How much is too much Distributor Timing

[Michael C]

Here’s the scoop.  I have two cars I’m working with.  Both 1970 (1) 280SL, (1) 280SEL both with the same motor.  BBB says to timing should land at 8 degrees ATDC.  (Not sure if this makes a difference but I’m in CA where the highest local octane is 91).

The 280SL is running the stock distributor (061 or 062 I really can’t remember) with a pertronix at about 4 degrees ATDC @ 800 RPM no pinging, and no problems.  

Question #1 is this safe?  It really likes a little advance in the timing.

The 280SEL is running a 123 Ignition / distributor at the recommended 8 degrees.  But I’m looking to get a little more pep.  Thinking about advancing the timing by about 4 degrees.  But want to make sure it’s okay to do so.  
Both cars run pretty cool.  Both are set within the CO% spec. Both have all the factory smog equipment of the day and all is working properly.  However both motors react like night and day.  

Question #2 what are most folks with late 280SL’s running for timing at idle?

I’m asking because I keep reading… set 30deg at 3000rpm and if it land close to spec at idle, you’re okay.  But are you really?  I just don’t want to hurt anything.

Any insight would be great.

Michael

[Iconic]

Since no one responded to Michael C's post, I will hijack it with a very related question.  Maybe the answers can still help Michael C out.
My car won't run at the 8 degrees ATDC spec at idle with vacuum connected.
I set it at 20 degrees BTDC at idle and it runs great with no ping. I mean no ping while driving and under load.
Also, when I remove the vacuum, the timing advances about 18 to 20 degrees, as it is supposed to.

Can my distributor be off a tooth (asked with not a lot of knowledge of this distributor or without knowledge in general    )?

Should I try to solve this issue if my car runs good?
If so, where would be a good place to start looking?
NOTE: This is a 1970 SL with USA emissions equipment.

Oh, by the way, For Michael C. I don't believe 4 degrees advance will hurt anything as long as there is no pinging under load (be careful on hot days too). But, I will be interested to hear what the expert say.
Thank you,
Mark

[ja17]

Hello,

20 degrees BTDC advance at idle is a lot!  I ran into this problem with a 123 distributor. The distributor was set up to run with a vacuum advance distributor instead of the standard vacuum retard distributors on many of these cars. The result was way too much advance at idle. Initial acceleration power will suffer since ignition spark will happen way to soon off idle. Engine ping can be hard to detect at times. You may notice the engine temperature being higher than previous.

You need to check and see if you have a vacuum in the line at idle. Next confirm that your distributor retards with vacuum.

[Iconic]

Joe,
As I look at the timing numbers, looking toward the rear of the car, the numbers to the left of zero are ATDC (retard direction) and the numbers to the right of zero are BTDC (advanced direction), correct?
If so, my distributor retards with vacuum because with the vacuum line on it reads 15 or 20 to the right of zero and if I pull off the vacuum line, it reads approx 35 on the right of zero.
Therefore, with vacuum, it goes back to 15 or 20 to the right of zero (BTDC I believe) and that is in the retard direction.

I can feel the vacuum at the line to the distributor.
So, I have vacuum and my distributor retards with vacuum if all of my statements above make sense to you.

This is a completely stock set up and original except for maintenance parts.
I've driven it 2500 miles this way.
Do you have any other thoughts?

[Benz Dr.]

Regardless of where you set your ignition timing it will always fire every 60 degrees. If you are out one tooth it will flash at a different spot on the crank shaft yet still be in time - it's just not in time with the marks on the pulley.
On most engines you can get at least 30 degrees of swing on the distributor. In other words you can adjust your distributor back and forth 30 degrees. You may not be able to do this while your engine is running because the engine will stall if you retard the ignition too much but it will move that far. 30 degrees just happens to be half way between the points of fire which in the case of a 113 engine is normally 60 degrees. ( will be diffrent if you run a V8 )
So, if you are out one tooth it will easily show up as being out 20 degrees on your crankshaft depending on where you set your timing. So, your distributor is not indexed correctly and you'd be surprised at how many engines are set up this way. You can add or subtract timing to your stated amount but the trick is knowing where TDC is on your distributor housing and not your crankshaft at that point.

It's all easily cured by moving the gear below the distributor until the center of the rotor points to the mark on the distributor housing. I think some are setting their rotor looking at it from the leading edge when it should be pretty much centered on the mark as a static measurement. 30 degrees is more than enough to get the indexing off and by turning the distributor to the next quadrant you suddenly find that it runs well but your timing light doesn't line up with your timing marks. I set them by ear and then by driving if they are not indexed properly if I don't have time to change them. Everything will still work but on timing sensitive late model 280SL's it's probably best to have it so you can actually put a timing light on the engine and know for sure. 

[ja17]

Hello,

Yes the BTDC numbers are on the right of "0" (TDC) as you look to the rear of the car.  Be sure you are using the correct scale on the front dampner. Some engines have two scales.

With vacuum line hooked up, the engine timing at idle should be 2 to 8 degrees BTDC depending on what distributor you have.At 3,000 rpms it should be around 30 BTDC.  

[Benz Dr.]

Most distributors will give you the full 30 degrees of advance. I set the 051 to give 10 degrees vacuum and about 20 degrees mechanical. Some mechanical advance parts will only advance 28 degrees so I add the extra 2 degrees to the vacuum pull rod by adjusting the length of the rod. They all leave with 30 degrees.

Most distributors will be fully advance long before 3,000 RPM. That's where everything should be fully advanced and it's usually somewhere between 2,5000 to 3,0000 RPM. If you set your engine to 30 degrees at 3,000 RPM you may be loosing some performance. According to what Joe just told us the real timing would be more like 32 to 38 degrees at 3,000  Having 30 degrees at 3,000 RPM is a check amount but not necessarily the full amount you should see .

[Iconic]

Joe,
Did you mean 2 to 8 degrees ATDC? (not BTDC?)
If I am reading the BBB correctly, the spec is 8 degrees ATDC at idle with vacuum hooked up to the distributor for my car (which is a 1970 with USA emissions).
I do have two sets of numbers on my damper and I am using the set closest to the engine (in other words, towards the rear of the car). That is correct, isn't it?

Dan,
I'll do the checks to see if the rotor is in the correct position at TDC. The distributor might be rotated a tooth.

Joe and Dan, I need to do the checks at 1500 and 3000 RPM to see if I am getting the net advance I should be.

Thanks to you both !!

[Ferrolanoman]

Iconic,
Messieurs Mercedes & Benz should be flogged for 1) making it near impossible to get a timing light near the harmonic balancer and 2) for putting two graduated and conflicting timing scales on it.
I too have a '70 280 4-speed US spec car and, after cleaning the harmonic balancer and making both sets of marks visible, used the scale closest to the radiator (as opposed to you who used the ones nearest the engine).
With the vaccum on, the car idled best at 10-12 degrees AFTER TDC. At the prescribed 8 ATDC it would run unevenly and was difficult to restart. However, much to my delight, it would advance to 20 BTDC at 2,000-3,000RPM, which tells me two things: 1)both mechanical and vaccum advances were working and providingg a total of 30 degrees of advance, and 2) I was using the wrong scale (nearest radiator), whereas you were using the correct (nearest the engine) one. I will try again with the rear scale next to see what results I get. Frankly, going by the 2 o'clock/10 o'clock lobe position on the cam together with the rotor pointing to the scribed mark on the distributor is pretty inexact since both dampner scales come pretty close at the pointer.
Finally, my 062 distributor has been converted to the Crane X700 electronic, though I'm not sure that that should make any difference.
I'll post my findings after using the second scale to see how close the results come to the 8 ATDC--30 BTDC.

[Benz Dr.]

I checked my timing last night and it was running right on 30 degrees ATDC. The idle timing was right about TDC which verifies that the distributor I'm running  is advancing the full 30 degrees that I set it at. I bumped it up to 35 total and it has a lot more throttle response. All on regular fuel and not premium. Engine does not ping.

 The later 062 distributors have a lot more vacuum advance/retard and less mechanical. Everything was set up at the factory and nothing can be changed, at least not easily. A properly functioning vacuum system is critical here because you can end up with only 10 degrees of total advance if the vacuum portion isn't working.
This system has a slower rate of timing advance from idle than the 051 or the very early units. On the the 051 or the early units the timing advances both by vacuum and mechanical all at the same time. On the 062 unit if you only have mechanical it will be topped out around 2,200 RPM and performance will suffer. If you happen to set your timing to factory specs or 8 degrees ADTC you will only have about 5 degrees BTDC at full advance - good luck with that.
Vacuum advance on the 062 can be as much as 28 degrees. This allows the timing to swing over to 8 degrees ATDC and the additional 20 degrees of vacuum along with the 10 degrees of mechanical advance will give you the total 30 degrees that's needed for optimal performance.
An easy check is to see what you have for full advance and what you have at idle. There should be about 38 degrees difference or something isn't working right. 

[Ferrolanoman]

Dan,
Thanks for your informative reply.
However, you did mean 30 degrees BTDC, in your first sentence--not ATDC. Correct?
So, my questions are:
1) Idle timing with or without vacuum, and at how many degrees?
2) At high RPM (2,000 to 3,000), with or without vacuum, and how many degrees of advance should I be getting?
3) Do I use the scale closest to the radiator or the one closest to the water pump--I unfortunately have both.
I do appreciate your real life experience guiding all of us in this procedure rather than the official M-B specs. It means a great deal to me to have the little car running as well as it can.
So, again, many thanks.
Ricardo

[ja17]

Hello Ricardo and Iconic,

There were two configurations of pointers used on these engines. The original early pointer is rectangular with the end cut at an angle to form the pointer. It is sort of a trapezoid shape. With this pointer the scale nearest to the radiator is used.

Later, the factory tried to make the timing pointer a bit easier to see and moved it. The new configuration of pointer is a triangle shaped pointer. With this type of pointer the pointer nearest to the engine block is used.

Look on page 00-7/2 in the BBB for pictures, illustrations and more information.

The offset between the two scales is 40 degrees. 

Another way to identify the correct one to use is remove #1 spark plug and watch the piston come to the top. Use a flashlight to view the piston top.

[Benz Dr.]

Dan,
Thanks for your informative reply.
However, you did mean 30 degrees BTDC, in your first sentence--not ATDC. Correct?
So, my questions are:
1) Idle timing with or without vacuum, and at how many degrees?
2) At high RPM (2,000 to 3,000), with or without vacuum, and how many degrees of advance should I be getting?
3) Do I use the scale closest to the radiator or the one closest to the water pump--I unfortunately have both.
I do appreciate your real life experience guiding all of us in this procedure rather than the official M-B specs. It means a great deal to me to have the little car running as well as it can.
So, again, many thanks.
Ricardo

Uh, yeah...... 30 degrees BTDC. My mind thinks faster than my finger - not fingers. I admit that I can't type but do a fair job at hen pecking.

[Ferrolanoman]

Joe and Dan,
All's well now that I found the correct scale on the balancer to be the one closest to the block, NOT to the radiator. At idle (~850 RPM) my engine is happiest near TDC, and I'm getting 30 BTDC above 2,500 RPM (no detectable vaccum). All in all, my impression, like Dan, is that the actual readings do not correspond exactly to the factory specs. Basically, setting the idle timing where the engine runs smoothly and starts easily will yield the desired 30 advance--if the distributor is functioning properly. Verify both settings with a good timing light to ensure that total timing is not too advanced and all should be well.
Thank you both for your good advice.

[Shvegel]

I am of the belief that my timing was too far retarded in the stock position on my 1970 SL as well. I never researched it but I am willing to bet that at least in the later 280SL models the European cars had a more advanced timing spec.

The USA emission regulations mandated a reduction in NOX(Oxides of Nitrogen) sometime around 1970. The way to reduce NOX is to reduce cumbustion temperature. The way to reduce combustion temp is to reduce cylinder pressure or retard timing. We know compression ratio is the same US to Euro. Cams are different which can be a way to reduce cylinder pressure and I am willing to bet the timing spec is more retarded on the US spec models as well.

[Jkalplus1]

Went to cruise night last night (first time post-Pertronix install) and tried giving the car a little more timing (2 degrees), to about 37 degrees at 3000RPM.  It responded well and pulls stronger across the range.  My idle was still over 1000RPM.  I added even more timing (another 2 degrees), idle went down, but idle was rough and the engine was shaking a bit (too lean I reckon).  I added a couple clicks to the FI pump, idle was smooth and a touch under 1000 RPM with the performance unaffected.  It is still too high.  The air adjustment screw is all the way in, so I cannot physically give less air to the mix.  I will try giving a couple more clicks to the pump.

I wonder if I am taking the problem from the wrong end, but the only way I see I can get my idle go down is by giving more timing.  My air screw being all the way in (cannot give less air), I will give more fuel (2 clicks), check idle, and add a bit of timing to the distributor to take the idle RPM down...take the car for a drive, check for pinging...nothing audible, pulls really well...what can be wrong?  I am using 94 octane (AKI) fuel exclusively.

The car currently has W6DC plugs that show the appropriate light brown color, gapped at 29 thousandths.  Tonight I will try my new BP5ES and I will gap them at 35 thousandths, see what happens. 

Please tell me to stop if I am doing stuff that can cause damage.  The way I see it, I am just having fun learning how my car works, and hopefully fix that "too fast" idle the garage people could not fix (they only used the air adjustment...and once it was all the way in, the idle could not possibly go lower)...so I see my options as:

1-more fuel
2-more timing
3-check linkage again, just in case

have a great day!

Jerome

[Benz Dr.]

Sounds like you have a vacuum leak. I would check to see if the slide valve is shutting off completely and that the throttle valve is fully closed at idle.

   I think there's some confusion about timing. On the 051 distributor you will get 30 degrees of timing which should happen before or at 3,000 RPM. What some are forgetting is that you also have to add the basic setting at idle which should be somewhere around 6 - 8 degrees for a total of 36 - 38 degrees. If you set everything to 30 ATDC your idle timing would be TDC - the engine will run but lack power.

[Jkalplus1]

Aha!, thanks Dan!  I'll check that.

[Jkalplus1]

http://www.sl113.org/forums/uploaded/ja17/2006429213348_warm%20up%20device%20parts.jpg

Is this the slide valve Dan mentions?  I am trying to find pictures of it, unsuccessfully.

[Benz Dr.]

That's the one. Make sure no vacuum can be felt after the engine warms up by removing the small air filter. Even a small amount will affect the idle air screw.
All of this should be in the the throttle linkage tour.

[Jkalplus1]

That's the one. Make sure no vacuum can be felt after the engine warms up by removing the small air filter. Even a small amount will affect the idle air screw.
All of this should be in the the throttle linkage tour.

OK, I see.  I remove (unscrew) the small air filter, and then I put a vacuum gauge in there? 

[Benz Dr.]

You should be able to hear air going in until the slide valve closes. Once it's closed enough you won't hear anything, so you place your finger over the opening and see if any vacuum is present. If it's still drawing vacuum after a drive, which should fully warm the engine, you will need to adjust the slide valve so that it closes.

[Jordan]

If you've removed the air filter it is easiest to just put your finger over the hole.  If it is drawing air when warm you will feel you finger get sucked to the opening and you will hear a definite change in the engine rpm's once your finger is over the hole.  If no air you won't hear any change in the rpm's.

[glenn]

jkalplus1,  Sounds like you have a 'rogue' air problem.  The engine should not run with the idle air screw full in, i. e. no air flow thru it.  At warmed up idle, the fuel should be minimum and the air should only be coming thru the idle air screw to support the min fuel.   You must be getting air from somewhere else---butterfly, a vacuum leak, the slide valve(WRD), ??  Timing, etc is independent of fuel/air ratio.  You need to sort out the air problem first.   At idle the engine burns about 1 oz (+ or -)per min- at 60 mph it burns 6-10 oz per min.   Good Luck. ..

[Benz Dr.]

Timing may be independant of the air fuel ratio but it's not when it comes to idle speed. All of them have to be triangulated so that the engine will maintain a constant and dependable idle speed.

When I had the same problem with no idle air screw contol I found that the warm up device wasn't shutting off fully. I would start there.