I may have found the problem. I think the cam bearings are incorrect for a Tonawanda block. According to what I've read, the Tonawanda blocks use 1) a different cam bearing set with two large and two small. 2) There is also a different install procedure. I'm pasting some of the info I found. The bummer is, NAPA doesn't have these bearings! Can anyone assist with the proper cam bearing set PN?
1987- ’94 WITHOUT BALANCE SHAFT: In 1987, a roller lifter cam was installed, so the block was changed again. Two bolt bosses were added in the middle of the valley for the lifter retainer that kept the rollers properly located on the cam and perpendicular to it. This same basic block was used through ’91 for everything, and in ’92 through ’94 for all of the engines without balance shafts except for one small difference – some of the blocks came with four bolt holes for the tunnel style retainer beginning in ’92. There were several different castings used, including the 10105867, 10172756, 14099073, 14093683 and 10066011 with the two-bolt retainer, and the 10172756, 14099073 and 10066061 blocks with the four-bolt retainer.
MORE ABOUT BLOCKS
There is one other subtle difference in the blocks. The cam bearing sets are different, depending on whether the block was made in Romulus or Tonawanda. The Tonawanda blocks use two larger diameter cam bearings, one in front and one in back, instead of only one large one in the front. Both bearing sets are available in the aftermarket. (Yeah but where?)
Technical Service Bulletins
Engine -Repair Differences Based on Production Location
GMC NUMBER: 92-6A-14
GROUP: 6A Engine Mechanical
DATE: October, 1991
CORPORATE NUMBER: 136119
SUBJECT:
INFORMATION ON APPEARANCE AND MECHANICAL DIFFERENCES OF THE 4.3L LB4 ENGINES PRODUCED BY
TONAWANDA AND ROMULUS ENGINE PLANTS
MODELS:
1992 S/T, C/K, AND G
The purpose of this service bulletin is to inform field personnel of the appearance differences and the mechanical differences of the 1992 4.3L LB4
engine, manufactured at Tonawanda, NY vs. Romulus, MI.
TONAWANDA - (LB4)
Engine Identification Number beginning with "T" located on the front of the engine block at deck height in front of the right cylinder head.
1. Engine painted as components; therefore the aluminum intake manifold will be silver in color.
2. Net Valve lash rocker arm assembly (new stud, ball, and nut).
3. Camshaft bearing order revised to allow engine plant assembly of the bearings from the rear of the block.
1. Largest outside diameter
2. Mid Size O.D.
3. Smallest O.D.
ROMULUS - (LB4)
Engine Identification Number beginning With "W" located on the front of the engine block at deck height in front of the right cylinder head.
1. Engine painted as an assembly. This is the appearance of previous model years; black intake manifold and engine block.
2. Adjustable rocker arm studs.
3. Camshaft bearing order is the same as previous years.
1. Largest O.D.
2. Mid Size O.D.
3. Smallest O.D.
Note:
Both engine plants will use a new camshaft with a smaller lobe base circle and a long travel roller lifter. These were engineered to be compatible
with the net valve lash (Tonawanda) feature.
