Engine timing and other adjustment trouble

[Tom Colitt]

Here is the latest update on my attempt to sort out all the engine trouble on my US spec 1970 280SL:

After I had been suspecting my "correct" ...062 distributor for some time now, I installed a ...061 unit, which looked virtually identical to my eye. I removed the advance/retard plate, cleaned everything thoroughly, checked the operation of the fly weights, lubed it all lightly with WD-40, wiped it clean, set the points and checked that the vacuum box turned the plate towards retard when vacuum is applied. I set the timing and noticed that at the correct 8 deg. ATDC with vacuum, without vacuum the timing went to 21 deg. BTDC . This tells me that the vacuum box on this particular used distributor (it also looks identical to the used one I had on the previous 062 unit) is advancing the timing by almost thirty degrees. The 062 vacuum box advanced timing by about 18-20 degrees between vacuum applied and not. Now, I'm guessing that any arbitrary used distributor could lie anywhere within that fairly broad range, which is why it seems like knowing the values for both the vacuum and centrifugal advance at any given rpm and load would be nice. Otherwise I can't see how one can expect the timing to be very accurate in most running conditions.

Practically speaking, when I drove the car with this "new" distributor for several test runs yesterday, I got pretty excessive pinging as I might expect with the higher vacuum advance rate than before. Well, today the engine ran quite well with very little pinging and without making any adjustments or changes whatsoever vs. yesterday. That is one of the big mysteries. Maybe something freed up that wasn't yesterday, but I really can't picture what is going on and how I can attain some reliability and continuity here?

While I was at it, I started getting curious about my missing wiring for the idle speed solenoid and found a fuse box with nothing connected and two red and green wires going to one side of it, on two different terminals. For the wiring diagram for the 280SE I've determined that these are probably the wires that connect to the solenoid. Unfortunately the 280SL wiring diagram has no constant idle speed solenoid. Can anyone with an "untampered" wiring harness (1969 to 71) please take any pictures of how this is wired to the solenoid and how (and where) the second terminal is wired to ground? I have enclosed pictures of my harness with the two red and green wires. While I was searching I found that the original harness had some vinyl electrical tape near the coolant overflow tank. When I removed it I found no damage to the harness as I had suspected, but oddly two short lengths of heat shrink tubing wrapped alongside the harness as seen in the pictures. There were no wires inside them or anywhere near, no holes in the factory heat shrink tubing, but it did almost look like the small pieces of tubing were there for a purpose, possibly even from the factory? Has anyone else ever seen this? I know this is getting very detailed, but I'm always interested in factory details like that (apparently I haven't paid that level of attention to the "minor" details of peripheral devices designed to make the engine run well     Here in Los Angeles you can go a long time with all sorts of cold start devices not working and never pay much attention.....

Finally, I also seem to have no fuel coming from the CSV. I checked it for voltage during cranking and it merely increased by less than 0.1V ? The cold start relay right next to the wiper relay does click when I crank the engine. What is the next thing to check?



I know those are all different issues, but I'm hoping that different individuals have experience with some of these issues and can help with what they know. I appreciate any definitive answers that you all might have (I know nothing's definitive, but more or less  

Thanks very much, Tom



Tom Colitt

[ja17]

***Tom mentioned he had been running on 87 octane fuel and his compression is 200psi!


Hello Tom,

These cars should never be run on regualr fuel. They are designed to use 100
octane. Since it is not available here in the USA, use 93 or 94 if at all posible! I am sure
this is a big part of your problem.

My wifes 280TE wagon doesn,t even like 91 octane keep away from 89.

Your compression is way too high, this will agrivate the problem even more.
You will never be able to set the timing to factory specs with compresson
like this.

Either your head has been over-milled or you have and extremely carboned-up
engine. Find a tank of as high as octane as possible set the timing by ear
so that the engine just barely does not ping and have fun. Your car should
run like a champ. However eventually you will  have to resolve the
compression problem or you will have to run on racing fuel in order to set
the timing to correct factory specs!

Now things are coming to light!


Joe Alexander
Blacklick, Ohio

[Tom Colitt]

Hi Joe

Thanks for all your help on this. It looks like I/we can stop chasing the pinging and the compression issues then and I'll just live with what I've got now (which is pretty good, actually, a real improvement over before) and then call it quits until I can rebuilt the head and or complete engine.

One more last thing that I really don't understand and it bothers me that I have no explanation for it: Obviously, my excessively high compression should not affect the fact that my timing will not advance to 25 to 30 BTDC at 3000 rpm with the vacuum connected. I've tested the timing many times now at 3000 rpm. The maximum advance I get is about 18 BTDC unless I rev it up very quickly (blip the throttle). If I hold it at 3000 rpm then the timing retards back to only about 10 deg. BTDC. (I'm guessing as I crack the throttle all vacuum initially collapses, then it gradually builds back up some at a steady 3000 rpm and retards the timing back to only 10 BTDC). Has anyone ever broken down how the centrifugal advance curves and the vacuum retard curve in the BBB (figure 00-0/7)? They don't seem to add up to 30 deg. BTDC at 3000 rpm with vacuum connected? These two curves counteract each other, right?

If I leave the vacuum completely disconnected I do get about 30 deg. BTDC at 3000 rpm.

I'm getting about 9 mls/ gal fuel mileage. Is it possible that the high compression alone could have such a huge negative impact on fuel economy?

Tom


Tom Colitt

[George Davis]

Tom,

according to the BBB, the 061 and 062 distributors have the same advance and retard curves.  The mechanical advance is 20 degrees +/- 3, and vacuum retard is 20 degrees +/- 3.

To set timing at factory spec (I assume 30 degrees advance at 3000 rpm), the vacuum retard should be disconnected.  This gives the correct maximum advance of 30 degrees.  With vacuum connected, I would expect less than 30 degrees, so 18 doesn't seem surprising.  As Joe noted, your maximum advance should be set so it just doesn't ping to compensate for the high compression.

With high compression and everything working reasonably well, your milage should be better than usual, not worse.  Your car, being a later US model, has an ignition system that behaves differently depending on operating temperature and rpms... provided that all of the switches and relays are working properly.  For normal, warmed up operation, you should get no vacuum to the distributor (i.e., no vacuum retard) over about 2400 rpm.  If things aren't working right, and vacuum is being applied to your distributor at all times, then you are probably running with retarded timing all the time, and power and milage will suffer.

JeffC is the guy who has this system figured out.

And on your CSV non-operation, I suggest checking the thermo-time switch.

George Davis
'69 280 SL Euro manual

[Tom Colitt]

George

Thanks for this excellent insight although I only can find where the BBB says that timing is 25 to 30 deg. BTDC "WITH" vacuum connected. (page 00-0/3.

Where are you getting without? It makes sense, but where does it say that?

Since all my US emissions and speed relays and two-way valve didn't seem to work as they should, I had connected the distributor straight to the manifold pressure. I know you are saying, "well, no wonder, as I am too, but please help me understand further by answering this question. Aren't the euro cars connected straight to the fitting at the butterfly valve as well and wouldn't that cuase their ignition to retard at higher rpms as well? But either way, you've brought me one step closer to unravelling and understanding this mess of the timing and US emissions control.

By the way the cold-start valve started working after I took Bob Smith's from down-under advice to check the contacts inside the cold start relay. Now it fires up quickly again, but it still will not "accept gas" for about a minute or more (rpm drops the second you open the butterfly valve) I.e. still too lean?

Thanks again, Tom

Tom Colitt

[tuultyme]

I have the 062 distributor in my 70 280SL.  With this distributor the timing is retarded at lower RPM due to vacuum supplied to the distributor.  As the speed reaches about 2200-2300 the speed relay shuts off this vacuum though the two way valve causing the timing to advance.  Originally I had no advance at the higher RPM. My speed relay was not working; would not shut off the vacumn above 2200 RPM. I sent my speed relay to be repaired by Beckmann Technologies and now it works fine; timing about 30 deg btdc at 3000 RPM. Others have replaced the speed relay with a modern unit; Check early posts on this subject.



Bruce; 268Blaugrun(green) 1970 280SL; IL

[George Davis]

Tom,

Yes, the Euro cars are connected to vacuum at all times, but the Euros of the same time period use the 051 distributor, which only has 10 degrees of vacuum retard, unlike the 061/062 which has 20 degrees.  So when vacuum is high enough to cause retardation, they are both going to retard, but your car much more so - with lost performance and fuel economy.

Your car's performance over 2200-2400 rpm will be "normal" if you disconnect the vacuum line, but you'll have too much advance under those rpms.  The real solution, like Bruce said, is to get the system working right.  Or, without a correctly functioning system to turn vacuum on and off when it should, an 051 distributor is probably the best bet.

Page 00-0/5 in my BBB (covering 1966-1973) has the advance curves.

George Davis
'69 280 SL Euro manual

[rwmastel]

quote:Originally posted by George Davis

....So when vacuum is high enough to cause retardation, ....

Oh, so that's my problem!  If I disconnect the vacuum line to my brain, I'll be smarter and think clearer.  I should have known!  

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Tom Colitt]

Thanks to all of you

I'm just going to try to find some working speed relays to get my system working again or look for an 051 distributor.

Meanwhile, the car is running like a champ, even with all the "retard" over 2400rpm (yes Rodd, some of that seems to have taken its toll on me too)  

Maybe my too high compression and the extra ignition retard are just about cancelling each other out, yet not helping with the gas milage....

Regards, Tom

Tom Colitt