Sorry for the slow update on this thread. As I said before, I get the family discount on all machine work (free), but the "cost" of that is that my stuff falls at a lower priority than paying customers. Sometimes it takes a bit bit before we can get to mine.
Here is the boring machine with my 340 block in it.
As a reminder of post #33:
This is a fairly simple and unassuming machine, but it very precisely bores cylinders
based on the deck of the block. This is why (in post #16), we worked to get the block completely square, flat, and with consistent deck height for all cylinders. Bores in a block are supposed to be perfectly orthogonal (90 degrees) to the crank and deck surface. In actuality, they can be off a couple of thousands (or "tilted"), depending on the operator and/or the machine on the day it was bored. My father-in-law likes to hone the last .005" in a block. So we will bore my block to 4.065". Since my block has a (worn) standard bore, we will be cutting .025" using the boring machine (4.040" + .025" = 4.065").
Like all machine work, the devil is in the detail and the setup. Cutting is quick, but setting it up exactly right takes the time. If you screw this up, you might have to sleeve the block or trash it - so check twice or three times!
The first thing we did is roughly check how "tilted" the bore was. This is simply done by using a square and looking for light between the square and bore. My bores were not very good, and had roughly a .007" tilt top to bottom. Again, this wasn't precisely measured, but it was used to get a general idea. Remember also that a worn bore is also not perfectly round or perfectly straight either. The thrust side of the piston wears one side more than another, and other machining errors can cause other wear issues and patterns.
If you look carefully at the picture, just above the deck of the machine on the shaft you will see two pins sticking out of it. The third is hidden in the picture, but these three are pins are set at 120 degrees apart (like a Mercedes Benz emblem). The shaft is put into the bore and these pins are then moved out. As they move out, they will precisely align the boring head to the center of the bore. The problem is, if the bore is tilted and worn funny, how far down the head goes will set to where it is aligned. In general, my father-in-law prioritizes the top of the bore, about 2 inches down to get below the worst wear. This is the area where all the force is exerted when the engine is running.
We also needed to check if the .030" overbore is enough. If the bores are severely tilted AND severely worn, then perhaps a .030" overbore is not enough. This is unlikely but better check and make sure. The bore is measured with an inside micrometer as shown below.
My bore was only worn about .0025", so not bad at all. So bottom line is not bad on wear, but bad on tilt. Then we did a test bore to bore out some, but not all of the cut. So instead of boring out to 4.065", we set a bore cut to 4.055". This gives us .010" in case some other issue turns up. Now remember, cutting the bores to 4.055" means we are cutting .015" beyond the standard bore size of 4.040". It also means that we are effectively only cutting about .0075"
per side of the bore.
Setting the cutting head of the machine is done using this tool shown below. It is a specialized micrometer that sets the depth of the cutting bit in the machine. It is inserted into a special slot in the boring shaft and pushes the spring loaded cutting head to a precise radius.
Finally, the boring depth must be measured and set. It must be deep enough to cut the entire bore, but not deep enough to strike any webbing or structural elements below the bore. My 340 block was easy with lots of room for error, but Chevy 350 blocks have little room for error - every block is different.
OK so then to boring. Here is a picture while the machine is boring the block. Even though the picture is a bit fuzzy, if you look carefully you can see a line to the right of the shaft where the cut is at.
Look at the picture below. Here is a great indication of bore "tilt". So cutting about .0075" off of each side of the bore at the top yielded this result at the bottom. You can see a shadow where none of the block was cut. In this case, the final .010" cut will remove this and then the .005" honing will go further, so we will be OK. But this just goes to underscore that these blocks were FAR from perfect from the factory!
Now once set up for the first bore, the others cut much more quickly.
Sorry about the wall of text here, but hopefully those interested will find this informative and helpful.
Next up is honing, but it will likely take a couple of weeks before I can get to that.
Hawk
I appreciate the confidence, but I have to hone (no pun intended) my skills first! I'm not sure which part of apprentice engine builder you two missed!!! I am nowhere near an expert - just learning, and I'm trying to suck up all the knowledge I can!
