Thursday, July 5, 2018

Head Games

I walnut blasted my heads a few months ago, and I didn't oil the valve seats well enough to keep them from corroding a little. Nothing major, but enough that I needed to do more than lap the valves in. What follows is a good example of wasted time, wasted money, and a whole lot of frustration. In short, if you're looking to do valve seat work, skip the next two miserable paragraphs.

I looked into getting a valve seat grinding setup, and wow, are they pricey! So I found a site that sells just the stones for about $14 bucks apiece and set about making my own self-centering stone holder. I cut the head off of an old exhaust valve to use as a pilot, drilled a hole in a chunk of aluminum, which I then heated up with a propane torch and dropped the aluminum onto the exhaust valve/pilot. After it cooled, I used a collet to hold the assembly in the lathe and turned threads on the aluminum portion to match the grinding stones I'd purchased. I then took the 45° stone for the intake seat, screwed it onto my new tool, and placed the tool back in the collet, set up my top slide to the right angle, and used a diamond-tipped dressing tool to grind the stone perfectly concentric. I wanted to make sure I didn't impart any weird tilt to the tool while I was using my drill to spin it, so I pushed a piece of 1/4" fuel line over the end of the tool and connected the other end to the drill. This seemed to work ok, except that the rubber hose allowed the tool to vibrate and caused some chatter unless I was careful not to apply very much pressure.

I worked through all three stones, re-angling them with a diamond stone on the lathe between valve seats to make sure the angle stayed true. Once I got to the 45s, I started checking the seat width. It wasn't until then that I realized I was grinding non-concentric valves. Whoops. I took a break to do some research, and came across a company called Neway. It took me some time to build up the nerve to pay for the tooling needed, but in the end I caved and picked up the stuff. After cutting a couple of the seats, I can say with confidence that was the right decision. Here's a picture of a valve seat that's had the 15 and 75 degree angles cut in it with their cutters.



It's a little tough to see, but the red line is what hasn't yet been touched. At its thickest, it's about .053, and at it's thinnest, it's around .018. That's pretty bad! The good news is, with the Neway system, I've been able to recut the seats concentric with the valve guides, and I'll be moving on to CCing the heads shortly.

This is what all of my valve seats look like now:



That's an exhaust valve seat, so the width is about .01" wider than the intake seats. They all look a lot more concentric now, though, so it's time to put new Dykem on the valves and seats and try to fit them together. I wanted to check for even contact between all the valves and seats, but I didn't want to remove any material. I decided to use toothpaste instead of lapping compound, because it's still abrasive enough to remove the Dykem but not enough to carve material away from the seats.




With all the valves and seats marked up, I put toothpaste around the contact area of the valves, placed them in their respective guides, applied a little pressure and rotated them 90 degrees back and forth a few times. I was really impressed; every single one of my seats showed clean, even lines around the entire 45 degree face, and every single one of my valves showed even contact around the mating surface. Consider me sold - Neway cutters are the way to go!

The last thing I did was clean up the toothpaste as best as I could and hose down the valves and seats with WD-40. Tomorrow I'll bring the heads to work and clean them up again in the parts washer, and then I can assemble the valves and springs into the heads for good.





Saturday, June 30, 2018

One step forward....

Actually, no steps forward for a long time. It's been pretty quiet on here for a while now. I finished assembling the short block on the engine by adding the flywheel seal, oil pump, etc. and bagged the whole thing to keep humidity out while I worked on the heads. I took a break to work on some Christmas presents on the lathe, and then I broke the lathe, so that needed repair... after that I started trying to recondition the heads myself. I don't think that was a mistake; the way I went about it was a little less than ideal, which caused more problems than it solved. That's all for another post though; this weekend I'm back at the fuselage, and making some serious progress... backwards!

Two years ago, I received the canopy I ordered. There's a long story of assumptions, misinformation, betrayal, and pretty poor customer service, but the bottom line is I've spent the last two years trying to figure out if I can even use the canopy or if I need to buy another one. It's a Dragonfly canopy, but the folks who made it insisted on molding it out of thicker acrylic than the design calls for. As a result, it bends a lot less than I anticipated, and trying to force it to fit has been difficult. Along the way, I realized how uncomfortable the seat is, because of the angle the seat back rests at. All it needs is to lean a few inches back to be much better.

So the plan was to cut out and replace the existing crossmember and seat braces, leaving the plywood shelf in place.


Here I've got the line marked, and just in case the sides got any squirrelly ideas, I put a clamp around the old crossmember to keep the dimensions stable. I clamped a straightedge on my line and used a utility knife to score through the plywood. I removed a chunk from my new line forward to the old crossmember. 


Looking good so far. The next step is to cut and fit the new crossmember and glue it in place. I just need to look underneath to mark the angles, and...


Whoops. There's an unexpected turn of events! The longeron doubler doesn't go quite as far as I thought it did. This just became a much bigger project.......

So I'll be replacing the plywood after all. I don't have any pieces that size left, but I can still cut the new crossmember and put it a little further forward. I had hoped to gain 3.5", but I ended up settling for 2.75". It didn't take long to fit the new member, which installed quite nicely.


With that in place, I cut out the old crossmember and seat supports, sanded and planed the remaining bits of wood away. 

I cut and fit new seat members, glued them in place, and left them to cure. 


This was enough for now. I'll still need to add all of the gusset blocks, but my goal this weekend was to get the plane to a point where I could sit inside and take measurements on total height required above my head as well as instrument panel height. I'll do that tomorrow when the glue's had more time to set up. Once I get those numbers I can finish the templates for the canopy frame, which I'l work on when I come back down in a few weeks. In the meantime, I'll keep working on the valve seats.