A few times I’ve had a hard time getting a valve out of the guide. It will go partway, and get stuck by the keeper grooves. I had one intake valve on my spare head do this, and I had to drive it out with a punch.
Afterwards I measured the stem closer to the valve and at the end. Nominally I measure 0.3130”, but the end of the troublemaker was 0.316”.
On the happy valves they were 0.313” everywhere. So I taped the unhappy intake valve to the happy one, chucked up the good one in my hand drill, and polished the mushroomed part with a piece of 320 grit. I chose that grit because it was on top of my junk box of sandpaper.
Interesting observations. I’ll be interested to hear about how it does on hot starts with no lash. I assume you’ll need at least some clearance (probably not 0.018").
I watched one of Andy Gaunt’s recent Aerovee assembly videos and he was talking about offsetting the rocker slightly, which pressed on the valve more toward one side to encourage the valve to rotate in the seat (at least that’s what I understood from his dialog - I may have totally misunderstood). If I did understand that correctly, could that offset put more pressure on a smaller area of the valve stem and just be mushrooming the edge. Maybe centering it a little more would spread the load more evenly and reduce mushrooming? Just curious.
The ball foot rockers (which is what Andy has, but he calls them elephant foot which is a different style) have a contact area smaller than the valve stem. Not by a lot - so we are just making this contact area off center.
I did not follow up on the other thread properly. I did do a ground run with a loose zero, I pulled the airplane in, and popped off the valve covers. Going through the 4 TDC positions I grabbed each hot rocker with a glove and gave it a tug, and found that I went from zero lash to some lash on the ones I checked. I also screwed up #3 exhaust somehow and it was way tight, and I ended up replacing that valve. I’ve been running 0.003” since then.
I have had the same issue removing valves from the cylinder head. On mine it is always the keeper ridges that have pounded out a bit. I take 220 or 240 grit emery cloth to the stems by hand around the keeper ridges and they come out smoothly after that.
I’ve never liked the ball adjusters nor the elephant foot adjusters. Just one more point of failure. I like using the solid adjusters like the original vw style and the ones Revmaster uses. They have a very small contact area so they won’t mushroom the valve stem end. They’re offset and have a better chance at spinning the valve like they are supposed to do when running. I’m using my old Revmaster rocker arms with solid adjusters on my Aerovee. They seem to get along
This is not a great picture, but the only one on hand.
I would recommend against using a zero lash setup. I’ve never not had exhaust valve creep in 25 hours. Even just a 0.001” or 0.003” loss in that time could potentially cause a burnt valve. 0.003” lash clearance may be fine, but I’d end up checking clearances more often.
