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Ignition Tuning Procedure

September 28, 2010 | Troubleshooting & Repair
By Ron LaDow Precision Matters
Copyright Ron LaDow, September, 2004


Parts Required
  • spark plugs
  • points
  • rotor (and get a condenser just in case)
  • distributor O-ring
  • plug wires (possibly)
  • distributor cap (possibly)


Any internal combusion (IC) engine needs ignition of the combustible mixture in a particular cylinder at the proper time within a very small margin of error. The ignition system on engines of our vintage are electro-mechanical systems. The 'electro' part tends to be very reliable; it's the mechanical part that needs the most attention. Wear on the various parts can cause very large margins of error.

Order the parts first. As noted above, you'll need a set of plugs, points and a rotor. Condensers are commonly replaced at a tune up, but commonly don't need to be, ditto distributor caps. Maybe the rotor falls into this category; you choose. Plug wires are good for at least 50,000 miles, but if you are uncertain, it may be worth it.

There are several spark plugs which work well in 356s. I use NGK B6HS, others favor an equivalent Bosch plug or even a platinum Bosch plug. Points are dictated by your distributor, as is the condenser. Plug wires are standard, and come in aftermarket or original spec at varying prices.

A standard box of shop tools should suffice, but get at least a minimum of reference data from an Owner's Manual or an aftermarket book. You should have a timing light of some known reliability.

This contribution will cover points-triggered ignition systems; someone else can describe the electronic systems


All this will be done from the top of the car, so if it was lifted to work on the valves, you can put it in the ground. If the rear wheels hold the positive camber when it's lowered, it'll keep the rear further up in the air and ease the strain on your back.

Spark Plugs

Spark plugs take a 13/16" socket, one with some sort of built-in retainer, either friction (commonly a foam sleeve) or magnetic. Wrench and extensions are favored in many varieties; look through your tool box, pick and choose.

Pull the terminals loose from the plugs (not by tugging on the wires), loosen the plugs with the wrench. They should then come out with fingers on the extension. Keep them in order as they come out; there is some information available.

Editor's Note:
Click here for highly detailed article on the removal and installation of spark plugs.

It's important to examine the condition of your spark plugs, as they can give you important diagnostic information about your engine. "Reading" plugs is a matter of experience and there is no way to describe the exact colors which should be visible at various points on the working end of the plug. Also, the plug color is largely the result of the last 2 or 3 minutes of operation, probably near idle on most engines. But there are a couple of obvious signs of which can be seen and described.

Debris filling the gap in the plug means that plug was fouled and probably not firing. What the debris is might be found below, or it might be a result of a bad plug, plug wire or terminal.

Oil on the plug means there is oil in the chamber; it should not be there. It came from around some tired rings or tired intake valve guides, or perhaps some other path. The choice on when your engine gets freshened is yours, and if the engine is not mis-firing as a result of the oiled plugs, you can use it for some longer period.

Shiny, small, metal balls on a white insulator is bad news; that's melted aluminum, usually from a piston top which is melting from excess heat. This does require more serious attention to the rest of the engine. Do not run an engine which shows this indication; it won't run much further anyhow.

A plug which is light tan to white all over also needs further investigation; that's commonly a result of a lean mixture, so the carbs should be examined. Might also be too much ignition advance or 'hot' spark plugs, and those'll be fixed soon.

Leaded gas showed even, repeatable color gradations across the spark plug face clearly related to fuel mixture. Modern gas commonly shows nearly black in good cylinders, but lighter near the gap and the tip of the insulator. If that's the worst result of getting the lead out, I'll take it. There are many more advantages.

A final word on spark plugs: Sometimes you get a bad one. Don't bother trying to clean one if all else is fine and one cylinder just lays down. Replace it. It is likely bad in some manner which is not visible or testable.

Get what info you can from the removed plugs and sort it as you will. Gap the new plugs (.025" on the NGKs), put a 'drop' (no more) of Never-Seize or equal on the threads near the start end, and take the screw-on tips off. Let me repeat: Take the screw-on tips off. It will preserve your vocabulary.

I start the plugs into the heads with the socket and extension, finger tips only, imagining the centerline angles as best I can. If one doesn't feel right, turn it backwards; there is a definite, tactile, 'click' as the two thread ends pass each other in reverse. You should then be able to finger-tip rotate it clockwise and start the plug. Start all four; go back with the ratchet or other driver and tighten them. You can feel the hollow washer crush; when it begins to 'take a set', it's done. Either refit the existing plug leads (adjusting the air cap grommets), or leave them loose for replacement.


Take the cap off if it isn't already. Rotate the engine until the rotor is pointing to #1 (about 5:oclock) and the OT mark on the pulley is aligned with the reference mark (or the Timing Kit).

Remove the coil primary lead from the distributor; this is a usually a slide-on spade terminal on the far side of the distributor, in some cars it's a female connector attached with a nut. At the same time, check to make sure the wire is tight on the coil at the other end.

Make sure the keys are out of the ignition and the car is out of gear and blocked (or safety-braked). Remove the hold-down nut and washer from the distributor clamp bracket, pull the distributor out and clamp the tail in a vise on the bench.

Don't bother trying to salvage the existing points, just replace them. Pay attention to the insulator paper strip when installing the new set; it can move or break, shorting the points to ground (it can be replaced with common materials). If you are replacing the condenser, now's the obvious time. Adjust the points to a gap of .016". Fit a new O-ring to the distributor tail if you have any doubts about oil leakage at that location. Put just a drop of engine oil on the felt pad under the rotor. Put a tooth-pick-dab of distributor grease on the contact of the points block and the cam (on the 'points' side, not the 'pivot' side). Do not use silicone lube anywhere in the distributor; it will migrate and cause problems.

Put the distributor back into the car, just the way it came out, refit the nut and washer. I always check the points gap at refit, even though I have never found a change. The gap is very important; it has a direct effect on the timing. Set it and confirm it before you do any timing tasks. Rotate the engine to do so, getting the points as far open as they will go.

Install the rotor. Do it with care, making sure you have the correct one and it is correctly fitted. Compare the appearance and fit with the old one if there is doubt.

Do not reconnect the coil primary lead to the distributor. If you are replacing either the distributor cap or plug wire harness, go ahead and do it now as all parts are in their proper locations.

Static Timing

I use the Precision Matters Timing Kit to either read the OT mark or index the pulley, so the following is from various sources:

  • Mark the pulley rim ~ .25" clockwise from the OT mark for 5*. Mark the pulley rim ~1.5" clockwise from the OT mark for 30*, both measured 'around' the rim with a flexible scale. Or, measure across the cord(s), since the error is trivial. Mark it with something visible; white-out or nail polish or what you can find.


  • Use a continuity tester clipped to the open blade terminal on the far side of the distributor and to a ground. A VOM with alligator clips works well; read the ohm scale. Where the engine is currently rotated (TDC #1 firing), the circuit is open and should show same.


  • Rotate the engine anti-clockwise until the points close and the tester shows the continuous circuit; go another 30* or so. Rotate the engine slowly clockwise until the tester just shows the circuit opening. Read the timing off the Kit or off the pulley marks and that scribe line. If it is not around 5* in advance of TDC (the OT pulley mark to the LEFT of the reference), adjust the distributor. With the stock clamp, loosen the clamp bolt and twist the distributor some small amount. With the Timing kit, note the timing difference, loosen the nut and rotate to the correct index. Rotate the distributor anti-clockwise to advance the timing, clockwise to retard. Iterate if required, but get it somewhere close to 5*-7*.

Dynamic Timing

  • Remove the continuity tester, refit the coil primary lead and the distributor cap (the rotor is in there, right?). Start the engine, warm it a bit. If it won't start or runs rough, look for the obvious; wire loose, rotor on the bench, etc. Possibly that bad plug mentioned earlier.


  • Shut it off, connect the timing light, and restart. At somewhere around 3,000 to 3,500 RPM, the marks on the pulley and the reference mark should stabilize in the timing light beam. Note that data as you will. And, when you release the throttle, the engine should return to idle and the marks should again stabilize at the static value you found earlier. Again, note the data.


  • Now you have both numbers. What is best for your particular engine is not established here, but the static should be between 4* and 8*. The dynamic should be between 30* and 36*. And they should both be stable.

A word about dyno and other tuning. An 'average' 356 engine on a dyno showed some 15% improvement in power between 'out of tune' and fully tuned, and some engines are even more sensitive to timing changes. Changing carburetors or exhaust systems hardly ever produces a horsepower difference of that amount. Absent a dyno, find that section of road and traffic where you can repeat acceleration and adjust the timing 'this' much or one index on the Timing Kit. Repeat the run; seat-of-the-pants tests will show the results here. Just fiddle and find what your engine likes.

Your next step is to tune your carburetors -- click on the appropriate link below:


Editor's Note:

This is part of our module on how to tune up your 356. Components include:


Aa493c9f9299cdb0d51a6d201e2b655c 2563
Steve Harrison
November 05, 2010 at 7:57 PM
Hello Steve,<br /><br />I have seen other people ask for them in the past. But one fellow asked and couldn't find them so I suggested to make them because they are quite simple actually. I sent him a traced pattern from mine because they were out of the car. Unfortunately they are still out, but that's another story... but I'd send you a tracing in the post also if you decide that route.<br /><br />Cheers,<br /><br />Steve
Aa493c9f9299cdb0d51a6d201e2b655c 2563
Steve Harrison
November 05, 2010 at 7:57 PM
Hello Steve,<br /><br />I have seen other people ask for them in the past. But one fellow asked and couldn't find them so I suggested to make them because they are quite simple actually. I sent him a traced pattern from mine because they were out of the car. Unfortunately they are still out, but that's another story... but I'd send you a tracing in the post also if you decide that route.<br /><br />Cheers,<br /><br />Steve