In the continuing saga of building my first internal combustion engine, I posted last week about encountering a problem with making a spring and having it come out the right dimensions. I've managed to get past that roadblock by making yet another fixture and another spring.
The end result fit the previously made parts better than anything so far.
That's the intake valve assembly, with the spring retainer on top and a piece of temporary wire through the valve that holds it in place. The fixture is in front of them. I had a spring from an old project that was just about the ideal size for the exhaust valve and that one just needed to be cut to length.
Intake on the left, exhaust on the right.
The next puzzle was the exhaust pipe (since there's nothing in the pipe it seems wrong to call it a muffler, like I did before). The tricky problem here was cutting off a thin-walled (about 0.015" thick) piece of bronze pipe that I made by drilling a 0.344 hole into a 0.375 bar. Not just cutting it off; cutting it off at a 30 degree angle. Two problems stood out: the first would be holding the work at the proper angle, and the second would be holding the pipe tightly enough to withstand cutting forces while not crushing it.
My solution: make a fixture by drilling a 3/8" hole in a piece of 1x2 pine, 30 off vertical, slitting the piece of wood in half along the 2" dimension vertically, and then clamping the wood around the pipe. Move the combination onto the Sherline mill, clamp it in the vise and cut it off with a thin slitting saw. Like this (at setup):
You can see a wood screw at top left, one of two screws clamping the front and back pieces of wood down around the pipe. After lining up the edge for the cut this way, I moved the pipe to the left side of the saw blade (in this view) and made a cut. The blade was too high, so I lowered the saw blade about half its thickness and made the cut again. Closer, but still a bit short of the right depth. Lowering the blade one more time, got me the right cut.
What's left? I don't know. I've gone through the drawings a few times, and I think I've made everything that goes into the engine. If there are missing parts, they would probably show up best if I go through the box of completed parts and try to put it all together. I suspect I'll cut a handful of custom washers and spacers. I know I need a set of ignition points, which the plans call out as: (1969 DODGE CHARGER, 383, 4BL, W/SINGLE POINT DIST.) I have a couple of auto parts stores within a couple of miles of home. Time to go get those.
Great job! Do you heat the spring until it glows, and let it cool, or just take the toaster oven up as far as it goes for a fixed time?
ReplyDeleteAir-cooled or quenched? I've made springs from music wire, but never had to temper them.
Nothing special about the points, other than physical size.
The angled, "slash cut" exhaust pipe reminds of certain 4-into-1 collectors that were cut that way. We used to call them a "baloney cut" pipe!
Spring: The spring is taken, still on the fixture, wrapped in steel wool and then both wrapped up in aluminum foil as a heat buffer. Take it as high as the toaster oven goes (450?), soak for an hour. Turn it off and let it cool on its own for a couple of hours.
DeleteThere was a discussion about soaking vs. not soaking on one of the forums I read. One of the other graybeards, a retired ME, said the wire will gradually lose it's strength after prolonged use if you don't heat treat it. He said, "the heat treating "seals in" the tensile strength of the music wire." I have to say that doesn't fit any mental model of mine. 450 seems too cool to heat treat, but the best metals air harden - you heat them and let them sit. In order, the best is air hardening, then water, then oil hardening is the low grade hardening. I thought they all had to be heated red hot. Maybe music wire is air hardening and I'm wrong about the 450.
And exactly right on the points. All that matters is they fit the part they mount to.
That's more like annealing to stress-relieve it than what I'd call heat-treating.
DeleteDoes it have pressed-in valve seats? Looks like there's a slug of copper in there that the valves seat against.
Yes, press-fit valve seats. The valves are lapped against the changes to make a thin contact area.
DeleteAnother thing that could have been done while cutting the pipe would have been to put a sacrificial wood dowel inside for support when the blade was going thru. Or, instead, not cut it but rather use a disk sander to form the angle.
ReplyDeleteI guess that there's usually more than 1 way to skin a cat.....
If you really need to get crazy fixturing fragile items, you can fill them with one of the alloys that melt in boiling water. One of the lowest-temperature ones contains Cadmium, which makes it good at wetting metals like a solder. I read on a train modeling site that dipping the workpieces in motor oil before filling them keeps them from getting wet, because the heat isn't enough to remove the oil film.
ReplyDeleteHot glue is another choice of filling.
Neon Madman and Anon 0219, all of those ran through my head; wooden plug, fill with wax or some sort of low-temperature casting alloy. I thought I'd give it a try without that and start over if I have to.
ReplyDeleteOn the valve spring retainer pin, don't know how the final assembly is done, but one way would be to bend the ends in opposite directions tp prevent walking and evenly support the washer.
ReplyDeleteOn the ignition points, Chevrolet V-8s before the electronic systems had point sets with a screw for adjustment even while running, very nice. This would be about 1980 and earlier.
Also, it hurts my heart to turn that much bronze into chips.
You are actually stress relieving the springs, and drawing back hardness brought on by the shaping.
ReplyDeleteStress relieving makes sense.
DeleteMy First ICE was a two stroke. For reasons ��
ReplyDelete