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|Subj: Replacing valve guides|
On a typical valve job, is it necessary to replace the factory valve guides? Or for a flight motor is it best to pull out the factory steel guides (regardless of condition) and replace them with manganese bronze?
|Craig Payne, Utah, Manual #6154|
|Reply from WW:|
|Most Corvairs that we use as cores in the shop still have good valve guides. We have flown the vast majority of
our hours on the standard factory valve guides. In a standard valve job, we leave the guides alone. If the guides are
excessively loose, I prefer to replace them with bronze guides. This work is best done by one of the shops that
specialize in doing this for Corvairs. We frequently use Wheelerizing in Brea, Calif.
|Subj: Removed head - cylinders too|
Hello again from Minnesota. I was working on the Corvair this weekend and found myself removing one of the heads. Two questions: How can I be sure the studs didn't rotate in the case? I tried to watch for movement but I'm just not confident that I didn't miss any minor movement. The other question: When I pulled the head from the case, the cylinders remained attached and the whole assembly came off with the baffles attached too. Any harm in this? Maybe this is somewhat normal but I had to take a rubber mallet and give the cylinders quite a few whacks to unseat them from the head.
Other comments: After I got the head and cylinders off, I thought I should remove the pistons, however the inner rod bolts seem very difficult to reach. Maybe with the other side off it's easier, but I could only get a socket on to break it loose, then the rachet just spun and spun (about 1/8" at a time). Any suggestions? It appears the engine has been rebuilt as there is some signs of wrench slippage on the rod nuts.
Tom Brant, Brooklyn Park, MN
|Reply from WW:|
|Occassionally, Corvair heads come off with the cylinders still attached. This is not a big deal. Kroil and light
taps with a rubber mallet can usually work them free. If the nuts came off the studs, they probably unscrewed without
turning the studs. I would not be overly concerned if you did not see any sign of movement. Generally, the studs that
unscrew have the nuts frozen on them.
You can reach any rod nut in the engine by rotating the crank to a favorable position and using a fine tooth ratchet and a 12-point socket. It may take a little work to loosen them, but if you study the issue with the socket in your hand, you'll see how it's done. To take rod nuts on and off, I find that the best socket length is part of the way between deep and standard. The socket we use is 1 3/8" long.
|Subj: Oil pressure and Exhaust|
I have 2 questions:
1. Can I use an Earl's T fitting to mount the stock Corvair oil pressure switch and a VDO oil pressure sensor to the stock switch mounting location? Should I use the Teflon paste on the NPT fittings? Then, is it kosher to drill and tap a 1/8NPT fitting on the bottom of the oil pan to mount the oil temperature sensor there?
2. I think I've found a cheap, repeatable, off-the-shelf exhaust system. You mount the stock iron logs, then you buy a 180 exhaust tube from Clark's, and cut it off at the point where the straight part makes the second bend in the wrong direction. Weld the cut-off bend in the opposite direction, and you have changed the U into an S that seems to fit the Dragonfly firewall pretty well perfectly. See any problems with that? How far should the exhaust pipe be kept away from the fiberglass bottom of the canard to prevent heat damage?
|Dave Morris, Dragonfly, Texas|
|Reply from WW:|
|I've studied your photos carefully. The 1/8" pipe plug will not tolerate having that kind of weight
supported off of it if the sensors are allowed to vibrate in any way. It will work if you make a bracket
that supports the mass of the sending unit and does not allow it to vibrate. (That has to be one of the
larger sending units I've seen.) While you can put the temp sender in the pan, I prefer to have them in
the oil stream, reading the temperature of the flowing oil. However, I understand the space constraints of
As for your exhaust system, I would make sure that the pipes pointed down at something like a 15 degree angle and were several inches below the canard. As I'm sure you're aware, room temperature cured composites do not like heat. In your favor, the prop blast will help to keep the area cool. The Clark's u-bend you have is a typical automotive bend which has necked down sections and is galvanized. This will make it hard to weld, and flow less than a mandrel bent pipe (like the tubing sold by Magnum Force racing). With a Dragonfly, pay special attention to isolating the gascolator from heat radiated by the exhaust.