Prop Flange Extension

This will be a quick post - as part of my power plant setup, I'll be using a 4" aluminum spacer to help streamline my cowl around the engine. At my place of employment, I've got access to a CNC mill and a larger metal lathe, among other things. I was able to pick up a 5" diameter 6" long piece of 6061 aluminum for about $40 on Ebay, modeled what I wanted in CAD, then went to the manual lathe to turn it. I should have taken more pictures, but I didn't think about it; I do a fair amount of machining at work, and it all feels pretty routine anymore. The first picture I have is after I turned the stock down to final inside and outside dimensions, except for the face that will abut the flywheel. I set it up on a rotary table on the mill to get a bit more precision with the 6 prop-mounting holes, but that was probably overkill.

 

Spot drill, undersize drill, final drill, chamfer the edges. Not exactly rocket science. I intentionally left about an extra half inch on the end that I chucked up for the majority of the turning work, so that the marks left by the chuck wouldn't be on the final part. When I reversed it to turn the remaining face, I used some orange .050" plastic shim stock between the jaws and the part to avoid marring the finished surface. Turning the remaining face was straightforward, though I took light cuts to make sure I wouldn't pull the part out of the chuck. 

After the final lathe operation, I drilled the other 6 holes and cleaned up the part. Nothing left to do but put it away until the engine is ready to run... except test fit it on the flywheel.

Whoops... This is a new problem!

Ok, ok, it's not really a problem... at least, it's not a mistake or a roadblock or a money pit kind of problem. The last few weeks have been pretty good - I finished assembling my heads,

made a plate for bolting the cylinders on to check deck height for each piston/cylinder set,

(btw, this gave me wacky results - I had to remake the plate to cover *both* cylinders at once, the same way the head will when the engine is assembled)

(Again, not like this.) and then made a new two-cylinder capturing plate and measured deck height at final torque.

Deck heights were all pretty darn close - I had a spread of 0.1997", 0.122", 0.1225", 0.125". Because I have a lathe handy, I was planning on chucking up the pistons and dusting them all perfect - but after doing the math, I realized that by arranging the heads correctly, my compression ratio would range from 7.976:1 to 8.021:1. In other words, a maximum difference of 0.045:1......... I think that's close enough!

I went ahead and painted the cylinder numbers on the case according to convention, and then marked the cylinders and pistons accordingly.

Since I wanted the heads on certain sides, I went ahead and marked them as well.

The last thing I have to do on the engine for now is bag everything up - each head will get a bag, each piston/cylinder will get a bag, and the block will get a bag. I don't want to have to carry the assembled engine up out of the basement when we move in a few months, so I'll just leave it in pieces until it's in a shop that's on the ground floor. After that, I'll assemble it and bag it again, until I need to take more measurements off it or am ready to attach it to an airplane. So what's the problem, you ask? Well, this engine has been about the only thing I can do related to my plane right now. Every couple weeks we travel to see the rest of my family, and I can sneak away for a few hours to work on the plane when we're there, but otherwise it's just me and the engine. Now that I'm mostly done with that, I'm not sure how I'll keep making progress... and if I'm not making progress, I'll drive my wife over the edge. :)

Getting Ahead

I was so excited to get past this hurdle - heads are finally (almost) in shape. I figured the best way to CC my heads was to install the valves and valve springs - turns out I was wrong*, but that's how I did it to start. Got them in pretty easy, once I figured out the tool:

I'm really, really opposed to buying single-purpose tools. However, there's really no way around this one - it was either this or some kind of press with a few hokey jigs, and I didn't have space for that nonsense.

Once I got the valves installed, I started prepping for the CC measurement process:

Ok, the first step is always to get the heads level. I figured the easiest way to do that was to set up the heads, then add shims until they were level. This turned out to be a huge project, because even with the heads just about perfect, air bubbles would still show up *not* directly under the hole in the plexiglas. So I'd have to start tipping the head, and by the time I got the bubbles where I needed them, the shims would have walked out of position and now the head isn't level anymore, and the bubbles zip off to some corner of the chamber. I spent more time re-stacking shims than I did on any other part of this project!

I failed to take pictures of the entire CC process - call me impatient, I just didn't want to stop what I was doing and get my camera out. I went through the process at least 3 times for each chamber, then averaged my results - which wasn't hard, considering my syringe only had 1cc graduations. I was still able to guesstimate quarter-cc accuracy though.

Final volumes were 56cc, 56cc, 56cc, and 55cc. I'm still not sure about the last one - but it was consistent, all three measurements showed 55cc on the dot. That was easy enough to fix with a rotary tool and a cutter, followed by a sanding drum to smooth away chatter marks. Now I've got about a quarter cc spread between all four chambers, which is definitely good enough for a VW.

I cleaned the heads and valves really well to make sure no shavings or abrasives remained, and then put them away for now. I need to measure the valve spring forces, but after that I can reassemble the heads and bag them for now.

Aside from matching all the chamber volumes, CCing the heads gives me the last unknown for my compression ratio equation. I've got 94mm cylinders with a 78mm stroke; that's good for 541.2918 cubic centimeters. I've got 56 cc's in the heads, and I want a compression ratio (CR) of 8:1. CR is calculated by adding the volumes of the cylinder, head, and deck height, and then dividing by the sum of the head and deck height. When I go through all that, I get a necessary deck height of 3.06mm, or about 0.120". Back in an earlier post, I made mention that with the cylinder shims that were on the engine, the deck height was 0.114"..... which is pretty close to what I want. I can add .01" by going with the next size up shim; if I felt really crazy, I could chuck up the cylinders and turn them down .004" to get exactly what I'm after. However, I'm so close to final assembly of all of these components, I don't want to risk damaging something - and I think being off a tenth on my CR is probably ok; the math I'm finding looks like I'd be splitting hairs over less than half a percent of my power.

*The easiest way to do it is smear just a little grease on the valves and on the valve seats, then push the valves in and give them a little turn to hold them in place. No leaks this way.

No turning back now...

Got my LocTite, and had a few free hours tonight, so I finished the crankshaft buildup by torquing the connecting rods to spec. Then I gooped up all of the head studs with Permatex Aviation 3H and installed those in the case halves. 

I got everything covered in moly grease, dropped in the cam lifters, crankshaft, camshaft, cam plug, and stud seals, then put the case together and torqued everything down just as if I was sealing up the case for real. 

I checked free rotation the whole way through, and man, is it nice and smooth. All the gears mesh up just fine, no weird noises or rough spots. With that, there was nothing left to do but tear it all down so I could add grease and sealer and put it back together one final time!

Got moly grease on the cam lifters, which in my case are hydraulic. Using moly on them really helped them stay in place; a big plus on aircooled VWs, since they want to fall out when you try to put the case halves together. Dropped in the crank and camshaft, then gooped up the cam plug with 3H and stuck that in its place. (Apparently this picture was actually before the cam plug was installed.)

Next came the excitement - spread 3H on the other case half, mate them together, and put all the nuts and bolts in.

I gave it one more free rotation check once everything was torqued and ready to leave, and sure enough - smooth as you please. I'm gonna have to find something else to complain about now that the crankshaft is doing what it's supposed to do. One final thing I did before I sealed the case up was check my end play at the flywheel. I've got three shims in between the first bearing and the crankshaft to act as a thrust bearing, and the remaining end play is shown below. I think I'm supposed to have it at around 0.005", but I'll have to check on that. I'll order a shim to put between the flywheel and the first bearing and call it good.