How to Rebuild Pontiac V-8s - Updated Edition. Rocky Rotella
A torque wrench accurately measures the amount of torque applied to a fastener during installation and indicates effective clamping load. Adjustable versions like this one give an audible click when the selected amount of torque is reached. A torque wrench is useful most of the time during an engine rebuild but is absolutely required when installing connecting rods, main caps, and cylinder heads. The price sometimes reflects quality and accuracy, so I suggest buying a name brand unit.
A variety of specialized tools are required to fit piston rings to a bore, install rings onto a piston, and insert a piston assembly into a cylinder.
Total Seal offers such products in a wide and affordable array of cylinder sizes.
Plastigauge is an extruded plastic thread designed to uniformly crush, giving a fast and accurate measurement of actual main and rod bearing clearances. It’s best used to verify that your machinist’s measurements were accurate and that clearance actually exists. Simply cut a small piece and lay it on a clean journal, install the bearing and cap, and torque it to the correct value. Compare the spread Plastigauge to the graduated marks on the cover to determine clearance. It should be wiped from the journal surface and bearing coating, but any residue quickly dissolves when in contact with oil.
My attention was first directed toward the carburetor and distributor in an attempt to improve engine efficiency at every point. Though part-throttle drivability had significantly improved, the effect on full-throttle performance was limited, and many of the same issues remained. A compression check proved that cylinder pressure varied throughout the engine. It indicated to us that something was amiss somewhere within the combination and the only way to accurately determine the cause and find a solution was complete engine disassembly followed by a proper rebuild.
Having had several positive experiences with a local machinist, I knew that with his help, we could make this 400 run the way it should. I discussed with him the engine’s existing operating condition, the goals that the owner and I sought, and the time frame we were working within. I explained that, because this was the GTO’s original engine and that it was entered into shows often, original appearance was a key factor. And because of time constraints and for ease of photography, we also needed to have him assemble the Pontiac for us.
A camshaft installation tool attaches to the front snout of a camshaft and provides the assembler with additional control and leverage, ultimately preventing bearing damage during installation. Though available for many other makes, a cam installation tool wasn’t offered for Pontiac applications until Tin Indian Performance began offering this unit, which retails for less than $25.
When dealing with camshafts, a few degrees of valve timing can make a significant difference in the way an engine idles and operates. A quality camshaft degree kit, such as this from Comp Cams (number 4936), allows the assembler to accurately install a camshaft at the desired position in relation to the crankshaft angle. A complete kit like this costs a well-spent $200 dollars.
This lifter bore fixture from Comp Cams (number 4925) is designed to be used in conjunction with its camshaft degree kit. When inserted into the lifter bore, the small extensions, which are intended to replicate a roller and flat-tappet lifter face, ride on the camshaft lobe for maximum accuracy.
The experience leading to the decision to rebuild your Pontiac V-8 may be similar to the example above, or it could be completely different. Nothing changes the fact that this 400 was running so poorly it was basically asking for a rebuild. Your Pontiac may not be quite as bad, but a tired engine needs attention too. Once you arrive at that point, you need to sort out your expectations and goals, set a realistic budget that allows you to achieve them, and prepare to get your hands dirty! ■
Valvetrain geometry can be affected anytime a block is surfaced or a cylinder head is machined. The easiest way to restore proper alignment of the valve stem and rocker arm is to utilize a specific-length pushrod. Comp Cams offers adjustable pushrods like this, which can be used to determine the required length of the replacements.
A dyno simulator computer program can never take the place of an actual engine dyno, but it can be a useful tool when determining the effects certain components can have on an engine’s performance. Performance Trends Engine Analyzer v3.4 is among the best programs available. It allows hobbyists to compare how different camshafts, intake manifolds, cylinder heads, and exhaust systems can affect engine operation, and it contains excellent displacement and compression calculators. I have used one for years and have found it to be an excellent learning tool.
Selecting a Machine Shop
Once you’ve laid out the rebuild path you plan to follow and have the proper equipment on hand, the next step is to locate a reputable machine shop in your area that can satisfy all of your needs. The best choice is one that comes recommended by fellow Pontiac hobbyists who have had direct experience with a shop. You may find some shops with several caveats and others with several attributes.
A magnetic pick-up tool is handy if you’ve dropped something like a nut or washer into a crevice or the tight confines of the crankcase. A telescoping tool like this or one with a flexible head is an inexpensive purchase at your nearest parts store.
In my opinion, a reputable, professional shop should be clean and able to perform such tasks as sonic testing, magnetic-particle inspection of components for cracks, fully machine a block and crankshaft, rebuild cylinder heads, prepare connecting rods, and completely balance a rotating assembly. It should also be able to procure replacement components, such as pumps, gaskets, and seals. Specialized procedures, such as nitride or cryogenic treatments, are often beyond the resources of typical engine building shops.
A complete tap and die set can be a valuable asset when cutting new threads into metal or restoring the shape of an existing one, but they’re generally rather pricy. Only a handful of basic taps of various sizes and thread pitches are needed during an engine rebuild to chase the threads found on any cylinder head or block.
If a machine shop must send any component to an outside company for specific machining processes, then the machinist should assume full responsibility for any failure that occurs and is found to be related to the component that was outsourced. Just the same, you can’t expect a machinist to stand behind any complete component you bring to the rebuild from an outside vendor. A machine shop technician must be able to work with a complete selection of compatible and complementary components because all the components must work in harmony to complete a strong, reliable engine. In addition, the machinist must be able to fully inspect each component and verify its parts, function, dimensions, and overall quality. If the machinist is not able to do this, the slightest problem or mistake can lead to a catastrophic failure. An example of this might be valvetrain failure related to cylinder heads that were improperly prepared by an outside vendor.
A valve spring compressor