“I am convinced that the two most misunderstood words in engine building are ‘bolt on’.”
According to my sister, a veterinarian, all dogs are descended from a common ancestor. Every member of canis familiaris, also known as the domestic dog, can trace its roots to grey wolves that walked the earth 14,000 years ago. This means that Duke, the chocolate Labrador retriever who rules the Reher household, belongs to a family that also includes yappy miniature poodles, towering Great Danes, and every mutt at the Humane Society.
I bring the diversity of dogs to your attention because it is an example of extreme specialization. Through selective breeding, humans have created an astounding variety of breeds with wildly different appearances and purposes – yet all of them are fundamentally alike on a genetic level.
Now consider the evolution of racing engines – after all, this is a column about motors, not domestic mammals. The vast majority of drag race motors are offshoots from the Chevrolet V8 family tree. And just as selective breeding has created dogs of every imaginable size and shape, creative engineering has produced a staggering variety of components. Yet while dogs can still interbreed, many specialized engine components are no longer interchangeable.
I am convinced that the two most misunderstood words in engine building are “bolt on.” In the days when I built small-block Chevys with factory parts and a smattering of aftermarket accessories, the term “bolt-on” was meaningful. You really could bolt on an intake manifold or change a cam using only the wrenches, screwdrivers and sockets you could find in any toolbox. Today it is more likely that you’ll need a lathe and mill to swap cylinder heads, intake manifolds, or valvetrain parts.
Even Detroit has made life more complicated for engine builders. For more than 30 years, virtually every part in a small-block Chevy V8 was interchangeable. Then in the mid-‘80s, everything changed. Chevy introduced new crankshafts with one-piece rear seals, new blocks machined for hydraulic roller cams and cylinder heads with reverse cooling. These changes affected other parts, requiring new flywheels, new torsional dampers, new valve covers, new water pumps, new gaskets – and suddenly you had to be an expert in esoteric part numbers to rebuild even a street engine.
At the same time, the aftermarket parts business was booming. The widespread availability of CNC machining equipment, along with an explosion in the number of people who could program them, allowed speed equipment manufacturers to produce their own parts. Instead of waiting for the next new casting from GM, racers turned to specialists like Dart, Brodix, Edelbrock and others to supply hardcore racing components. It’s now possible to build a complete small-block or big-block Chevy V8 from a vast array of aftermarket parts.
Racers have certainly benefited from the work of aftermarket manufacturers because we have access to reasonably priced parts that can dramatically improve performance. When I put a conventional Dart or Brodix big-block cylinder head alongside the D-port castings that we used 20 years ago, I am astounded by the differences. I would have loved to have a pair of today’s off-the-shelf heads on our Pro Stock engine back in 1980 – we would have been unbeatable! A second look reveals that the only similarities between the factory and aftermarket castings are the head bolt patterns – yet many racers still regard these heads as “bolt-on” parts.
The downside to the aftermarket revolution in racing components is that each manufacturer concentrates on only one piece of the puzzle. Every manufacturer strives to make better parts than his competitors. In cylinder heads, for example, the ports get taller, the valves grow longer, and the valve angles become flatter. Since we are no longer working on a “universal” Chevy engine, these changes ripple through the entire engine assembly. Suddenly we need a raised-runner intake manifold to match the ports, new pushrods to complement the longer valve stems, and new valve covers that will clear the shaft-mounted rockers and large diameter valve springs that are necessary to take advantage of the improved airflow.
The proliferation of parts has produced pitfalls that can trap even experienced engine builders. For example, the length of the lifter bosses varies in both factory and aftermarket blocks. Yes, you can drop a set of roller lifters into a Gen VI big-block, but if the tie-bar hasn’t been raised to accommodate the block’s taller lifter bosses, the roller won’t contact the camshaft’s base circle. If you set the valve lash with the tie-bar resting on the top of the lifter boss, you get .200-inch clearance instead of .020-inch clearance. And when you fire up that engine, you’re going to break valvetrain parts instantly.
The trend in sportsman drag racing is toward bigger and bigger engines. Big engines make big power, but they can also cause big headaches because everything has to fit inside a tighter package. You buy a stroker crank from Company A, connecting rods from Company B, and pistons from Company C. If you are a crankshaft manufacturer, you concentrate on building the best possible crank – and you don’t really worry about whether your crankshaft counterweights will clear the Company C’s piston skirts. Similarly, Company C focuses on building lightweight pistons – providing clearance for Company A’s new crankshaft counterweight design isn’t on its radar screen.
So who has to make sure that the crankshaft counterweights clear the piston skirts – along with the block, the camshaft, the oil pan, the windage tray, and everything else? The engine builder.
It’s better to assume that parts don’t fit than to assume that they do. That’s not being negative – it’s just being realistic. The problems you find when you first assemble an engine are relatively easy and inexpensive to solve. It’s the problems you discover after the engine has blown up that are back breakers. For example, if you simply assume that the crankshaft flange thickness is correct for your torque converter instead of actually measuring the clearance, don’t be surprised if you burn out the thrust bearing.
Even a part as apparently simple as a distributor can cause serious problems. The housing for a Chevrolet distributor has a groove that transfers oil to the right-hand oil gallery. If this groove is misaligned because the block/head/manifold combination positions the distributor too high, the right-side lifters, pushrods, rocker arms, and springs are going to starve for oil – and they can’t survive very long without lubrication. Perhaps the distributor gear doesn’t engage the drive gear on the camshaft properly – how do you know unless you check? One of the final steps in engine assembly at Reher-Morrison Racing Engines is to verify the position of the distributor. We don’t install the oil gallery plugs in the back of the block until the very end of the assembly process so we can visually confirm that the distributor’s position relative to the block and cam is correct.
Professional engine builders have the advantage of seeing more variations in engine components and are therefore more likely to spot potential problems. If you are building your own engine, my advice is to take your time and check every part you bolt on. Don’t rush to make this weekend’s race if it means taking shortcuts. It’s the pieces that almost fit that can be the most troublesome – the camshaft drive that’s cocked just a little on the block or the pushrod guideplate that’s just a little out of alignment.
When I started racing, we had three network television stations and one universal racing engine. Now I can choose between 200 channels on cable TV and literally thousands of engine components. My dog Duke doesn’t worry about such things. He just wants to know when I’m going to stop writing and feed him his dinner. Life is much simpler for dogs than for drag racers.
Reher on bolt-ons: Bolt-on thing is something that needs to be talked about, a real miscommunication now. Words I see over and over again. I want to caution people that we are in an era when less bolts on in bolts in than ever has.
As we develop parts as an industry, less and less standardization, more people doing things on their own. Take blocks for example, god knows how many people making heads. Careful attention has to be paid to lifters, that’s a mistake that’s made frequently. Different length lifter bores, tie bars don’t clear, people drop lifters in an assume they clear but they don’t. Not touching the cam, eventually touching it, off they go until they break.
Issues like Gen VI block, cam drives don’t fit, front covers don’t clear. Worst situation is when something almost clears because it’s not obvious. It went on, but you have to pay attention.
Crankshafts, counterweights may or may not clear the block and pistons. As we go to bigger cubic inch motors, you can just about count on them not clearing. People miss distributors a lot; gear may hit the block, may be a manifold alignment problem with block that keeps it from going in. Sometimes it goes in and it’s high, doesn’t have contact with cam or worse yet it’s block an oil passage.
Not all crank flanges are the same, can’t assume that his torque converter is going right in. I see people burn thrusts out worse than we did with clutches when in with zero clearance or has tension on it.
That happens more and more, got one company building heads, another building manifolds. Everyone is trying to improve stuff, valves are .200-.300 longer than they were, changing valve angles a little bit, everything’s changed a little bit. Even conventional parts don’t just bolt on.
Something as simple as oil pumps. You’ve got a wet sump pan, Speed Pro or whoever built for stock block. If main cap is slightly different, aftermarket block, they put the dowels and bolt holes, but that doesn’t mean the body of the pump doesn’t hit the main bolt or body of the cap.
Cranks, cam drives, distributors, oil pumps, lifter are most often screwed up.
Cylinder heads, all different valve lengths, pushrods become major issue. Person has to pay attention to tip to roller position, ingrained in you to drop parts in, if the slip in they probably don’t fit. Guideplates don’t line up, pushrods hit port wall, then we get into the situation with a lot of aftermarket valves, is the tip length right? Is the tip sticking up enough that the rocker arm clears the retainer? Go for extra spring height with deeper retainer, then retainer hits the rocker. It’s not real obvious.
If you have titanium valves that need a lash cap, do you have the right keeper to clear the cap? There are different lash cap depths, shallow and deep. Last thing you want is a lash cap bottoming out on a keeper, next thing that happens, bang, split the keeper, valve drops.
Heads, just talking conventional stuff, does the valve cover hit, clear the valve springs. Edelbrock not necessarily building manifold for Dart head; yeah it will go on there, but are the bolt holes lined up, distributor in the right position?
Don’t get yourself in corner where you have to hurry up, say I’ve got to get this together. Right now we have to look at stuff more than ever had. An advantage to racer because we have better parts, but because we have more aftermarket people building them, they’re not checking them. Not a universal engine anymore like they were when we waited for the next GM head. Everyone is competing to make a better part, and they are for most part, but interchangeabilty goes away because we’re building parts that aren’t identical to production line piece.
If you take a current Brodix or Dart head beside a 1980 D-port head, they’re distant relatives, yet they’re assumed to be a direct bolt on. I would have loved to have a set of current Dart or Brodix heads to race on our Pro Stock in 1980. It’s still perceived as bolt-on, a lot of it’s advertised as bolt-on. Since we bolt stuff together everyday, you couldn’t bolt anything on without a lathe and a mill. We’re experienced veterans with 30 years engine building.
A public service that needs to be said. A lot of people are needlessly tearing stuff up, learning expensive lessons the hard way. Professional engine builder has worked it all out, not doing for first time in garage. A lot of pitfalls out there. Now you’re putting engine together, piston options by thousands, as engines get bigger everything getting closer. Almost better off with mindset that won’t fit because you’re more likely to find problems. Just think, I wonder what doesn’t fit about this?
Distributor: We don’t put oil galley plug in until after distributor is in, last thing we do so we can see how it’s lined up, then plug goes in.