You’ve dismantled the engine down to the block, it’s time to inspect the block for cracks and other defects. It can’t be stressed enough how important it is to thoroughly inspect any of the parts you may reuse, including block, crank, rods, head, and so on. Flatheads are notorious for cracks and they must be checked carefully.
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Because of their age and the nature of their construction, all flathead Ford V-8s have cracks, hot spots, and rust buildup that might cause failure down the road or even before you get on the road. To identify defects, how bad they are, and whether they can they be repaired at a reasonable cost, it’s best to seek professional advice at this stage.
Once the block is de-rusted and cleaned, it can be inspected thoroughly for cracks and other damage that need repair or replacement.The inspection should be diligent, because failure to spot something critical could cause expensive engine failure later.
A competent machine shop probably can run other block-checking tests, such as pressure checking and sonic testing of cylinder wall thickness.
Flatheads can crack just about anywhere, but the most common spots are along the pan rail, in the outside walls, between the cylinder bores, and inside the ports
The most common form of crack detection, after visual inspection, is Magnafluxing. This non-destructive system employs a large electromagnet and fine greenish iron powder. The powder is sprinkled over the area to be inspected. The magnet is activated, and current causes the iron powder to collect and indicate where the cracks are. This process is best left to a professional.
The electromagnet is placed on the block, which is sprinkled with fi ne iron powder. After that, the magnet is activated.
The iron powder collects to indicate the location of cracks. In this case, the crack is located inside the port and needs stitching (see Chapter 6).
This pressure testing kit is available from Speedway, but it is expensive if you are only ever going to build one engine.
Pressure testing is another must-do procedure if you are at all unsure of the block you have chosen. The block plate mounts to the deck, and the other two plates block off the water pump surfaces. As air is pumped into the block, you either submerge the block in water or spray the critical areas with soapy water. If the water bubbles and the air pressure drops, you know you have leaks.
You can also use a pressure tester later to check your crack repair techniques. Pressure test kits cost approximately $250. Rather than make this investment, you might have the test done by a machine shop.
If you are restoring or building a traditional-style hot rod and intend to use stock iron heads, they too must be thoroughly inspected. Because they are more than 60 years old, the heads might be warped, cracked, and/or corroded. They might also have been surfaced more than once (and maybe not well), so give them a thorough going-over. The good news is that plenty of stock heads are available.
If you intend to reuse the stock crank you must check it very carefully because it is the heart of the engine. Original Ford and Mercury cranks are of excellent cast alloy steel; if they check out, they cannot be made better. The Ford had a 3.1875-inch bore and 3.750-inch stroke, whereas the Merc had a 3.1875-inch bore and a 4-inch stroke. Hence, the extra 16 ci.
Check the size of the main bearing journals and the connecting rod journals to see if your crank has been previously ground and if there’s room for another grind.
Some say that the mains can be turned .050-inch undersize, and that could be correct. However, the problem today is obtaining bearings of that size. Scat and most other companies make only .010-inch undersize bearings, but Van Pelt offers standard through .030 undersize versions. The same applies to the connecting rod journals, so check the bearing size carefully to make sure that the crank is usable.
Cranks that have been over-ground can be built up with weld and then reground. However, it’s probably better to find a crank in good shape. Better still, buy a new crank.
Use a dial indicator to check the crankshaft for alignment and runout. If the crank is a little out of line, your machine shop should be able to straighten it. To correct it, the shop sets the crank in V-blocks, measure the out-of-round, and applies pressure (usually hydraulic) to the opposite side of the bend.
Despite the myriad minor changes in flathead specifications, all flathead connecting rods are heat-treated, carbon manganese steel forgings, and all measure 7 inches center to center. Early rods (1932–1948) had a single bearing for two rods that rotated about the crank journal as well as within the rod. These are knows as fully floating bearings. From 1949 on, rods had individual bearings.
By the time the 8BA blocks went into production, Ford had improved its casting techniques and there were far fewer core shifts. Therefore, on the whole, the 8BA blocks are better than earlier blocks. Nevertheless, when purchasing a block, it’s a good idea to perform a sonic check to measure the wall thickness. Always perform the test after all rust removal to prevent false readings.
The prices of sonic testers vary greatly. A professional tester from Dakota Ultrasonic can cost more than $1,000, but Sony has a $75 model. If you are building only one engine, you have to balance the cost of purchasing special tools against the cost of paying a machine shop to do the work for you.
Knowledge of your block’s wall thickness is paramount to moving forward. You might not know how your engine has been treated, how many re-bores it has had, and how good they were. Previous machinists (which could include either professional shops or shade tree mechanics) who worked on the block might not have adhered to recommended specs. Therefore, accurate testing of wall thickness is very important.
According to Mike Herman, the wall thickness should be no less than .200 inch on the thrust side and .135 inch for the minor thrust. The wall thickness of a standard block is about .300 inch in the center of the cylinders. The minimum safe wall thickness is .090 to .100 inch. If the walls have been bored beyond their limits, the result could be difficult-to-detect internal failure.
Written by Greg Kolasa and Posted with Permission of CarTechBooks