No perskules testasin kyllä että ne olis toiminut.... no pistetään tekstinä, tuo yksi pdf ei kyllä onnistu
porting terms
First we have to know the different parts of the port.Floor-as the head would be on the engine the bottom of the port would be the "floor",and the top of the port would be the "roof".If we turn the head upside down and take the valve out,we would be looking into the "bowl"of the port,it looks like a bowl.As the port "floor" goes toward the combustion chamber,it turns into the bowl,this is called the "short turn radius",this area of the port job "short turn radius"will give the home porter the most increase in air flow.We will start with the exaust port on my next posting.
We will be doing most of the work on the short turn (we want to give it a radius instead of a sharp edge or corner)and in the bowl of both the intake and exaust.Iwill tell you some don'ts,don't open up the seat I.D. on either intake or exaust,yes this will increase the air flow numbers at high lift,say .500 but it will kill the low lift numbers,we want the low lift numbers to be as high as possible.We want to deshroud the intakes to the seat,in other words,after the seats have been ground,we don't want any ridge from the seat to the combustion chamber,as in when the valves have been sunken into the head.
porting tools
Things you will need.Eye and ear protection is a must.Good lighting,a face mask,and a fan to blow the powder away from you.A hand grinder,if you have an air compresser,use a couple of air die grinders,their cheep.An electric hand grinder will work,one that takes 1/4 shanks.A drill will work but not as good and it is real slow gooing,air is the cheepest way to go and it does a good job,and the tools are light.One large stone,about 1 in dia. one small stone,about 1/2 in dia,a 1/4 shaft that will take sanding rolls,we need to use no finer than 80 grit sanding rolls.
You will also need a tool to remove the guides,they don't have to come all the way out just enough to get them out of the way of our tools,if you are going to be using the guides that are in the head,you can drive them out with a bolt slid into the guide from the bowl end and tap lightly with a pin and hammer,heating the head will help,it is possible to work around it however,but it can be a pain.
exaust port
Some think that the intake port is all important,the exaust is just as important as the intake,we have to get out what we get in,and if we do it wright it will help bring in more fuel-air,mixture.With the valve out,and the head upside down,take your grinder with the small stone and start to radius the short turn,getting rid of the ridge all the way around the inside of the bowl,once you are satisfied with the stone work you can use a "flapper" wheel to get it real nice.Again,don't open up the seat at this time.
claying pistons
When we try to get as much cam,valve,or piston dome,we have to check the clearence of the valve to piston as if it were running.We do this by putting a line of modelers clay across the top of the piston,from valve pocket to valve pocket over the top,and on the sides of the dome,to check piston to head clearence.Then, with the pistons down in the cylinder,we assemble the engine and set the lifters,and slowly rotate the engine so that the valves and piston come close to each other,then we take the heads off and simply measure the thickness of the clay on the sides,and the thickness of the clay in the valve notches,this is only required when we put in real high lift cams or high domed pistons with head milling.With moderate lift cams we can go in the spark plug hole with a wire coat hanger(about .100 thick)and rotate the engine while looking in the hole and moving wire around as we rotate the engine,if it "grabs"the wire we have to get more clearence,with real stiff springs,.080 is about as close as you want to get.My valve springs have 200# on the seat and 550# open,on the nose of the cam.
We will come back to the exaust after we do the valve job.The best flowing exaust valve is the "R" tulip valve,if you choose to not run this valve,because it has a longer stem,or what ever reason,you can get a standard length 1 3/4 ex.valve in the nail head design.
Intake ports
If you are doing a 900 and it still has the smaller valve,it's good to go with the larger valve but DON'T open up the seat I.D.to match the bigger valve,you will have a better transition from the 45 degree cut to the bowl and we have a more gradual entry into the combustion chamber,this will give you more low lift air flow.The first thing we do is in the combustion chamber and it is called deshrouding the valve.I use lapping compound to locate the seat,now I take an old valve with a smaller head dia.and install it,to protect the seat from grinding,you should just see the edge of the seat with the smaller valve in place.We now take our grinder(allways keep the tool moving and take off alittle at a time) with a small stone or cutter,I use a tappered carbide cutter,and remove the ridge so that the 45 degree seat goes unabstructed into the chamber,you can make nice with a sanding roll or flapper wheel.
My next step on the intake port is much like what was done on the exaust bowl.All the work done on the intake will be done in the bowl area.We want to put a gentle curve on the short turn radius.If,like in some cases that Ihave done,the ridge or sharp edge(corner)isn't very big,as far as height,we still work as nice radius on it,only smaller,working all the way aroud to the sides of the bowl.The bowl should be round and smooth,no ridges,or sharp edges.After you are done with the bowl we work our way,out the port(toward the manifold),you need to go no farther than 3/4 of an in.from the short turn radius out.Now from the manifold end of the port,some heads have a machined area that goes in about 3/4 of an in.and at the end of the machined cut it leaves a ridge sticking out into the air stream.If you have this and it's on the roof we want to level this down.Over working this end of the port at the stage of porting we are doing does no good,polishing the intake does no good,working the floor at this end of the port does no good.Almost all of the increase in air flow comes from the turn into the bowl and the exit past the seat and valve.
valve terms
Some valve terms,stem,head,face,margin,back cut,tulip,nail head.The face is the surface that that the valve grinder works to match the seat on the head,we want this wide.125 with NO back cut.Here's where common sence thinking will hurt you.After the face has been ground,there is a sharp edge on the top of the face cut that car guys will almost allway get rid of,to increase flow,but in our case,it will hurt the flow by alot.The margin is the thickness of the edge of the valve,we would like this at about .060,minimum,.040 on the intake and as thick as .100 on the exaust.The tulip valve on the intake is a must,but some tulips flow better than others,I use the kibblewhite precision machining brand.The 'R" exaust valve flows the best by far,but some will choose not to use this because of the extra stem length,but in any case we want to go to a larger exaust valve,and I will explain why in my next post.
valve job
First the exaust.If you went to the over sized exaust valve,we have to explain to the guy grinding your seats what you are doing,it's more work and some will charge extra,some won't.We want the normal triple angled seat,30 45 60 angles,some grinders use different angles than this that's ok, nothing special exept the seat has to moved out to the larger valve size.One 45 cut on the valve.After the valve seats have been cut,we want to blend the bowl cut(60degree) to make a nice radius going out the chamber into the exaust port,I lap the seat so as to clearly see it,you really don't want to hit the seat with your grinder now,I use the sanding rolls on a shaft working from the port out to the seat,just get close to the seat it's very risky at this point.We want the exaust seat to "funnel"the exaust out.Main things to make good air flow out the exaust port,bowl has nice radius out to port,the tulip valve,wide margin on exaust valve,and a radiused seat to exit the exaust.If the valve has been sunk quite deep in the head we have to also deshroud at this time,I don't suggest you do this unless it's real deep,because it's easy to destroy the seat at this point.You can ASK your machinest to make a wide"deshrouding"cut with his 30degree stone this will help alot.If he does this no further work is required on the exaust.
After the valve job(seat grinding)the angles will have sharp edges that we want to radius or blend,the only one we have to blend is the corner or edge that the 60 degree cut has made in the bowl.So we blend the bowl to the 60 degree cut getting rid of the sharp edge and making it a curve or radius.The other point,the deshrouding,is when the exaust valve seat has been ground,there is a ridge left in the combustion chamber that is like a wall to the valve at low lift.If the valve is sunk say .030 then the first .030 of lift will give you little air flow,if the grinder uses a large stone and he moves this "wall"out,extending the 30 degree cut, away from the valve,then we do no more to deshroud the falve.Hope this helps,but if not we can try again.
last of the porting tips
We will finish up with the intake seat and valve grinding.The usual grind will again be 30/45/60.If the 60 has a real sharp edge we want to smooth it out a little.Like the exaust seat we use a sanding roll and work from the bowl to the 60 degree cut,stay away from the 45 degree cut(the actual seat)don't over work the blending of the 60 to the bowl,just break the sharp edge,a long(wide)60 degree cut helps low lift flow.If you end up with a ridge on the seat out side the head of the valve we have to deshroud the valve,using a smaller valve to protect the seat while we sand or grind out the ridge.
porting goals
The goal here was to explain to the home builder that he can do some porting that will benifit the power out put of his engine.You could end up with an intake with good low lift numbers and a flow of about 120 cfm @ .400 cam lift,the lift of a stock sportster cam,p or q.Astock head will flow about 20 cfm less.The exaust could flow about 100 cfm @.400 valve lift,about 80% of the intake.There are head porters that will charge you as much as $700 or more for this much air flow,and they will tell you that,that is all you can get from an ironhead,bull,my maximum reworked heads flow 175 cfm @.600 valve lift,they will flow more if you keep lifting the valve but with an iron head thats about the limit on valve lift.Iwill sell you a 120 cfm head for around $300 plus parts(with home porting you might have 120 with my flow bench testing you will have 120 or more cfm @.400)We can go as high as 140 cfm for a 1000 cc engine or 160 cfm for a 74 in iron head.The more air we work to get the more it costs,time is money.
engine cases
When building a high out put sportster engine the first thing we have to look at are the cases,and their weak spots.All cases up to and including the 1972(if it has a speedo drive hole)will break at the speedo drive out let on the right rear corner.Do we then use only the later cases,no, we can make the early ones stronger(as strong as or stronger than the newer ones)We first make a donut shaped piece of al. to go over the machined surface of the same shape that surrounds the counter shaft bearing.Pre heating the cases and keeping them bolted together,we weld the speedo hole shut and weld the "donut"at the same time.I can do this for you for about $125.I am not trying for a sale hear but giving you some options.The next weak spot,but not nearly as weak as the corner,and this could be for real high out put engines only,is the timing plug hole.I weld it shut,then make a "donut"to go over where the hole was,weld it in place,and redrill the hole,only smaller. I have never broke an unmodified timing hole,engine without some thing going seriously wrong on the inside first.
IHTom.
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