Click on a thumbnail to see the full-size image
A Distressed Distributor Can Ruin Your Restoration
By Doc Frohmader
You know that customer? The one who waited not at all patiently while you found the parts, got the machine work done, and finally assembled his vintage or performance engine? The one who appeared to be in substantial pain when he wrote that $4,000 check and grudgingly tossed it on the counter with trembling hands?
Well, now he’s back and whining about how it doesn’t run right. It hasn’t the power he expected. He’s fried a valve. It burns too much fuel and has lousy throttle response. And it’s all your fault and he wants you to fix it all, pay for everything, refund his money and hold his hand. Sound at all familiar?
I hate to tell you, but to some degree it may actually be your fault you’re in this position. You see, while you may be the best engine builder ever to grace the world you may not be making it clear that after the long-block is built there’s more to deal with. Carburetion and ignition top the list. This time I’ll talk a bit about ignition and perhaps save you some grief.
Trouble comes in several flavors. The first is simply a distributor that is not in good repair. On old iron this is not exactly exceptional. While that old engine might have been built and run to the ground several times, the distributor was probably pulled and replaced without much more than a set of points to keep it alive.
You know I’m right. So by the time you get a hold of it, it’s got a bizillion miles on it and seen better days. Bushings get worn, shafts wear, advance weights chew up the pins, springs turn to rust and crust, and cams go round. In every one of those cases, it will cause running problems.
A good many can be repaired, or in some cases another distributor located. In any event, either you or your customer has to make sure the distributor is still in good working shape. It is certainly an ‘extra’ expense, but how much sense does it make to throw a junk part in with an expensive rebuild and potentially cause damage you’ll be blamed for?
If you have an otherwise good distributor but have a worn cam, you will have erratic points opening and all the attendant problems. Unfortunately, sometimes it’s hard to find a suitable replacement. For that matter, we know that points style distributors can’t match the performance and durability of HEI units and that is also a good reason to wonder about a change.
There’s a great way to solve for both scenarios. Pertronix and Crane both offer electronic/HEI conversion kits to cover all but the most esoteric distributor applications. These items do not rely on the perfect condition of the distributor cam to make them work and they are simple bolt-in kits. Moreover, they work very well.
Both are a true electronic conversion with the high energy spark, no points float, and extraordinary durability you expect. They also cost well under $100. For those customers with restorations, they can both be used with conventional coils and, other than one extra wire from the distributor, are impossible to tell from stock. You can also swap the points back in at any time with no damage.
The major problems, however, come from timing issues. Gary Breyer at B&H Speed in Wood River, IL, and I have worked together for years. He always gets my distributors before they go into one of those high-profile engines I get involved in. I have him go through each one to put it in shape and then have him re-curve each unit to suit the engine.
Each engine, based on cam, induction, compression, header/manifolds, vehicle application, performance level, uses, and more will require a little different advance curve than the next. Getting them right can mean the difference between a happy customer and the customer from hell.
There are several considerations for re-curving a distributor, including initial timing, total timing (excluding vacuum advance), mechanical advance, vacuum advance, when the mechanical is all in, when the mechanical starts, when the vacuum advance starts and when it begins.
Initial timing is simple. This is the timing you set when idling the engine and twisting the distributor. It is simply the number of degrees before or after TDC this static timing is set. As a general rule, the more initial you can run without starting problems the more efficiently the engine will run. In general, most vintage engines can stand up to around 10 degrees or about one-third of the total of mechanical and static timing.
Mechanical advance is a little more complex. The combination of weights, springs and weight cam produce a situation where the faster the engine turns, the more advanced the timing is. Engines require more timing as RPM increases for efficiency. In general, vintage engines can run somewhere between 18 and 28 degrees of mechanical advance timing. Combined with the initial timing, this gives you a total of 32-36 degrees.
While this may seem straight-forward, it’s a little more complex. First, there’s the matter of when the mechanical advance curve begins. If it starts too early, you can end up with too much timing too fast and see detonation or poor performance. If it comes in too late, you lose efficiency because you don’t have enough timing between initial and mechanical. In general, mechanical timing needs to begin at something around 1,000 rpm. It takes experience and knowledge of the engine to get it just right.
In addition, there’s the matter of when the mechanical advance is fully in. Again, in general this is usually somewhere between 3,000 and 3,500 rpm. The same advantages and liabilities result from when full advance is too early or too late for the engine and application.
The weight of the weights, the tension of the springs, the shape of both the weights and the weight cam can be altered to shape the advance curve to your needs. In general, the heavier the weight, the faster the curve begins. The heavier the springs the later the curve begins.
The shape of the weights relative to the weight cam determines the shape of the advance curve (you want it smooth and even) as well as the limits of the advance. Be aware that the wrong combination can put the effective curve outside of the engine’s capacity and could defeat your efforts.
Vacuum timing is a debated issue. For the most part, vacuum advances improve fuel mileage and efficiency under cruise conditions. A vacuum pot reacts to engine vacuum as an indication of engine load. The more load, the less advance an engine can tolerate, the less load, more. The trick is to get the best performance by tailoring the vacuum advance curve to the engine and application. This involves the total amount of vacuum advance available, the engine vacuum level at which the advance is fully developed, and the point at which vacuum advance is completely deleted relative to engine vacuum.
This will depend heavily on the cam the engine is using because as you know different grinds will mean different engine vacuum production. While a stock engine may make as much as 22 inches, there are performance engines getting 8 inches. If you use a vacuum advance curve meant for one with the other, it just simply will not work right.
For those of you who have the equipment and experience to do your own distributor work in house, I suggest that you use this kind of information to convey to your customers the need to get the distributor in the right shape, perhaps convert to HEI/electronic, and certainly check or re-curve the distributor to get the best from their investment. It will not only result in fewer complains and failures, but help to demonstrate your professional status.
The more you know and the better you can transmit that knowledge to your customer, the better impression you will make. I know several shops that consistently get more jobs for better money than the local competition because they look and act the part of the pro.
For those of you who do not have or do not want to get involved with setting up to do distributor work, I suggest you use the same information and develop a relationship with a quality professional as I did with B&H. You can discuss this issue with your customer before he packs up his new engine and gets into trouble. You may have an opportunity to sell both of you some serious satisfaction insurance. If nothing else, by bringing up the subject and making it clear that the best of engine building will fail if the rest of the components are not suitable, you are giving fair warning.
By doing so, you have more than a leg to stand on when the customer returns, demanding satisfaction for something HE did and not you. For those valued customers who will listen and heed your warnings, you will have increased success, enhanced your reputation for skill and experience, and developed a positive influence that will make your business relationship even better.
Doc Frohmader got his first car at the age of nine and has been an engine builder and enthusiast ever since. firstname.lastname@example.org
231 N. Old St. Louis Rd.
Wood River, IL 62095
Crane Cams, Inc.
530 Fentress Blvd.
Daytona Beach, FL 32114
440 E. Arrow Hwy.
San Dimas, CA 91773