The Power Stroke is a durable engine designed to last a long time. Most Power Stroke engines that are in need of a rebuild generally have between 350,000 to 400,000 miles. There are a few daily-driven trucks out there with this many miles, but most of these are used for businesses such as construction or towing. A Power Stroke rebuild can be expensive when compared to rebuilding a traditional gasoline engine.
One convenience with this rebuild is being able to use aftermarket parts. Over the years, more companies in the rebuild industry have started offering parts for these 7.3 and 6.0 Power Stroke engines. While these aftermarket companies may offer reputable parts at a less expensive price, the major expense of the rebuild comes from the teardown, cleaning, and machining. The engine pieces are bigger and heavier than their gasoline counterparts.
This Tech Tip is From the Full Book, HOW TO REBUILD FORD POWER STROKE DIESEL ENGINES 1994-2007. For a comprehensive guide on this entire subject you can visit this link:
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The final rebuild total often depends on how many new parts need to be purchased. The average price of a rebuild (including engine removal, machining, reassembly, and installation) often starts around $8,000 to $10,000. This does not include rebuilding or replacing the turbocharger, fuel injectors, or any electrical components (such as sensors or actuators) that you may need.
After the engine has been torn down, all parts need to be “hot tanked.” This refers to a vat-type cleaning system with strong chemicals that removes all grease, dirt, soot, and debris so proper measuring and machining can be performed. With the dirt and grease out of the way, a good cleaning of the engine components also indicates what condition the engine is in. This is when you take various measurements to help indicate what machining needs to be performed. You also inspect many parts for cracks that require repair and/or replacement of parts, should damage be found.
In order to perform a first-class rebuild, certain steps and various techniques can be performed while machining to ensure long engine life. Pay close attention to little details such as piston height. On the 7.3 and 6.0 engines, the piston comes out of the bore approximately .030 inch. This is very important in machining, because it affects compression ratio. This is where the proper pistons need to be determined based on how much the bore is worn and whether the deck of the block needs to be resurfaced.
Most engines with considerable mileage need to be overbored in order to “square” the cylinders. Diesel blocks are thick castings, so core shift isn’t as much of a problem as bore taper. I find that Diesel blocks often develop bore taper between .004 and .006 inch. The most common overbore for the Power Stroke engine is .020 inch. Most of the time, if the cylinder bores have not suffered any damage, performing a .020-inch overbore is sufficient to bring the cylinder bores back into serviceable condition. This includes a fresh sealing surface for the piston rings and a taper that is within factory specifications.
The block is placed in a boring and milling machine and is squared. For a .020-inch overbore, you have to take into consideration how much piston-to-wall clearance the piston needs. Diesel applications generally have .0055-inch piston-to-wall clearance. For example, a 7.3 engine has a stock bore measurement of 4.11 inches. If you overbore the cylinders .020 inch the finished bore would be 4.13 inches. The piston measures 4.1245 inches, making the piston-towall clearance .0055 inch. When boring the engine, .017 inch is removed from the block with the carbide bits and then the remaining .003 inch is removed by stones in the finish honing process.
While the block is still set up in the milling machine and the overboring process is complete, the block’s deck needs to be resurfaced. Most Power Stroke engine blocks typically warp between .004 and .006 inch across the deck. But remember, the pistons came out of the block approximately .030 inch. So in order to machine the deck of the block .010 inch, the piston needs to be shorter, or “destroked” .010 inch.
Mahle Manufacturing offers Diesel pistons in destroked sizes so the deck of the block can be milled. If the pistons were not offered in a “destroked” application, the deck would be milled and the piston would protrude the block .040 inch. This would alter the compression ratio of the engine along with other characteristics of the burn cycle.
When decking the block, several passes are made in order to properly machine the deck surface.
After the cylinders have been overbored and the deck has been milled, the block is removed and the cylinder heads are placed into the milling machine and squared. Typical warp in a Diesel cylinder head is also around .004 to .006 inch. For this application, the cylinder head was out around .003. The machining of the cylinder head was the same as the block. For the first pass, .003 was taken off at a slow cutter speed. On the second pass, .001 was taken off and the cutter speed was increased to leave a finish of a 30 Rockwell (Ra).
To finish the cylinder heads, check the valve-to-guide clearance. For Diesel applications, as much as .005-inch valveguide clearance is acceptable.
The valve seats also need to be resurfaced. For the 7.3 and 6.0 engines, the intake valve has a 30-degree seat and the exhaust valve has a 37.5-degree seat. The valves need to be refaced also.
In most Diesel teardowns, the intake valves often take most of the abuse. Replacement of the intake valves is the most common practice. In order to rebuild the cylinder heads properly, the injector cups need to be replaced.
For any rebuild, the crankshaft should always be checked for straightness. Most cranks need to be ground or polished in order to be true. The maximum out-of-round limit for the Power Stroke engine is .0002 inch. For most rebuild applications, the crankshaft is usually ground .010 inch. The remaining .0002 is removed by a hand-held polisher with a 600-grit belt. The belt is then changed to 800-grit and polished again for perfection. The rod journals are done the same way.
The connecting rods also need to be machined. This is also called reconditioning. The center of the rod can be resized in a rod resizing machine starting with 320-grit stones to remove the most metal, then using a finer stone of 500-grit to finish.
The little end of the connecting rod utilizes a bushing. The bushings need to be measured also but are usually okay. Most of the time, the bushings can be polished for cleanup without having to be replaced.
If you really want to enhance the internals of your Power Stroke, take the time to have it balanced.
The object of balancing is to match the reciprocating weight, which is the pistons, wrist pin, rings, and the little end of the connecting rod to the reciprocating weight, which is the counterweight of the crankshaft with the big end of the connecting rod with the bearings. The balancing of the engine makes for much smoother operation and longevity of engine components.
Written by Bob McDonald and Republished with Permission of CarTech Inc
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