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The Tune Up

Updated: Oct 25, 2022

A Transcontinental Co-operative Effort by Norman Nock (California), Dudley Haines (Alaska) and Reid Trummel (Florida)

Originally published in the Austin-Healey Magazine

The tune-up. This magical term is used very haphazardly and is frequently described as the corrective action for many problems, ranging from the noise of a broken gear or a worn brake, to a dead battery, or to the lack of power caused by a slipping clutch. A more accurate definition of a tune-up might be “the measurement and adjustment of the various components in the car that work together to make smooth and reliable mechanical unit”. If you’re sure that a tune-up is what your car needs to keep it running up to factory standards, and you don’t want to take it to the local tune-up shop for their “$39.95 special”, we’ll pass on some of Norman’s forty years of experience in tuning up British cars, along with some ideas gleaned from various other sources over the years.

We’ve put a title on each separate job to be done in a tune-up. You can take each of these sections individually until you’re sure the car is running to your standards before you go on to the next section. The job of tuning up your car can actually be lots of fun for the novice, provided you do three important things:

  1. Do NOT wait until the last minute. Schedule some time — on several separate days — to do the job. This is very important because if you don’t, you’ll get frustrated when things don’t go as smoothly as you’d like. And remember you won’t know all of the little things that make a job go smoothly. You’ll be learning as you go.

  2. Get as many of the published tune-up and service manuals as you can find, and take the time BEFORE YOU START to read the section in them about the work you plan to do that day. For Healeys there are several good manuals available. See the ads in the car magazines for Classic Autobooks, under Austin-Healey. Also, look at your back issues of

  3. Healey Highlights for good technical articles, and get the factory service manual.

  4. Jot down your approach to the day’s project, based on what you’ve just read. Then before starting, have a CLEAN workplace. This is very, very important if you expect to get accurate results. Then gather all of the tools you’ll need.

You may find that you need to go buy something, like compression gauge, or a feeler gauge. While you can probably borrow some of these from friends, they’re so cheap at the discount auto stores that it’s better to get them for yourself, especially since you’ll be able to use them for years to come. OK, now that you’ve brought your brain and your work area up to speed, it’s time to start.

You need to ask yourself how complete you want to be in your turn-up. If you’re trying to fix a specific problem, you’ll want to do some diagnosis. If you plan to do a complete tune-up, you may not need to do any diagnosis, since you’ll be adjusting everything anyway. We prefer doing a complete tune-up, so we reduce or eliminate the chance of any problems when we’re far away from our tools.

You know, it’s kind of interesting how far people go and how frustrated they get just because they don’t know how to diagnose a problem, or because they take it to an incompetent mechanic (or they take it to a good mechanic, but can’t describe the symptoms well enough for the mechanic to be able to go right to the problem). They end up paying lots of money and spending lots of time and still have the problem. In fact, they often give up, sell the car, and forever after tell everyone what a lousy car it was. Sound familiar? The more tenacious of these people (or those who haven’t yet given up) have even been known to see a similar car going the other direction on the freeway, and frantically turn around at the next exit and race after the other car to flag it down. Then they inevitably ask each other “How do you like your car?” and “Who do you have fix it?” Well, with a little pre-season planning and effort, you can bypass all of this, Let’s proceed!

Do A Compression Check

The first job you need to do is a compression check. Run the engine until it’s up to normal operating temperature. (Run it about ten minutes after the water reaches its normal temperature, so the oil is thoroughly warm.) Then turn it off and clean the area around all of the spark plugs. Now, remove all of the plugs. Here’s the first place where it’s important to be careful: be sure that nothing gets into the spark plug holes. Put the plugs on the workbench in the same order as you took them out, because you’ll want to analyze them in a few minutes. Now put the compression gauge into the front plug hole. Have a friend crank the engine, with the throttle pedal all the way down. Write down the reading. Go to the next cylinder and do the same, and so forth until you have done all of them. The readings should jump to their maximum within three or four revolutions of the engine. Now let’s look at the readings we’ve written down. 120 to 150 psi is the normal reading for Big Healeys, and each cylinder’s reading should be within 10% of each other cylinder. If they are not, the problem could be:

  • Worn or broken rings

  • A blown head gasket

  • Damaged or burned valves or valve seats If each reading is within 10% of each other, but they’re under 100 psi (pounds per square inch), you could also have the problems listed above—just on more cylinders!

Any of these problems is going to require “surgery”, but you can do some more testing to narrow it down to the specific cause:

Put about one ounce of engine oil into the cylinder that had the low compression reading. Take another compression reading immediately.

  • If the reading doesn’t come up, the valves are probably to blame.

  • If the reading does come up, you probably have worn or broken rings.

  • If you have low compression readings in two or more cylinders (especially if they are next to each other) you probably have a blown head gasket.

Spark Plugs

Now let’s look at those plugs. Note these things about each plug:

Which cylinder it came out of.

  • Is the inside brown or black in color?

  • Is it oily or did it have gas on it?

  • Is the center electrode rounded, or still nice and square?

  • What is the measurement of the gap between the center electrode and the “finger” that comes from the side of the plug?

Now to analyze what you’ve noted.

  • If all of the plugs are brown, your carburetors were probably tuned properly. If two or three plugs positioned together were black and the others were brown, the carburetor that feeds those cylinders may be adjusted too rich.

  • If a plug is oily or has gas on it, it probably wasn’t firing at all. You may have a bad plug wire, or weak voltage going to that plug. Or the plug gap may be too wide or way too small. If the back plug (number 6 cylinder) is oily, you may have pending problems with your brake servo unit.

  • If the center electrode is rounded, it takes more voltage for the spark to cross the gap than it does with sharp, square edges. You can carefully file the electrode to allow the spark to be as strong as possible.

  • Adjust the gap to the measurement given in the service books. It’s .025” on most Healeys.

The best thing to do, of course, is to replace the plugs, especially if they’ve gone over 10,000 miles. Don’t forget to adjust the gap on the new plugs.

If the plugs don’t screw back into the cylinder head by hand, the threads in the head should be retapped with a 14mm plug tap. If you have never tapped a treaded hole, get some advice and a little demonstration from your auto parts store or mechanic or friend. It isn’t hard at all, but you must be careful not to start the tap crooked and cross-thread the head. In fact, do this: Get one of the $8.95 tap and die sets at the discount tool store, and tap some bolts you have lying around the garage. It won’t take more than five minutes to get the hang of it.

By the way, the threads of 14mm spark plugs are standardized worldwide. There’s a misconception that some countries make a special 14mm thread that can’t be interchanged. This isn’t true!

At this point, you need to make a little test, if your car has been converted from positive ground to negative ground. First, look at the battery. If the larger of the two posts (which should be marked “+”) has the cable that leads to the car body or the engine block (both of which are “grounds”), then your car has positive ground and has not been altered. Most recent cars have negative ground, although Austin-Healeys had positive ground.

Over the years, a lot of Healeys were converted to negative ground, primarily to accommodate newer radios and other electrical accessories that required a negative ground. If it is the smaller battery terminal that leads to the body or engine on your car, then you have a converted negative ground car, and you need to check out your coil. Find the two small wires leading from the coil—not the large spark plug sized wire. The wire on the negative side of the coil will have to go to the distributor to avoid a loss of high tension voltage to the plugs. The negative side of the coil will be marked with either a “—” or “SW”. Early British cars had coils marked “CB” and “SW”, for “contact breaker” and “switch”. These coils are not effective with a negative ground battery. Get a newer Lucas coil, which supercedes the old coil In the Lucas parts book, being sure that it is designed specifically to work effectively with negative ground batteries. These newer coils will have “+” and “—” markings and spade terminals. This little trick is usually overlooked, and it could be why you haven’t been able to get your car to run as strongly as it should. Again, this applies only to cars that have been converted from positive to negative ground. While checking the coil, it should be removed, thoroughly cleaned, and checked for loose terminal connections or cracks. If it is OK, put it back on the car. If it’s not in the original location, it’s wise to move it to its original location for optimum operation.

The Distributor and Points

Now it’s time to take look at the distributor and points. Don’t stand on your head under the hood trying to do distributor work. It’s not only uncomfortable, but you can’t be as precise as you need to be. The only proper way is to take it out. First, put the car into third gear and push it forward or backward until you have the engine at “top dead center”. (Fig. 1) To determine top dead center (known as “TDC”) you have to find the arrow or mark on the front of the engine that is used to line up with the mark on the crankshaft pulley. See your service books for an illustration under the section entitled “timing your car”. Be sure to clean the pulley and the engine block by the mark so you can be precise. The engine is at top dead center when the two marks line up. Now take the car out of gear. Now, carefully make a mark on the distributor body and on the engine block that line up, so you will know just how to position it when it’s put back together. Next, remove the distributor cap and write down where the rotor arm is pointing (like “1 o’clock”, or “6 o’clock”, etc.) You’ll want it in the same position when you put it back. Now see your service manual for instructions and illustrations on how to remove the distributor.

Clamp the distributor in a vise. (Fig. 2) Be careful not to clamp it too tightly. See the plates that the points are mounted on? Try to rock them back and forth. If there is movement, both the upper and lower plates will have to be replaced, or the point gap can’t be accurately adjusted. Now take off the points and the plates they’re mounted on. Under them, you’ll see two centrifugal weights with little springs mounted to them. Both weights should be able to freely swing out. If they don’t the sleeve they’re mounted on is frozen to the shaft. Remove the bolt in the center of the shaft, and note the position of the cut-away on the side of the shaft with respect to the drive dog that has a gear or offset driving tongues. The cutaway and the drive dog have to be replaced in the same position. If the cam sleeve is frozen, remove both springs by using two screwdrivers to pry off the cam sleeve from the distributor shaft. Now clean, oil, and replace the cam sleeve. You will notice that there is a looped end on the heavy spring which allows free action by the light spring at the beginning of the advance movement. See that it all works freely.

Now test the vacuum unit by sucking on the input side of the unit, If your tongue or lip sticks to the hole, the unit is holding a vacuum. If it does not stick, the diaphragm is leaking, and needs to be replaced. There are numbers on the vacuum unit, but they aren’t the part number. They’re operational specifications. The numbers 4-11-7, for example, indicate that the Unit commences to function at 4 “Hg” of vacuum, and that maximum advance occurs at 11 “Hg”, and that the maximum advance is 7 degrees. You may need these specifications if you have to order a new vacuum advance.

Another distributor problem that can be hard to find is the distributor shaft itself. Try to wiggle the shaft from side to side to see if there is any looseness there. If so, rotate the shaft until the point sare just barely closed. Then wiggle the shaft back and forth while measuring the point gap. If the gap opens more than .003” (three thousandths of an inch), the shaft must be rebushed. (BJ8’s don’t have a bush, but they can be fitted with one.) Take It to a local shop to have it done.

Now for the rotor arm and cap. The rotor arm should be replaced regularly, because it is a known potential problem. When it fails, it fails inside the arm and the engine stops. It’s impossible to seethe cause by visual inspection. Inside the distributor cap, the fixed electrodes (the brass contact areas around the inside) need to be cleaned down to shiny brass. Norman has seen foreign material build up on these electrodes to the point where the spark won’t jump from the rotor arm to the electrode. Also, be sure the carbon brush in the inside center of the cap isn’t too worn, and check to be sure the cap isn’t cracked. Finally, be sure you have the correct rotor. If a four-cylinder rotor is used on a six-cylinder car, it can cause problems that are very hard to find. Now that you’ve gone through all of the tests for the rotor and cap, we’ll tell you that it’s far better to merely replace them with new

proper parts, since they’re not very expensive. The dependability factor makes it well worth it.

Now to the plug wires. Plug wires installed on most cars today are of the high resistance type with carbon impregnated linen fiber or glass fiber center conductors. These wires are very fragile. This wire has a resistance of 4,000 ohms per foot. Any wire that exceeds a resistance of 17,000 ohms per foot should be replaced. Also, look carefully at the plug sockets at the end of the wires. If they are worn, corroded or bent, replace them. You can still get plug wire that has actual wire centers, and they’re much better as they aren’t so fragile, and they’ll carry the current more effectively. Their disadvantage is that they cause considerable radio resistance noise. However, you can buy resistors that will dampen out this noise. You might want to try this method. First, talk to your radio store for alternatives. Like with the rotor and cap, we’d replace the plug wires if any wear is evident, as the problems they cause are hard for the amateur to find, and the cost to replace them is minimal.

The last distributor job is to install new points and a new condensor. Don’t ever put in new points without a new condensor. Again, when this little one dollar device fails, you’re stranded, and it’s hard to trace the cause. And always replace the rotor when putting in new points. Now, set the points to the correct factory gap, which is £014” to .016”, and put a small dab of cam grease on the cam on the distributor shaft. Be careful not to put too much grease or the wrong kind of grease on the cam, or it will be thrown onto the points. By the way, a matchbook cover is about .015” thick and can be used as a feeler gauge in an emergency.

Replace the distributor in the exact same position it was in when you took it out. After the distributor is back in the car, you need to test the points to be sure they aren’t grounding out. To do this, rotate the engine until the points are closed (a third gear “push job” again). Turn on the ignition. Open the points with a screwdriver. If a spark occurs, you’ve installed the points correctly! If there’s no spark, see that the little wires connecting to the points are not touching the pivot stud of the points. See that it only touches the curved spring. Also, be sure that any insulator washers or bushes on the point stud are in place, or it will ground out. See the service manual for the exact placement of all these parts. Finally, be sure the braided ground strap from the breaker plate to the distributor housing isn’t shorting out. Put the rotor and cap back on and spray the wires and distributor cap with a silicone spray to waterproof them.

With everything installed and plugged in, we can set the ignition timing. While there are several ways to set the timing, we’ll describe the best way for the amateur. It’s called static timing, and you don’t even need a timing light. First, take out the number one plug (front plug) again and stick a wood dowel that is at least eight inches long into the hole, We’re going to determine the top of the travel of this cylinder. Put the car into third gear and push it back or forward until the dowel is pushed out as far as it will go. Now we’re about ready to find top dead center (TDC), but first we need to make up a little tool, so take a break for a minute.

We’re going to make up a test light. Get about two feet of wire (about 14 or 16 gauge) and cut it in half. Solder one end of each half to a small 12 volt light of about the size used for dash lights. Of course you want to solder one wire to the base of the lamp and the other one to the side of the lamp. Now connect one wire to the small wire on the distributor that goes to the coil, and connect the other one to the frame or other good ground. Turn on the ignition. The timing marks on the crankshaft pulley and the engine block should be nearly lined up. If they aren’t lined up, line them up now. Next, put the car into third gear again, and push it backwards by hand, by turning a road wheel until the test light goes out. Now push it forward until the light comes on and just barely goes out again. If you look at the timing mark on the pulley, you will see what position the timing mark is in. The average British car is timed from between Top Dead Center (which is where the two marks line up exactly) to 3/4 inch Before Top Dead Center (which is where the mark on the block is opposite a point that is 34 inch before the mark on the pulley). The specifications on your book will give these measurements in degrees of rotation—not in fractions of inches of measurement on the pulley. So, to convert degrees to inches, measure the circumference of the front crank pulley and divide by 360, Multiply that figure by the number of degrees in the book to get the measurement in inches. Provided your car still has the stock diameter crankshaft pulley, here are the measurements:


Timing should be at:

The mark should be made at:

AH 100-4

6 degrees before TDC

5/16 inch on pulley


6 degrees before TDC

3/8 inch on pulley

3000 MkI

5 degrees before TDC

5/16 inch on pulley

3000 MkII & III

12 degrees before TDC

3/4 inch on pulley

Sprite MkI

5 degrees before TDC

At the first pointer

Sprite MkII 948cc

4 degrees before TDC

1/32 inch after first pointer

Sprite MkII 1098cc

​5 degrees before TDC

At the first pointer

​Sprite MkIII

5 degrees before TDC

At the first pointer

Sprite MkIV

7 degrees before TDC

1/16 inch after first pointer

Measure this distance on the pulley and clearly mark it. Now for the actual timing operation: In order to alter the timing, you have to loosen the distributor collar bracket under the distributor on the shaft, and rotate the entire assembly slightly one way or the other. Look at the illustrations in your manuals, under ignition timing. Push the car back or forward, still in third gear, until the mark on the block is precisely opposite your new mark on the pulley. Put the car in neutral again. (The ignition is still on.) Now rotate the loosened distributor until the light just barely goes out. Hold it very still, and tighten the collar bolt. And presto—you’ve got it! Don’t forget to turn off the ignition before you take a break.

Carburetors—those famous SUs!

(And great carburetors they are too, we might add!)

While SU carburetors aren’t all that complex, it is quite a chore to actually rebuild them, and since we’re talking about doing a tune-up in this article, we won’t get into the actual rebuilding process. If the car is running reasonably well, it’s probably best to merely adjust them. Be aware, however, if you have a 100-6 or 3000 model. You have the Type HD carburetor and you may split the diaphragm as you try to adjust it. If you do this, a dangerous leak will occur. So watch carefully for leaks during the adjusting process. If you do get a leak, your carburetors will need to be rebuilt. For this process ,either refer to the service manual, or take them to a professional.

On to the adjusting process! First, remove the air filters. (Isn’t this a fun chore on big Healeys?) Now reach into the chamber and raise the piston slightly and allow it to drop back down. A sharp clunk should he heard. If a clunk isn’t heard you won’t he able to get a smooth idle. By the way, if you don’t know what we’re talking about when we talk about the piston, you’re not doing the reading we asked you to do before starting the project. To fix the non-clunking piston, take off the “bottle” (which is the “pot” part of the carburetor) and withdraw it, holding the piston within it. Note which carburetor you took the bottle and piston off of, since you need to be SURE to replace it on the same carburetor. Be careful not to damage the brass needle attached to the piston. Take the piston and bottle to the workbench and pull out the piston. Now watch the oil from the top of the piston drain all over your hand. Pretty neat, huh? OK, now thoroughly clean all of these parts .Finally, put them back on the carburetor.

Don’t forget the big spring that goes between the piston and the bottle. Be careful when installing it not to bend or mark up the needle. Put oil back under the plug in the top of the bottle and try the clunk test again. If it still doesn’t clunk, the needle or the “scat” into which the needle goes may be bad. In either case, it’s rebuild time.

Now for the actual’ adjusting procedure. It you have the aforementioned HD carburetors, screw in the “slow running valve” screw until it bottoms. Then unscrew it 3½ turns. Start the engine and bring it up to operating temperature. Next raise the “piston lifting pin” very slowly. (See the manual for an illustration of where the piston lifting pin is for your carburetor.) If the engine speeds up, the mixture is too rich, If the engine slows down, the mixture is too lean. Adjust the mixture by turning the jet adjusting screw on HD type carburetors, or the jet adjusting nut on HS and H types of carburetors. Adjust the mixture until you have obtained a setting between rich and lean, but slightly toward the rich side.

Now turn off the engine and have a friend sit in the car and hold the throttle pedal wide open.(We’re sure your spouse or, friend will be tickled to do this, since by now you’ve been in the garage for so long that they’re aching for your company . . . Right?) Reach your fingers in through the carburetor throat to where the “butterfly” is located. (We know—another new term. Back to the ol’ book again!) This butterfly should be wide open to give maximum power upon full acceleration. If it isn’t, adjust the linkage until it is. Your friend can go now. Start the engine and warm it up again and pull the choke all the way out. The engine should speed up and then become rich and stall out. If this happens, your choke is adjusted properly. If it doesn’t happen, look at the trusty book and adjust the choke linkage.

If the carburetors still don’t run right, its rebuild time!

The Fuel Supply

We need to check the efficiency of the fuel pump. Since fuel can be defined as gasoline, and gasoline can be defined as very flammable, explosive, and dangerous, we really have to use some good sense here. First, roll the Healey out of the garage and at least twenty feet from the house. Then get the garden hose hooked up to the water faucet and run a little water. Have it close at hand. Then get a fire extinguisher at hand. By the way, if you don’t carry a fire extinguisher in your car at all times, you need a bit of a lecture. Ask your fire department for that lecture! Get your spouse or friend with the extinguisher in hand and the hose close by.

Now, let’s start. Remove the gas line from the first carburetor it goes to. Place a can of at least two quarts capacity under the hose. If the hose won’t reach outside the engine compartment, go to the store and get enough hose to reach outside of the engine. You’ll have to get a little bit of tubing too, to connect the two hoses. Don’t shortcut this step, because it’s too dangerous to do so.

OK, now mark the can where one quart of fluid is. Next, turn on the ignition and listen to the familiar click, click, click of the fuel pump. Time it for one minute. If it hasn’t pumped one quart in the minute, you either have a faulty pump or there is a restriction in the line. In either case, take it to a professional for repair. A bit of free advice: It’s worth it to carry a spare fuel pump with you, because they do fail and it’s not too hard to change one on the road if necessary.

Conclusion, or Hurray! We’re done!

Once you’ve done all of this work with one hand under the bonnet and the other thumbing through the factory service manual, you should get satisfactory results. But don’t get too frustrated. Bear in mind that it takes years of experience to know everything about keeping your beloved Healey in top operating condition. It’s impossible to reduce all of it to writing. If you run across a problem you can’t solve by following this article, take your car to a professional. But whatever you do, don’t just throw up your hands and give up and sell the car. Healeys are too neat for that!


(If you still haven’t had enough fun let’s adjust the valves and check the rocker arm assembly.)

Adjusting valve-rocker clearance.

Let’s adjust the valves now. You can adjust them with the engine cold, which keeps from burning your fingers! Get ready for some more of our now all-too-familiar third gear car rocking action. The valves will be adjusted to just a little over .012 inch, which means that a .012 feeler gauge will fit just a little loose between the rocker and the valve stem. Now, in order to adjust the valves in the correct order, follow the “magic 9” method for four cylinder cars, and the “magic 13” method for six cylinder cars:

  • On four cylinder cars, move the car until the number 1 rocker (at the front of the engine) rocks the valve fully open. This means the rocker is pushing the valve to its lowest position.

  • Loosen the locking nut on the number 8 valve. (#1 + #8 9, which is where the term “magic 9” comes from.)

  • Insert the feeler gauge between the valve stem and the rocker.

  • Tighten the rocker adjusting screw until the two surfaces just barely drag on the feeler gauge.

  • With the screwdriver still in the slot holding the adjusting screw stationary, tighten the locking nut.

  • Next, move the car, turning the engine until the number 2 rocker opens the number 2 valve. Using the “magic 9” method, subtract #2 from 9 to get 7. Therefore, you will adjust the number 7 valve.

  • Then go to the number 3 valve, to adjust the number 6 valve (9 - 3 = 6), and so on until you’re done.

  • On six cylinder cars, use the same procedure, starting with the number one valve at the front of the engine—except use 13 in your formula. For example, 13 minus the #1 valve adjust the #12 valve with the #1 valve open. 13 minus the #2 valve equals adjust the #11 valve with the #2 valve open, and so on.

Well, that’s it! We’ll offer a serious note here. We know this article is quite long, and may therefore discourage some of you from doing a tune-up yourself. It’s long because we’ve tried to cover parts of a tune-up that professionals may take for granted but which you need to know, We also know that some of you will read the title of this article and skip directly to the last paragraph! For both of you we offer this:

Doing your own tune up is very rewarding. You not only get a feeling of accomplishment, but you will be much better prepared to diagnose a problem should your car quit you on the road. This added feeling of confidence will let you have a lot more fun with your car, because you’ll be much more likely to use it.

It’s well worth the effort. Try it! You’ll be glad you did!

Not what you were looking for? Don't forget you can check our back issues using the AHCUSA Magazine Index.

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