72 280SE M130 MFI - Need Help timing this beast...

[Bdub03]

Hey Guys. I've been searching all over the place as well as reading both the Haynes and Mercedes BBB trying to figure out the correct way to time my 72 280SE MFI engine. The book(s) say 6 degrees ATDC with the vac advance connected @ running temp. I've done this and the car is beyond sluggish.

Specs for earlier models say to plug the vac advance line and time @ 30 degrees (guessing ATDC???) @ 4500rpm's. My shop tach only goes to 2500rpm's. How are you guys achieving this as none of the M130 108's had tach's stock.

If it helps. I've replaced the following:
Fuel / air filter
plugs
wires
cap and rotor
Hot Shot electronic ignition + their coil

Thanks in advance

[Frank Reiner]

Disconnect vacuum, 30 deg. BEFORE TDC @ 2500 RPM (plus a bit)

[Bdub03]

Thanks Frank. When you say plus a bit do you mean rpm or timing? The car has other issues as well and everyone says to get timing set right.

Symptoms also include:
Crank for 30 seconds before it fires.
Once warm it will always fire immediately.
Sound of a misfire however when you pull plug wires individually there no evidence one cylinder is at fault.
Stuffy head... It's been cold in Sac.

[68_280SE]

The 70-72 280SE USA 6 cylinder MFI cars have a speed relay that shuts off the vacuum to the vacuum retard on the distributor at specified RPMs. If the speed relay isn't working then you might not be getting the full ignition advance at higher RPMs.

The Mercedes Factory shop manual lists some very different timing specs for 1972 USA 6 cylinder MFI 280SE cars compared to the 70-71 USA 6 cylinder MFI cars. 72 specs are: 6 degrees ATDC at idle, 36-44 degrees BTDC at 3000 RPM and 40-48 degrees BTDC at 4500 RPM. The speed relay should cancel the vacuum retard at 2500 RPM and give an additional 20 degrees of advance when the retard is canceled. If the speed relay is defective you may not be getting the full timing advance at higher RPMs. That's why you really need a tach that can go higher than 2500RPM so you can verify the timing at higher RPMs.

The speed really was defective on my 1970 and I was never able to get the timing set correctly until i replaced it with a good used relay.

I also am attaching a shot of the specs out of the shop manual just for reference.



John

[Frank Reiner]

Bdub:

The "plus a bit" was directed at engine speed (since you are tach limited).

Here's an alternate method:
No vacuum, 10-12 deg. BTDC @ 600-700RPM
Then increase engine speed while observing centrifugal advance; advance should stop increasing at about 36-38 deg., but probably above 2500RPM.

The vacuum controls mentioned by 68_280SE were instituted primarily for emission control purposes, and even when new, and operating as designed, degraded performance, and increased fuel consumption. You can operate quite satisfactorily without vacuum.

A necessary first step is valve adjustment, and compression test, in that order.

[Bdub03]

Thanks guys. Much appreciated! I have a new valve cover gasket and grommet's waiting and ordered the 17mm claw tool. I plan on adjusting valves this weekend as well as running a compression test.

I have no problem ordering another tach. Do you guys just use autometer/VDO standard tach's hooked up to the neg coil wire?

Is this the speed relay?

[Wrightbenz]

Originally Posted by Frank Reiner

Bdub:

The "plus a bit" was directed at engine speed (since you are tach limited).

Here's an alternate method:
No vacuum, 10-12 deg. BTDC @ 600-700RPM
Then increase engine speed while observing centrifugal advance; advance should stop increasing at about 36-38 deg., but probably above 2500RPM.

The vacuum controls mentioned by 68_280SE were instituted primarily for emission control purposes, and even when new, and operating as designed, degraded performance, and increased fuel consumption. You can operate quite satisfactorily without vacuum.

A necessary first step is valve adjustment, and compression test, in that order.

Interesting since I will be doing this very soon. I am working on a 68 280se though.
Anyone have the specs for my car?

Any special procedure for seeing the timing on mine?

It's very interesting how many year to year changes Benz was making to these cars back then. It seems the more I read the more small differences I find in the mfi and many other things such as this.

[Bdub03]

I don't mind sharing the love. Here is what I've found in my OE Maintenance manual. My guess is the process is the same for all engines with the exception of the timing spec and any specific electronics added. Did you convert to to an electronic ignition or still using points? My engine is a 130.980 which I found on the original service stamp card

[Wrightbenz]

Originally Posted by Bdub03

I don't mind sharing the love. Here is what I've found in my OE Maintenance manual. My guess is the process is the same for all engines with the exception of the timing spec and any specific electronics added. Did you convert to to an electronic ignition or still using points? My engine is a 130.980 which I found on the original service stamp card

So it looks like my 68 280se would be 30 degrees BTDC with vacuum disconnected correct? And this is at 4500 rpm,s which apparently is hard to find a tach that goes this high.

[Bdub03]

Hey guys. I hate a beat a dead horse but I'm still playing hell trying to get my 108 Timed correctly. Here's what I've done:

Valve Adjustment - Improved performance and idle 10 fold. WOW!
Compression check - 137-147 psi. Looks about right for an older M130

Timing has been set @ 6ADTC on idle w/ the vacuum line attached and still runs like crap. I want to make sure I'm reading the timing mark correctly After vs before TDC.

Also, I picked up a cheap tach that'll give me readings @ 4500rpm's. There has to be something I'm missing here. Any help is appreciated.

[Frank Reiner]

Bdub:

You are reading the timing markings correctly.

Refer to Post #5; what was the result of observing the action of the centrifugal advance?

Just about every production, road-going, passenger car engine of the last 60 years will run very acceptably with initial advance of 10-12 deg., centrifugal advance of 36-40 deg. total, and an additional 5-8 deg. of "vacuum" advance at light throttle cruising.