T head engine by Brian

[brian Rupnow]

I had to take my chainsaw over to my oldest son's place and play "Johnny Lumberjack" this morning and take out a couple of big trees for him. This left me with a bad case of "lazyitis" this afternoon, so I made two parts for my engine that didn't require a lot of thought. The brass part is the adapter for the Traxxas carburetor, the aluminum piece is the exhaust.

[brian Rupnow]

Ah Heck---I couldn't wait to see how they looked on the engine, so I tapped the cylinder head and installed them!!!

[Ringo]

Brian gets more done with Lazyitis, than the rest of us when actually working !!

[brian Rupnow]

I ran into something a bit strange yesterday. When I threaded the ends of the exhaust and carb adapter for the engine yesterday, the parts were held in the lathe chuck and the die was held in a collet in the tailstock chuck. No problems were encountered, I even ran a standard 3/8"-16 nut up the thread to ensure that everything was Kosher. When the cylinder head was tapped 3/8"-16 it was held in the milling machine vice and threaded by hand with a tap and standard handle. After screwing things together yesterday afternoon, they were crooked!! It doesn't show in the picture I posted, but they were quite visually crooked. I didn't want the Loctite to set up, so I disassembled things. This morning I held the cylinder head in my mill vice and a tap in the milling machine spindle and turned the spindle by hand, and the tap was cutting metal. I ran the tap in until it bottomed out, removed it, and cleaned up the ends of the cylinder head. I then held the inlet (carb adapter) in the chuck of the milling machine, applied a bit more Loctite and turned the spindle until the shoulders on both pieces were touching each other. I must have had the tap turned at an angle when I first threaded these parts. I would stand and deny that I would make such a dumb mistake, but I can't figure out what else it could have been.

[brian Rupnow]

It hasn't been a horrible morning, but it sure as heck hasn't been productive. I have one valve to show for it. Beside the valve sets a piece with a 0.1875" hole reamed thru it to check the valve stem for when it is exactly the right size. I can't even begin to tell you why it took so long, but suffice it to say, I've never sanded on anything in my life as much as that valve stem to bring it down to size. I did use a live center in the tailstock to keep the outboard end from flexing while the valve was machined. Maybe tomorrow I'll get lucky and make another valve.

[nickel-city-fab]

I would stand and deny that I would make such a dumb mistake, but I can't figure out what else it could have been.

I don't think you made any mistake, let alone a dumb one.
I think it's just the way things are when you cut a thread with a tap or die by hand.
The best we mere mortals can do is "close enough".
That's why single-pointing threads is so much better --
-- the machine assures good alignment.

[The Artful Bodger]

Brian, if I may draw your attention to my little lash up..



I did a topic on it titled Red Neck shaft finisher.

N.B. If anyone wants to comment on my little ensemble please do so on the original thread.

[brian Rupnow]

And as the sun sets into the golden west, two valves are finished. The second valve went quicker than the first, but with that extra long stem both valves required more attention than I have ever given to a valve before.

[mattthemuppet]

I've tapped holes crooked by hand before. All you have to do is start it a little tilted and it'll follow its own way. I try to always start taps in the same set up that I drilled the hole, even if they're finished by hand. Never have a problem doing it that way

[brian Rupnow]

Today, the crooked carb adapter and exhaust have been straightened. I hunted around in my box of assorted springs, and come up with two likely candidates for valve springs. I made two brass stepped bushings which fit over the end of the valves (which are shown in place with "handles" still in place) and retain the valve springs when they are compressed. I still have to cross-drill the ends of the valves for 1 mm pins that hold the spring retainers in place. Not a whole lot to show for a days work, but then I didn't work on the engine most of the day. It was a beautiful 88 degree sunny day here today, and I didn't feel like doing much!!

[brian Rupnow]

Today was a semi quiet day, finishing up little things. The valve seats were cut with my special George Britnel tool. (Actually a larger version of my original tool for valves with 1/8" stems). The valves were lapped into the seats using first 320 grit paste, then 400 grit paste, and finally with 600 grit paste. Then the "handles" were cut off the valves because they were no longer needed. A bronze endcap for the exhaust system was turned, drilled and loctited in place. I found that I had screwed up the design of the valve cages, by not leaving a "tit" of material on the end of the cages to register the springs on. I fixed the design drawing, but rather than remaking the valve cages I turned a couple of "add on" bushings to the end of them with a cavity on one end to fit the o.d. of the valve cages and a cavity on the other end that the o.d. of the valve spring would fit into. The rods hanging out the end of the valve cages are temporary, just in there overnight to ensure correct positioning of the bushings until the loctite sets up. If you don't have this spring locating feature, the spring will ride against the side of the valve stem and cause problems. Tomorrow I will probably make the tappets. I picked up a piece of 01 steel yesterday, long enough to make the tappets and the cams from. ----Both tappets and cams will be flame heated and quenched in oil to harden them.

[brian Rupnow]

Today was tappet day. Doesn't look like much, but these were all machined from a length of 3/4" diameter 01 steel. They will be flame hardened and quenched in oil, as will the cams when I make them. The cams are almost the only remaining part of the valve train to be machined.

[brian Rupnow]

The tappets have been heat treated and assembled and installed in the bushings in the tappet guides. The valves are ground and cut to length, assembled with springs and keepers. I have a couple of sewing needles installed as temporary cross-pins, until I see how everything fits together. I may have to cut one coil from the springs, but I won't hurry to do that. They can always be shortened later. I'm very happy to see that the valve stems line up properly with the tappets.

[brian Rupnow]

Today I have prepared a piece of 01 material to make two cams from. The length of the piece is determined by the depth available in the three jaw chuck which is attached to my rotary table. The center diameter is determined by the maximum bore inside the chuck. The diameters at the ends are equal to twice the 0.382" dimension on the drawing, which determines the size of blank to cut the cam from. The material is just long enough to grip in the three jaw chuck with 3/4" of material stuck up above the chuck jaws. The cams will be .688" long, which should keep the cutter above the chuck jaws. I go a little bit crazy every time I make a cam, because I don't do it often enough to remember all the set-up steps. Attached are the picture of the prepared stock, a drawing of the cam, and a model of the milling machine cutter and the cam in their relative positions on the milling machine. The milling cutter will be turning clockwise, and the center of the mill spindle will be offset from the centerline of the rotary table chuck by 0.346" and 0.200" which, as you will notice on the drawing is the centerline of the flank radius. This should give the cams being cut a 99% chance of matching the drawing. Every time I do this, I write myself a bunch of notes on how to do the set-up, and then read thru all of my notes before I do it again.

[brian Rupnow]

Today was not a good day. I fought the cams and the cams won. The cutting tool slipped in the holder. The stock slipped in the chuck.
I was overwhelmed by a hoard of zombies. I was bitten by a rabid bat. I was stung by a murder hornet. My day has turned to crap. Perhaps a different approach to making cams will be investigated.