The term “blueprinting,” as applied to building high-performance engines, has for decades been thoroughly abused. To many, it’s often a flip reference to the fact that the engine builder took the time to measure the main and rod bearing clearances with Plastigage. To others, the term takes on a much more critical meaning, especially when talking about lifter bores.
For the purpose of this story, we will focus on a subject that is rarely discussed, yet has far-reaching effects on engine performance. For most amateur engine builders, the thought may never occur that all 16 lifter bores on a pushrod V8 engine are not in exactly the same position called for in the original design of the cylinder block. When dialing in the cam with a degree wheel, the common approach is to only check the intake lobe on the Number One cylinder and assume the rest are in the same position. We’ll admit to using that approach for many years. Sure, we considered checking several different cylinders to verify the timing numbers. We just never got around to it — until recently.
Diagnosing A Lame Engine
If you build enough engines, there is the potential for a situation where one (or more) fails to perform as well as its cousins. It rarely responds to tuning, exhibits odd or inconsistent behavior, makes far less power than it should, and is generally just lame.
The 350ci small-block Chevy we had the misfortune to own fit all of the above descriptions of engine malaise. This was a brand-new crate engine, yet it steadfastly refused to properly respond to multiple camshaft, induction, and ignition system modifications over several years of trying. To put it bluntly, it was a pig.
Finally, the engine failed altogether after we discovered serious backlash between the camshaft drive gear and the distributor. We disassembled the engine and found a bad cam bearing that we blamed for all its ailments. But once repaired, the engine resumed its bad habits and again exhibited the distributor drive gear backlash that created an incurable off-idle hesitation. This was caused when ignition timing would retard 15 to 20 degrees for roughly a half-second during mild acceleration from idle before the timing could advance.
This demanded more investigation, so we again pulled the engine and began searching for a solution. It was at this point that, quite by accident, we ran across a series of short online videos created by Ron Flood at Cedar Machine, in North Branch, Minnesota. In one of these videos, he described a ‘70s-era 455 Oldsmobile block that had previously killed several flat tappet camshafts and lifters. Cedar Machine discovered that the block suffered from severely misaligned cam housing bores that did not parallel the crankshaft main journals. This prompted us to evaluate our misbehaving small-block as perhaps suffering from a similar predicament.
Finding The Problems With The Lifter Bores
A subsequent discussion with long-time NHRA drag racer and race engine builder Bob Lambeck suggested a simple test we could perform to measure the position of the lifter bores relative to the camshaft. The procedure was as informative as it was simple. We already had the cylinder heads removed while the short-block was still intact. Lambeck instructed us to set up a large, professional degree wheel to accurately determine the position of top dead center (TDC) for the Number One cylinder. This step is vital in order to produce accurate results.
With that accomplished, the next step is to position a dial indicator mounted on a magnetic base directly in line with the Number One intake lifter. With the dial indicator zeroed on the base circle of the lobe, we then rotate the crankshaft until the degree wheel indicated TDC and record the lift shown on the dial indicator. With our particular camshaft, the lift value was 0.042-inch. Other camshafts with more or less aggressive profiles will produce a different lift number. The actual lift isn’t significant. What is important is how close all eight intake lobe lift numbers are to each other. With consistent lift numbers, this means the lifter bores are close to the same position relative to the camshaft.
As our testing quickly revealed, none of the intake lobes were even close to being in a consistent position. Lambeck told us that he prefers to see 0.002- to 0.003-inch or less of variation to qualify a Stock or Super Stock block as acceptable. Ideally, of course, the TDC lift numbers should all agree with zero variation. But that seems unlikely with a production block.
As you can see from the accompanying Intake Lobe Lift chart, our test of this particular cylinder block was far from repeatable. We did have one pair of intake lifters that checked the same, but of immediate concern was that the largest variation was a massive 0.016-inch between cylinders two and three. We then turned the crankshaft through another lift curve to measure the amount of crank movement for a given amount of lobe lift which revealed that 0.010-inch of lift (on this particular cam) was equivalent to 5 crankshaft degrees of cam timing change in opening or closing points for our engine.
Our small-block’s 0.016 inch of difference between cylinders two and three meant that this built-in error factor would produce no less than 7 degrees difference in opening and closing points between these two cylinders. We followed this intake evaluation with a similar test of all 8 exhaust lobes and discovered a narrower error factor with a maximum deviation of only 0.009-inch compared to the intake’s 0.016-inch. Even so, it was obvious this engine block had a major problem.
What this test revealed was that while we assumed that all eight cylinders were opening and closing the valves at the same time, this was obviously not the case. The reality was, that this engine was more like eight cylinders all operating with different valve opening and closing numbers while still connected to a common crankshaft. An analogy would be like four rowers on each side of a canoe pushing paddles in eight different directions!
While this test revealed our engine’s inherent problem, it immediately created even more questions. While this test can be performed on any pushrod engine, we must admit that this procedure also creates its own set of variables. We used TDC on Number One piston to extrapolate the TDC position (at 90-degree increments) for the remaining seven cylinders. If we had used the actual TDC for each cylinder, that might have been more accurate but then we would introduce the variable of potential crankshaft throw index inaccuracy.
Figuring Out What’s Out Of Whack
Even more of an issue is that this lift at TDC test does not clearly indicate whether the problem is with camshaft bore alignment, lifter bore position inaccuracy, or possibly, errors with the camshaft itself. The most probable answer is that the results are a combination of all three. The only way to break this down is to have a good machine shop use their BHJ fixture to accurately establish a true crankshaft main journal alignment and then use that centerline to check the cam housing bore position against the crank centerline.
Cedar Machine, for example, often machines the cam bores and then uses oversize cam bearings to accurately return an errant block to proper cam alignment. Once the cam journals are properly aligned in both the horizontal and vertical planes, the lifter bores can then be tested for position accuracy.
All of this can be measured and corrected by a properly equipped machine shop like Cedar Machine, but it does not come without a cost since this work demands precision. We spoke with Al Parker of Parker Machine & Performance in Newton, Iowa, and he told us in no uncertain terms that our one-piece rear main seal cylinder block could be repaired but it wasn’t a cost-effective plan. His recommendation was to simply find a more accurate block.
During a subsequent discussion on this topic, Bob Cook at John Callies, Inc suggested that a simple indicator would have been to do a compression test of all eight cylinders and then compare the pressure readings. If the cranking compression varied due to wildly different opening and closing intake and exhaust positions, this would have been illustrated as significant variations in the cranking pressure. This is not a precise test, but certainly, a quick and easy way to connect the diagnostic dots in the right direction.
We next purchased another, used, one-piece rear main seal SBC block and performed the same intake and exhaust lobe check with a different camshaft, and came up with much more consistent numbers. The intake lobes on this used block checked with a spread of 0.006 inch, but only between two of the intake lifter positions from the lowest lift to the highest at TDC. The other six holes tested with barely 0.003 inch of spread — which was quite encouraging. The variation on this second block still represents a difference of roughly two to three degrees of cam timing variation between two cylinders. But because a full blueprint repair of cam bore alignment and lifter bore machining might ring up a machining bill well approaching $1,000 or more, we will stick with this block as an acceptable candidate for a mild street engine rebuild.
This story is not intended to create the impression that all production blocks are junk. That is probably not the case. However, if you are engaged in the art of engine building, this simple test procedure will offer another clue as to the quality of your foundation.
This is certainly not shockingly new information. Quality machinists have been aware of these relationships for decades. What this story should point out is there is a far deeper level to the term blueprinting than merely degreeing the cam on one cylinder or assuming that the lifters are where they are supposed to be. This story reveals that this is not always the case but that with a little extra degree wheel effort, you can easily identify a good block from a poor one.