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So, despite yesterday’s poor leakdown test, I was up at 4:30 this morning to eagerly continue my journey westward. I was sitting in the airplane at 6, ready to go. Low ceilings and visibility were all around, but forecast to improve mid-morning. So I sat there for 3 hours, and decided to do a little research on VW air-cooled burned valves.

And I learned that the burned valve in my AeroVee demonstrated all of the attributes of a classic burned valve. It was eroding from the edge (hence the low compression), and had the characteristic green crescent on the edge.

Now I became very apprehensive about continuing. I messaged Bryan and voiced my concerns, and without a moment’s hesitation, Bryan and Adam gave up their entire Sunday to help take the wings off and load the UHaul. These guys possibly literally saved my life! People like Bryan and Adam renew my sometimes waning faith in human nature, and I’m so grateful for their assistance.

So it’s a 2,000 mile UHaul home to California tomorrow, with the Sonex tucked safely behind. Am I disappointed to not be flying home? Sure. But I’d rather be safe than sorry!

Burned valve. 80/13 on the leakdown test.


Crack between valves:


These are mofoco heads.

Edit: in theory these heads were off 10 hours ago for new rings, and the valves were not burned. Can that happen this quickly? Interested to hear what the VW gurus think.

I wonder if the valve stopped rotating, it looks like the burnt part of the valve is right near the crack but might just be a coincidence.

Murray Parr wrote:I wonder if the valve stopped rotating, it looks like the burnt part of the valve is right near the crack but might just be a coincidence.

It's not the best picture, but the burned part was not aligned with the valve.

Bryan,
What kind of borescope do you have?

That valve doesn’t look too bad. I would triple check to make sure your rockers have the correct .004-.006 gap as being just a little off can cause the valve to open early or late and mess with compression measurements. It’s very common for that measurement to move around for a while after a rebuild. If you do decide to put a new valve in it, it is a relatively simple job as long as the seat is still good. I use an oxygen sensor socket to push down on the valve spring in a drill press and then a small magnet on a stick to grab the keepers. If you lap the new valve to the seat you should be able to tell if the seat is fully sealing or not.

As far as the location of the mark vs the crack between the two seats it should be irrelevant if the rocker arm geometry is setup correctly. One of the reasons that the rockers are not perfectly centered on the top of the valve is so that the valve rotates slightly with each stroke. Any marks lining up would indicate either incorrect rocker geometry or a sticky valve guide keeping things from turning.

Well, perhaps the AeroVee would have gotten me home. And of course the forecast over the western half of the US looks great this week. Never mind. It’s all good.

bvolcko38 wrote:Bryan,
What kind of borescope do you have?

Bill, something Adam got on Amazon for $70. It's chinese, has a forward & side camera. It works well enough!

kmacht wrote:That valve doesn’t look too bad. I would triple check to make sure your rockers have the correct .004-.006 gap as being just a little off can cause the valve to open early or late and mess with compression measurements. It’s very common for that measurement to move around for a while after a rebuild.

Keith,
That valve was cooked. It is a little easier to see when you are moving the camera around than in the static picture. We could see a gap. Also we did check & set all the valves. The #1 exhaust was at 0.005", and my manual says 0.006-0.008. We reset it to 0.007. But besides the picture and the 80/13 leakdown, there is this:
1) Very low compression when turning over by hand
2) With the leakdown test going, you could easily move the prop around off TDC and it didn't want to take off like a normal engine.
3) With the leakdown test going, air was pouring out the exhaust pipe.
4) We moved the prop around to open the valves and look at the seats. They were horrible. It was clear they were not sealing well.

Sounds like the worst case of "get-home-itis" I've ever heard.

By the time Adam flew back from Sonex with a pair of new heads, Bryan and Hambone could have had the engine ready for the install. 4-5 hours later it's time for a beer, a nap, then onward.

Gotta be worlds cheaper than a 2000-mile U-Haul rental to boot.

Another interesting thing we found was there was a distinct click, 12 per revolution, when you turned the prop slowly over. We looked at the Aerovee manual and figured out there are 12 magnets on the PMG. Popped off the starter, popped off the stator cover and the noise went away. Three of the 4 screws that hold the stator to the cover were a little loose, so the stator could move around. Redid the loctite, retorqued the screws, noise was gone.