Cylinderhead
Here I will present some basic information about building a durable cylinderhead for the 175. What type of parts work best, what they should look like and how they should be installed. The topic of cylinderhead modification and theory is very complex, I can only present the very basic concepts here. While I do some of my own machine work like modifying valve guides and cutting valve seats, I leave the machining of the actual valves, the porting of the head to the experts. How you modify and port a cylinderhead will depend much on how you intend on using the engine, what carbs you plan on using, your rpm limits, compression, fuel type and many other factors.

 

175-Cylinderhead-1.jpg (19162 bytes) Here is what a finished cylinderhead should look like. Clean, flat gasket surface, combustion chambers smooth/polished, valves cleaned of all deposits. Valves in this head are stainless steel, 1mm oversize, exhaust valves are special alloy stainless steel to tolerate very high heat.

Both intake and exhaust valves are made from "blanks" meaning they have to machined to fit from a generic size valve. I'd give you the part numbers and sources but that would make things too easy.
Guides-1.jpg (17902 bytes) Here we see a set of valves and guides removed the from the head.

At the top, from left to right are: SS intake valves, SS exhaust valves (with guide "blanks" slipped over them), and stock exhaust valves.   The stock exhaust valves can be quite durable if properly prepared.

On the bottom from left to right:
Stock valve guides, used bronze guides, newly machined bronze guides.

The bronze guides are also machined from blanks as seen on the top row. The tops of the guides come ready to accept late model valve stem seals.

Bronze guides will eventually become a necessity on a high performance engine, they retain oil better, wear the valve stem less and are less prone to binding in the high heat encountered in a race engine.
Guide-tool-1.jpg (8729 bytes) This is the valve guide installation tool I made. The long thin tool on the bottom is for driving the guide in and out of the head. The smallest diameter section fits very precisely into the guide bore. The large spacer helps to align the tool and guide for installation.....using the large flat ends to sit on the valve spring seat to keep everything aligned. The small spacer is used with the tool to ensure that the guides are installed at the proper depth.

Guide machining and installation is a pretty tricky business and requires great precision in taking measurements and machining the guide. Removal and installation requires heating the cylinderhead to about 250 degrees but no more than 350 degrees.

This work is best left to a professional if you have any doubts about your skills.
Valve-1.jpg (15867 bytes) Here is a problem I've encountered with SS valves. Note the "cupping" of the sealing surface of the valve. This was more than likely due to the valve seat being improperly cut, or just worn out, leaving a slightly rounded surface for the valve to seat against. With the high spring pressures used in a race engine the "rounded" valve seat will pound it's shape into the valve.

To help prevent this and to ensure proper valve sealing it's always best to check the valve seats and re-cut as necessary to provide a nice flat sealing surface and all the proper valve seat angles.
Valve-3.jpg (20069 bytes) Another image showing the "cupping". Note the small gap where the ruler meets the sealing face of the valve..you can see light between the ruler and the face. That's not good.
Neway-1.jpg (16388 bytes) This is the tool I use to cut the valve seat angles. It's from a company called "Neway" and it works very very well. I have both "freshened" up worn seats and restored seats that were in very bad shape with this tool. The valves seats I have cut with this tool have held up very well under the abuse of racing.

The theory and operation of this tool is too complex to go into here. The Neway website can be found here: http://www.newaymfg.com/