'71 300SEL cam timing marks are a smidge off....

[Treozen]

Hello all - Our patient today is a 1972 (not an 1971) 300SEL 4.5, U.S spec car.



Here she is:



Usually I'm monkeying around with American "hot rods" but I got it into my head to buy a '71 300SEL and even though it really doesn't fit the mold (Quiet, four doors, no fins) there's something about this car that defies logic, and I find myself pulling it out for a drive, instead of aforementioned "hot rods" but my 300SEL needs a little help and so I come to you for some assistance. The car seems to run "ok" but has a miss and runs rich...and by rich I mean the richest running car ever - I have enough black soot on the shop floor to draw in...not even kidding. I could write "please fix me" in the black dust. It seemed to be doing ok, but then it started to stumble and the idle was terrible - bad enough that I very much doubt it was firing properly on all cylinders.


I decided to give it a tune up, and I figured it was good sense to check and change the timing chain. Upon inspection however, the chain seemed in very good shape - tight, clean, no wear marks on the guides or tensioner, and it had been replaced at least once with a currently available chain (brand stamped into the chain matched my new one) I almost left it alone, but I noted that with the balancer indicator at Zero (0) and the passenger-side cam timing mark aligned, the driver's side looked like this...



Now, not being accustomed to Mercedes, I didn't know if that was 1 tooth off, a stretched chain, or 14 teeth off. So I decided to just try adjust it, given that the chain really did look good...perhaps someone just installed it wrong and jumped a tooth. I took the sprocket off, adjusted the cam (that was fun) put the chain back on the sprocket and then put the sprocket back on the cam (even more fun). everything lined up perfectly. Then I spun the engine around a few times by hand, and ......everything had gone right back to where we started....see picture above. SO...I said, perhaps the chain is stretched after all. I had my wife help with changing the chain - all went well and we got everything back together. I again turned the engine over by hand, and for all our hard work we achieved......(see picture below)



YEP....we achieved absolutely nothing. Its exactly the same, and remember I already reset the cam, so technically everything should have been right on the money.

So here is my question..... does this actually matter? Aside from being less than factory prefect, is this going to be an issue? I'm looking to have the car run well, but I'm not looking for every ounce of perfection...it is almost 50 years old. For the sake of completeness, here is a picture of the passenger side at the same moment - note the alignment. ...Also note that someone appears to have scribed their own timing mark?...wasn't me. I know ideally both cam timing marks should align, but its not that far out - perhaps half the width of the timing mark - not sure what that means in degrees.




Valves need adjusting, and I have tools coming for that. I'm also going to replace all the injectors and the fuel pressure regulator - fuel pump and filter already replaced.



Thanks,

[cth350]

I wrote a longer reply before and just lost it. It started with "lovely car!" and bravo to the wife for sharing the adventure in maintenance and upkeep. The car, when sorted out will be a dream to drive.

To your specific question, M116/M117 timing marks do that. To get the timing spot on, there are "offset woodruff keys" that can shift where the cam lobs sit relative to the gears. What matters is when the valves open & close. There's a spec for that, not everybody works that hard to set it precisely.

Regarding running rich, of larger concern is the way the djet (d-jetronic) system reacts to vacuum leaks; which is to say "very poorly". Find and fix as many as you can. The big sucks, pardon the pun will be the hose leading to the manifold pressure sensor on the firewall, the line that leads to a check-valve or two for the body's various vacuum devices, the two pieces of rubber on each injector and the 8 little rings that connect the two halves of the manifold together. That last one requires actual work to cure, so it tends to be ignored. You could retorque the bolts that hold the two halves together as a start for that. The hoses in the idle circuit can also contribute to a vacuum leak.

The fuel pump, fuel pressure regulator and fuel damper work as a system to keep the pressure at 32psi. Adjust the regulator if you need to and ensure that you've got that to spec and that it hold pressure for several minutes before there's a drop. If there's a drop when the pump is turned off, find that and cure it. If that doesn't happen, you don't need to replace the regulator. I plumb a fuel pressure gauge with a tee at the cold start valve.

In the idle circuit, there's a big screw to adjust along with a little screw on the brain box (that's all in the book), have a CO % meter in the tailpipe to try and get it dialed in. Make sure the distributor ignition timing is to spec first.

Regarding individual injectors, there's a direct relationship from the trigger points closing to the injector firing, plus variability provided by the brain box regarding how long the injector stays open. You can use a stethoscope to listen for each injector firing. To improve the quality of the circuit, you can clean the trigger points in the lower half of the distributor. Frank Mallory said just use a dollar bill rather than sanding the points. Also, under the battery tray is where all the ground lines from the EFI wiring harness end up, loose and retighten them to improve the ground quality.

All of that can be found in other threads here, spend some time searching for them.

-CTH

[Tony H]

It would be a good idea to change the timing chain guides-they are more critical. If a guide breaks it may bend valves. There are 2 often overlooked guides near the crankshaft inside the front cover also. Also the timing gears wear and change valve timing. They should always be replaced when changing the timing chain (the crankshaft gear also-it's just as critical) If you have no service history even more so.

[Treozen]

Originally Posted by cth350

I wrote a longer reply before and just lost it. It started with "lovely car!" and bravo to the wife for sharing the adventure in maintenance and upkeep. The car, when sorted out will be a dream to drive.

I hate it when i write a post and then...zap....I lose it. Most often by hitting backspace and instead of deleting a letter, the webpage cycles back the prior page....most irritating.

Originally Posted by cth350

To your specific question, M116/M117 timing marks do that. To get the timing spot on, there are "offset woodruff keys" that can shift where the cam lobs sit relative to the gears. What matters is when the valves open & close. There's a spec for that, not everybody works that hard to set it precisely.

Ok, well that's good to know. The car does run better now, but I suspect the new plugs have only bought me a temporary reprieve until they foul out again.

Originally Posted by cth350

Regarding running rich, of larger concern is the way the djet (d-jetronic) system reacts to vacuum leaks; which is to say "very poorly". Find and fix as many as you can. The big sucks, pardon the pun will be the hose leading to the manifold pressure sensor on the firewall, the line that leads to a check-valve or two for the body's various vacuum devices, the two pieces of rubber on each injector and the 8 little rings that connect the two halves of the manifold together. That last one requires actual work to cure, so it tends to be ignored. You could retorque the bolts that hold the two halves together as a start for that. The hoses in the idle circuit can also contribute to a vacuum leak.

Great - thanks. I'll check all those out.

Originally Posted by cth350

Regarding individual injectors, there's a direct relationship from the trigger points closing to the injector firing, plus variability provided by the brain box regarding how long the injector stays open. You can use a stethoscope to listen for each injector firing. To improve the quality of the circuit, you can clean the trigger points in the lower half of the distributor. Frank Mallory said just use a dollar bill rather than sanding the points. Also, under the battery tray is where all the ground lines from the EFI wiring harness end up, loose and retighten them to improve the ground quality.

I've also found a way to measure and adjust the trigger points, so I have the distributor in my hand here, and will see where the trigger points are as well - they look "ok", but I'll try get exact degrees and see if they are in spec or not.

[Treozen]

Originally Posted by Tony H

It would be a good idea to change the timing chain guides-they are more critical. If a guide breaks it may bend valves.

So I have a new set of guides, but the chain I took out seemed every bit as new and tight as the chain I put in, and the guides look equally perfect - not a mark on them. The "old" chain was the same brand name as the new chain I had, and had a master link - so a recent change, and I believe the guides were changed at the same time.



I have reason to believe the car was fairly well maintained up to a point, but it sat for around a year or two years not being used at all, and probably longer than that as a infrequent driver. Seems to me that maintenance was performed but some parts were just worn and not replaced - injectors for example look very old, if not original, and all the electrical connectors are shot (plastic parts mostly broken). So I'm going to replace them all, new rubber parts, injectors and new electrical connectors.

[cth350]

The PO either got old or got tired of replacing parts without seeing progress. That is how I got a 600. One 4 digit bill too many for the guy. The car now sits waiting for me to pay a 5 digit repair bill, so at least it's not costing me money to maintain it.

Replacement injectors are pricey. I'd be wary of replacing just because they look shabby. The wire harness, that's different. It will be brittle and frayed. Addressing that never hurts (well, except the wallet).

Once it runs nicely the next step is rides nicely. A 300sel has a rather unique air suspension system that should give you endless hours of comfort and joy. Not to mention more work, once something needs repair. When it works, even moderately well, it is in a class of its own.

-CTH

[Treozen]

Originally Posted by cth350

The PO either got old or got tired of replacing parts without seeing progress. That is how I got a 600. One 4 digit bill too many for the guy. The car now sits waiting for me to pay a 5 digit repair bill, so at least it's not costing me money to maintain it.

Replacement injectors are pricey. I'd be wary of replacing just because they look shabby. The wire harness, that's different. It will be brittle and frayed. Addressing that never hurts (well, except the wallet).

Once it runs nicely the next step is rides nicely. A 300sel has a rather unique air suspension system that should give you endless hours of comfort and joy. Not to mention more work, once something needs repair. When it works, even moderately well, it is in a class of its own.

-CTH

Injectors etc, already ordered, so - in they go.



I made a modification today that has not gone well. I made a degree wheel for the the distributor and found my trigger points were in a range of 150 - 158 degrees. I was able to adjust that range down to 113 - 116, and I read that 110 is the goal....car HATED it. Ran horribly, had to get the idle up just to keep it from stalling and sounded like it was running on 6 cylinders. I am 98% sure my degree calculations were correct - its not really that hard, so I was surprised at the result. ****UPDATE - I fixed this. I doubled checked timing (bang on) and removed the distributor again to see how I messed up the trigger points. Somehow, one set of points (out of the four) was closing for only 60 degrees, and was not opening at the same point every time. I have absolutely no idea how it got this way, but I adjusted them back to around 116, double checked the rest (range of 115 - 122 degrees) and the car ran better than ever - I'd say 85% of optimal. ****

I suspect however that since the only change has been to the trigger points and its gone from running at about 80% of "normal" to 40% of "normal" that I messed something up and will need to readjust (**Update - yes, I did***). I'm not even sure trigger points have a significant impact on rich versus lean. I've ordered a wide-band 02 sensor and related AFR handheld - been meaning to get one for a while anyway, so we'll see.



I also found I may have been using the wrong timing mark on the harmonic balancer.... In the picture, I was using the line nearest the pointer, which I took to be Zero TDC (since it has a Zero next to it) I didn't realize that was the Zero part of 10, and only after cleaning did I realize there is actually another Zero and line to the right - and that's what I need to be using for timing.







Curiously, everything seemed to line up (cam marks, etc) even when I was using the wrong timing mark....sigh...more investigating tomorrow, too dark now to continue, but I am sure that is not helping.



Always good to come away from a days work with more questions than answers.

As to the air suspension - on most days, and if I've driven it some, the car will maintain its ride height for about two weeks, after which its noticeably low in the front. Other times though I can see a reduction in the front after only 72 hours, its somewhat variable. When I first got the car I measured the drop at about 1/4 - 3/16 inch per day, but that seemed to improve with use.

[Benz Dr.]

I set ignition timing to around 10 degrees BTDC which is higher than the factory setting. Anything less than 8 degrees and they won't make good power.

[Tomguy]

D-Jet is EFI but it's open-loop so while better than a carb, it's not smart enough to know what you did leaned it out, and compensate accordingly.

I can't speak to the actual angle the D-Jet trigger points should be, but I can measure a set I have in my basement on a distributor (I think from a 4.5, could be a 3.5, but they'd be the same angle either way). I think 150 sounds familiar, though.

[Treozen]

Originally Posted by Benz Dr.

I set ignition timing to around 10 degrees BTDC which is higher than the factory setting. Anything less than 8 degrees and they won't make good power.

I set it at 7 degrees BTC, that's what I've read most often if you also have removed the vacuum retard - which I have, because my vacuum can on the distributor leaked and so a) wasn't working at 100% and b) was really just a vacuum leak and c) I wasn't able to find a good one....so...off with its head!



I'll check it on the road once I do valve adjustments and new injectors.

[Treozen]

Originally Posted by Tomguy

I can't speak to the actual angle the D-Jet trigger points should be, but I can measure a set I have in my basement on a distributor (I think from a 4.5, could be a 3.5, but they'd be the same angle either way). I think 150 sounds familiar, though.

Most often I've read 110 degrees as the target for trigger points, multiple sources, so I used that as a basis. Once I rechecked and fixed my one point that was only closing for 60 degrees, and somewhat randomly at that, the car seems to run very well - my Trigger points are now in a range of 115 - 122 degrees, as opposed to the 150 - 155 where they started. I have a few tips to share as well for any future adjusters out there, to perhaps avoid my initial mistake:


1) Always fully install the trigger points, with both attachment screws, before every test, just like you would if you were installing back into the car. I found even the difference between hand-tight, and "installation" tight on the two screws was enough to change the reported degrees...so yes its annoying, but 100% necessary.



2) Understand that a change to one set of points may cause a small change on another set. I found several instances where I'd see even up to a 5 degree shift after making a change on an entirely different point set. Each of the four points are connected, so it makes sense. I didn't always note a change, but sometimes.



3) Double check all points after you set (and are satisfied with) the adjustment on any single point. This way you can identify any relationships between changes made to one point, and another.



4) Test by rotating the rotor in the proper direction of travel - i.e. the direction the distributor rotates when installed (clockwise). I am not 100% sure if this actually matters, but my results seemed more consistent. You can turn the rotor back and forth of course, but test from the close point clockwise, not the reopen point anticlockwise (backwards)



5) Once you have your points set, do a final test of all four, and do not remove the points again. If you do, retest. The reason here is that after near 50 years, the engagement and position of the trigger point "drawer" with the the screws tightened, isn't as precise as it used to be. Mine has a little slop frankly - 1/16 that way, or 1/16 this way is possible, and every bit changes the engagement of the points and the distributor shaft. So install the way you want them, ready to back into the car, then do a final check...and leave them alone if the numbers are right. If you plan to add grease or whatever, do all that first.



6) Sometimes, you'll adjust the points and get no reading at all. This means you've adjusted (bent) the contact to the point where there is insufficient contact left with the points to connect. ...Basically, you've gone too far. You may find you can't get to the magic 110 degrees (I couldn't) so don't shoot for perfection, but rather an improvement that is relatively consistent.



7) Finally, when making the adjustments, its often an exercise in tiny tweaks, that you are not even sure made any difference. Often times I honestly couldn't see a difference, I just did a firm "tweak" that essentially looked the exact same, BUT....even the smallest change can make a big difference in degrees. Use your test to see where you are, not your eyes.



FYI - My highly technical degree wheel was made from the plastic lid of a peanut can. My distributor holder was....the rest of the peanut can. My pointer was a safety pin....not exactly rocket science.







Good Luck.

[cth350]

nuts to you?

Good job. -CTH

[Benz Dr.]

Originally Posted by Treozen

I set it at 7 degrees BTC, that's what I've read most often if you also have removed the vacuum retard - which I have, because my vacuum can on the distributor leaked and so a) wasn't working at 100% and b) was really just a vacuum leak and c) I wasn't able to find a good one....so...off with its head!



I'll check it on the road once I do valve adjustments and new injectors.

Without vacuum, you would probably loose at least 10 degrees of timing on the top end. Given that prospect, you should definitely bump up your ignition timing. These engines are more than thirsty enough; don't make it worse with late ignition timing.

[Tomguy]

Not sure how losing the vacuum retard (and having it set at 7 before versus the stock 5 after) would cause you to lose anything on the top end?

You can always make sure the mechanical advance is kicking in by verifying you're around 30-35 before top at 3000+ RPMs.

[Graham]

Do you have the M117 shop manual? It is available on-line at MBUSA Startek under the 107 chassis. Also here M117 4.5L

Some of the numbers in this thread seem a bit inaccurate for a 72 4.5L M117 (i have one!) Check the manual (timing in section 07.5)

A 'few' points:

- Timing marks are closer than I could ever get. Don't worry about them!

- The 72/73 have metal backed chain guides. Unlike later cars with plastic guides, these do not break and being unobtainable are better left in place.

- Fuel pressre spec is 2bar +0.1 or 29-30 psi. I run my car at 32-34, but have adjusted the MPS using an AFR gauge to compensate for the higher pressure.

- The knob on the ECU adjusts idle mixture only. Mixture under load conditions is adjusted on the manifold pressure sensor (MPS). Only do that if you have a good exhaust analyzer that can measure %CO or AFR. Specs are available. (I installed a full time AEM wide band AFR with dash display)

- Getting the trigger points back to under 120deg was a good move. To do that, a tool/gauge is usually needed. We call it Norbert's tool. It ensures all points are adjusted equally. I acquired a brand new set of triggers and measured them. They were just over 100deg, I believe. The exact angle is not so important, but lower is better. I would say 100-130 range should be OK.

- Trigger points fire injectors in pairs and tell ECU when to inject. The MPS measures manifold vacuum and in part determines how much to inject. However, the other main input to ECU, is engine rpm. This also comes from the trigger points. When closing angle is too high, points may bounce, it seems and the EU may think the rpm is higher and therefore inject more fuel?

- Re vacuum - you can set timing quite accurately using a vacuum gauge either off tee in MPS hose or off a connection at the back of the engine that goes to locking system. I found that I could rotate distr until I got to max vacuum - about 16-17 "Hg, then back off a little. Then check timing. With vacuum retard line connected, about 5deg BTDC at 700rpm seems to work best. Then check at 3000rpm. The centrifugal advance should get you to about 27degBTDC. If not, the centrifugal advance is sticking.

- A bad TS2 (coolant temperature sensor) can contribute to rich mixtures. This is an important input to the ECU. Check all sensors vs specs in Section 07.4 of FSM.

- One vacuum leak that is not obvious, is right through the AAV. AAVs are prone to sticking. It should be removed, taken apart and cleaned if you suspect it is sticking. It should be totally closed at 150F, otherwise you have a vacuum leak!

- New Bosch injectors hard to find. I see some by Standard Motor Products. Still 8x$56!. The originals in my car are 48 yrs old and all I did was clean and flow test them.

- One of best upgrades I made, was rebuilding my injection harness. cushjbc on Benzworld R/C107 forum is the expert and helped me with parts/advice.

- Many of us have installed a Pertronix 1885 to replace points. Eliminates one wear component. For under $100, a good upgrade. Info here and on BW