With Wings As Eagles: Car/Mechanical Entries

smells like...

2011 September 28 00:01

An auspicious day. Drove to Knoxville to get oil in New Beetle changed and 2 new tires. The desk dude fixed the roll pin in my switchblade key so it now folds smoothly (it's been bad since I got the car).

I had a fairly productive day at work; got some stuff moving.

This afternoon evening drove most of the way to office-away-from-home. Sirius Satellite radio had a town-hall Q&A with band (surviving members of) Nirvana, hosted and MCed by John Stewart. It's the 20th anniversary of the release of their album Nevermind. There was apparently a contest and the winners got to go to Sirius/XM studios in New York and be there to ask their questions.

It was a 2-hour session, and it was interesting hear them talk about their experiences. They played a few songs too. One was they played the demo tape the'd made recorded on a boom box of "Smells Like Teen Spirit". It's interesting to hear it in that unproduced format.

I was planning to grab a hotel room for the night anyway, but I thought it was auspicious that the session was ending as I was approaching the exit, and the full version of "Smells Like Teen Spirit" started to play, and I got to crank it up and listen as I drove to the hotel and parked. I don't know that I'm a huge fan of the band, but I certainly have a lot of nostalgia for that song. (it came out my Freshman year of college).

And I got room 137 in the hotel, which is a nice bit of physics nerd numerology.

The pressure's on

2011 September 26 09:37

Instead of flying, I stayed home yesterday, because I've been busy a lot lately and it was nice to have a day to work on the car.

Before driving, I did a bunch of stuff in the garage and adjustments to the engine. I have a relatively cleared work bench. I've collected together all the parts that I want to have in my spare set for long-distance driving, and all the VW tools are packed back in the tool box. I have a spare distributor which I was going to pre-time. My plan was I'd leave the distributor cap with the spark plug wires hooked up, and change out the rest of the distributor. However, it turns out that the notches in the distributor bodies are on different sides, so to do that I'd have to unplug all the spark plug wires, which is a pain, so I didn't bother. If I need to swap in the distributor, I'll have to statically time it, which will be fine.

I checked the valve clearances. Given my past problems with valves drifting, I was rather worried when cylinder #1 had much higher clearance than spec; it was like .014 inches rather than .006. The clearance getting larger is the natural way the engine wears, and is not indicative of a problem (clearance getting smaller is a big danger sign), so it's not catastrophic, bit a bit worrying since I just set them 600 miles ago when I assembled the engine. HOWEVER, cylinder #2 was similarly out of spec in the benign direction. Going to measure #3 (now on the opposite side of the engine), I've never hoped so much that a measurment would be out of spec. But cylinders #3 and #4 were similarly out, so I can only conclude that this is a symptom of the brand new pushrods settling in. I'll have to check it again in a thousand miles and hopefully it will remain stable.

I also wanted to run the engine for a while to get it to operating temp. I made sure the carb was adjusted properly. While I had the engine hot, I decided to spend some time and do an oil pressure test. When I re-built the top half of the engine, I replaced the oil pump because the old one was worn and had been put together by an idiot. I bought an entirely new pump, blueprinted the gears and body, sanded and polished the cover plate, and then installed it.

When I got the car, the oil light flickered at idle when the engine was hot. This is a sign that something in the oil system is worn; it's usually a combination of the main engine bearings wearing out and/or the oil pump. I did an oil pressure test; it was definitely out of spec. The test is:
30-weight oil, oil at 70 degrees C, 2500 rpm
new engine, oil pressure should be 42 psi; wear limit is 28 psi
Before the engine rebuild:
30-weight oil at 62 deg C, 2500 rpm, pressure was 18 psi
Since the rebuild, the oil light has never flickered at all, so I knew I had improved things drastically, but I didn't know how much. My test yesterday:
30-weight oil at 67 deg C, 2500 rpm, pressure was 42 psi
So it's well above wear limits, which is great, but it's nearly up to new spec. That's awesome! That long Monday Night Football game I spent sanding the (cast iron) cover plate until it was smooth was worth it!

I also drove the car yesterday to run errands. This was the first drive out of the driveway with the electronic ignition, which seems to be working stably. Yay!

The point of eliminating the points

2011 September 22 09:10

I've been working for a couple of weeks on getting electronic ignition set up in my vintage Beetle. I bought one setup, which turned out to be badly made and really wasn't going to work. That's another story. The story for now is that Monday I bought a Pertronix electronic ignition module from vwparts.net on Monday, it arrived yesterday mid-afternoon, and about sundown the engine was running successfully.

Here's what the inside of a classic VW distributor from the factory, with old-style "points" installed:

The shaft in the center of the picture rotates when the engine rotates. The shaft isn't round; as the shaft rotates, the lobes of the shaft push against the rubbing block (red arrow), moving the points arm (marked with blue dots) and opening (disconnecting) the contacts (green arrow). Then the lobe passes and the arm closes the contacts again. When the contacts are closed the black wire is electrically conneced to the distributor body; when they're open it isn't.

The reason for doing this is complicated, but the important thing is that something inside the distributor closes a switch and opens a switch in response to the rotating of the engine. This points setup is a simple way of accomplishing that goal. The problems with it are that there are several points of mechanical wear. The points degrade from the constant sparking and need to be replaced. The timing of the engine drifts as that wear happens. Eventually, the bearings of the distributor shaft wear out because of the constant pushing from the rubbing block.

The inside of the distributor in the car now looks like this:

The black ring marked with red dots fits down over the shaft and locks onto it, so that it always rotates with the shaft. It has 4 magnets in its rim. The black box marked with green dots contains a magnetic sensor and the other electronics. As the black ring rotates, it senses the small magnets going by, and in response, it electronically connects and disconnects the black wire to the distributor body, just like the points did.

The advantages of this approach are:

So as long as the unit works, the timing will never drift and nothing needs to be replaced or probably even adjusted.

One additional consideration; the points worked by using a mechanical switch to connect the black wire to the distributor, and the movement of the switch (the points) was provided by the rotation of the motor. With the electronic system, the electricity has to be delivered to the electronic module to power it. So instead of one wire coming out of the distributor, there are now two.

The black one goes to negative side of the coil just like in the points setup. The red wire goes to the positive side of the coil (which is hot when the key is on) and powers the electronic ignition module. I've put a fuse in the positive line, just in case something inside the distributor touches, it won't burn up the wiring.