Oldsmobile engines from 1964 onward originally used a 45 degree cam bank
angle (CBA). This angle is formed by the intersection between the
cam centerline and perpendicular lifter centerline. By 1968, all
Olds engines were using a 39 degree CBA. In the years between,
39 degrees was used mainly on blocks found in Toronado's, and
45 degrees was being used everywhere else. The CBA also affects the
pushrod hole angle in the heads.
There are a couple of ways to check for cam bank angle,
and if it is a Toro 425 block:
Find the engine ID number/letter on the shelf behind the water pump,
ahead of the intake, just above the timing chain. Now, at the RH [passenger]
end of this shelf is an upright wall that runs fore-aft. This means the
block is a big block.
It should get fatter toward the front. Right near the top, in the fatter
part, there should be a drill spot, at about a 45 degree angle [parallel
to the even-bank head bolt holes] and just barely drilled into the wall
or rib, until the diameter got to about 3/8". If that drill spot is
there, then the block is almost w/o a doubt a 39-degree cam block. Every
1966 to 1967 Toro 425 and 1966 to 1967 442 400 engine I have seen so far had this drill
spot and had a 39 degree cam bank angle.
Basically, the way it worked out was that if the early (pre 1968) big
block had 0.921 lifters, it was an advanced [for the time] 39-degree block,
and if it had the normal 0.842 lifters, it was an old 45 degree block.
Anyhow, the presence of the drill spot on a pre-1968 big block means a
39 degree block and heads. Easy to spot, too.
- Mondello claims that some 330 blocks had a rare 0.842 lifter/ 39 degree
- Finally, Mondello goes another step further- says there's some 425
[non-Toro??] blocks with a 0.250" drill spot which are also [???]
39 degree units.
- 307's with 7A heads used 0.921" hydralic roller lifters. Those with
5A heads used 0.842" hydralic flat tappet lifters.
Please refer to the Engine
Rebuilding Cam Bank Angle section for more information!
[ Thanks to Chris Witt for this information ]