MACHINING AN ENGINE, Part 1
With the last month's low compression and vacuum test readings, we began our machine work on the straight 8. This will include restoring the valve train, new rings, cylinder honing, rod and crank work. While we were waiting for parts, we decided to drill out the stud that broke when we were removing the head. Not a total surprise for a 62 year old steel stud to break, but it was an extra challenge that we had hoped we could avoid. On engines this old, the studs are metal-fatigued and stretched to the point where they generally won't hold torque. This can result in a blown head gasket later on. When replacing them, it is best to go with new "interference threads" on the block end. Their threads are cut at a slightly different angle and allow a better stud-to-block seal, helping to prevent seepage from the water ports (we always use anti-seize on these threads). We got our studs and chrome acorn nuts from Kanter (800-526-1096). The stud was broken close to the block, so we first center-punched it, taking extra care to hit exactly dead center. If the center is off, everything will be off, and could result in thread damage. Starting with a 1/8" drill bit, we drilled out the first hole, then increased our bit size to 1/4", then 3/8", until finally we had a perfectly centered hole. As we got to the bottom of the hole, the bit grabbed the broken piece of stud and pulled it out, leaving a clean hole that just needed the threads to be chased. To prepare for the new studs, we chased each of the head stud holes, rinsed and blew them out with air, then test-fitted the studs. They all fit great and will be permanently installed later on.
All of the exhaust guides were worn and the intakes weren't much better. New guides are available, but we felt they had too much clearance for the quietness we wanted. We decided to install bronze guide liners to allow tighter tolerances, because bronze is a more porous metal and will hold oil better. This is necessary with the unleaded fuels of today, to help eliminate "valve rattle". To install the liners, we reamed the worn guides with a self-pulling reamer, then pushed the bronze liner into the tool's installation sleeve. We then put the guide driver into the sleeve, leaving a little of the liner protruding from the bottom of the tool to help align it into the valve guide. After aligning it up straight, we used a small ball peen hammer to tap it into the guide. Usually at this point, you would cut off the excess liner, but ours were the correct length. We ran a broach through the liner with an impact gun. The broach does two things: burnishes and reams. This is important because it bonds the metals together. After broaching the guides, the valves will have a correct fit. Before grinding the valve seats, we deburred the bowl areas and match ported (ground the shape of the port to the gasket) the port entrance. Then, using our Sioux seat grinding kit, we put the proper pilot in the guide and the correct stone onto the driver, and ground our valve seats. The exhausts were 45 and the intakes 30 , to match the valve angles. We cut another angle at the top of the seats, 30 on the exhausts and 90 on the intakes, then 60 at the bottoms. The seats are narrowed to adjust the location of the seat on the valve for better performance and to prevent burning. They are also cut toward the inside to keep heat from the edge of the valve to prevent burning. After grinding the valves, we lapped them in, so they would immediately seat (for lapping, see Ask Joe, front section).
The lifters on the 356 Custom 8's are hydraulic and have to be calibrated upon installation. There is a tool available from Packards International (714-541-8431) called the "Hydraulic Gauge Tool". To use it, first remove all valve parts, including the hydraulic plungers. Place them on a bench in the order in which they were removed. Install the valves without springs. Bring #1 piston to the top of its compression stroke (#1 cylinder inlet and exhaust lifter bodies will be at the base of their respective lobes on the camshaft). Place the plug gauge of the gauge set in the lifter body and, while holding the valve down on its seat, check the clearance between the plug and the valve stem, using a feeler gauge. The clearance should be between .030" and .070". If less than .030", face off the end of the valve stem until the desired clearance is obtained. Repeat on all valves.
The hydraulic plunger must be bled before installing them into the tappets. This is done by putting them in a vise, being careful to cover the jaws with wood blocks to prevent scratching the plungers. Close down the vise until it bottoms out the lifter, getting all the oil out of it. Then clean the lifters with mineral spirits using a guide brush, followed by final buffing using a fine wire brush on a bench grinder. Blow off residue with air and install into the tappets.
Next month, we will assemble our valve train, recondition our rods, hone the cylinders and a lot more! See you then...keep 'em driving!