Basic Block Machine Work

Daydreaming and fantasizing about what could be, if money were no object, offers every racer a chance to relax and drift away from daily problems. But, reality has a way of creeping up like a silhouette against a blank wall. For the weekend racer, reality means getting the biggest bang for your buck each and every time a checkbook is flipped open.

Keeping with our format of dealing with real-world problems, we called on the services of veteran race engine builder Ed Pink to offer some expert essential information on basic block machine work, tips on how to spend budgeted funds, and what to look for when having machine work done by a shop.

We set our parameters for the story based on three different budgets: First, for the weekend racer with a very small budget, $500 was allocated for basic machine work on the block. The block we chose for Phase One is a used, two-bolt main, standard 350-cid Chevy. In Phase Two, we bumped the allowance to $1,000, aiming at the racer who may have some financial support from sponsorship. And finally, we kicked the ante up to $2,000 in Phase Three for the racer who has sponsorship on a full-time basis and has more funds available.

Headwork and special machining on aluminum or aftermarket blocks is not included. The blocks used in Phase Two and Phase Three is designated as a Chevy Bow Tie, however, what is discussed can be applied to any project block. According to Pink, the work illustrated in this story is based on the criterion of being essential to a quality final product. In other words, the work performed, in Pink's opinion, is all necessary to build a quality engine. All work is based on typical pricing (as of this writing) at a first-class machine shop. Cut-rate, backyard, or brother-in-law garage deals were discarded. "If machine work is not performed by a very high-quality shop, one [that is] in touch with the needs of the racer, using top-of-the-line equipment," Pink says, "then whatever money is spent on block preparation can be considered wasted." He continues, "So, if you walk into a shop, and the owner says, 'Ya just leave it, I'll handle it later,' just say no."

Phase One--We’ve Got $500

In Phase One, we have a used block and $500--the budget racer has little room for error. The block must be inspected, hot-tanked (cleaned), and Magnafluxed for cracks. Next, Pink recommends pressure-testing the block for leaks by placing the block (filled with air pressure) into a water reservoir. If the block is good--no leaks, no cracks--the next step is to bolt up the main caps (without bearings), measure for diameter size and concentricity, and align. Here comes the kicker! Because we are dealing with a $500 budget, the following scenario may be possible. In the rare occasion that the block in question checks out, align-boring may not be necessary. Remember, we are on a $500 budget. But, if the mains are out-of-round, then align-boring or align-honing will be mandatory. The usual cost for the honing or boring of the mains is $180. Once the mains are align-bored or honed, the centerline of the crankshaft is established.

Next, the block is decked. To deck a block, all four corners of the block are measured to the centerline of the mains (crankshaft) to determine if the block is square (also to set deck height). If the block is off, the head surface is machined until it measures the same, rear to front and side to side (0.001 to maximum tolerance). With the block square, the cylinders can be bored. In our Phase One example, Pink suggested that the block be bored 0.030-inch over. The cylinders are bored or power-honed using a torque plate. To be sure the bore size is correct, Pink suggests that at this time, you ask the machine shop person doing the job about which piston size to use in the engine and piston-to-wall clearances.

With the cylinders bored, we need to stop and do some calculations. We began with $500. The hot tank, pressure testing, and the Magnaflux test cost about $105 to $130. If the mains need to be align-honed (bored), add $180. Decking the block runs about $180. On the high end we have spent about $640; on the low end, $575. If the block did not need to be align-bored (honed), the cost would be $400 to $460. Throw in a few odds and ends (Welsh plug installation, fitting the cam bearing, and so forth), and you have spent the $500 budget plus a few extra bucks--but you have a quality basic block ready for assembly.

Phase Two--A Grand

With a fresh $1,000 budget, we can begin anew. In Phase Two we hot tank, pressure test, and Magnaflux as in our first phase, but this time there is no hesitation about align-boring/honing the mains. Also, the block, when decked, is surfaced on a mill using a special squaring fixture to ensure a perfect 90-degree angle to the centerline of the crankshaft. This fixture bumps the cost of decking/squaring the block from $150 to $190. Also upgraded is the cylinder-boring process. This time, the cylinders are power-honed (with the torque plate), using several different hone-grit surfaces (stones) to achieve near-perfect tolerances (rough cut is #133 stone, finish rough cut is $525 stone, fine cut is #625 stone, and finish cut (super fine) when running moly rings is #820 stone). The cost for this process is $180.

After the block is square--mains honed and aligned--and cylinders bored, Pink suggests opening up the main oil feed or gallery to the center three main bearings ($22). Next, Pink will drill and tap the oil restrictors to the lifters (restricting the oil flow to the lifters) front and rear of the block. What this means is that the holes are drilled and tapped, and then tiny set screws with drilled orifices are installed for a cost of $40. Next, the three front oil galleries have the soft plugs removed and are machined to accept 1/4-inch pipe plugs for $15. To regulate oil flow in the valley chamber, Pink drills, taps, and uses 1/4-inch pipe fittings to block the valley chamber oil drains (-8 fittings) for $15. Next, Pink machines, drills, and taps all core plugs (freeze plugs) for special "button head" screws. For $100, the screws are installed and safety-wired so they cannot blow out. Finally, it runs about $70 to fit the cam and install the cam bearings. If we hit our adding machine again, the price tag for our Phase Two block has reached $950. Add a few miscellaneous items and the budget is consumed.

Phase Three--Two Grand, Total

Now we have $2,000 to spend. Once all the aforementioned steps are completed, we begin the final stage with the installation of aftermarket four-bolt mains and aftermarket studs for $200 (labor only/no parts). If you use a Bow Tie block, then aftermarket four-bolt mains are not necessary. In this "premier" block, Pink machines an oil groove into the main saddles of the block for better oiling to the main bearing; that costs $115. If aftermarket four-bolt mains are used, the cost of align-boring/honing is $220. Notice that this is slightly higher than our tow-bolt mains on the blocks used in Phases One and Two. The reason? The aftermarket mains (steel) include rough or smaller bore sizes and must be machined to fit the cast-iron block--more work, more money.

Also, our Phase Three block receives an additional alignment procedure. In this stage, the cam holes in the block are actually align-bored and the holes fitted with a 0.030-inch-over cam bearing. This $250 step is not the same as simply fitting and installing cam bearings as found in Phase Two. Here, the cam bore and bearings are aligned perfectly, and this puts the cam and crankshaft in the same line. Also, the oil groove behind the cam bearing is enlarged on all five journals of the block (wider and deeper), which costs $160. With the oil capacity increased at the cam journals, the center main bores must be drilled for more oil capacity, so that's $22. At this point, Pink considers using special fixtures in boring the block to ensure that all of the cylinders are parallel to the crankshaft and in perfect line. The extra cost of this upgraded boring process is about $40. Another step is relocating the dowel pins to a correct position in line with the cylinder head, also $40. Lifter bores are up next. They are machined and aligned, sleeves are installed and machined, and oil galleries are drilled, honed, and deburred. Then the lifter bushings are honed to size (labor only/no parts) for $290. If the block must be converted from a wet-sump to a dry-sump oil system, the machining work is about $110. Suddenly, our $2,000 budget is close to being depleted.

Despite many more modifications engine builders make to blocks to help build horsepower and reliability, what we have given is a basic look at block machine work--at what must be done to have a fighting chance of building a strong engine. As a final footnote, Pink suggests that when you have a block machined--following the procedures explained here--talk to the shop and determine whether you can handle certain jobs at home. Labor-intensive jobs such as deburring, clearance grinding, redoing freeze-plug fitting, and grinding burrs from valley surfaces may be handled by the budget-minded racer. Remember, the work done to your block is only as good as the shop performing the task, so ask your fellow racers for recommendations. Be sure the shop you pick does race engine work and understands the needs of a racer.