Wednesday, April 28, 2010

Prepping Knuck Heads for Big Valves

I intended to post something entirely different, but at the moment, Blogger is not letting me cut and paste, so rather than rewriting something I have saved in another program, I will do something fresh.

Some time ago I started a series on installing bigger intake valves in a Knuckle head. This will be the second part of that series. When I left off, I had finished installing new exhaust seats. The seats from Rowe machine nicely (something that cannot be said for the 60+ year work hardened original seats. This also allows you to set the stem protrusion of the new valves, avoiding mis-matched depths.

If the intake nipples were removed for replacement (and in most cases they should be), now is the time to re-install them. I like to use JB Weld on the threads of the nipples, along with a stock type rivet. The epoxy is particularly important when porting, since some of the inner threads inevitably will be ground away. Here's a tip: from here on out, keep a set of used intake nuts screwed on to the nipples to protect those nice new threads.

Now that the new seats and intake nipples are installed, it is time for porting work, if you plan to do so. Doing this before new guides are installed allows you to do the best possible job. Disregarding the area just below the seat and the short side radius, the remainder of both ports should be shaped and finished as per the final product. I like a 50 grit on the intake, and a polished exhaust. However if the exhaust port is to get a thermal barrier coating, there is no point in spending extra time doing a fine polish.

With the majority of the porting work done, it is time to paint the heads. This needs to happen before guide installation, since the spring cups are held in by the valve guides. For a stock look, I use a semi-gloss black, and bake it on at about 200 degrees. Many of the hi temp paints available need this heat cycle to enable them to stand up to standard parts wash fluid. Nothing worse than keeping the new paint looking good through the whole process, only to have it get sticky and wipe off during the final wash prior to final assembly.

While the paint is drying on the heads, it is a good time to make sure the spring cups are ready to go. Often you will find a small crack just below the return tube. Be sure to weld these before going any further. Next, all of the gasket surfaces on the cups should be attended to. I use several purpose built forms along with a small hammer to return them to their original shapes. Don't forget to re-flatten the bottom portion that the guide will seal against. Once the cups are all in shape, they can be Parkerized if you are going for a stock look.

Guide installation, cutting the seats, and final porting work will be covered in the next installment.

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