- Rebuilding Engine


Rebuilding Engine

[Please refer to the Engine Buildup section as well!

Cam Bank Angle, Lifter Size Considerations

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.

45 degree blocks used 45 degree heads and the same for 39 degree blocks and heads. If swapping heads between 45 and 39 degree blocks, you must watch for pushrod interference at the bottom of the head. To put 45 degree heads on a (455) 39 degree block, you have to bore the push rod holes to .562" i.d. Applies to "A" heads and some "B" heads.

Angle  Lifter  Notes
 45    0.842"  All 330's.
               Non-Toro D-block 425's, B-block 400? ['65 442].
 39    0.921"  E and G block 400's, '66-7 Toronado 425's. Some '66-7
               non-Toro blocks. Late 307's?
 39    0.842"  Most Olds engines 1968 and up. [exception: late 307's?]

There's 2 kinds of 425's: Toro and Non-Toro. There's a BIG SIGNIFICANT difference:

  • The Toro 425's use .921" lifters on a so-called '39 degree' bank angle.
  • The other 425's have the common .842" lifters on the rarer 45 degree angle, as do the 330 engines.
  • 68-up engines are ALMOST entirely .842" lifters on 39 degrees. The only difference this might make is:
  • .921 lifters are more expensive- like $100 vs. $35 for .842" units, per set.
  • 45 degree cams can be more difficult to find, but any REPUTABLE supplier can supply the grind you want in the configuration you need [Mondello, Dave Smith, etc.]

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.
  • The surest way to determine cam bank angle is to take an old lifter apart, modify it by fitting a small, say, ¼" rod into it that sticks out a foot or so, and is perfectly coaxial with the lifter. I.e., do it in a lathe, not with a hand drill. Install this 'lifter' with the rod sticking way out in any lifter bore. Using a 90 degree square, check the angle between the block deck surface [where the head bolts on] and the rod in the lifter. If the rod is perpendicular to the block deck, it's a 45 degree block. If it's off by a readily visible amount, nominal 6 degrees, then you have a "39 degree" block.

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 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 CBA combination.
  • And, much later, the 307's and 350 diesels used the 0.921 lifter, in roller form, and of course being 1968 and up engines all had the 39 degree CBA too.
  • 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.

If you were to install a 39° cam in a 45° block, one cylinder bank would have its camshaft timing advanced by 6°, while the other would be retarded by 6° (assuming the timing-chain set would install the camshaft straight-up in relation to a 39° engine). If you degreed the cam according to the #1 lobe, however, the odd bank would be installed straight up, but the even bank would be 12° retarded!. The reason it's not 3° advanced and retarded (totaling the 6° difference in the cam bank angles) is because the camshaft degrees are measured at the crank, which is double the actual camshaft degrees (hence, the 328° W-30 cam did not have a lifter lobe that was above the base circle for almost the entire lobe, but rather only for 164° of the cam's circumfrence.

The engine is not going to run right with the wrong CBA cam, no matter what you do. Indexing it to one bank would only make the other bank worse. Adjust the timing won't work either. The motor will run very badly and loudly at idle, but it will run. Once you got it above maybe 2000 RPMs, it will be fine, but you can hide just about any mistake at that engine speed. Spring the $120 for the correct cam, and $40 for the correct lifters; you'll be glad you did.

[ Thanks to Chris Witt, Bob Barry, Chris Fair for this information ]

Block Boring

I do believe sonic testing is necessary for .125 over bore. That's 482 CID with stock stroke!

Budgeting the Rebuild

You can save a considerable amount of money if you do the tear down and build up.

Now some cost estimates:
Hot tank and inspect block, heads, crank, and cam $200 - $300
Turn crank and new bearings $175 - $200 *
Cylinder head job, hard seats and valves $100 to $150 ea **
Lifters/rings/seals/timing chain/gasket set/bearings $250 - $300
So far your you've spent $825 - $1100

* Assuming the crank needs turning.
** Aluminum plating the valve heads is a little cheaper, and works very well.

If you get a low mileage block, you may not need to turn the crank, and save the better part of a C note. If the bores are just a few 0.001"s over size, it is often possible to knurl the pistons and reuse them. This is usually not the best idea. If you got a high mileage block, you may need to bore, which means pistons, so add a couple of C notes.

Pitfalls, the engine got hot and the heads have an amazing array of cracks. This is why you pay for a clean job and inspection. They can see a lot of potential damage by magna-fluxing the engine, prior to spending a lot of money on a bad part. Crank is too bad to turn, or is already well undersize. Same goes for the bores. About 0.060" is about all that is safe to overbore a cylinder without going to much inspection expense; and the casting may not be square enough to support more anyway.

Be careful in terms of purchasing salvage yard components. In rounding up 455 parts to build an engine, and so far I've accumulated bits and pieces of 5. Out of the five all incomplete but two: I've salvaged one good block, another that will bore good at 0.010" over and another that is good but is already at 0.060" over. I have one almost usable crank already at 0.030" under, several good cams. I got five heads, none of which were useable, four, actually five unusable cranks. These engines were donated from under workbenches, and in clunker cars. Good 455 components are not impossible; but are starting to be difficult.

Figure on spending close to $2000 for the engine, and then add the tranny. And this is if you do the tear down, and build up yourself, ie, the bargain basement. A shop will be at least $1000 higher, and YMMV.

Including their labor, for a rebore/ground crank/stock-type rebuild, with valve job and everything, figure around $1600-$2600, depending on labor charges, the performance machine work done to it (i.e. degreeing cam and balancing, which is highly recommended, 3-angle valve job, etc), whether they pull and install it or you do, what old things break and need replacing, etc. You could be pushing $3000-$3500, depending on what extras you need/want to be done (decking block, align-honing, adjustable valvetrain, etc.). These prices will vary with geography, though

Good luck with this; it won't be cheap. If you have the time and skill, you might be able to save a few hundred by doing it yourself, but then you'd have to spend much on that on the tools you didn't already have and couldn't borrow. Then again, you'd have all those neat tools.

Don't skip hot tank and magnaflux, even though it costs a few bucks. And don't let a wise guy tell you he can repair ten dozen cracks in a head, or bore 0.10" because they cannot routinely guarantee satisfactory work under this set of circumstances.

When the block is clean, paint the inside with electrical motor insulating paint (that strange orange colored stuff), and the outside. After painting, get a set of taps and clean up every thread. Remove overspray from the inside of bearing seats and the cylinder bores. Check that every bolt hole, gallery, and block passage is clean, clear and not blocked.

Even if the cylinders do not require boring they do require a bit of honing to seat the rings, so make sure that procedure is accomplished.

The only special tools that are required to reassemble the motor are a torque wrench and piston ring compressor.

Also replace the fuel pump, water pump, distributor cap, coil, wires, and rotor. A rebuild on the distributor should be considered too. Use an aftermarket roller timing chain and sprockets. Do not use genuine Oldsmobile timing chain parts. The factory uses a plastic cam gear (for noise abatement) and that is always the first mechanical part to fail. It is amazing how split, cracked and hammered one of those plastic gears can get and still work; but it will fail. If the engine is under a good load, and the timing goes, it can wrack the entire valve chain, when the pistons come up and slap the now stuck open valves. There are always two open valves.

Also get a chassis manual, Mondello's Catalog or Technical Reference, for the torque specs, and any other trivia that the 455 might need.

Get one of the modern cams w/lots of lift & little overlap. They give nice low to mid rpm power & will absoluteley double the gas mileage of a stock 455. The idle is smooth as silk, but the engine does come alive.

I also rejetted the carb; in my case to Buick GS Stage 1 specs (this was 1973). There are some nice articles on choosing jets & metering rods for your cam & other needs. This produced a nice smooth running engine w/lots of instant throttle.

I also got rid of the EGR; although I don't believe that I would have needed to do that to help my engine. An Edlebrock aluminum intake was substituted (O4B?).

The distributor was recurved to match the rest of the car. A competent hot rod shop can do this. Consider though, a newer breakerless distributor though. These will do wonders for reliability & driveability. They will still have to be recurved though. Kits w/instructions can be bought for you to do this yourself.

[ Thanks to Cliff Feiler, Bob Barry for this information ]