Tune up help for a '74 450SL - Page 2 - PeachParts Mercedes-Benz Forum

rickjordan · #16 07-01-2012, 07:18 AM

The timing at idle is now set at the factory spec of 5 degs ATDC. The idle RPMs are also now set spec at about 750. Spec is (700-800) All of this is per the factory service manual. So you are saying that I need to rev the engine to 3 grand and check the timing there? The engine is running so much better except for the heat. I don't recall seeing any mention about checking the timing while running the engine to 3 grand.

Graham · #17 07-01-2012, 07:41 PM

Quote:

Originally Posted by rickjordan

The timing at idle is now set at the factory spec of 5 degs ATDC. The idle RPMs are also now set spec at about 750. Spec is (700-800) All of this is per the factory service manual. So you are saying that I need to rev the engine to 3 grand and check the timing there? The engine is running so much better except for the heat. I don't recall seeing any mention about checking the timing while running the engine to 3 grand.

Checking at idle doesn't tell you a thing about the condition or operation of the centrifugal advance.

The FSM provides timing data at idle and at 1500 & 3000rpm. This is for good reason. Use the data for a "standard" M117 for best performance.

Good luck with your problem.

rickjordan · #18 07-01-2012, 08:18 PM

Good point. In the manual they did list "Standard" "California" and "Federal". We went with the Federal one. Though I still don't remember seeing a spec for 3K rpm. I certainly could be wrong and I will look at that.

Again keep in mind this is the first car in a very very long time that I have had to adjust timing. Looking at the crank and the timing degree marks, I assume "advance" is to the right of 0. We could see 10, 20, 30, with 5 actually having a distinct mark. So if I get this up to 3K and adjust the timing to 30, once we let off the gas, it should return to 5......?

When we started out, the timing mark was at about 10. We turned the distributor clockwise, it went to 5. Again this was at idle. I will follow your advice and check it again at the other 2 rpms. I am to do this with the vaccuum line on the vaccuum advance, correct?

rickjordan · #19 07-01-2012, 08:48 PM

Is the spec chart you are referring to called "Firing Point"? In the first column titled "Adjusting value of firing point" with out vacuum at 3000 rpm... 30. The next column is titled Test values ignition adjustments with/without vacuum at idle, 1500, and 3000.

Per this chart, the idle timing is 2 deg TDC with vacuum. At 1500, the timing is 15-19 degs without vacuum and at 3K, it's 30.

They mention to remove "both vacuum lines for adjustment". Other than the one that goes to the vacuum advance, where it the other one they are talking about?

Graham · #20 07-01-2012, 10:44 PM

Quote:

Originally Posted by rickjordan

Is the spec chart you are referring to called "Firing Point"? In the first column titled "Adjusting value of firing point" with out vacuum at 3000 rpm... 30. The next column is titled Test values ignition adjustments with/without vacuum at idle, 1500, and 3000.

Per this chart, the idle timing is 2 deg TDC with vacuum. At 1500, the timing is 15-19 degs without vacuum and at 3K, it's 30.

They mention to remove "both vacuum lines for adjustment". Other than the one that goes to the vacuum advance, where it the other one they are talking about?

The first column is Adjustment value at firing point. It is hard to read their minds, but for the "standard" engine they say to adjust at 3000rpm without vacuum. For the NA the adjustment value is at idle. My guess is that in NA because of emission laws, they want to be sure of the idle setting. In Europe & ROW, they are more interested in performance. This is just my guess as to why there is a difference.

It is hard to SET timing at 3000rpm. I usually set it at TDC at about 700rpm (with vac). Then speed engine up to 3000rpm (without vac) and see how far it advances. Keep making small adjustments until you get about 27-30deg at 3000rpm.

The advance marks are to your right when looking down at the engine. It is easiest to get under car and mark the 0, 20 and 30 deg lines with chalk or paint.

Regarding vacuum, if you have just one vac line on the vacuum diaphragm, then you should block it for the 3000rpm test and have it in place for the idle test. Some cars have advance and retard - Not sure how to handle those!

BTW, while setting timing, A/C must be turned off because it turns vac retard off.

Tomguy · #21 07-02-2012, 11:06 AM

The best idle timing should be on a plate on your rad support & say how to do the measurement. Graham brings up a great point to make 100% sure to do this with the AC off!!

As far as advance, yes it will take away from the timing you set previously. The adjustment on the emissions tag assumes that the mechanical advance works right. To test this, pull the distributor cap. You should be able to turn the rotor to the right (clockwise) a bit, and when you let it go it should return back to where it was. If you can't turn the rotor at all the mechanical advance is stuck and this will easily lead to overheating on highways, lack of power, lack of fuel economy etc.

Another thing that can cause high temps is valve clearances. I am pretty sure the '74 has mechanical ball studs so make sure to adjust the valves (on a "Cold" as in 70°F engine, give or take 20°). Do a search on the forums for valve specs because I forget them

WANT '71 280SEL · #22 04-16-2013, 05:19 PM

What should the dwell be set to on our 117's? I'm about to put mine on a timing light at a friend's since I had the distributor out and the points replaced. I'll keep on searching...

Thanks!

David

meltedpanda · #23 04-16-2013, 09:49 PM

Your point gap is measured in degrees of dwell...factory setting is 30-34 degrees. If you set the gap at .012-.014 inch you should be in the ballpark, but, if you can, check it with the meter and re-adjust as necessary. Shoot for the low end, i.e. 30 degrees so the dwell will stay within spec as the points wear

WANT '71 280SEL · #24 04-18-2013, 10:16 PM

Thanks Ron. I also found the same information posted by Graham. I think I set mine to 0.06, which probably explains why it isn't running great!

Thanks again,

David

meltedpanda · #25 04-18-2013, 10:49 PM

hope you get it sorted out
Graham is the expert on these ol gals!