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1979 Chevy Corvette - Shark Attack: L98 Engine Disassembly

Now that we've chosen our engine, it's time to start rebuilding it

Chris Petris Oct 19, 2005
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We were bragging about how the one-piece, rear-main-seal blocks don'tleak oil, and here's a leaking rear seal. The one-piece, rear-sealcrankshaft hub becomes distorted if the flywheel bolts aren't torquedproperly to 65 lb-ft. The flywheel had three really tight bolts; onebolt was torqued correctly and two bolts were finger tight.

Now that we've had a while to mull it over, the '87 L98 Corvette enginemakes good sense for our Shark Attack Corvette. While we could haverebuilt the original 350 engine, the old-style small-block driprails andtwo-piece crankshaft seal would have come back to bite us later. We knowthe history of this L98 and even though it has 100,000 miles on theclock, it's still in fair shape. The L98's previous owner opted for a383 cid engine to gain some stealth horsepower. He found the replacement383 engine in a local newspaper at a low price and, once disassembled,the internals reflected why it was so reasonable. We're not implyingthat purchasing an engine in this manner is a bad thing. But thepurchaser needs to know what to look for and should, at the very least,remove the oil pan to look at all the rotating pieces.

We'll discuss the high points of what to be aware of when looking for anengine for your project, especially if you want a bargain.

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Once the intake was removed, this crud was discovered above theroller-lifter guideplate. The same crud was found in a similar area onthe same side of the lifter valley. This is not from poor oilmaintenance. The block was seeping coolant from the coolant passages,where it mixed with the oil and created the sludge.

In many cases, an engine is sold because it burns oil or has a vibrationproblem. Anytime a stroked engine is built, vibration can become anissue if improper parts are used. If you find a stroker engine that justneeds to be ringed (it needs only piston rings and bearings to be asgood as new), ask the seller if he has a balance card for the rotatingassembly. Although balancing isn't a necessity, it's a good idea whenworking with stroked engines. It also gives you an idea of how well theengine was built to begin with. The stroked engine should come with theflywheel and harmonic balancer balanced to the crankshaft and otherrotating pieces to avoid vibrations. Depending on the 383-strokercombination, it could be an internally or externally balanced rotatingassembly, so the more info you have the better off you will be.

Small-block Chevy two-piece rear-main-seal crankshafts are internallybalanced, meaning the flywheel is neutral balanced. The 400 small-blockengine is the exception, with its two-piece seal and external balancing,including the harmonic balancer. The one-piece rear-main-sealcrankshafts are considered externally balanced because a balance weightis required on the flywheel. The one-piece-seal crankshafts also use aneutral- balanced harmonic balancer.

Make sure you look at all the pieces carefully for cracks and corrosion.Check the cylinders for corrosion. If corrosion is severe, the block mayrequire sleeves. Rotate the crankshaft at least two full revolutions tofeel for smooth, steady rotation. If the crankshaft has hard spots whilerotating or doesn't turn a full revolution, it's best to leave that dealand look further.

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This is more evidence of an engine that was running well and had a goodair/fuel ratio. The exhaust ports have a light tan color and the innerpart of the cylinder head is clean. The oil was changed regularly,keeping dirt and sludge out of the engine, or so it would seem.

During disassembly, a few things must be done to avoid severe depressionand a massive loss of funds. If you plan to use the original connectingrods during the overhaul, mark the connecting rod and cap with a scribeor a stamp. If the connecting-rod caps are mixed up, the crankshaft willnot rotate when you assemble the engine. The connecting rods arefinish-bored with each cap in place. A cap from another connecting rodwill not line up properly, causing an egg-shaped connecting rod bearingbore.

Be aware of the connecting rod's position during disassembly and takephotos if necessary. If the connecting rod or piston is installedincorrectly, the piston can be positioned off center, causing thepiston-pin-boss area to rub hard against the connecting rod. When theconnecting rod is installed correctly, it's centered in the piston-pinarea.

Look at all the components carefully before and after cleaning. Use amagnifying glass to carefully check around the main bearing andcylinder-head-bolt threads in the block for cracks that can develop.Check the cylinder heads for cracking where the retaining-bolt washersrest on the head.

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We cleaned the area with brake cleaner; the dark area is where thecoolant was seeping out. This area also shows a crack to the right ofthe dark area that should be marked so the machine shop can Magnafluxit. This area will be prone to cracking or porosity. Once the block iscleaned, the area can be welded or epoxied, depending on the severity ofthe damage.

Once all the pieces are out and inspected, a trip to the machine shop isnext. Before leaving for the machine shop, we stamp each component witha distinguishing mark to ensure we get back the components we sent outto be rebuilt. We aren't saying machine shops can't be trusted, but it'seasy to confuse parts with no distinguishing marks.

Tell the machinist about anything that seemed odd during disassemblybecause it may not be noticeable later during machine work. Most machineshops measure the cylinder block and crankshaft for wear while you waitif you make an appointment. This will allow time to discuss the bestplan of attack if you have a severely worn component.

When you load up your pieces for the trip to the machine shop, securethem so they don't roll around and become damaged. The shop can alsoclean the tin pieces (oil pan, timing cover, and such) at a reasonablecost, saving a mess in your garage.



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