Part of the reason for the shrouding of exhaust valve stem with guide is to prevent heat from hitting valve stem (it hits the valve guide instead) The counter bore isn't there to support valve stem. I usually shorten the step to about 1.5mm instead of completely removing it and re profile stem nose. Honda did a bunch of work on this several years ago but I cant remember where they published it. (but I know I did read up a lot) It not usually a good idea to take guides out 'cold' (unless its a Harley where the seat inserts fall out if it gets hot ;D) Usual temp is about 350deg F, don't go much hotter or you can get separation of dome/head. Re-heat head to fit new guides, usually there is going to be anywhere from 0.004" to 0.007" interference fit. PJ
Last Edit: Nov 16, 2006 9:31:50 GMT -5 by crazypj22
There are three types of people in the world, those who can count and those who can't I dabble in rocket science, when I'm not picking my nose
hey jack i work in vws for 38 years here in puerto rico and iam a 650 freak for many years i do my oun heads wen was a regular drill work mecanic learn every day your work is very good and smart looking at the pictures i learn a lot from 1 to 10 i give you 10 chocolates
All the linked images in the porting section will lost sometime at the end of February or the beginning of March. I don't use Photo Buckets anymore or any site to host pictures, I have no back up system to keep images alive. I signed up one more time to keep the images alive, after ninety days they will lost. Just giving a heads up,if you want this information with images you need to start coping it.
Beekay.............I would never in a million years even think of pulling the porting text,it's up there for a reason. For some reason Photo Buckets has change their free service guidelines of usage to host pictures,etc. I just noticed recently on other forums that alot of accounts have been either inactive or deleted completely and while not fully active with the garage as much,I was concerned about the images in the porting threads being deleted by PB. What you can do is # the photos in sequence and down load them "as is" to your computer cuz I believe I used one photo more than once to illustrate certain areas to work and if I start moving images around certain shots will be lost. Sorry for the inconvenience but it's not my doing.
Hey Jack I'm trying to follow this thread as well as possible. Something I'm noticing here is that you advised against bronze guides, yet on the second page about halfway down, I'm seeing bronze guides. Has something changed with that?
Also; The epoxied D shaped port that you mentioned on the same post... no pic. I'm very interested in that. Was that port design per the Mototune site recommendations?
I'm beginning to take seriously that the port cross sectional area/valve size is disproportional. This, after hearing a variety of opinions which are unanimous in agreement on that.
So that Mototune D-port concept is beginning to make a lot of sense, especially considering that it raises the floor while reducing the cross sectional area at the same time, widening the short side radius.
If possible, any updates on this would be hugely appreciated.. Not just by me, I'm sure.
[glow=red,2,300]Pocket Power[/glow] There are several means in which one could begin to increase an engines " Volumetric Efficiency". So lets look at them first
2) camshaft replacement
3) exhaust system upgrade
4) and finally head port modifications
Now out of these four items,which would come first? If were my motor,the port modifications would come first on the list being that there's no sense in tring to increase an engines volume efficiency if it can't properly inhale or exhale any increasements,so any improvent on either end,will be a benefactor on the power output,a exhaust system upgrade is a major plus in seeing drastics results along with port modifications, carburation rejetting will be needed most likely and finally,install a HP camshaft to keep those valves off them seats longer and your off to the "Moon"
A great deal of power typically hides under the valves, around valve guides and in the port bowl(or pocket),just begging to be unleshed by you and your grinder and this is generally referred as to " Pocket Porting". The idea is to remove the rough casting flaws from the factory to a smooth finish were there's no resistence to flow along the bowl area,alongside the port to the guide boss area and even profile the guide boss to a degree. Remember when pocket porting, you need to stay within 90% of the valve to avoid fuel seperation from the seat but we're safe here>
Now for some,you'll find it much easier to remove the valve guides to gain better access to those tight spots and it does make a world of difference. Just make sure you mark weither its for the right or left exhaust port and make a indication point as to line the guide back in it's original location in the spring seat area. [glow=red,2,300]One word of caution in regards to bronze guide replacement. Stay the hell away from them,they distort to a point where they need a guide within a guide to straighten them out!!!!!!!![/glow] If your guides need replacement,have the stock guides honed out and install a .060 solid bronze Kz liner not the cheap grap,these are solid bronze liners!!!!!
The one thing that jumped at me ,even after the porting,is the port volumes are still over the limit for it's given exhaust valve size,which should be in the vicinity of 85 to 90% of the valve to maintain higher speeds of velocity to expell the gases and pull harder weither on the street or track,"Velocity is a MUST" IT's my opinion that a choke down would be in order for this type of correction to speed velocity and have I got a port in the works,you bet ya. There'll be no close up shots of this port untill I've tested it's effectiveness as a producer. Jack
Here's a angle shot of the D shape that's epoxy filled for testing purposes only, The floor and the rightside turn,should in my opinion should take the low lift #s to the moon. This picture does this port no justice at all !
There is a formula to deteremine appropriate port volume VS valve size but I don't have it and the cross sectional area should be in the neigborhood of 60 to 75 % of pocket width,along with engine displacement and stroke,the longer the stroke,the greater the cross sectional area to avoid choking the air supply at higher RPMs. As far as bronze guides go,they last a long time on the intake side but on the exhaust,there life expectency is quite short from my experience. The D Shape intake port I've been working on has been sent off to get flowed,should have some data on it's flow gains/ losses sometime next week and the D Shape starts at the entrence of the intake not to the seat, the XS intake has always shown greater gains by widing the floor to the short turn. The floor was raised 2 mm ,along with re profiling the pocket and roof with a cross sectional area of 1.57sq inches. Crossing my fingers that this D port blows away my previous low lift #s by 10 to 15%. I taylored the port to yield the best street performance when used in conjuction with either the 256 or shell#1 grind.
On to a few of your questions though,one of the reason the British motorcycles have smaller port volumes,BSA's in particular is the inherited longer rod ratio's where velocity is more of importance than volume. Like any engine combination,it's all about gaining the most to yield gains in velocity and CFM's with the smallest port volume without compromising top end breath-ability. There;s a good article over at Britbikes.com titled A-65 overhaul, where the guy turned his ports into a D shape and is quite pleased with the performance.
As far as the XS having great low to mid range power,these engines have relatively small cam lifts with a port design to delivery the goods where the valve sees the most action before peak lift and it's that area under the peak lift( around mid lift) where you wanna focus your attention to delivery the plus gains to pack the cylinders before the valve reaches peak lift for a broader power band. If you feel the power is lacking on top end you can either install larger valves or a camshaft with longer duration and higher lift to increase the fuel mixture to the cylinders. I'm no expert here as everyone has their own ideas how to port the XS head,it's all a balancing act,you gotta experiment to find the right combination that the engine and you like.
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