Monday, December 19, 2011

At Long Last ...

It certainly seems as though this has taken an awfully long time. More than once I have wondered if the rapture would arrive first ...but I finally have, in my possession, the production version of the oversize Knucklehead intake valves that have been in the works for well over a year. At a 2.060" diameter, these are a full 5/16" larger diameter than the stock valves they replace.

Bigger intake valves in Knucklehead motors has been a "speed trick" for nearly as long as Knuckleheads have been built. These valves are the proper diameter to "do it old school" by removing the existing seat insert and grinding the new seat directly on the head. By blending the material from the bowl into the I.D. where the old valve seat was, you will wind up with a "choke" of 90% which is just about right for good flow on a Knuckle head.

Back "in the day" automotive valves were typically shortened for use as oversize Knuckle intakes. While period correct, they have a few drawbacks. Shortening the valves require the use of a lash cap on the valve tip to prevent premature wear, which can throw off rocker geometry. Often automotive valves have a lot of "tulip" which requires the bottom of the already short Knuck guide to be further shortened. They also tend to be very heavy, which does nothing for performance. These 5/16 stem valves address all of those problems.

For some time now, savvy engine builders have been aware that a late model Iron Head Sportster valve was a good choice for an oversize intake valve for a Knuckle due to their similar length. Though the XL's 1.940" diameter valve was easy to come by, its thinner (5/16" vs 3/8") valve stem still left it a "not so easy" upgrade. No problem getting valves, but few engine builders are inclined to machine their own valve guides. That's why I took the initiative to have a production run of 5/16" bore valve guides manufactured for Lee's Speed Shop recently. Of course that still leaves an issue with the stock valve seat inserts. A 1.940 or a 2.0" intake valve does not fit onto the stock Knucklehead valve seat insert, and requires machining for an oversize valve seat insert.

Not so with the 2.060" valve. As mentioned above, once the old seat insert is removed, a seat for the new valve can be ground or cut directly on the cast iron of the head (just as Iron Head XLs have always been). This 60+ year old performance mod for Knuckleheads has never been so easy! They are now in stock, and ready to ship.

Now, chances are, if you are paying close attention you will have caught on to another logical use for these valves. If an Iron XL intake valve is a suitable upgrade for a Knuckle, then it follows that an oversize Knuckle intake valve may be a suitable upgrade for an Iron XL! That's right, a 2.060" intake valve may (I have not had a chance to try it out yet) be a good bet for a maximum effort Iron XL drag motor. In case anyone is interested in trying it, the overall length of the 2.060" valve is 3.675 as compared to the R series XL intake at 3.690.

If you are wondering why anyone would set out to produce and market performance parts for a motor that has been out of production for over 60 years, then you are in good company, for I often wonder that myself. Still, it does seem that I have a corner on the market least for the moment.

1 comment:

Mark said...

Lee, thats great I'll be ordering up some valves and guides sometime after the 1st.