The next step is to place the block in the blast machine. The block is fastened inside a rotating fixture and steel shot is thrown around by a high-speed paddle wheel. The ash and rust is completely removed in about 10 minutes of run time. Jet washing with hot soapy water after that removes the rust residue and leftover shot. The engine block looks brand new at this point and the machining process can begin.
The first machining operation to do on the engine block is the main bearing bore work. If the block is machined properly, most of the block-machining operations were referenced off the main bearing bores. You can check main bearing bore size by torquing the main caps and measuring roundness and diameter by using a dial bore gauge. It is not quite as easy to check for alignment. Some old-school books show the use of a straightedge and feeler gauges, but I consider this method to be a waste of time. I have set some factory blocks on a mill and indicated the end main journals until they read zero on each, and run the indicator along the center three mains and found some to be within a few tenths, and some to be off by .002!
Some people wonder why they wipe out main bearings with a .0025 main bearing clearance. If you want to avoid a future headache, just have the mains align honed and be done with it. This process is one that requires some skill and experience; be sure to select the right shop to do the job. I have seen many blocks that were line honed and were far from “aligned.” If you are installing aftermarket caps, the block must be align bored and align honed anyway, so you are good to go.
Boring the cylinders is simply a method of sizing the cylinders for an oversize piston. The cylinders at my shop are bored .005 to .008 under final size. Some literature specifies that you can bore within .003 and then final hone, but depending on the finish after the boring operation, that amount may not be enough to remove tooling marks. It takes more time in the hone, but you are guaranteed the proper finish with the extra material. Engine blocks at my shop are bored on a very large Cincinnati CNC machine. A precision bar goes through the main journals and cam tunnel. When the block is set on the machine fixture, each bore is machined exactly 45 degrees from main/camshaft centerline, and parallel to them. The bore locations are referenced off the cylinder-head dowel pins, and bore spacing is set at 4.625 inches in the boring program. This ensures that all of the machine work of the block is “blueprinted.”
The blasting unit houses the previously thermal-cleaned, completely dry engine blocks or cylinder heads. They are fastened inside and rotate 360 degrees while a high-speed paddlewheel throws steel shot at the parts. Five minutes later, a previously rusty engine block looks like brand new and is ready for machining.
Block Decking
The next block machining operation is to deck the block for the purpose of making the surface flat for head-gasket sealing and machining a predetermined deck height. Deck height is referred to as the distance from the crankshaft centerline to the cylinder-head gasket surface of the engine block. I make the surface absolutely smooth and am convinced that a smooth surface seals the best on any gasket. Rough finishes to “bite” the gasket simply leave peaks and valleys. I’m sorry, but I don’t want any valleys in a sealing surface. The deck surfaces are cut immediately after the boring operation without the block being moved from the fixture; therefore, the deck surface has to be perpendicular to the bores and parallel to the main journals. The cutter is referenced (or zeroed) from the main-journal centerline. And if a deck height of 10.600 inches is desired, then the cutter is raised to 10.600 inches and the deck is cut.
A thermal cleaning oven does a great job of cleaning all of the oil and grease from an engine block, cylinder heads, or parts. It is not a good idea to thermal clean aluminum heads or parts. The amount of heat required to clean properly affects the heat treatment of the part and can soften it considerably.
Honing
The honing process is one that seems to attract many different opinions on how it should be performed. I have tried many procedures and found that they all seem to work about the same as long as the cylinder is straight and round. Some finishes seem to help on different tension rings but, in general, I wouldn’t worry about the different finishes that some engine builders prefer to create. I also stress that you can’t get the bores too straight or too round. This is the single most important part of the honing process. When I hone cylinders, I install a 2-inch-thick torque plate. I have not found different results between a steel torque plate and an aluminum plate. I simply use the aluminum plate for everything.
At BTR the block is set up on a precision fixture that holds it at 45 degrees to engine centerline. The block is bored and decked in one operation; therefore, the decks have to be parallel to the mains and perpendicular to the bores. With the cutter referencing off the precision main bar, deck heights can be cut very easily to any desired dimension.
Blueprint specifications for small- and big-block Oldsmobile engines.
I use a 150-grit stone and bring the bore to .0025 to .003 inch of the final dimension. A 220-grit stone can be used to finish also, but the 150-grit stone simply reduces honing time and heat. I hone .0003 inch under the final dimension with the 220-grit stone. The final step is to give each cylinder three up-and-down strokes with a 280-grit stone; the same with the 400-grit stone.
The Sunnen CK 10-cylinder hone does a great job of honing cylinders round and with little distortion. Newer, more advanced honing machines are available, but many top engine builders prefer this machine.
There are disagreements about whether diamond stones should or shouldn’t be used for performance applications. My feeling is that the stone is the better process, because as the stone wears, you get fresh stone to cut with. The diamond really doesn’t wear away much, which leaves a rounded grit over time. I can’t say it is wrong to use the diamond abrasives; it’s just my preference to use the stones and it works for me.
Camshaft Thrust Surface
All Olds blocks have the same thrust-pad dimensions, with the notable exception of diesel blocks. The thrust pad for these blocks is .050 inch deeper than for gas blocks. Less material is machined on that thrust surface to maintain proper lifter-to-cam lobe relationship when using a conventional non-diesel Oldsmobile camshaft. A common procedure that I use is to machine the camshaft thrust surface into the front of the block for a roller thrust bearing, otherwise known as a Torrington bearing. Over the years, I have seen many blocks scored in this area.
The reverse rotation of the distributor gear forces the camshaft against the block and can sometimes wear in this area. The ultimate solution is to machine a pocket into the block that allows a one-piece thrust bearing to fit snugly into the front of the block, so that the camshaft rides on that roller surface and cannot wear. The bearing to use is the Cloyes PN 9-220 roller thrust bearing, and the pocket needs to be machined 2.930 inches around and .140 inch deep for the bearing to fit properly. The .140-inch depth is critical, mostly because of the lobe-to-lifter relationship.
On a roller-cam application the lifter should be in the center of the camshaft lobe. It is critical to have the lifter