Engine Timing on a 1981 BMW 320i
(North American model; automatic transmission)
There seems to be a number of posts (on www.BMW320i.com ) referring to the procedure to use in adjusting the timing on our bimmers. I've worked on numerous engines – mostly with mechanical points to check and dwell to set, and have learned a few things that I can pass along.
For this particular discussion, I will focus only on adjusting the timing of the 1766 cc engine in my '81 BMW 320i
. This is a car built to North American specs, and it has an automatic transmission, so some things are different from the other models out there.
I use the Haynes repair manual, specifically the North American supplement at the back. I'll also restrict this to adjustment of an engine that already runs, and that has the correct valve adjustments made to it! (Sometimes
the "sewing machine" noise of the valves is mistaken for pinging.) Why adjust the timing? I'm a firm believer in the saying "if it ain't broken, don't fix it!" Sometimes just getting the proper octane
fuel will make all the difference – so start with a good tank of higher quality fuel; if you had pinging with cheap gas (87 octane), it will likely disappear with good gas (92 octane).
Here are some things that will lead you to making an adjustment to your timing:
§ You are experiencing a pinging noise when trying to maintain or gently increase speed going up a hill, or attempting a moderate acceleration on the flat § Your acceleration is really sad – not what
it used to be; parts are worn and/or someone else has recently adjusted the timing and performance is now worse § Your idle speed is low, erratic or not where it should be, and you haven't changed linkage or parts § You're doing a tune up and want to optimize the performance of your engine
Timing marks.
What tools are needed?
Most recommend a strobe light. This attaches to your car battery to power the bulb, and a pick-up attaches to your #1 cylinder spark plug wire to cue the bulb to flash. An alternate method appears toward the end of this.
What is the procedure? 1. First mark
, or at least make a mental note of, the alignment of the distributor casing with its base parts. You may have to revert to this position if you strike out!
2. Bring your engine up to normal operating temperature, and remove the vacuum line(s) at the distributor. (I have only one line going to the base of a vacuum pot; other models have two.) Plug the lines with golf tees. 3. Hook up the strobe timing light to the battery, and put the pick-up onto the #1 spark plug wire just before the spark plug. Aim the light down into the little tiny hole at the rear of the engine (see photo) and
press the light trigger. With 2000 RPM set, confirm that the timing mark on the flywheel is centred in the hole. (According to my Haynes manual, the timing will be 20-28 degrees before TDC.)
5. When you've got the timing mark (long pin for me; ball bearing for most others)
where you want it at the desired RPM, tighten the distributor bolt, and then recheck the timing to see that it has not changed. 6. Remove the golf tee(s), and plug in the vacuum lines. Test drive!
7. Repeat as necessary.
There is a plethora of timing marks used on these engines: short pegs, long pegs, ball bearings, lines, etc. For my car, there is a short peg to show top dead centre (TDC), and a
long peg that will show up in the tiny timing hole as the proper timing mark at a fixed RPM. I believe that most engines for the 320i have a ball bearing pressed into a hole between the teeth to represent the proper timing
mark. As marks may get dirty or covered in thick oil, it is best to find your mark, clean it off with a sharp edge, and maybe drop some liquid paper whiteout onto it to
help you to see it with the timing light. Here's a photo of my tiny timing hole, viewed from the passenger's side...
Two 10mm wrenches are nice, but spanners will do if that's all you have. You'll be using them on the
nut and bolt that is on the base of the distributor (see photo). When it's loose enough, you can rotate the distributor left and right.
4. If an adjustment is needed, loosen the nut on the base of the distributor (see next photo), and
rotate the distributor a small amount (restrict the initial movements to about 1 cm or 1/3 inch) to the right, then back to the start point and off to the left, all the while illuminating
the tiny bit of flywheel visible through the little tiny hole. (Other cars are so much easier than these to see the timing mark!) You will notice that the engine surges and the RPM changes as you rotate the
distributor, so an assistant sitting in the car adjusting the gas pedal to keep the desired RPM is almost essential.
Alternate method: An old mechanic showed me this in the '60s, and it works relatively well (in my opinion) for most cars. You should not
need an assistant to help with this method, unless your engine is prone to stalling.
1. No strobe light, no problem! Prepare the car for making an adjustment as described in numbers 1 – 2 above.
2. Loosen the nut on the base of the distributor (photo), and prepare to rotate the distributor a small amount (restrict the initial movements to about 1 cm or 1/3 inch).
3. At idle RPM, rotate the distributor to advance the timing (on my car that's clockwise – most would be counter-clockwise). The idle RPM will normally increase as you advance the timing.
4. Now rotate the distributor in the opposite direction (counter-clockwise on mine) to retard the timing). The idle RPM will slow down and the engine will start to stall. Don't let it!
5. Set the distributor at that point where you're going from advanced timing to retarded timing and the idle RPM just starts to fall off. 6. Tighten the distributor bolt.
7. Remove the golf tee(s), and plug in the vacuum lines. Test drive!
Cautions: Having the timing too far advanced can damage the pistons and ruin your day and savings account! Notes:
If a test drive results in poor acceleration from a stop, it is likely that the timing is retarded too far. Conversely, if the pinging is still there but has gotten worse, your timing is advanced too far.
Bad timing does not cause every noise under the hood, so again I say: "if it ain't broke, don't fix it!" For excellent information and photos on replacing or repairing fuel lines and fuel tanks, proceed to:
Good Driving!