912 Ignition

Improvements

Here's what I've done to the ignition system:

New Bosch 050 distributor
Added Pertronix electronic points
New Bosch coil
New wires
New Bosch W5AC Plugs

Aside from that, everything is original :^).

Note:See the new description for timing the engine with a timing light at the bottom of this page.

Distributor Advance

The owners manual recommends timing at 3 deg. before top dead center (BTDC). Pertronix instructions suggest 5 deg BTDC. Duane Spenser recommends 28-32 deg advance at 3000 RPM. What is going on here?

The answer lies in your distributor. The distributor is mechanically advanced with a vacuum retard on later cars. The mechanical advance is operated by centrifugal force. The faster the engine the more force the more advance. However, there are some limits. At low RPM there is a range that occurs before there is enough centrifugal force to start the advance curve. At high RPM the advance mechanism reaches a mechanical limit preventing further advance.

The factory engine manual includes an advance curve graph for the distributor which has degrees on one axis and distributor shaft speed on the other. Remembering that the distributor shaft runs at half the speed on the engine (so that the cylinder will fire on every other rotation) we can pick some points on the curve. There are two curves on the graph. The distributor advances until the it reaches some stops then flattens out. The graph is for the 022 distributor which was original equipment on the '66 cars like mine. The two curves show the range of acceptable advance, probably based on production tolerances, spring rates and wear. The table is showing engine RPM vs advance on a distributor test machine. The actual advance will be an additional 3 degrees, the distributor is rotated by that amount per spec unlike the data from the test machine.

This data is from a distributor test machine, not from the car.

RPM	Min Advance	Max Advance
800(1)	(2)1.5	3
1000	4.5	9
1200	7.5	11
1400	9	12
1600	10	13
1800	11	14
2000	12	15
2200	13	16
2600	14	17
3000	15	19
3400(3)	16.5	19.5

Note:

The text in the engine manual asks to set the timing at 3 deg BTDC at 650 rpm.
Off the graph - estimated
The max advance is between 16.5 deg and 19.5 deg at 3100 engine RPM.

The point to all this is that the actual advance is a function of the engine RPM. Higher RPM, more advance. Since we can not readily adjust the advance curve it is best to set the maximum advance - near operational RPM rather than at idle.

Modern engines control the advance electronically based in part on information from the oxygen sensor to determine optimum burning of the fuel.

Pertronix Ignition

	I got my first Pertronix electronic ignition in 2000. It required some modification to the rotor to get it to fit inside a 050 distributor. The bottom of the rotor had to be filed down before it would fully seat on the shaft. See the notes with the picture to understand what had to be done. Since then the magnetic sleeve has been redesigned and this modification is no longer required. The electronic points will not provide any hotter spark, hence you can not expect to see any improvement in power. However, the points are maintenance free, unlike the mechanical variety. Easier to tune and fewer tune-ups are their advantage. I have heard reports of a failure mode in the Pertronix installation. Be sure to connect the wires to the coil correctly. The RED wire goes to the +12 Volt side of the coil and the BLACK to the ground side. Reversing the wires can burn out the Pertronix unit. If there is any question about which side of the coil is +12 V, check it with a volt meter before connecting the wires from the distributor. Latest word is that current versions of the Pertronix fit on the 050 with out modifying the rotor. Will sent a couple of pictures and some commentary.
	Dave - I just finished installing a new 050 with Pertronics pointless ignition. Works great! No more point float above 5000rpm! I did discover something about the installation to pass on. After reading your write up I was all prepared to shave the rotor - didn't have to. When I tried to install the sleeve over the cam it wouldn't go so I had to scrape a little plastic from inside the sleeve to get it to slip over the edge of the cam. While I was at it I measured it so I knew how far down it should go.
	Once it slipped over the edges the sleeve went down about 80%. I then used a large socket over the shaft to tap the sleeve down as far as it should go. The rotor is lifted by less then a mm, which is within the tolerance of the cap. The shaft extends beyond the sleeve by 19mm. If yours is less than this then I suspect the sleeve is not seated all the way down. They did make the sleeve extremely tight.
	This picture shows the height of the sleeve above the lip of the housing for reference purposes. --Will

First Tune-Up

I first had my car tuned by Harry Pellow at HCP Research. Several of his books provide recommendations that match pretty well with other printed material on how to tune the car.

I bought a timing light from Sears. After using this one for a couple of years I have upgraded to to a Digital Timing Light. See the bottom of the page for details.

There are no marks on the engine pulley except for top dead center (TDC). Correct timing is critical.

The car now starts and runs well.

Cylinder Definition

This diagram is from the factory 912 engine manual.

The arrow on the diagram shows the direction of travel.

Cylinder 1: Front, right side

Cylinder 2: Rear, right side

Cylinder 3: Front, left side

Cylinder 4: Rear, left side

Firing Order

The owners manual defines the firing order as 1-4-3-2.

Set TDC for Cylinder 1

The crankshaft rotates twice for each revolution of the distributor. Top Dead Center (TDC) is marked with a small line on the rear edge (away from the engine - toward the rear of the car) of the crankshaft pulley. Mark this line with some white paint for good visibility. The distributor shaft has a tab that fits into a slot in the engine for drive. The slot is off center which determines how the distributor meshes into the engine on installation.

The factory manual specifies:

"Set cylinder 1 to TDC; here the central slot in the head of the distributor drive shaft should be at right angles to the longitudinal axis of the engine and the smaller segment of the drive shaft head should point toward the V-belt pulley."

Distributor Differences

The alignment of the 'central slot' described above is not the same for the 022 and the 050 distributor. That for the 050 is rotated about 60 degrees clockwise compared to the 022. This means that the spark plug wires from the right side of the engine are nearer to the rear of the car into the distributor cap and those from the left side are nearer to the front. The 022 installation is more symmetrical, with the left side entering the left side of the cap.

If you have the 009 distributor, take it out and throw it away. The 'advance curve' describes the way the distributor controls the timing at running speeds. The 009 advance curve was designed for a VW beetle and is not aggressive enough for the 912 engine. Buy the 050.

Spark Plugs

The old ones were labeled Bosch W225T1. The new ones are Bosch W5AC. These are copper electrode plugs. Luckily I have a spark plug removal tool left over from an old Porsche, probably the 944 which works well for removal and installation of the plugs. The rear ones are just behind the carburetors and are painful to remove and install.

Ignition Wires

The new ignition wires do not have a final rubber sleeve over the end of the plug end insulator. Since this is a fair weather car, I did not try to rescue those left on the old insulators. The wires were numbered, but not in cylinder order as shown above. I moved the number tags to match the cylinders.

Static Timing

The firing point is 3 degrees before top dead center (BTDC); this is equivalent to approximately 3.6 mm (9/64 in.) on the pulley rim. Turn the crankshaft clockwise until the distributor rotor points to a small notch in the distributor housing and, at the same time, the "OT" mark is 3.6 mm to the left of the vertical make on the crankcase housing below the generator support.

Static Timing Procedure

This is the information from the factory manual. I don't recommend it. Instead use a timing light. This procedure could be used when you are getting the car started for the first time after installing a new distributor.

Rotate the crank pulley "OT" mark 3.6mm to the left of the engine mark.
Remove the distributor cap and rotor arm.
Loosen clamp screw at the base of the distributor body.
Connect a 12 volt test lamp in series between terminal 1 at the distributor and the ground.
Switch the ignition on.
Turn the distributor body clockwise until the light goes out (contacts closed), then turn slowly counter-clockwise until the exact moment of point opening (the instant when the light goes on again).
Tighten the distributor clamp screw.
Reinstall the rotor arm and distributor cap.

The ignition timing for all four cylinders is correct when the test light lights up at the precise moment when the pencil mark on the crankshaft pulley lines up with the stamped mark on the crankcase.

Results

Wow! Now the car starts easily and revs to above 5000 RPM, pulling strongly in all gears. It might even be generating close to 100 HP... Well maybe not, but I'm happy with the result.

Dynamic Timing

If you get the recommended Sears timing light (the one with the knob on it that you can use to set the dwell angle) this procedure is very easy.

This description is pretty elementary, so forgive me if I seem to be talking down to you.

Timing lights flash a strobe light when triggered. The light illuminates a mark on the engine pulley. The trigger is supplied by the pulse from a spark plug wire. We use the number one cylinder to make the measurement. The trigger sensor on the Sears unit uses induction with a little clamp on a pickup. Power to the light is supplied by connecting to 12 volts.

More description detail is available by clicking on the picture to see a larger view.

Pictures

	Find the top dead center mark (TDC) on the flywheel and rub some white paint into it. The timing marks and the clamp you must loosen to rotate the distributor is plainly visible in this picture. The only mark on the pulley is TDC to help to set the timing.
	The induction pickup is clamped around the number 1 spark plug wire.
	You can get 12 volts for the timing light from the coil.
	The car must be running at idle to make the measurement. There is a loose wire from the wiring harness that will engage the starter when touched to the voltage regulator B+.
	All set up and the engine is idling. Point the strobe at the pulley and pull the trigger. The strobe light is illuminating the "OT" mark on the pulley to the left of the mark on the engine. The specifications are to set it at 3 degrees before TDC. The strobe will illuminate the TDC mark about 3.6 mm (9/64 in) to the left of the engine case mark with the engine running at idle when it is timed correctly. With my Pertronix electronic points, I set the idle timing to 5 deg BTDC - about 1/4 in to the left of the engine mark. If you are using the recommended timing light, just dial in the desired value and rotate the distributor until the "OT" mark lines up with the engine mark. Don't forget to tighten the distributor clamp.

Update - February 2003

912 engines should be timed at the upper end of the distributor RPM scale, not at the bottom at idle. This requires either a marked pulley, a mark on the pulley at 30 and 32 degrees or a timing light that has a settable offset. Above 3000 RPM, the 050 distributor does not change very much in advance with increasing RPM. The weights are near their limit of travel. The factory recommended setting is 35 deg at 3000 RPM. Duane Spencer recomends 30 degrees of advance above 3000 RPM provide more power with modern California gasolines. Since we can not adjust the advance curve, the procedure is to let the idle advance fall where it may.

Last modified: Thu, 13 Feb 2003

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