Tuesday, June 12, 2007

Prepping the Flathead for Porting

As noted in the previous post on Joe's Flathead , these was some serious discrepancy in the valve sizes. The intake valves were stock diameter (1.940") but the exhaust valves were way oversize at 2.164". After some hemming and hawing and a bunch of measuring, I decided that by putting new seats in the exhaust I could reduce the valves size there to the standard oversize Rowe valve for a UL (2.050") without sacrificing air flow. At that point it only made sense to use the same oversize valve in the intake. Normally one would like to see a larger valve in the intake than in the exhaust, but in this case I felt we were doing pretty good to just get them back to the same size.

By comparing the first two pictures, one can see the 27 degree "backcut" that I added to the intake valves to enhance flow.

Once new valve guides were installed and sized, machining the cylinders for seat inserts was a piece of cake thanks to my Kwik-Way 044 seat and guide machine. After the exhaust seats were installed, the same machine allowed me to cut the seats with the special radius cutters in preparation for porting. If you have never seen this type of cutter, it is really pretty neat. On a standard 3 angle valve job, it cuts all three angles at once, and since the width of the 45 degree is built in, it is pretty tough to mess that part up. On the special radius cutters I have for porting work, the top angle and the 45 are normal, but from the 45 to the bowl is a specially shaped radius in place of the normal 60 degree angle. For the Flathead I used a cutter with a .060" wide seat in both the intake and exhaust for a little better heat transfer.

With the seats cut, it was time to go on to the porting. In any port job, the seat area in one of, if not the most important part in getting good flow. That part of the job is made much easier and more consistent with the use of the radius cutters. The ports themselves had previously been reworked by someone, so only needed a little shaping to make them good to go. The relieve job that had been done, well, that was another matter.
Next time we'll discuss the "relieve" part of "port and relieve" and also talk a little about valve shrouding and the heads.


Jack Hester said...

I have a set of Shovel heads, that have been badly boogered by some previous owner. A seat has fallen out, and not sure if it wasn't some oversize seat intalled improperly. I'm thinking of using these heads on a future build for Land Speed Racing, and am interested in salvaging them. My question is that can you rebuild the aluminum around the seats and install better seats? Thanks.


St.Lee said...

It should not be too much of a problem to fix the shovel head, either with just an oversize seat, or with welding and then a new seat. The seat and guide machine I have makes machining for oversize seat installation a piece of cake.