The most important thing is to make sure that the bearing surfaces are spotlessly clean—both the bearing itself and the bearing saddles in the block and the main caps. Check the clearances and follow the clearance recommendations. Chevrolet recommends main bearing clearances of 0.002 to 0.003 inch with a crank thrust clearance (also called crank end play) of 0.005 to 0.007 inch. If the crank has been reground, make sure that the radius from the crank cheeks to the journal are not going to interfere with the side edges of the bearing. Chamfered-edge bearings are available to clear cranks with large journal radii.
Chevrolet Performance offers a main bearing kit for a standard 350-ci engine as PN 12499102. Always use a main bearing set that has a groove cut in the half of the bearing that fits in the upper position in the bearing saddles of the block. The lower bearing half should not have a groove, and it fits in the main bearing cap. Do not use fully grooved bearing shells.
Block Dowel Pins
Sometimes when you acquire a block, a number of the dowel pins are missing. Here are the GM replacement parts for Gen I blocks:
| Block Dowel Pin Part Numbers | |
| Part | Part Number |
| Rear Block/Transmission Dowel Pins | 01453658 |
| Block Deck/Head Locating Pins | 585927 |
| One-piece Rear Oil Seal Housing/Block Locator Dowel Pin | 9441003 |
Some folks wish to offset the cylinder head locations from their original blueprint location for racing purposes. Offset head locator pins are available from aftermarket suppliers. However, this is not something a novice engine builder should try. At times, the block is misaligned to the transmission bell-housing locator pins on the rear of the block. Offset block/transmission dowel pins are also sold on the aftermarket.
Generation II LT4
In 1996, Chevrolet also introduced the LT4 350 small-block V-8 as an engine option in the 1996 Corvettes. This Gen II small-block 350 engine has a number of changes when compared to the 1992 to 1995 Gen II LT1 350, which has 300 net hp and 330 ft-lbs of torque in production vehicles. The 1996 production LT4 engine is rated at 330 net hp, and used revised aluminum heads with 2.00/1.55-inch lightweight valves. The exhausts are hollow stem valves that are partially filled with a mixture of sodium and potassium to improve valve cooling and reduce weight. Static compression is 10.8:1 (the Gen II LT1 has 10.4:1) with the small chamber LT4 aluminum heads and revised pistons that have the smaller valve reliefs.
The LT4 heads (PN 12555689 or 12363287) have intake ports that are raised 0.100-inch higher than those found on the 1992 to 1996 LT1. The port contours have been reshaped and improved for more flow and increase the intake port volume to 185 cc. The exhaust port contours have been changed on the LT4 head for smoother flow. Stud-mounted, self-aligning Crane roller rockers with a 1.6:1 ratio are used along with single-coil 110/260-pound spring-pressure valve springs. The LT4 head (PN 12555689) uses a non-adjustable net lash shouldered rocker arm stud. A steel roller cam and hydraulic roller lifters increase the capabilities of the valvetrain to 6,300 rpm.
This motor used reverse-flow cooling and its heads can be interchanged onto the LT1 block, provided that you use the production LT4 electronic TPI manifold. Use the new-design LT4 intake manifold gaskets, which fit the revised intake manifold bolt-hole spacing and bolt angles. The LT4 uses a one-piece rear main seal crank, which is externally balanced, and 5.7-inch powdered metal rods. These engines may now be even more rare than the SB2 race engine. ■
Used Engine Blocks
If you are about to buy a used block, here are some things to think about before buying: How has the block or complete engine been stored? Has it been kept inside in a clean, dry place or has it been sitting outside? Has it been covered up? Why is it being sold? Did a rod bearing spin? Was it burning large amounts of oil before it was pulled out? Is it covered with rust, dirt, or 200,000 miles of grease? If water was left in the block when it was stored or if rain or snow has gotten into it, has the block suffered a freeze crack? Some cracks are practically impossible to spot when the block is covered with rust, oil, grease, or who knows what. If the crank and rods are still in the block, can you turn the motor over? Is it locked up or does it turn over smoothly?
Check the casting numbers and dates. What do they tell you? If the heads are off the block or if the seller lets you remove the heads, check the bore of the motor. Has the block already been bored 0.040 inch over or larger? Are the cylinder walls clean, rusty, or cracked?
Look at the threaded bolt holes on the block. Have any of the threads been stripped? Are bolts broken off in the holes? Are all of the main bearing caps still on the engine? Are dowel pins missing?
Some problems may not be found on a used block until you take it to a machine shop and have it cleaned. You may find cracked cylinder barrels, cracked water jackets, or cracks caused by broken connecting rods hitting pan rails, oil passages, or cylinder barrels. The main caps may be mismatched or from another block.
Some of these problems can be fixed. Cylinders can be sleeved, threaded holes can be heli-coiled, and cylinders can be bored out and cleaned—up to a point. Some problems cannot be fixed. Cast-iron blocks with cracks in the outboard water jackets, with major damage from a broken connecting rod, or with more than one cracked cylinder barrel need to go directly to the dump or metal recycler or back to the guy who sold it to you.
The point is, there are times when the cost of fixing a used block is too high. Keep looking for a block that doesn’t need major repair. Try to find a used engine that is still running in a vehicle so you can hear it and maybe drive it to get a better idea of its condition. Millions of Chevy Gen I and II small-blocks are out there, so you shouldn’t have any trouble finding a good, rebuildable core motor with the features that you want.
CHAPTER 2
GASKETS AND FASTENERS
When it comes to sealing your small-block Chevy, there several areas you’ll need to address due to design changes. First, you must determine whether you are building an engine using the familiar two-piece rear main oil seal or with the new-style one-piece rear main seal that was first introduced in Gen I blocks in 1986. Adapters are available, both from Chevrolet Performance and aftermarket suppliers, which allow you to use a one-piece, rear-main-seal-style block with an earlier two-piece seal crank.
When searching for gaskets, it is important to note that many different materials and applications are available from Chevy and aftermarket suppliers. Also, Chevrolet has discontinued many different gaskets and seals over the years but gasket companies such as Fel-Pro Gaskets, SCE Gaskets, Cometic Gaskets, and others that specialize in sealing engine components may have exactly what you’re looking for.
There are a variety of intakes and heads available, so make sure you have the correct intake setup for your application. Most GM intake manifolds are supplied with rubber end gaskets that fit on the block between the two head surfaces. Many aftermarket manifolds recommend using a gasket sealer instead.
Intake Manifold Gaskets
There are now five different production intake manifold gasket types, and which one you use depends on whether you are building a Gen I, Gen II LT1, Gen II LT4, or Vortec small-block. The intake manifold bolt angles, the bolt spacing, and the position in the cylinder heads and intake manifolds, and some production port positions have been altered from what you may be familiar