CANADIAN ENGINE REBUILDER: Heads Up for The GM LS1

General Motors’ classic nomenclature was revived for the 5.7L V8, but this doesn’t mean the old problems remain.

Referred to as the GM 5.7 VIN G engine, the Series III, Generation III or simply as the LSI, the engine was installed in Camaro, Firebird and Corvette models from 1997 to 2000. The result is that there are many opportunities for you to run into one of these engines in your machining business.

Engine shops should be aware of a few cautions regarding the cylinder heads on these engines.

If you are heat cleaning or straightening the cylinder heads, for example, you should not allow the heads to be exposed to heat greater than 204 degrees C (400 degrees F) and you should avoid a direct-flame process.

Also, the process for checking the straightness of these heads should be executed meticulously. Heads should be within three thou (0.003″) within any 6.0″ and a maximum of 0.004″ (1 mm) as shown in the Figure 1 diagram showing straight edge positions. You should repeat the checking procedure on the cylinder block with a maximum out of straightness of 0.004″ (1 mm).

If the heads require surfacing, ensure all shop personnel are aware of this and also that they understand that the minimum thickness on these heads is 4.732″ (120.20 mm) as shown in Figure 2.

Furthermore, if the measured valve guide to valve clearance indicates wear beyond service limits, the current available repair from General Motors is to fit it with oversized-stem replacement valves. A thin wall guide liner may also be considered.

When the cylinder head is being serviced for a valve job, General Motors says that the intake valves are to replaced, not ground. The intake valves are of an ultra-light design and have insufficient material for grinding, hence the “Replace Only” recommendation.

Reseating the valve seats can, however, be accomplished using conventional, accepted methods as they can be ground or machined.

Refacing Angle for Valves and Seats

Intake Valven/a

Intake Seat46 degrees

Exhaust Valve45 degrees

Exhaust Seat46 degrees

Starting with the 1999 model year, valve stem seals were color coded to indicate their specific location. The valve stem seals for the intake valves are black while the seals for the exhaust valves are brown. There is also a specific tool for installing these seals (GM Part # J42078) and shops are advised to use this tool or an equivalent for the proper installation of the valve seals.

Rocker Arm Installation

There is also a specific procedure for installing the rocker arms on this series of engines.

1) Rotate the crankshaft until the number one piston is at TDC of the compression stroke. The rocker arms for the #1 cylinder will be in the off cam lobe lift (unloaded) position. Also, viewing the engine from the rear, the non-threaded pilot hole in the crankshaft’s rear flange will be at the 10:30 position.

Note: Firing order of the 5.7 VIN G, Generation III engine is 1, 8, 7, 2, 6, 5, 4, 3.

Cylinders 1, 3, 5 and 7 are on the left bank (as viewed from the flywheel end of the engine).

Cylinders 2, 4, 6, and 8 are on the right bank (as viewed from the flywheel end of the engine).

2) With the #1 cylinder at TDC, tighten the following rocker arm bolts:

Tighten the exhaust valve rocker arm bolts for cylinders 1, 2, 7, and 8 to 22 ft.-lbs.

Tighten the intake rocker arm bolts for cylinders 1, 3, 4, and 5 to 22 ft.-lbs.

3)Rotate the crankshaft 360 degrees (one full turn). This will bring all the previously loaded valves (those on the lobe) into the unloaded position necessary for tightening of rocker arms.

4) Tighten the following rocker arm bolts:

Tighten the exhaust valve rocker arm bolts for cylinders 3, 4, 5, and 6 to 22 ft.-lbs.

Tighten the intake rocker arm bolts for cylinders 2, 6, 7, and 8 to 22 ft.-lbs.

Shop owners are reminded, as always, that a detailed approach to cleaning, disassembly and assembly are important factors in the success of a rebuild. When combined with professional machining, the result is an engine that will provide many years of reliable service and, in the case of this particular engine, spirited driving, too.

The material printed here was provided by the AERA-Engine Rebuilder Association.