327 Bottom End (Inspection and Assembly)
Article by Mark Trotta
Rebuilding a 327 Chevy bottom end includes inspection and/or replacement of pistons, rods, crankshaft, harmonic balancer, and oil pump.
If the motor is already on an engine stand, you'll want to flip it over to remove the oil pan.
If you're not pulling the motor out of the car, oil pan removal on a C2/C3 Corvette requires loosening the tie rod assembly and swinging it out of the way. Having the car on four jack stands makes this possible.
After the pan is removed, clean all traces of the old gasket with a razor blade and gasket scraper.
Cast vs Forged Crankshaft
All 327 engines that went into Corvettes (until the 1970's) had a forged crankshaft. The easiest way to tell is, a cast crank has a thin casting line, and a forged crank has a thick casting line.
Shown above is a forged crank.
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Is Plastigage Accurate?
For checking bearing clearances during engine assembly, Plastigauge is a valid, inexpensive alternative to verniers and micrometers.
Shop: Plastigage
Green Plastigage Measures .001" to .003"
Red Plastigage Measures .002" to .006"
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Crank and Rod Journal Sizes
Up until it's last year of production (1968), Chevy 327 engines had a smaller journal crank and connecting rods than the later 350ci small blocks (11/32" rod bolts until about 1968, large-journal rods had 3/8" bolts).
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SBC Oil Pump
Small-block Chevy engines were designed with a very good lubrication system. This engine received a new Melling M55 oil pump. Oil pump bolt gets torqued to 60-70 ft/lbs.
Because of the age factor, the shaft bushing should also be replaced. The old one was tight (as it should be) and needed to be cut off with a razor-blade.
While it was off the car, the pan was sanded and scuffed down to bare metal and painted Chevy Orange with a spray can (no primer needed).
Read: Spray Paint Engine
Before the pan was bolted back up, the bolts were soaked in brake parts cleaner, and the bolt holes in the block were cleaned and tapped.
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SBC Oil Pan Gasket
Some SBC oil pan gasket sets come with a choice of thick and thin front seal. Early small-blocks take a thin front seal.
To find out which front seal you need, lay a straight-edge (here I'm using a piece of wood) across the front of the pan and measure the depth of the "half moon". A 2-3/8" measurement requires the thick seal, 2-1/4" requires the thin seal.
The Felpro OS5197C2 oil pan gasket set comes with the thin seal only.
Shop: Felpro OS5197C2 Oil Pan Gasket
SBC One-Piece Oil Pan Gasket
Several aftermarket companies offer a one-piece oil pan gasket for the small-block Chevy, but these are thicker than the original gasket and may require longer oil pan bolts to properly secure. I've never had leakage issues with the 4-piece gasket, so I continue to use them.
NOTE: Small-blocks up to 1978 have oil dipstick on the left (drivers) side. Later models have oil dipstick on right (passenger) side. The oil pan gaskets will be different!
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SBC Oil Filter Canister
Two types of canister filters were used on first-generation small-block Chevys. Filter #PF131 is for 1956-1957 engines, and filter #PF141 is for 1958-1967 engines.
Through the years, many of these original canisters were taken off and replaced with the less-efficient but easier to replace spin-on oil filter. If your engine is missing one, replacement canisters are available.
The replacement canisters are licensed by GM and very authentic.
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Before installing the new filter and gasket, make sure you get the old gasket out!
Sometimes it's hard to tell if it's still up there. Shine a flashlight up there, and use a sharp awl or pick to stab it and pull it out.
The original canister seal is square and should come with the new cartridge filter.
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SBC Harmonic Balancer
Several harmonic balancers were used on small-block Chevy engines, depending on the horsepower of the motor. There are three bolts holding the crank pulley to the damper.
Chevy 327 crankshafts never came from the factory with a harmonic balancer bolt, but it was, and still is, a popular upgrade. The crank from this engine had the fourth bolt in the center.
Always check that the timing pointer is correct for the engine. Otherwise, you'll have a hard time getting the timing at it's best spot.
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Related Articles:
Read: SBC Cylinder Head Assembly
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Break-In Oil
Lucas 10631 SAE 30 is a high-zinc break-in oil used for flat tappet camshaft break-in. No moly supplement or additional additives are needed with this oil. Not recommended for passenger cars with catalytic-equipped emissions controls.
Shop: High Zinc Break-In Oil
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