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- Nov 26, 2009
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Narley ports made easier.
The first release version of Narley ports (Harley XR750 ports adapted to Nortons) required welding the port floor and raising the port to get a larger radius leading up to the valve seat. In reality – no one is going to be welding up the intake port floors because space is tight and the welding is too difficult (the exhaust port floor has easy access and can be easily welded). After a lot of careful study I discovered that you can combine the best aspects of the 28mm Norton port (its steep downdraft) with the generous floor radius of the KR 750 port. Norton 750 heads with the 28mm ports can be converted to the 850 bolt pattern. The drawing below shows both intake ports laid over each other.
Here's the combined intake port with the unused parts of the drawing above erased. You can see that the intake port is greatly improved. You have the steep section of the 28mm Norton port joining up with the optimum cylinder filling radius of the XR750 port as below.
Look how much the floor radius is increased – The intake floor radius is doubled from 12mm to 24mm. The exhaust floor radius in increased from 15mm to 22mm. This is accomplished by re-angling the valves away from each other and re-shaping the port floor leading up to the valve seat. Going to larger valves allows an even greater floor radius by moving the valve further outward toward the squish band. A very important feature of the drawing shown below is the relocation of the valves so they have more clearance between them to avoid valve clash with higher performance cams with more overlap (most high performance Norton cams have less optimal wider lobe centers to avoid valve clash). Stock clearance is approx 3/16” between the valves on the seat. The moved “Narley” ports provide over ¼ between the valves even though the valve heads are larger in diameter (up to 43mmm intake and 36mm exhaust). This means that the roof of the bowl must be re-shaped – first by welding to add filler and then careful porting according to the new specs. Welding in the bowl area is not difficult because there is enough room to get in there with the welding tip. See the “fill” areas in the relocated port images below.
AC
The Norton valve layout found in stock Norton heads was originally designed for the 650ss. It was never redesigned for the larger bores we are using today. The valves and guides are too close together. Re-angling the intake guide and valve so it is more vertical than the usual big valve 26.5 degees and moving the intake valve away from the exhaust gives the space necessary to achieve these ideal high flow ports. The larger the bore - the less valve shrouding. Trimming the bottom of the rocker end and raising the valve tip helps to restore rocker geometry. I haven’t shown all the dimensions in these images (too crowded) but they are available along with other details. If someone steps up and creates such a fire breathing head – we would see higher HP figures than ever. Put in a motor with todays lightweight low stress reciprocating components combined with longer rods (less reversal snap) giving higher RPM capabilities would raise the bar in classic racing and put Norton twins in the front of classic racing again where they belong.
The first release version of Narley ports (Harley XR750 ports adapted to Nortons) required welding the port floor and raising the port to get a larger radius leading up to the valve seat. In reality – no one is going to be welding up the intake port floors because space is tight and the welding is too difficult (the exhaust port floor has easy access and can be easily welded). After a lot of careful study I discovered that you can combine the best aspects of the 28mm Norton port (its steep downdraft) with the generous floor radius of the KR 750 port. Norton 750 heads with the 28mm ports can be converted to the 850 bolt pattern. The drawing below shows both intake ports laid over each other.
Here's the combined intake port with the unused parts of the drawing above erased. You can see that the intake port is greatly improved. You have the steep section of the 28mm Norton port joining up with the optimum cylinder filling radius of the XR750 port as below.
Look how much the floor radius is increased – The intake floor radius is doubled from 12mm to 24mm. The exhaust floor radius in increased from 15mm to 22mm. This is accomplished by re-angling the valves away from each other and re-shaping the port floor leading up to the valve seat. Going to larger valves allows an even greater floor radius by moving the valve further outward toward the squish band. A very important feature of the drawing shown below is the relocation of the valves so they have more clearance between them to avoid valve clash with higher performance cams with more overlap (most high performance Norton cams have less optimal wider lobe centers to avoid valve clash). Stock clearance is approx 3/16” between the valves on the seat. The moved “Narley” ports provide over ¼ between the valves even though the valve heads are larger in diameter (up to 43mmm intake and 36mm exhaust). This means that the roof of the bowl must be re-shaped – first by welding to add filler and then careful porting according to the new specs. Welding in the bowl area is not difficult because there is enough room to get in there with the welding tip. See the “fill” areas in the relocated port images below.
The Norton valve layout found in stock Norton heads was originally designed for the 650ss. It was never redesigned for the larger bores we are using today. The valves and guides are too close together. Re-angling the intake guide and valve so it is more vertical than the usual big valve 26.5 degees and moving the intake valve away from the exhaust gives the space necessary to achieve these ideal high flow ports. The larger the bore - the less valve shrouding. Trimming the bottom of the rocker end and raising the valve tip helps to restore rocker geometry. I haven’t shown all the dimensions in these images (too crowded) but they are available along with other details. If someone steps up and creates such a fire breathing head – we would see higher HP figures than ever. Put in a motor with todays lightweight low stress reciprocating components combined with longer rods (less reversal snap) giving higher RPM capabilities would raise the bar in classic racing and put Norton twins in the front of classic racing again where they belong.
