Last fall I picked up a spare AeroVee. A few weeks ago I was having problems with valves and I pulled a head off the spare motor. This motor had Empi heads from Sonex and they had about 20 hours on them. As I started looking at the seats and valves, they were really not great. I was considering a head swap but held off.
We know the purpose of the hobby is to buy tools. So I ended buying a Neway valve seat cutting set. I’ll talk more about that over in the tools section. But in playing with the new toy, I made a discovery.
The Neway tools use a tapered pilot that jams into the valve guide. Cutting is done concentric to the guide. What I found is that both exhaust seats in this head were not very concentric with the guide. It cut on one side at first and I had to cut a lot to clean up the opposite side.
I have a new set of CB Perf heads that I’m going to put bottom plug holes into. I have to get the Bridgeport to my hangar and tool up first. But I’m also going to do a 3 angle valve job on the brand new heads and see how good the machining is.
I am thinking that a valve job on new heads will improve the sealing and longevity of the valves. Stay tuned.
Wow, Bryan, you must be my improved better brother. I also picked up a spare Aerovee last fall. It’s a 2.1 with Empi heads. My current engine is a 2.0. Note of interest, I’ve had both heads on my current engine rebuilt with new valve seats. The first one I had rebuilt with new Empi valve seats. This is now on cylinders #3/4. Since installed I’ve been loosing my exhaust valve clearance at around 10 hours flight time on #3. Still have fair compression on that cylinder when pulled through cold and hot, although I’ve not done a leak down. The second head I had rebuilt I had CB exhaust seats installed, it is now on cylinder #1/2. I’ve had almost no valve clearance loss on those exhaust valves. I wonder if the CB seats are harder material than the Empi seats.
I think that is a possibility. It’s also possible the machining is better on the CB heads. It was discouraging how much material I had to remove to get the seats to cut all the way around. I really think they are not centered well on this particular head.
I’ve got all 4 seats cut in this head and they look really good. I’ll have to check the valve geometry as I think they may need another shim under the rocker blocks. I’ll be curious if this head has better valve lash stability when I’m done, just because of better concentricity.
I’ve posted this in the old forum but worth another broadcast I believe. The heads I’m working on now probably have the best casting quality I’ve seen, but still not good enough. Check out the casting flash in what is probably the most critical cooling fin location:
