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E12 Ignition Timing

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528i Timing

Timing your engine is not difficult and the results will astound you for the improvements afforded other problems from idle settings to optimum mileage. It is assumed that you have already performed the Ljetronic Throttle Body Adjustment.

All you need to do the job is a timing light and a 10 mm wrench. A reasonably competent friend is a good idea for increasing amusing banter and decreasing the time you ' ll otherwise spend running around the front bumper adjusting the distributor and checking the results with the timing light

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Lights vary slightly in their hook ups so read the directions. The one pictured above is fairly standard, attached to the battery and #1 plug wire as noted. Attach with the engine off.

Use a 10mm wrench to loosen the distributor clamp fixing bolt. The clamp should be loose enough to allow you to grab the cap with both hands and rotate it clockwise and counter-clockwise, but snug enough to hold its position when released.


Remove the vacuum line(s) that connect to the distributor and plug them.

On the bell housing, driver side, under the heater hoses ( in the dark ) is the timing window. This is where you or your assistant will be pointing the timing strobe light to see the little ball to center it on the point by twisting the distributor clockwise or counter-clockwise.

This steel ball, usually labeled with Z, is the 22 degrees before top dead center (BTDC). All distributor-based M30 motors use this reference for timing. The difference in specifications is at what RPM that point in the timing curve is reached. The US 528i is timed at 22 degree BTDC at 2200 rpm. Other cars will reach that point at a different RPM, so check your shop manual. On a manual transmission car, be sure to use the Z-marked ball and not the mark labeled 0|T which is top dead center. Automatic cars use a short and long peg for timing marks.

Everything connected, vacuum lines plugged, no wires hanging in the fan, etc., start the engine. One points the strobe at the timing window on the bell housing, the other twists the distributor to make the ball in the window move around.

Because the timing will change with RPM, you will want to be sure that the engine is running at the specified RPM. A dwell/tachometer is useful as it allows you to see the RPM from your vantage point on the driver's side of the engine. Some timing lights are digital and include precise digital tachometers on the handle.

You should rev the engine to the rated RPM and then look at the cutout for the steel ball. If you don't see it, let the RPM drop and then rev it again while watching for the ball. If it passes the window before the RPM point, the timing is too advanced and the distributor should be rotated clockwise. If the ball is not seen up to the rated RPM point, the timing is too retarded and the distributor should be rotated counter-clockwise. I have fairly long arms and can reach the vacuum canister of the distributor from the driver's side. If you can't, get your helper to rotate it or put the timing light down and move the distributor from the passenger's side.

If it's just you, do both, running around the bumper. The object of the game is to center the ball on the point on the right side of the window casting. When that's done, engine still running, tighten the 10 mm bolt under the distributor. Check the ball has' not moved in the window.

Shut the engine off, disconnect the light and reconnect the vacuum lines.

Done ! You will have noticed the idle increasing / decreasing as you moved the distributor. With the timing set and the vacuum lines connected, if the idle isn't magically way better to perfect, you now have established the first step to getting it there.

Don Daynes comments:
To understand why the timing is set at 2200 RPM (528i US spec) you must understand the mechanical advance feature of the distributor.

A properly functioning mechanical advance will advance the timing as rpm increases. This is accomplished with small weights working against a number of small springs. Centrifugal force moves the weights. The weights in turn move a plate inside the distributor that advances the timing.

In the case of the e12 528i BMW asks us to remove and plug the vacuum advance hoses. This is done so it does not affect the timing during the timing procedure. Similarly the RPM must be increased so the mechanical advance weights move against the springs to their maximum position. Both of these prerequisites must be accomplished in order to use the 22 btdc timing mark BMW specifies.

If you set the timing at idle, say 900 RPM, your total advance would be much too high because the mechanical advance has not been take out of the equation. Too much advance can cause pinging and engine destroying detonation.

If you were able to set the timing at 900 RPM with no pinging I would suggest checking the mechanical advance function of your distributor. Remove the cap, grasp the rotor turn it (sorry I don't remember which way). In one direction it should feel and act differently, moving further and seem to be working against springs, returning to the original starting point when returned. There have been a few documented cases of seized mechanical advance components here on the board. Peter F. is one. Check yours. Repair if nessary and for goodness sake follow the tried and true timing proceedure it just may save your engine.

 

Brian Smith adds:
I would add this information regarding the usage of the 2200 rpm timing specification.

In case that one of the distributor's springs in the mechanical advance system is broken, or the weights have become stuck, setting the timing to specification at 2200rpm serves to reduce the chance that the timing could be set grossly too far retarded or advanced, thereby safeguarding against substantial pinging at higher than 2000rpm engine speeds (and risk of engine internal damage) and against excessive exhaust system temperatures (and risk of manifold and cylinder head damage.) Do not use your exhaust manifold as a combustion chamber via super retarded ignition timing. An even idle is only one aspect of a properly timed ignition system, and certainly isn't proof thereof.

 

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