MUSTANG RESTORATION: ENGINE DESASSEMBLY AND INSPECTION- STEP #1
Cylinder wear was pretty minimal. There was no ridge/step at the top of the cylinders, just the normal discoloration that comes from the residue of unburned fuel above the top ring. The wear marks on the cylinders matched the wear pattern on the piston skirts, as expected. There was a very faint residual pattern from the previous rebuild, which indicated we might have the option of just doing a cleanup hone instead of re-boring and re-honing. After checking the bore dimensions with the appropriate equipment, however, we decided to go ahead with the re-bore to .040-inch over. The clearance that would have resulted with just a cleanup of the existing .030-inch bore would have been on the high side of the allowable range. We wanted to go with the better pistons anyway, so we decided the extra cost and effort of going to .040 inch over was well worth it for the improved performance, efficiency, and durability it would provide over the longer term.
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MUSTANG RESTORATION: ENGINE DISASSEMBLY AND INSPECTION – STEP #2
The crankshaft journals also showed a very favorable wear scenario. There were no significant scratches, scoring, or other signs of unusual wear. Since we are not building a race motor, we should be able to get away with just a mild polishing of the journals. Had we wanted to build a higherperformance engine, we would consider special machining of the journal edges, oil holes, etc., to reduce stress concentration and/or increase the oil supply to the bearings. These measures are not needed for our application and in some cases could actually be counterproductive to a regularly driven street vehicle. We plan on running relatively close bearing clearances to get maximum life and smoothness from our engine. We won’t need the extra bearing clearance normally provided for engines that will be raced or extensively driven under heavy load.
MUSTANG RESTORATION: ENGINE DISASSEMBLY AND INSPECTION- STEP #3
Further examination of the crankshaft revealed that it was an undersized unit; the main and the rod journals were .010 inch undersize. This was apparently done to remove surface imperfections. Special equipment is used to grind the crankshaft journals to the desired final size, usually in increments of .010 inch or less. While you benefit from removing any scratches, do not remove too much material. This weakens the crank to some degree by making the journals smaller but, more importantly, you reduce the hardened surface layer. In our case, the .010-inch reduction isn’t enough to cause such problems, but a smaller crankshaft and/or a higher power level could be sufficient cause for concern, such that it may be advisable to replace the crankshaft rather than to risk a catastrophic failure under load. A crank with .010-inch-smaller journals is definitely a better option than one with any imperfections that could act as stress concentrators. For most rebuilds, it’s okay to use one.
MUSTANG RESTORATION: ENGINE DISASSEMBLY AND INSPECTION- STEP #4
The cylinder heads showed no signs of trauma, but they did reveal a few items of interest. First, while not extreme by any means, there were some signs of mild valve recession, but this was expected because there were no hardened valveseats or valveseat inserts. This engine was rebuilt when leaded gasoline was still readily available, so there was no need to use hardened seats or inserts. The use of tetraethyl lead in gasoline has since been banned, thus creating a problem for older vehicles because lead lubricated the valveseats. When we rebuild these cylinder heads, we will install hardened valveseats to eliminate the problem. There was also evidence of somewhat leaky valveguides. The presence of oil in some cylinders, primarily around the edges of the valves, indicated some of the valveguides and valveseals were allowing oil from the upper head to run down the valvestem onto the head of the valve. A small amount of such oil is normal and acceptable; too much not only reduces performance and efficiency while increasing pollution, but it can also result in carbon deposits on the head of the valve. This also helps explain the different exhaust port coloration we observed earlier. Our engine had a couple of cylinders with above average leakage, but it wasn’t to the point where deposits had formed or it noticeably affected how well the engine operated. If allowed to persist, performance would deteriorate. We’ll replacing the valvestem seals when we recondition the cylinder heads, so this shouldn’t be a concern.
MUSTANG RESTORATION: ENGINE DISASSEMBLY AND INSPECTION- STEP #5
Pay attention to the water passages at the top of each cylinder. These areas are more likely to show signs of cracking or indicate if there was a problem with a head gasket. The proximity of the hole to the cylinder, and the distance from the head bolts, make this the most likely spot for trouble that might result from detonation or knock, causing high-pressure spikes in the cylinders. Our engine looked fine and showed no signs of such trouble. You can also see that two adjacent steam holes were plugged at the factory. These are left open on some applications if there might be a concern over the formation of air/steam pockets and/or if there is a need to increase coolant flow between the block and the heads. If these holes are plugged in your engine, you should probably leave them that way unless you plan to make a lot more power. If you do open them up you need to ensure the heads and the head gasket are compatible and the passage holes line up. Our heads did not and we’re not upping the power by much anyway, so there was no point in our case.
MUSTANG RESTORATION: ENGINE DISASSEMBLY AND INSPECTION- STEP #6
After the stock, iron cylinder heads have been cleaned, they need to be further checked for defects like cracks. A strong magnet and some iron powder, as shown, can be used to do this. Simply attach the magnet to various points on the head and then discharge some of the iron powder in the immediate area of any suspected crack. If there is a crack, the iron powder lines up around it instead of in a uniform layer. Also, a Magnaflux kit, which contains a special crack-detecting dye, is helpful for detecting cracks in castings. Most cracks are clearly visible to the eye, but sometimes this may not be the case so using a method such as this can help prevent putting a lot of wasted work into a part that must be repaired or maybe even tossed. The point is to make sure your parts are in the condition they need to be for your intended use. Our cylinders heads were fine.
Written by Frank Bohanan and Republished with Permission of CarTech Inc