This is a "snap gauge" being used to find the inside diameter of the rod bearings. Then, an outside micrometer can be used to measure across the "T" and the crank journals to find the clearances.
Next I installed the “deck plate” on one side of the block, tightened the fasteners to 80 lb.ft. with ARP lube and let it sit overnight to allow the block to relax from the violation it received from the main and head bolts. That is something I learned in my schooling for what I thought at the time was going to be my career in Tool and Die making. That didn’t really work out; I got bored. Anyway, metal does not instantly change its shape is the very basic version of what I’m saying. Especially brittle metals like cast iron. So, although it’s not a huge amount of difference between just bolting things on and honing versus letting the block “equalize” overnight, I know it matters so I do it this way. It’s a curse.
In this case I didn’t get to hone the block for a couple of days because I work on my stuff when I don’t have customer engines or family obligations to deal with. So, it was a very relaxed block! The first step was to adjust my dial bore gauge to be zeroed at my desired final bore size of 4.043” which will give me a piston to cylinder wall clearance of .007”. I had left about .004” to hone after the boring operation because I did not use the deck plate for boring the block. The block measured about a .001” distortion at the tops of the bores in and around the cylinder head bolt areas which was demonstrating the amount of distortion the block see’s when the cylinder head is installed. Note: If the block was not filled with Hard Blok to within one inch of the deck surface it would have been distorted much more than it is. Also, this older 1972 block is much beefier than the newer “roller” blocks that I was using previously in Muscrate. The first step in honing is to get the hole closer to final size and closer to being round and “straight” from top to bottom.
For the initial removal of cast iron I used a Sunnen AN-101 stone set which is a 70 grit material. This grit goes through cast iron like a hot knife through butter and I quickly removed .0025” from each cylinder bore. Next up was a switch to an AN-201 stone set, which is a 150-grit material. As the stones get finer and finer the operator needs to start paying closer attention to what is going on and specifically making sure that the stones do not become “loaded” with grit and stone pumice from the operation. If this happens the stone can become glazed over and nothing much will happen besides heating up the block and giving inaccurate size readings.
I removed another .001” from the bore and now was developing a pretty round, straight, and smoother cylinder. With a manual stroke machine such as mine (meaning the operator physically moves the honing head up and down in the bore), it becomes necessary to frequently stop machining and use the dial bore indicator to check the circumference and length of the bores to make sure there is not an out of round or “bell” shape developing. Some blocks can be a real pain in the butt to keep straight and require the operator to “dwell” a certain amount of time at the bottom or top of the bore to keep things straight. This is learned from experience.
Next up I installed the AN-501 stones that are 280 grit. This grit is normally the final step in street type engines or even some dirt track engines which get the living wee beat out of them for lap after lap and usually have higher coolant and oil temperatures than a drag engine will ever see. I finished out the last .0005”(that’s a half of a thousandth of an inch) and established a nice “cross-hatch” finish that everyone likes to see. A final check with the dial bore gauge showed that my bores were round within .0003” and straight (up and down) within .0003”.
Normally, I would stop at this point with the stones on all but the most critical performance engines because the end user (customer) has to be a little more careful and diligent with keeping oil changes frequent, temperatures under control, etc. to keep things happy. And of course, the oil retaining “cross hatch” will wear away sooner than it would with a rougher beginning finish. For this engine, however, I went to the next step, which is a N37-J87 stone (400 grit). Being careful not to “load” the stones I made 10 medium tension strokes in each cylinder and called it good. Any more and I risk burnishing the surface of the bore -- not cool.
Last step is a quick five strokes of a “plateau” brush hone (very fine finish) that basically smoothes out any sharp edges left by the stones and makes for nearly instant ring sealing. A final check with the dial bore gauge shows round and straight within .00025” top to bottom and all around. Good enough! Ah man! Now I have to do the other side! What fun!
