Have finished machining the B18 cast iron conversion guides (bronze is not needed in this application, and really is only necessary for racing applications) to be used with B20 valves which have .312-inch (5/16″) diameter stems that are hard chromed and smaller than the original .343-inch (11/32″) stems for improved air flow. The end of the intake guides have also been tapered for better airflow through the port. The top end of the guides were machined for modern valve seals. Valves with chrome-plate stems and finely machined guide id's with a honed finish will last a very long time in street and highway use.
The new B20 exhaust and intake valves are in the center of the photo above shown in comparison to the B18 guides and valves on the left and the right. The dark spots near the valve head will disappear after a second blending angle is cut on the back side of the head for improved flow, after the new valve seats have been established in the head.
Both sides of the valve heads and the end of the stem where it meets the head have been lightened somewhat (compare them to an untouched valve below) by machining the two sides in the lathe and then swirl polishing the backside of the head. The 42MM B20 intake valve heads have been turned down to 41MM which is larger than the original 40MM B18 intake valve heads. B18 and B20 exhaust valve heads are both the same size.
Next up, install the guides in the head and machine and press in exhaust valve seats, and cut larger intake valve seats. And finally, relieve the combustion chambers, and do some very minor porting behind the valve seats.
Delete the DOT in the following link and replace it with a period to learn more about what was involved and view pictures of how the guides were machined @
http://theoldmotorDOTcom/?p=165294
Information
Jul 9th, 2017, 06:54
Engine rebuild
Threaded Mode