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w114 - question about timing

16K views 36 replies 5 participants last post by  rumb 
#1 ·
I've never set timing on a car so please understand my ignorance.
I bought a timing gun with an electronic meter and RPM gauge. When the gun is at 0 deg while pointing at the pulley it shows the chalk mark (a white line - black in my sketch below) before the timing indicator. When i set the gun to around 5-6 degrees the mark is right on the mark. Does it mean that my timing is wrong? (My vacuum gauge is in lowish 16s):


I have 1973 280 if that matters.
 
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#2 · (Edited)
How to Use an Advance Timing Light | eBay

I dont know the timing specs for your car, is it a M110 or a M130 engine?

First you need to check the dwell. that is how far apart the points are open. you can use a feeler gauge or a dwell meter. I have one like this:"

https://www.summitracing.com/parts/...iueTmMUL2tLV7WtS_wsECPuxvLBptiqhyghoCXvXw_wcB

as the dwell changes so does the timing, that is why you need to do that first.

The MB timing specs usually show 3 rpms with associated timing advance values.

idle, something like 1500 rpm and 3000. This is to verify that your vacuum and mechanical advances are working properly. all 3 set points should meet spec, if not, then something else is wrong with your distributor.

with your gun, set the dial on "0" and point at mark, the mark will show your timing.

the dial is used to see what your timing is at different speeds, instead of reading the marks on the crank damper you turn the knob until the crank shows "0" it just makes it a little easier to see what it is, but you can do it either way.

Someone else can supply the specs if you dont have them.

In your pictures, with the gun knob on zero you should see -5 on the crank, same thing if your knob is -5 then the crank would be on zero.
 
#3 ·
I don't always know what the white mark on the harmonic balancer means. I assume it's the mark where someone once wanted to have the timing set.

With points, the rider can wear down over time. The effect this has is a later opening of the points, which means a later spark. So as the points wear down, your timing will get later (more retarded, more towards ATDC, less advanced). For this reason, when using points, I'd prefer to set the timing a little on the advanced side. That's the right of the TDC mark side when viewing from the front of the car. So if the white mark is the TDC mark, and you are at 5 BTDC, you might have a good setting right there (for at idle). I think you'd want to to be much more advanced at 3000 rpm.
 
#11 ·
Southern hemisphere. Ha Ha below the Mason Dixon line? I didn't want to confuse you but gave the page out of the 110 Mercedes manual. The other test values are without vacuum at 1500, 3000 and 4500 rpm. The "Installation value refers to a static timing position" i.e. ignition on but not started with a static timing light. Having said this, I will say my 280sl will not run with factory specs which calls for 8 degrees ATDC, no mater how much I adjust the idle screw. It runs perfect at 5 degrees BTDC. So you may have to play with it a bit. Sort of like a girl friend or wife. You just have to know their position that makes them happy.
Will
 
#12 ·
My apologies, i didn't mean to appear ungrateful but rather point out how green i am about the issue.
So basically you are saying - based on your experience with your 280SL - that i should adjust the timing by moving it around to find the best setting rather than relay on factory specs?
 
#17 ·
The vacuum method is a good one, as it automatically compensates for engine wear and altitude. I use it on my MG. I do check after with a timing light just to see if it is somewhere near spec. My 250S is set about 5-10 degree ahead of spec as that is where it runs best. So I would say, yes on these older engines do what works best.

Give the vacuum method a try and see if it starts well, accelerates well and doesnt ping then you are good.
 
#18 ·
Thank you guys for your wisdom. Before i loose your interest here are some more questions.

I messed around today with my carb frustrated that i can't get it to idle properly (i needed to screw in the idle speed screw way past maximum recommended to get to 850rpm - on Weber 38). Out of curiosity i disconnected vacuum to vac advance and the RPM jumped to 1080 and the vacuum jumped from wobbly 16 to strong 18. I thus tuned my carb with vac advance disconnected and got to idle great at 850rpm (and steady 17 vacuum) withing recommended 1/2 to 3/4 of speed screw setting:
>> with vac advance: 850rpm (speed screw way in), wobbly ~16 of vacuum
>> without vac advance: 1080rpm (before changing settings of the speed screw), steady 18 of vacuum

So my question is - is my taming set wrong? What will happen if i drive with vac advance disconnected?
 
#19 · (Edited)
What is your timing at 1500, 3000 and 4500 with the vacuum disconnected as specified in the instructions?
The purpose of these test points is to verify if your mechanical advance is working as it is suppose to do. Then when you connect the vacuum at idle it will tell you if that is working.

Where is you vacuum line coming from? can you take a picture of that location and of your distributor?


what is it at idle (900) with vacuum connected?

what is your distributor part number?

does your disti have one or two vacuum lines? 1 advance and 1 retard.

It almost sounds like you have vacuum retard instead of advance. -- never trust your previous owner - verify everything.

and did you set your dwell? what is it set to.

Need specifics in order to proceed with diagnosis.

Here is some reading explain what vacuum advance does.
Ask Away with Jeff Smith: Understanding Vacuum Advance and Why You Need It - OnAllCylinders
 
#21 ·
Weber 38.
Base settings:
Mixture screws 1 out.
Speed screw 1/2 to 3/4 in.

My settings (WITHOUT vac advanced connected):
Screw close to engine is 1.25 out, screw far from engine is 1 out.
Speed screw is somewhere between 1/2 to 3/4.
The engine idles at 850rpm with 17 of vacuum.
 
#23 ·
More tests i've done today with some videos.
For those who don't like videos here is a quick summary.
I get 3 vac ports at my carburetor - 2x with manifold vacuum and one with ported vacuum. (below readings are with ported vacuum).
My carb is set within base settings with idle speed screw around 3/4 of the way (so i get little bit of vacuum from the ported vacuum nipple - steady 4 that increases to 8 at slight throttle).
Without the ported vac advance connected all is good at the car idles around 850rpm, BUT when i connect the vacuum my idle drops to 670rpm (so to get it to 850 i need to screw in the speed screw way past 3/4 that's recommended as maximum).

I've read enough t know that vac advance is important so having it disconnected is a temporary fix. SO question is - what to do next?
Didn't get a chance to check dwells because quite frankly i have no clue how to do it.

And here is what i my vac ports on my carb:


Here is what my idle looks like with NO vac advanced (idling around 850rpm):

at 0:40 you see what it looks like with 7deg dialed in on the timing light.

Here is what my vacuum gauge looks like with the above setup (NO vac advance):


And here is what my idle looks like WITH vacuum advance connected (idling around 670rpm):

(at the end of teh video you can see what vac gauge looks like with this set-up)

And what the same set-up looks like WITH vac advance at 7deg dialed in on timing light:


And lastly, here is what my RPM/vacuum looks like at 850, 1500, 2000, 3000rpm:
 
#24 ·
"Without the ported vac advance connected all is good at the car idles around 850rpm, BUT when i connect the vacuum my idle drops to 670rpm (so to get it to 850 i need to screw in the speed screw way past 3/4 that's recommended as maximum)."

What is the timing with and without the vacuum attached? (at idle)

with it, your timing should be more advance, which should speed the engine up. yours seems to do the opposite.
 
#26 ·
Sorry for being anal about this, but what is the timing with and without vacuum. Based on what you have said, I'm expecting the timing to be more retarded with vacuum.

Your last test we have verified that the diaphragm works.

If this is true, then it seem you have a vacuum retard distributor, which may be incorrect. What is the Bosch part number on your distributor?
 
#28 ·
part number should be down on side as shown in this thread
http://www.benzworld.org/forums/vintage-mercedes-benz/1708410-w114-carbs-engine-problem.html

I think what I see in the vids is 7 w/o vac and 0 with vacuum. what is not clear to me in video is whether that is 7 btdc or atdc. can you pls verify those measurements? The picture if pretty fuzzy when showing the timing gun.

if BTDC than that means that it is advancing the timing with vacuum, which really should increase the speed.

can you pls verify those measurements?

When diagnosing I try to go back to the most basic things to start with fresh known's.
 
#29 ·
The number on the side of the distributor 0 231 310 002.

I marked the harmonic balancer and it looks like this (you can see the chalk mark someone else made too):


And here is what the timing mark shows at various settings. WITHOUT vacuum connected:


And WITH:


And here is where the mark ends up at 2800rpm WITHOUT:


Hope it helps. Thanks!!
 
#30 ·
Thanks for the info.

First, looks like you have the correct distributor! It is a vacuum retard type. That is why the idle drops when you connect the vacuum.

The chalk mark that someone else made is the correct setting mark for at idle with vacuum. It should be set to 4 degrees after TDC, and it looks like you have 9 ATDC. Advancing the 5 degrees or so will speed your engine up some and give it more pep.

You may not understand using the knob on your gun. you should turn the knob until the timing mark lines up with 0 degrees on the crank and then what the knob says is what your timing is set to. Your second picture where the crank mark is on 10 ATDC and you say the gun is on 14, that is meaningless. you should keep turning the knob until the crank mark is on "0".

To set your car,

-1. set your fuel mixture to smoothest idle as discussed in other thread.

1. connect the vacuum line,

2. put your knob on 4 ATDC point and shoot, while turning the distributor until the mark you see is on "0". (or just set the knob on "0" and turn disti until the mark is on the chalk one 4 ATDC.
3. disconnect the vacuum line and use the 3 test values of 1500, 3000 and 4500 rpms and see what your timing is for each. These 3 test values will show if your mechanical advance is working correctly.

1500 rpm = 13-17 deg
3000 rpm = 31-35 deg
4500 rpm = 37-41 deg

If you are not able to get these numbers that means your mechanical advance is gummed up. This happens on old disti, the springs break or stuff just gets stuck.

Let's set the timing correctly and measure the test values and then see what we need to do next.



(now that all being said I found this post about a 1973 280 with a non stock carb:
1974 Mercedes 280 114 / 110 ignition timing - PeachParts Mercedes ShopForum

"The suggested timing setting is 4 degrees AFTER top dead center, vacuum line connected, idle speed 950 rpms, WITH vacuum being supplied at idle.

I set my timing ('73 280, automatic) with the diaphragm DISCONNECTED at 10 degrees BEFORE TDC. I usually plug the vacuum line and run it with no vacuum retard connected. This is because I converted from the Solex 4 BBL to an Autolite 2 BBL and I don't have all those Mickey Mouse vacuum solenoids hooked up. I hook up the diphragm every year at emissions testing but other than then I run on straight manual advance timing.

You can advance or retard the initial timing to meet your needs (for more "pep" advance it, for better mileage slightly "retard" it)"



The official MB settings may not exactly work with the carbs you have, so first try them, then maybe try to alternative mentioned above.
 
#31 ·
Quick follow up to understand better. Numbers to the left are AFTER and numbers to the right are BEFORE, correct?


First, looks like you have the correct distributor! It is a vacuum retard type. That is why the idle drops when you connect the vacuum.

The chalk mark that someone else made is the correct setting mark for at idle with vacuum. It should be set to 4 degrees after TDC, and it looks like you have 9 ATDC. Advancing the 5 degrees or so will speed your engine up some and give it more pep.
 
#33 ·
Great and THANK YOU!
I'll probably just do what Mike is doing in that link: 10 BTDC with vacuum disconnected because i too don't have the "Mickey Mouse vacuum solenoids hooked up".

He mentions: "You can advance or retard the initial timing to meet your needs (for more "pep" advance it, for better mileage slightly "retard" it)"
If i went for better mileage would i do 12 BTDC... or 8 BTDC? I'm trying to fully comprehend what retard means in this specific example.

Thanks again!
 
#34 ·
I FINALLY got a chance to play with my timing.
This is what i did:
1. i checked dwell angle - and it's about 38-39 at idle with 850rpm (didn't check deviation at 3000rpm though will do tomorrow):


2. Adjusted timing so with the light it hit around 7-8 (my rpm jumped from around 850 to around 970). I kept on adjusting timing to 10 BTDC without vacuum (middle of the 8-12 recommended). At 10 the rpm dropped to around 920. (BTW my timing seems to jump around 3-4 degrees - so it's really levitating around like 8-12)

3. I adjusted idle speed screw to bring rpm down to around 850.

The result is that:
a.) the car doesn't "crawl" as nicely as before while in D and foot is off break.
b.) i started hearing knocking in the engine bay.

So my question is do i go back to 7-8 BTDC as this is when i was getting most RPMs?
 
#35 ·
retard it even more ~12btdc or more - until the knock goes away.

Engine knock, or pinging, occurs when a separate pocket of air-fuel mixture ignites after the spark has ignited the air-fuel mixture within the combustion chamber. Engine knock can be prevented using higher octane fuels, retarding ignition timing, or by using a lower compression ratio, among other solutions.

https://www.yourmechanic.com/article/what-does-it-mean-when-an-engine-knocks
 
#37 · (Edited)
you are reading that chart incorrectly. the 7 deg value is just a test value for when the engine is being cranked/started, not what you set it to.

You just need to adjust to get rid of the knocking, so just try different values and go for test drives in between until you find something that works for your engine.


also did you check for correct spark plugs?
 
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