Ignition timing

Thank You,
Honestly you guys were fantastic. Yes I am starting to think that I need to get prepared for the inevitable day (sooner than later) that I need to refurbish the Trigger Points. 1 more question if I may. The service manual states that for a 1973 Mercedes 450 the timing need to be at 5 Degrees ATDC but a lot of people I have been talking to state it should be BTDC (I have it set at 750 rpm, 2 degrees BTDC with a dwell of 28 degrees - supposed to be 30 - 34 but finding hard to adjust to this). The car is surging a little at idle by app. 25 rpm but this could be another issue - possibly T/P's?? It also has an ignition module next to the coil but it is not connected at the bottom so I'm not sure what it does.
Anyway, what is you opinion of the timing mark?
Regards
Peter

Hi Peter,

as we are now talking igntion and no more trigger points, I have moved the subject.

Regarding your ignition timing, it depends on your ignition distributor. You will find infos here under 107 SL workshop manual .in chapter 07.5-500 . Read your distributror no and check there. First adjust dwell, then timing. And do not forget that it needs adjusting and verifying at 1500/min, 3000/min and of vacuum adjustment!

Will do and great reference list.
Thanks You!

Ive got a 1974 450SL and I’ve got my timing dialed in at 30degrees btdc without vacuum. Which ends up being tdc +-2degrees with vacuum line. I’ve been told to keep the vacuum line disconnected and plugged. But it ran a little sluggish at times. So could I keep it timed to 30degrees btdc without vacuum and connect the vacuum line to achieve tdc+-2degrees?

Although my distributor isn’t listed there. Mine anppears in the national version ands ends in 403 007. The standard version for m117 doesn’t show my distributor. Job 7.5-500

Hi Unknown,

please sign ur messages so that we need not guess ur firstname and can greet u.

Your ignition distributor is mentioned in 07.5-500 in chapter B country version US. It shall have 18-22° BTDC at 3000/min with vacuum. And it shall achieve 5° ATDC with vacuum at idle. 

Ur ignition distributor has double vacuum box for advance and retard and it has 2 levels of rpm adjustment. Pay attentin not to mix advance and retard vacuum line,

My apologies,

My distributor doesn’t have but one vacuum port and from the service manual it’s the retard port.

I have it set to 30degrees btdc without vacuum@3000rpms per the chart is 7.5-500.

If I connect the only vacuum line the timing drops to 1 or 2 degrees btdc.

-Joshua

Hi Joshua,

you are right, it has only retard. Bosch Microfiches have wrong information here. Mercedes is right.

However you should set to 18-22° BTDC at 3000 rpm, not 30° BTDC. That is what Mercedes tells in that document on page 2 for Model Year 1974 USA.

Yes I know that is what the charts say. But people on Benz world
Forums claim to set it to 30btdc@3000rpms to have it run better..

They would say since I’m in the USA, that the 5atdc w/vacuum at idle on the decal was just to meet the emissions standards of the time? But I’m still unsure. It seems to run better now that it’s dialed in at 30btdc@3000/rpms vacuum disconnected. Reconnecting the vacuum line and having it at tdc+-2degrees or so instead of 5atdc at idle seems to run it better.


So in summery I have it dialed in at 30degrees btdc@3000/rpms without vacuum. I reconnected the vacuum line and it now reads tdc +/-2 degrees. According to the charts first page I still have the m117 in my 74. So I wasn’t sure if it would matter what distributor was in there. Vs what the spec says.

Hi Joshua,

first u ask and then u claim that ur distributor is not listes and now you have a predetermined opinion from Benzworld.

By increasing the timing at 3000 rpm to 30° BTDC u will shift the timing be -10° . Thus u make it 5 BTDC +/- 2° at idle if u connect vacuum. If u omit it, it will change further to 17 BTDC . Ur car will not run properly with that.

Remember that your car switches off vacuum anyhow if A/C compressor is running. That would normally change idle timing to 5 to 7 BTDC. I do not see a good reason for changing timing overall to 30 BTDC at 3000 rpm. If u want to omit exhaust reduction at idle, dicsonnect vacuum line but leave it to 18-22° BTDC at 3000 rpm.

Yes, it is listed in section B under year 1974 in the national version chart and not in section A for the standard version. So which chart should I follow for timing spec of the job 7.5-500. 

Right now the car runs and sounds fine at the setting I have it at with vacuum connected. At idle it shows tdc+-2degrees now. 

Joshua1974/450SL wrote:

Yes, it is listed in section B under year 1974 in the national version chart and not in section A for the standard version. So which chart should I follow for timing spec of the job 7.5-500. 

Right now the car runs and sounds fine at the setting I have it at with vacuum connected. At idle it shows tdc+-2degrees now.

Some of the people on Benz world forum know these cars too and they claim these things. I’m siding with the factory manual. 

Hi Joshua,

standard for Germans is Europe version and not US version as we are middle of the world   SO in Mercedes-Benz documents u always have to check for US version.

Remember that a running A/C will further advance your timing. I would set to 20° BTDC at 3000 rpm and disconnect and seal vacuum if u like to eliminate exhaust gas reduction at idle.