Tuning a Six Cylinder Healey

Originally submitted to the Austin-Healey Magazine by Doug Reid


Preliminary Checks (optional):


1. Remove the valve cover and gasket. Remove the 12 rocker shaft bracket nuts with their washers and disconnect the oil pipe at the union. Lift off the shaft assembly. Compress ac ouple of the rocker arms against their springs so that the bearing surface of the shaft is revealed. Check the underside of the shaft for wear by scraping a fingernail across the area where the rocker arm is normally located. Ridges that a fingernail will catch on indicate excessive wear of the shaft.


2. Check that the cylinder head nuts are torqued to 75-ft. lbs. following the torquing sequence shown in figure 1.


3. Replace the rocker shaft assembly. Torque the bracket nuts to 26-ft. lbs. working from bracket 4 and alternating. You may want to use Lock-Tite to insure that the assembly stays down where it belongs. Reconnect the oil pipe at the union. Be VERY careful when playing with this oil line, if at all possible, the upper banjo part should never be removed from the shaft bracket it screws onto. The journaled bolt which holds the banjo onto the bracket is fine-threaded; it cross-threads easily and wears the threads in the pot metal with each removal and replacement, eventually failing to fit tightly and seal. Make sure there is a copper washer on each side of the banjo.


Tuning:


1. Remove the distributor cap and note the position of the rotor. Remove the clamp plate bolts and the vacuum advance line and pull the distributor off the motor. While firmly holding the bottom shaft and driving dog stationary, press the rotor in the direction of the arrow on top. The rotor and cam assembly should be able to move approximately ¼” in this anti-clockwise direction and then snap back smartly when pressure is relaxed. Failure to do so indicate seized shafts, necessitating the removal and cleaning of the cam assembly and the central shaft it screws onto. Observe the movement of the contact breaker base plate while sucking on the vacuum diaphragm opening. Don’t get carried away with love for the car — slobber in the vacuum advance will not enhance performance. Remove the rotor arm, points, and condenser.


2. Thoroughly clean all interior and exterior surfaces of the cap and distributor. Carefully examine the cap for evidence of electrical tracking; this is especially important when a hot coil is in use. Check the condition of the central carbon brush, and replace the cap if there is any sign of wear, cracks or damage. Early cars take caps with the Lucas number 418861; BJ8’s take #54412474 or DC 16. Record the distributor number stamped on the side of the body for parts reference.



3. Remove sparking plugs in order, noting any differences in appearance. On MkIII cars with servo units, compare #6 plug with #1. If #1 is dry but #6 has a slimy residue, a leaky servo could be the cause. Most Healeys were delivered with Champion plugs, which are over-rated junk and have a reputation of giving poor high speed performance after a few thousand miles. (see chart, Fig. 2) NGK plugs are less expensive, and a highly recommended alternative. Mr. Finespanner uses only NGK’s, because they last three times as long as any other and even deliver better as mileage. Clean plugs thoroughly and regap to 0.025” for standard coil; 0.028 – 0.030 (uniformly) for sports coil.



4. Clean off any protective coating on new points using a soft cloth. Lightly buff point surfaces with emery cloth. Avoid contamination when installing new goodies. Rotate the distributor shaft until the heel on the moving contact is centered on one of the cam lobes. Adjust the stationary contact until the gap is 0.014” – 0.016”; i.e., a clean 0.015” feeler gauge is a slip fit. Hold the distributor at eye level and observe the alignment of the points. All too frequently the final tightening of the point adjusting screw will throw the two surfaces out of parallel and radically change the settings – this is especially true on late model cars with the one-piece points (Lucas Quikafits).


If tightening results in misalignment the stationary contact must be carefully bent back, using small ignition pliers, until the surfaces are parallel again. Do not bend the moving contact. (Figure 3) Dr. Bowen of the Healey Haven recommends using Blue Streak LubriPoints in BJ8 cars to avoid this problem. The part number is LU-1617 XP and they align properly when torqued down. Readjust the gap to 0.015” and refit the distributor to the car with the rotor positioned properly. NOW, spend a few bucks and buy a good quality dwell meter, and use the meter after the feeler gauge to insure exact adjustment – this is the only I way you can be positive of optimum point setting and engine efficiency. The Book sez 35 + 3º, but set points at 34º since dwell increases as points wear. A dwell meter can also be used to diagnose point resistance, misalignment, and wear of the distributor shaft bushing – it’s truly one of the soundest investments an owner can make, and can pay for itself in a couple months in terms of gas savings.


For those owners who would like to avoid this hassle altogether and improve performance and mileage at the same time, Mr. Finespanner recommends changing to a breaker less electronic ignition system. Many companies make such an animal, though it’s not easy to find one for a car like a positive ground Healey. But for those of you with one-piece points – some BJ7’s and all BJ8’s – there is a great English unit available called the Piranha Ignition System. Mr. F. uses them because they’re made in Blackburn, Lancashire, where all the holes are that fill the Albert Hall in the Beatles song. Any experienced owner can install the Piranha and no special tools are required; it’s also guaranteed for two years or 100,000 miles. The increase in performance and mileage is incredible. Pickup and acceleration are substantially greater, and one tri-carb Healey we know of fitted with a Piranha unit and NGK plugs averaged 25 + mpg. at 80 mph.


5. Rotate engine (anti-clockwise at distributor) until #1 piston is at TDC; that is, #1 intake has opened and closed and the crank pulley has been turned further clockwise until the timing pointer aligns with the notch. Note: On older engines it is important to confirm TDC and adjust as needed for normal wear. Lacking a proper dial indicator, insert a wood pencil into the spark plug hole and slowly rotate engine back and forth until movement by the pencil cannot be detected, indicating TDC. This position spans a range of 3-5 degrees, corresponding to 1/8” – ¼” measured on the circumference of the pulley. Remark the pulley if there is a substantial difference relative to the factory mark. Remember that some engines came from the factory with improper markings. The wooruff keyway in the crank pulley can also tend to wear over time, resulting in “slop” in the pulley, clunking noises, and incorrect timing readings due to the notch jumping all about.


6. Twist the distributor vacuum advance adjuster until it is centered in its possible travel on the threaded shaft. Loosen the distributor clamp bolt (these clamps are available new from Lucas, part number 421191). With a 12-volt indicator on the low-tension lead to the distributor, rotate the distributor body until the points just open and the light comes on, and then tighten the clamp. You must, of course, have the ignition on but the motor not running to make this static timing setting. The spark is now set to about 6º BTDC.


7. Place one or two drops of light oil in the depressor atop the distributor shaft that the rotor arm fits over, and a dab of silicone-based grease on the cam to lubricate the moveable contact. Install anew rotor (#418726) and refit the cap and plug wires. Insure that the positive (CB) terminal of the coil is hooked to the distributor by the white-switched power wire. Start the motor and use a timing light to adjust the distributor to the proper stroboscopic advance for you model. Recheck the dwell after setting timing.


8. With the engine idling, observe the valve gear as operating temperature is reached. Oil should dribble out of the holes on the top of the rocker arms at idle. Increased speed – up to 2800rpm –should cause the oil to shoot out the holes in little columns approximately ½” high. Excessive flow, streams of oil 1” or more high, especially when speed is increased, indicates bad wear in the rocker shaft.


9. Stop engine when at temperature. Pull the plugs, block open the throttles with a spacer between the stop arm and rest, and attach a remote starter switch across the solenoid. Using a compressor tester, check each cylinder in turn, cranking the engine through four or five revolutions. Permanently record results. Reading should uniformly exceed 100 psi with variation among cylinder not to exceed 10 – 15%. Average for a good Healey is 150 – 160 psi. New motors just run in will show around 190 psi of compression. Readings under 100 psi indicate badly worn rings. Recheck seriously low cylinders after introducing a teaspoon of engine oil at the plug hole. Do NOT use a glass eye dropper, even if you name is Gary. Use a teaspoon or a long necked oil can, and give her a couple of squirts. Substantial compression improvement after oiling indicates ring failure. Little or no change suggests leakage due to poorly seated valves. Close throttles and remove remote switch.


10. If you have not yet checked the rocker shaft as in “Preliminary Checks” above, slacken the adjustment of one rocker until the arm can be moved clear of the pushrod. Compress the rocker arm against its spring and check the bottom of the shaft for grooves. Any badly worn shaft will not retain a proper valve setting for long. Adjustment of valves must be made with the tappet on the back of the cam, so gap valves according to this sequence.

  • With #1 valve all the way down, gap #12.

  • With #2 valve all the way down, gap #11.

  • With #6 valve all the way down, gap # 7.

  • With #12 valve all the way down, gap #1.

  • etc., etc.


11. Note that the sum of the “down valve and the one to be adjusted is always 13. You can also count from opposite ends of the motor to determine which valve to gap next. For example if #5 (from the front) is down, the fifth one from the rear of the motor (#8) gets set, and so forth. Adjust clearances to 0.012 hot. Always recheck gap after adjustment to be sure tightening the locknut did not change the setting. Replace spark plugs.


12. Restart the motor and adjust and balance carburetors for mixture, slow and fast idle at normal temperature. Slow idle should not exceed 750 rpm on early models and 900 rpm on MkIII’s. Stop engine.


13. Install vacuum gauge using tap located on top rear surface of intake manifold. With the engine again at idle make the following observations:

  • Vacuum reading in range of 18 – 22 inches.

  • Much lower, steady reading = intake side leak(s).

  • Steady pulse = one valve, plug, or cylinder gasket leak.

  • Unsteady pulse = as in c. but more than one cylinder.

  • Unsteady, varies with speed – sweeps larger with speed = valve springs. Sweeps smaller with speed = intake leaks.

  • Steadies with speed = ignition, carburetor, or distributors fault.

With engine idling, loosen distributor and advance (rotate clockwise) to obtain maximum steady vacuum reading. Now retard until vacuum reading is ¼ -1/2 inch below the maximum readings. Engine is now in time if: a) vacuum readings in range, b) ignition is in time when checked with light. Note: maximum advance is about 35º or about 1 ¾” on the circumference of the pulley.


14. Set throttles to idle engine at 1000 rpm. Now check cylinder balance by testing how well pairs of cylinders run the engine. Read and record vacuum level for each pair as follows:

Run On

Short Out

1 – 6

2-3-4-5

2 – 5

1-3-4-6

3 – 4

1-2-5-6

Vacuum levels between pairs should be about the same. CAUTION: Use well-insulated pliers to manipulate plug wires.


15. Stop motor. Remove tools and gauges and replace valve cover, renewing the gasket as needed. Note that the gasket is not symmetrical. Reinstall crankcase and cover breather hoses. During subsequent running, observe any tendency to “ping” under load or to “run I-on” when killed. Use the micrometer adjuster to retard the spark and reduce ping associated with variations in fuel. Alternatively, advance spark to improve performance if engine will tolerate the adjustment. Running on is most frequently caused by too fast motor idle.


Now you’re ready to go out and test the quality of your handiwork, but try to pick an area that is not frequented by uniformed representatives of the state (not that they could catch you anyway, right?).


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