Thursday, January 8, 2009

Engine Progress

If you follow this blog regularly, you may be wondering how the vintage Drag bike (Vinnie for short) is progressing. This will be a quick update.

I have tried to spend a few minutes on the bike every day, rather than spending large amounts of time all at once. Last week I worked on the heads. The intake ports looked fairly good, a testament to whoever did the original work on these heads "way back when". I did a little clean up on the intakes, but got a little carried away with the exhaust ports. If you ever look carefully at Knuckle exhaust ports, you will notice that they have more humps and deep valleys than they should. The port shape seems to have been determined more by the shape of the outside surface of the head than by what was needed to get the exhaust out.

I couldn't resist filling in these valleys in an effort to improve the exhaust ports. I cut out a piece of steel to fit in each valley and then brazed them in with enough extra brass to smooth thing out nicely. After polishing, the exhaust ports are looking pretty nice.

Since the engine will not get any top end oiling, it will also not get spring covers (cups). This makes the valve job much simpler. For one thing the guides can be installed very simply, without worry of oil leaks. It also makes custom guides for the 5/16" stem intake valves much simpler. All I had to do is get a couple of guide blanks from Rowe and turn them down to the appropriate diameters and lengths. Unfortunately the blanks are only .750 O.D. to begin with, so they are not the best answer if using spring covers.

After installing the guides I replaced the exhaust seats. It has been my experience that the stock seats are so hard that it is very difficult to machine them; particularly for a high tech radius seat. Better to get new ones in there now and make the rest of the job go smoother.

I finished cutting the seats with a radius profile on exhaust and a 5 angle on the intakes. This is the same intake seat profile that I use for all of my porting (the 5 angle gives better wet flow characteristics on the intake than a full radius).

So far, so good, but there is still much to do!

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