Please bear with me as I need to text each shot and take a few more pictures
A few members have approached me asking me to go alittle deeper in depth of the exact procedures I use in re-profiling the guide and the boss area surrounding the guide itself. The methods I use to contour the guide is common practice when porting any head as it's free Hp to reduce the resistance of flow and the flow charts I've provided speak for them selfs regarding what's available with little effort and it's quite obvious the XS head is no exception either. It just goes to show that the protruding exhaust guide and boss area in fact does impede exhaust flow and velocity. A good analogy example to describe the influence the bulging guide and boss area have on flow resistance is to place a fan of medium size on high,then cover half of the frontal section of the fan with cardboard and take notice of air movement. Now take that same piece of cardboard and cut it in half and cut a 1/4 off the bottom or more doesn't really matter, then place in front of the fan on high and take notice of the increase in cfm velocity just by slimming up the cardboard...same principle of application
First step is to completely clean the head by means of either sand blasting or bead blasting. I prefer to sand blast,then for the final finish,I'll glass bead the head.
Second step is to provide some type of alignment marks to reinstall the guide to it's original position and whether or not this has any significants on proper valve alignment to seat, I don't know but it's a step I use when working with original cast iron guides. The guide in the picture is a bronze guide from Kibble-white that's been machined to accept the Megacycle 440 lift cam and it's been from my experiences that a iron guide is more suitable for street use,as the life expectancy of bronze is short lived by 20 to 30,ooh miles or sooner.
To remove the original guide place the head in an oven set at 350 degrees with the cap facing up for approximately 45 minutes,then tap or press out the guide and let it cool down before you commence to rework it. From A ( bottom of inner spring step) to B,the dimension of length should be between 1.355 to 1.360 and the dimensions for B to C should be about .215 on angle. These cutting steps are done on a simple wheel grinder,nothing fancy here. When you get ready to reinstall the guide,reverse the procedures but do not freeze the guides,just apply grease of a low melting point or Vaseline and apply some to the seal to hold it in place, once the guide starts absorbing heat from the head,the freezing effect is completely lost in a matter of seconds,then just drive the guide home, when the guide fully seats,you'll head a dull thud sound and when the head completely cools down,install a exhaust valve and hold the head up to a light source and pull on the stem to seat the valve and check for exposed light that might exhibit between the valve face and seat. If extreme amounts of light exist,then the guide is out of alignment not being centered with the seat,then proper alignment will require installation of a manganese bronze liner for correct centralization of the valve stem for proper seating of the valve face to seal.
When you start to work the exhaust pocket,remove just enough to clean up the casting flaws in the bowl and the corners. You want a smooth transition from the seat down to the valve guide and this is where you'll have to make a judge mental call as to what's needed to clean up port but just follow the info that's outlined in the porting section,along with what I've provided here for ya and your head should perform strongly and remember use your finger for feed back of surface irregularities in the bowl,corners and the very important SHORT TURN.........SMOOTH....SMOOTH....SMOOTH.........if possible
This is the cutter that I prefer to use when re-shaping the guide boss area cuz it's small enough to fit in tight quarters and removes smaller amounts of aluminum giving me more control to contour the boss to the desired shape I'm after.
In these two shots,when you start to rework the boss,I always start with the long side and work towards the front. Start at center of the valve stem and work it by removing aluminum at an angle and when you feather the boss,you want the tip of the feather to align with the center of the guide and gradually wrap the feather tip around the guide till it shows a SLIGHT off centered look. JUST LOOK AT THE PICTURES I"VE PROVIDED AT THE END OF THIS POST. It's really quite simple and the second one will be a breeze This is the long side of the port and roof and what you're attempting to do is speed the air up along this section of the port to reduce resistance of flow.
In the first shot it's semi finished but in the second picture I used 80 grit,120 grit and for the final finish I used scott bright using a coat hanger attached to a drill. I don't bother with giving the exhaust port a mirror finished cuz eventually carbon will adhere to the ports,just a waste of time in my opinion.
Now for the good stuff. I can't begin to tell ya how many hours I've spent welding and re-shaping the exhaust port on this head during the last few years,hoping to find the perfect port shape to at least pick up the low to mid lift #s cuz the 400 to peak lift #s are about as good as they get using this port shape. What really holds this head back in the low to mid lift #s is the short turn the turn either has sufficient material to work with or it doesn't or you can weld filler in to fill the voided areas but it's not an easy task either. I have quite a few heads laying around and only ONE exhaust port that has a PERFECT short turn from the factory,imagine that ;D and I using that for future reference to alter the turn but only until I can successfully gain better access to rework the turn by means of welding. Letter" A" is the turn leading up from the Short Turn, again I've played with that turn numerous times and if too much material is taken out or reshaped incorrectly,you'll loose velocity and the #s will drop dramatically to the bottom. When working the ST corner, you want a smooth radius from the seat leading up to the lip step in the port and again,use your finger to feel. If in doubt,it's better to take out less than trying to put the material back in or get assistance.
Letter "B" is the outside turn that I'm still playing with and with this turn,you either have enough material to work with or you don't. Letter "C" in the middle section of the floor,just smooth it out.
There are several exhaust shapes floating around form various reputable XS enthusiast and each one of them has a place whether it be for street or racing. You've got to remember #s are just that cuz in the end your motor has the final say as to what it likes
These shot are of the sleeves I install to reduce back pressure as the exhaust pulses enter the header,you simply want a smooth transition at the section and those are the cutters I use to trim the sleeve. I 've flowed a head using these sleeves and no loses were recorded,so all is good
The demensions of the sleeve are outside- 1.542, inside is made to my bushing driver 1.118 and the width is.475 ,now the width is set to provide a recess incase the lip of the header pipe extends inside the port from gasket compression,you can make it flush if you wish,I just choose this width to avoid problems in the field.
r80rt: :)This is a splendid write up, THANK YOU!!!!
Dec 26, 2015 16:54:05 GMT -5
mashermoto: What the what is this shoutbox for? Or should I shout, WHAT THE WHAT IS THIS SHOUTBOX FOR!
May 12, 2016 22:22:21 GMT -5
motormike: Good Day ...just a FYI.. Wild Cat is this Labor Day weekend. Still go'n on. A few 650's still make the scene. Various rides at different skill levels each day.. awards dinner sunday eve. BS in the park'n lot after dinner.
Aug 23, 2016 7:57:01 GMT -5
lsettle: First post in over 6 years!
Aug 28, 2016 19:45:17 GMT -5
kardon: Wow quiet here, where did they all go.
Oct 7, 2016 2:18:13 GMT -5
gggGary: XS650.com LOL
Feb 16, 2017 20:49:02 GMT -5
buell88: Anybody have any idea who built the xs650 tracker used in the Draggin Jeans Ad on Pipeburn?
May 16, 2017 16:24:09 GMT -5
joshua: The regulator/rectifier unit I got from Mikes PMA has closer hole spacing than original. Are we supposed to mill the holes to fit?
Jun 7, 2017 19:25:58 GMT -5
joshua: My bad. I found the bracket they supplied to mount the rectifier/regulator... Uh oh. How is this meant to work? Which way is it meant to mount? Looks like I have to use some spacers or something. Good instructions would be nice.
Jun 7, 2017 22:09:52 GMT -5
craig8johnson: Not sure if this is the right spot or not but oh well...
Jul 11, 2017 18:04:15 GMT -5
craig8johnson: I'm checking the charging system. I'm afraid I might have fried the last battery. With the solid state regulator (after market) what should it be charging at. The book says, I think, 15 volts. I'm hitting 17 when revved. Is that too high?
Jul 11, 2017 18:06:19 GMT -5
gggGary: Yes 17 volts is too high, about 14 volts is max, sounds like you don't have the right regulator or it's wired wrong.
Jul 13, 2017 6:54:33 GMT -5
dean: Just saying Hello, new member who is going to fix up a 79 XS650 that has seen its better days. I will definitely have lots of questions coming up.
Jun 23, 2018 16:45:32 GMT -5
tt650: Trying to breathe life into a 1980 that's been stored (indoors) for 25 yrs. Air filters are dry rotted. Have cleaned carbs but she only runs briefly on choke then stops. Need jet setting info and other ideas that might help her idle and rev.
Jul 3, 2018 19:15:19 GMT -5
trix13: Hey everyone! New to the forum and am fighting those gremlins!! New charging system, ignition switch, coil and fuse box. Resistance is higher than normal on the ignition pick up so I'm trying to find one. No such luck yet.
Aug 16, 2018 8:50:48 GMT -5
trix13: Also, even though all of my connections are clean, I cannot seem to find out why , when at higher rpms, I hit the signals and the rpms pulse with the signals...hahah. same with the brake light. I appreciate all input!!
Aug 16, 2018 8:55:08 GMT -5
bob99: how do I post a question. I am new to the forum
Jun 6, 2019 10:52:10 GMT -5
adlpc: Hello all! Been enjoying your edifying posts and discussions - and as a fan of the XS650 since my early teenage years happy that I now own a 1980 Special which I plan to turn into a vintage half faired racer. Thank you all for being here!
Oct 1, 2019 0:58:56 GMT -5
jimothyj: Hello everyone, I just joined & wish would have known about this site in 2014 when I brought my 1974 TX650A back from the grave. I have spent a good deal of $$ and alot of time on it. Just painted it and working on electrical, I will post pics soon,
Apr 10, 2021 2:14:13 GMT -5
louisvan: trix13 - I had a problem with my 1975 SX650. When I got to highway speeds, the engine lost power. The problem was in the connectors. At a certain vibration and the wind pushing on the wiring loom, the connector lost continuity. A bad crimp to the wire.
May 20, 2021 1:19:09 GMT -5