2 \cb3 \expnd0\expndtw0\kerning0 \outl0\strokewidth0 \strokec2 image}


"]http://http://www.mototuneusa.com/thanx.htm[/URL]


I did this to my dr650 head, and it worked well.
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Old 05-27-2015, 01:27 AM   #12
amockalypsenow OP
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Cool. From what I've read, there ain't much more to get out of these heads.

So I will clean up some casting warts, and fill in the smog passages with JB weld, and chuck it back together.

Thanks all.
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Old 05-27-2015, 09:34 AM   #13
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No more XL600?

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Old 05-27-2015, 10:02 AM   #14
amockalypsenow OP
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The 600 is in Gutemala. I will be returning to it in summer, and riding on. That bike has a ported head and the twin flat slides and rides so darn nice!

This xr650r is my American ride.
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Old 05-27-2015, 11:05 AM   #15
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done a bit of that... ramping the guide bosses, tapering ends of the guides, bowl cleanup etc. a few years ago I did some research to try going beyond the obvious clean up. heres a couple links....

http://tractors.wikia.com/wiki/Cylinder_head_porting

http://www.hotrod.com/how-to/engine/...-head-porting/


I also built a flow bench. my bookmarked links are too old & get 404s but this one still works. theres lots of stuff out there.... just tikes time to filter it

http://www.dtec.net.au/Flowbench%20Design%20Guide.htm


oh yeah.... if you work the combustion chamber, CC the head before & after. you can do the math & control your compression ratio with base gasket thickness. if it gets too low, put the head on a surface plate
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