engine and drivetrain Ignition Timing Methodology

[Guest Anonymous]

I grew up using a timing light - on non computerized engines that permitted manual timing setting via turning a distributor body. I recently rebuilt a 9.5:1 stock M10 and found that when I use the factory timing settings, the engine runs well - but it is no barn burner. The distributor has been checked on a distributor machine and it is within specs offered by the factory manual. With 32/36 DGV stock 4-speed at 2100 miles, regular 76 petrol - W8DC's are clean and she gets averages approximately 22 mpg.

I searched the archives and see there are two schools: CD says use the light. PaulW and someone named BigDog say ditch the light and use the ear. I tried the latter and am amazed that I can add as much as 7 degrees initial advance with barely a ping in second gear up a hill. MPG's have increased to 25 mpg, the car idles smoother and runs faster. This may seem strange, but I have been told the exhaust doesn't smell as strong. Plugs are spotless and do not have any obvious indicators of being overly lean or too hot a heat range for my normal operation.

So here is my question, and please, I do not wish to throw mud. CD, or someone who advocates the strict use of a timing light, at what point do you deviate from the stock settings? CD, when you had yours, did you ever experiment with different timing settings and, if so, what were your observations?

Can you explain why my engine seems to benefit from the ear method or why I am wrong. Lastly, I admit I have not used an exhaust gas analyzer, but am I doing any harm?

[Kidasters]

Actually, the timing on your car is not a fixed point. If you look in the "blue books" it is actually a curve that follows this formula (y = 23.151Ln(x) - 142.95, where Y is the degrees of advance and x is the engine RPM's with the vacuum advance unplugged). So - when you are tuning by ear, you hear the engine sound better at a certain RPM's. I bet if you checked that against my formula, you'd see it matches to where you should be.

When I set the timing in my car by ear, it matched the formula within a few degrees when I checked it with the light.

Ken

[wegweiser]

Hey Andrew,

I'm HOPING that you're referring to European fuel - where Octane must be rated differently. Here in the states - for optimum performance, I run 92 or 93 RON Octane rating.

Caveat: Mine's a 9.5 motor with Dual Webers - delivering rediculous amounts of fuel - so I have few worries about it running too lean and/or melting down at higher rpms.

My ignition timing is currently set to max out at 33-34 deg BTDC at 4000 rpm using a recently produced (2001 era?) "002" mech adv distributor. This puts it at about 8-8.6 deg BTDC at 900 rpm idle, according to my notes from last summer. YES. I keep a notebook with this data - as you ALL should!...especially you guys with DCOEs.

How'd I figure these numbers out, you ask?

I used an ADJUSTABLE timing light and marked the TDC notch on the front crankshaft pulley. I toggled the light advance button until the TDC mark lined up on the timing cover pin at 3800-4000 rpm.

Yes. I admit it: I used a timing light - here's why:

repeatability

Here's why I don't use a std non-adjustable light on the flywheel ball:

there were numerous compression ratios offered on the M10 cars (8, 8.3, 8.5, 9, 9.3, 9.5, 10:1?...yet only TWO flywheels (not counting the early 6 bolt units) used from 1971-1976. There were also several (5, 6?) distributors, offered. Specs also applied to fuels available in the 1970s.

Now - assuming that your motor is bone stock, has lost no compression, nor gained any, has an original, properly functioning distributor curved specifically for THAT piston configuration...then....*MAYBE* using the ball / blue rep. manual technique, makes sense...or if you don't trust your ears and ass-dyno.

In 20+ years - I have yet to find a car that fulfills all the above criteria. I learned to adore adjustable timing lights while tuning a dual IDF Weber'd VW bus motor...because to MY ears anyway....the thing ALWAYS sounded like it was gonna hand-grenade. A timing light made me feel safer - that I wasn't setting it too advanced.

I spend very little effort worrying about timing at idle. Instead - I concentrate on where the advance curve stops (3800 rpm +/-) and let the idle advance fall wherever it may. Generally - I've found 27 deg - 33 deg at full advance seems to yield decent results, but each and every motor seems to respond differently. A single degree here or there, CAN make a dramatic difference in performance...and longevity. There are those that might say I've just been lucky, but I've logged HUNDREDS of THOUSANDS of miles using this technique, without meltdown, in over 10 2002s. Yeah...buy the highest Octane you can buy. I mean...do any of us drive these cars 'cause they're "economical"? Puhleeeze!

A good adjustable light can be purchased from OTC tools. I paid about $130 for mine I think. I friggin' LOVE it!

Hope this helps!

Paul Wegweiser

Baltimore

[Kidasters]

yeah - good point. I use an adjustable timing light as well. Craftsman actually. I've heard their timing light is one of the best.

Ken

[fiftytakedowns]

I just set my timing to factory on my 74 tii to 25º and its at 2700 rpm.

I thiink it only makes sense to use a light, however but to Log in (like the guy was saying) what esults you get at certain degrees, cause then you can monitor every move in evey direction. ...Yeah I know Im kinda stating the obvious, but...

DO you guys think it should be more advanced....? 27º -33º, could sound like I am loosing some power, or MPGs. How much of a difference could the octance make if it is a later degrees.. (91 octane)

[Guest Anonymous]

My ignition timing is currently set to max out at 33-34 deg BTDC at 4000 rpm using a recently produced (2001 era?) "002" mech adv distributor. This puts it at about 8-8.6 deg BTDC at 900 rpm idle, according to my notes from last summer. YES. I keep a notebook with this data - as you ALL should!...especially you guys with DCOEs.

I am running Mahle European Tii popup Steinways which I was informed gives me a 9.5:1 ratio w/ Weber 32/36. Compression reads 175 in 1.2.3 and 4. I do run regular fuel with moroso octane booster - just because I have quite a bit of it. (Needed it for the 70 GTO I recently let go) I use a snapon digital light. I tried running a stock 008 distributor and found that when set per the factory recommendation @2400 rpm, I had a rough idle. If I advanced the distributor by some 7-9 degrees so that I am at approximately 39 to 40 degrees at 3850, idle is extremely stable and the engine seems considerably stronger through 5800.

My engine seems to benefit from more advance than the norm. For grins, I tried what I think is a distributor from a 73A (168 021 JFUD4) which has approximately 44 degrees total advance according to the shop's Allen distributor machine. This distributor also has a vacuum retard that is manifold fed so that it will run more advance after the throttle is cracked. This provides a curve that slightly mimics the 008 except it continues through 3850. I have used my ear to initially set the timing and have found the timing light pretty much confirms my hearing.

I have not put the car on dyno, but fuel economy is mid 20's and the car will satisfy all demands - with air on, full passenger load and over steep grades at speed. Valves are set to .007 cold.

[Guest Anonymous]

Welcome to my nightmare Paul Wegweiser

Baltimore

Does BMW now recommend non-detergent oil? Or is the picture proof that the newer engines will run with Hunt's BarBQ sauce as an oil substitute? Are the spare ribs in the sump? lol

[tjones02]

Ouch! Dueling VANOS... I hope you're changing the oil separator while you're in there. OR... is that motor just plain toast and the car waiting for a long block in the pretty BMW box. I like changing motors that come in those boxes. :-b

If the timing cover looks like that just imagine what's lurking inside those VANOS units.

I just loovve it when the oil filter disentigrates from 20k + on it......

Have any M54 head bolts pull the threads out due to severe overheating yet?

[Stacey]

I have a similar set-up to Paul's. I use a variable speed timing light to set at total advance off of the front crank pully. My ears get the final veto over what the timing light comes up with - ala "European" or "Bigdog" method.

And my variable timing light is one of those tools I didn't realize how badly I needed it until I had one.

[tjones02]

Paul, have you tried a vacuum advance dizzy? I've seen that they've got much more advance in them. and tend to work better on carbed '02s. Good for power and economy.

I've been thinkin' about firing up my Grandfather's old Sun distributor machine and playing around with some curves. With that and my friend's wide band O2 meter.... mmmmm tasty.

32 to 36 degrees max advance is good for many '02s.

Any decent advance timing light and the butt dyno is the way to go.

BUT, for the inexperienced using a timing light for the first time, the blue book method is bomb proof.

Take notes fellas, tests are next week.

[wegweiser]

Sorry for the thread hijack all, but the reason I'm into this motor in the FIRST place, Tom- is the PLASTIC oil sep. behind the left timing chain rail finally gave up.(clogged and broken) (They were kind enough to install it topside and outside, at the intake on later V8 motors) Car was spewing foul oil smoke - at a mere 82K miles. Bought the $800 worth of cam fixture / VANOS sprkt tools, now I've reassembled it twice (thought I might have been off a link on the chain the first time, spent all day Friday tearing it back down again to triple check my assembly) only to find out the left bank VANOS unit is probably the cause for cam adaptation fault code(s) afterall - gee...small wonder. (Using AutoLogic software/hardware) It's a pity, too - the car runs GREAT - 'cept for the pesky check engine light! Tried swapping VANOS servos from left to right, but the symptoms stayed right side.

...and I don't get to take a vacation til this 'uns fixed and back in the owner's hands. Too many gears, too many chain links for my taste!

I have a half gallon plastic jug FILLED with the stuff I cleaned out of the oil pan and covers...it's the consistency of room temperature butter. Easily 2 quarts worth. I have a photo at the shop of a 12" screwdriver standing upright in the stuff.

...that's what happens when bean counters do the math instead of the engineers.

Paul Wegweiser

[rho]

Just to clarify the 'Timing by Ear' process.

I've read that you rev the engine to 2K. Adjust dizzy advance until it starts to stumble/miss then back off slightly. Drive car and if it pings under load retard the timing a bit until it stops pinging.

Is 2K rpm the same for all dizzys?

[wegweiser]

hmmm....that's a new one for me. Sounds a little "iffy" to be honest. If you're stumbling at 2000 rpm, you're not even close to correct timing IMHO.

add'l note:

If it's not 90+ degrees outside, and the motor diesels when you shut it off - your timing's off. If the motor cranks over real slow and labors to fire up after your adjustments - you're still not there yet.

ign timing at 2000 rpm is often different depending on which distributor you have. check out graphs of BMW distributor curves per rpm, for more detailed info.

take notes, be methodical, patient, use your senses and your brain, and you won't melt your motor. If you dive in to it carelessly, like it's trivial and unimportant - you'll be buying pistons.

Paul

[fiftytakedowns]

Actually, the timing on your car is not a fixed point. If you look in the "blue books" it is actually a curve that follows this formula (y = 23.151Ln(x) - 142.95, where Y is the degrees of advance and x is the engine RPM's with the vacuum advance unplugged). So - when you are tuning by ear, you hear the engine sound better at a certain RPM's. I bet if you checked that against my formula, you'd see it matches to where you should be.

Ken

DOes this formula Apply to TIIs as well (the formula) or is there a differnt formula?

It seems like most of this is about Carbed 2002s, but I am curious aobut how it may, or may not pertain to Tiis.

trying to learn some stuff for next time I do timing.

[Kidasters]

This is what I came up with for a carburated 2002. I didn't figure it out for a tii. Basically though, anyone can figure it out. In the blue books, BMW tells the max and min advance for different timing at different RPM's. I just plotted them, and then had excel give me the formula for a line that went directly between the max and min points.