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1974 450SL (US), 2005 SLK200 (UK)
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Discussion Starter #1
My car idles at about 600-650 RPM. I checked the initial timing warmed up and it was 17 BTDC.

I adjusted the distributor and set it to 3 ATDC (as far as it would turn) and the car seemed to have a bit more vibration and I could hear a metallic noise (could be a heat shield rattling - don't know) so I adjusted it to 3 BTDC and it seemed happier there.

At this point I had a small amount of smoke near cyl #4 and some smoke coming out of the right-hand valve cover breather port. I guess either the gasket was not seated quite right or some oil was split when I recently took the cover off.

I then performed some tests. At 1500 RPM with vac I got 12 BTDC (spec is 11-15). At 3000 RPM with vac I got 18 BTDC (spec is 18-22). I couldn't get a proper reading at 4,500 RPM because my wife became a bit scared and couldn't hold it steady. Engine sounds great at 4,500 RPM.

At 4500 RPM the car produces tons of blue smoke out of the exhaust. If I let it drop back to idle then the smoke goes away within a minute or two. This seems repeatable.

I turned the car off and left it for a few minutes then turned it back on again. It Idled nicely at 650 RPM or thereabouts and this time no smoke from the engine bay or breather port. However taking it back up to 4,500 RPM the smoke from the exhaust reappears.

There is no smoke on startup.

I did a search on here but it seems smoke with high RPM is not that common?

Any ideas what I should test next?

Thanks, Andy
 

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Discussion Starter #2
I see that D-jets don't have a PCV valve but they do have something similar. I'm wondering if this could be a cause - high vacuum doesn't cause it to open so pressure builds forcing oil into the cylinders?


Andy
 

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1973 450 SL
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If you pull the plastic/rubber tube from the driver's side valve cover to the idle control body (where the aux air valve and idle screw are), you will find two things. On the valve cover port, you should have a wire helix spark arrestor that should be removed and cleaned periodically. On the other end of that tube on the idle control body, you will see a PCV looking device - same thing, pull it and clean it out.

There is another spark arrestor at the rear end of the passenger side valve cover where the tube from the air cleaner connects.

See attached article 07.6.1-690 from the service manual
 

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1974 450SL (US), 2005 SLK200 (UK)
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Discussion Starter #4 (Edited)
I cleaned out the parts with three passes through my ultrasonic cleaner using heating and Simple Green. Pic below. Sadly I still get blue smoke at 4,500 RPM. Anywhere else that I can check? Is there a way of testing the "PCV valve"? It rattles when I shake it and I can easily press the plate and see the pin coming out of the other end - spring seems to be working smoothly.

I removed the breather hose from the left-side valve cover and I still get smoke.

Looking in the baffle in the left-side valve cover I can see oil residue down in there but I don't know if it is clogged or not - any hints on how to check?

Thanks, Andy

2619229
 

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Discussion Starter #6
Hi Brad, no it doesn't. It's a Federal model.

Andy
 

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Discussion Starter #7
I removed the breather hose and put my fingers over the port while revving the engine. The most I could feel was a very very slight breeze from it. Is that normal?

I haven't checked the valve clearances yet - if they are wrong could that cause this symptom?

Thanks, Andy
 

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If your hand was over the valve cover port, you wouldn't feel much. I think the blow-by gasses are pulled from the driver's side valve cover by the idle control which really means it is being pulled by the throttle body. Blow-by gasses are pulled from the aft port of the passenger side valve cover by the air cleaner which again means it is being pulled by the throttle body. See the black arrows in the diagram of 07.6.1-690 attached to post #3.

Unique to the passenger side port, it also appears that fresh air is pulled into the valve cover - might feel a pulsating pull with your hand on that port. See the small white arrows at that port in same diagram.
 

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Discussion Starter #9
Here is what I thought was going on - at low speeds/idle the vacuum is high and the PCV valve is closed, so nothing exits the breather port on the driver's side valve cover. When RPMs are high or at WOT then the pressure in the crankcase increases and this pushes open the PCV valve allows the blow-by gasses to escape the crankcase via the driver's side valve cover. Do I have that right or am I misunderstanding?

I figured that if the pressure in the crankcase was high enough to force oil around seals then I should be able to feel something escaping the valve cover?

If the blow-by gasses are pulled by the idle control is that something else that could be causing this problem? Note that I don't have an idle problem - drops to around 600-700 RPM.

Thanks, Andy
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I can't help much here, but I would do a vacuum test and do or get a compression test done. Just as a starting point.

I recall Fonzi having a car that blew a lot of blue smoke. At the time, we discussed valve guides.

Re timing. With distributor turned almost completely CCW, you should be at about 5-8 deg BTDC. I could be wrong, but don't think you could get 17degBTDC unless distributor was a tooth off. (I think we discussed this before). Then when you increase rpm, it should go to about 27BTDC if centrifugal advance is working properly (also for best performance).

Another good check, is to hook up a vacuum gauge to the line from valve cover to MPS or the small vacuum line at rear of passenger valve cover. Then check vacuum at idle, Rotate distributor to provide max vacuum. You should get about 16+" Hg. Back off just a touch and that is usually about the right timing. Warm engine up first.

The vacuum gauge can tell you more. I used to have better links. This one covers some of the info : Vacuum Test - A Vacuum Test Can Tell You More Than You Think
There are many more such guides on-line. Here is one more:
 

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Discussion Starter #11
Re timing. With distributor turned almost completely CCW, you should be at about 5-8 deg BTDC. I could be wrong, but don't think you could get 17degBTDC unless distributor was a tooth off. (I think we discussed this before). Then when you increase rpm, it should go to about 27BTDC if centrifugal advance is working properly (also for best performance).
This is confusing. In order for me to be able to line up the scribe mark on the distributor body with the rotor when the balancer shows TDC I have to install the distributor at a certain point. Then I need to turn the distributor almost as far as it will go clockwise to get to TDC. If I turn it fully clockwise I can get to 3 ATDC. So most of the adjustment range of the distributor is BTDC. 17 BTDC wasn't anywhere near fully counter-clockwise.

That doesn't seem to match up at all with what you are describing?

If I insert the distributor a tooth off then the rotor won't line up with the scribe mark at TDC - right?

Andy
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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This is confusing. In order for me to be able to line up the scribe mark on the distributor body with the rotor when the balancer shows TDC I have to install the distributor at a certain point. Then I need to turn the distributor almost as far as it will go clockwise to get to TDC. If I turn it fully clockwise I can get to 3 ATDC. So most of the adjustment range of the distributor is BTDC. 17 BTDC wasn't anywhere near fully counter-clockwise.

That doesn't seem to match up at all with what you are describing?

If I insert the distributor a tooth off then the rotor won't line up with the scribe mark at TDC - right?

Andy
On my engine, if memory serves me, i locate the rotor at the mark before inserting. Then insert with distributor held ccw from where you expect it to end up. Then one seated rotate body until rotor points to scribe. On my car, that is almost fully ccw. I recall cush saying his was different, but others posted that theirs were similar to mine.
Those numbers 3atdc and 17btdc - were those measured with timing light. Something doesn't seem right to me, but I have to run. God luck.
 

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Discussion Starter #13
Hi Graham,

I made a video showing me going through your steps.
  1. First I set the engine to TDC on the balancer (not shown).
  2. I remove the distributor and adjust the rotor so it is lined up with the scribe mark.
  3. I then try to insert the distributor rotated as far counter-clockwise as possible, however this is limited because the vacuum element hits the valve cover.
  4. Once inserted I rotate the distributor to line the mark up with the rotor.
Now looking at the screw slot the distributor is rotated as far clockwise as possible. This is different to your car where it is almost fully counter-clockwise.

In this position, using a timing light, I get 3 degrees ATDC. Therefore all of my adjustment range is BTDC.


What is the difference?

Thanks, Andy
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Our cars are of course different,, so bear with me.

If you adjust with timing light so you are at TDC or even 5deg BTDC at idle without vacuum, then presumably distributor will be partly ccw from where it was initially. The scribe mark is just a starting position before timing with light.

If you ignore my step two, you could likely rotate shaft a bit and try and insert one tooth back so that slot has better adjustment range. I recall having to do this when distributor didn't end up where I wanted it.
 

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Discussion Starter #15
Since installing the Pertronix every time I remove and reinstall the cap (and I am careful to make sure it is seated properly) I get lots of scary noises and no running engine - it always takes me two attempts to put the cap on before it is happy. I'll give your idea about the rotor a try when I get the courage to deal with the cap again!

I hooked up my Mityvac to the manifold vac port. Timing is 5 ATDC at 750 RPM with vacuum (matching spec plate on radiator cross member).

At warmed up idle it holds rock steady at 12 "Hg. I understand 1 "Hg needs to be added to compensate for every 1000ft above sea level, so the sea level reading would be 14 "Hg?

Increase RPMs to 1,500 - vacuum rapidly drops to 5 "Hg and then slowly climbs to 11 "Hg. No twitching - all very smooth.

Going back to idle the vacuum jumps to 17/18 "Hg and then slowly lowers to 12 "Hg. Again all very smooth.

From my basic understands this consistently slightly low reading indicates retarded ignition timing or a small intake leak.

I then gave your suggestion a try - I slowly rotated the distributor counter-clockwise. The vacuum increased to 15.5 "Hg (17.5 "Hg at sea level?) then the engine started struggling so I rotated it clockwise until the reading was 14.8 "Hg. Idle revs were increased of course - engine sounded smooth, not struggling.

I then used my timing light to check the timing - 16 BTDC. This seems very early.

I set it back to 5 ATDC.

Questions:

1. What does it mean that higher vacuum requires such early timing? Should I use that setting?

2. It seems that the vacuum at the timing spec is lower than it should be - but is it enough to bother worrying about?

3. Back to the high RPMs and tons of smoke. My limited understanding of the vacuum results is no valve seal, guide or piston ring problems. That would point back to high RPMs = pressure building up that forces oil into the chambers?

Thanks, Andy
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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The 5deg ATDC spec is for emission reasons. I was advised early on to set timing further advanced.for better performance. You might try setting initial timing at idle to something like 10-14degBTDC with vacuum disconnected.

That 18deg BTDC number seems odd. If you set as above, you should go back to about TDC to 5degATDC at idle. Is it possible that vacuum is not reaching the distributor or that the vacuum element is not working (you can test it with mityvac with cap off and see if connector moves,

By the way, A/C must be switched OFF when setting timing (even if is not functional) (A/C ON and coolant over 100C switch disable vacuum to distributor)

Don't like that noise from distributor. Do the contacts in the cap look like the rotor has been hitting them? Is rotor fully seated?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Since installing the Pertronix every time I remove and reinstall the cap (and I am careful to make sure it is seated properly) I get lots of scary noises and no running engine - it always takes me two attempts to put the cap on before it is happy. I'll give your idea about the rotor a try when I get the courage to deal with the cap again!
In this link, an Aussie mechanic suggests turning rotor about 1" back from mark while aiming for center of adjustment slot. Sounds about right, but as he says, a bit of trial and error required.

 

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Discussion Starter #18
That 18deg BTDC number seems odd. If you set as above, you should go back to about TDC to 5degATDC at idle. Is it possible that vacuum is not reaching the distributor or that the vacuum element is not working (you can test it with mityvac with cap off and see if connector moves,
Uh oh.. I tried this and the arm from the vacuum pod does not move. The vacuum slowly drops as well.

Looking at the EPC it seems the vac pod is not a separate part? Is it possible to service this? Didn't see anything in EGv107.

Andy
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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The vacuum pod is a separate part on my car. It is a different one though. I went to my epc and it seems to have stopped working :( But on nemigaparts it does show 3 numbers for part 20. Need epc to confirm which one is used on 74.
 

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Discussion Starter #20
Thanks! I see it now - yup - I require the expensive version of course. :rolleyes:

Andy
 
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