Author Topic: Compression test on European M116.985 in 1977 350SE  (Read 444 times)

Berggreen

  • Newbie
  • Posts: 11
  • W116 Enthusiast
  • Location: Gentofte, Denmark
Compression test on European M116.985 in 1977 350SE
« on: 09 August 2020, 02:41 AM »
Hi All

I posted another topic around a week ago about sudden blue smoke from my 12/1977 350SE, which had been standing as well as started and stopped many times for quite a while during some body repairs. Also, I believe it has been standing as well for a long time, before I bought it in Germany and brought it up to Denmark in March this year.

The engine is the original in the car (checked the datacard) and it has done 327.000 km, and I don't believe it has been renovated - at least I have no documentation to show it has. In any case, it is smoking a lot less now and I cannot see any noticeable oil consumption on the oil pin, even though it does give a puff of blue smoke at de-accelleration on the highway exit and at warm starts, where it is also more difficult to start.

So, I decided to do a compression test to get a first impression of the condition of the engine.

The compression test was done with the following comments/details:

- the engine is a M116.985 - European version with 1st generation K-jettronic, before the upgrade in 1978.
- did it with cold engine, as I did not fancy getting burn marks from the exhaust manifold trying to dig out the spark plugs!
- fuel pump relay disconnected
- plug removed from ignition coil
- full throttle when cranking
- measurements taken after 5 strokes of the needle on the gauge
- did not do a wet compression test, as I did not see any low compression readings
- spark plugs have not done more than about 4-500 km max.

Results: (1-4 left side standing in front of the car with 1 closests - 5-8 right side with 5 closests)

Cylinder 1: 170 psi - spark plug white
Cylinder 2: 174 psi - spark plug white
Cylinder 3: 170 psi - spark plug white
Cylinder 4: 177 psi - spark plug white

Cylinder 5: 179 psi - spark plug wet with oil
Cylinder 6: 177 psi - spark plug white
Cylinder 7: 164 psi - spark plug white
Cylinder 8: 166 psi - spark plug white

I have attached two pictures, showing the typical white spark plug, which all look about the same, as well as nr. 5 which was wet with oil.

Nr. 5 is wet with oil, but compression is the highest of them all. So I am puzzled, and I would like to hear your opinions.

So what do you think is the verdict here?  ???

Thanks,

Christian  8)

revilla

  • Classic
  • **
  • Posts: 346
  • W116 Enthusiast
  • Location: Aix-en-Provence, France
Re: Compression test on European M116.985 in 1977 350SE
« Reply #1 on: 09 August 2020, 03:02 AM »
Hi Christian,

Your description of smoke when decelerating (long downhill then accelerating again) corresponds perfectly to valve seals. Either too hard or worn.

I had an engine that did that. To test this theory back then, I added a quarter of heavy/dense/high viscosity oil additive. The one you find at any auto store. Brands vary but Winns or STP would do.

If after adding the additive blue smoke disappears or diminishes significantly, you have in fact valve seals that need to be replaced.  The additive is not a permanent solution but rather a mean to test the valves theory. It treats the seals so they can seal better, but the condition will come back eventually.

Also, I have seen engines smoking like that when too much oil is added by accident. As with the valve seals theory the smoke is bluish and not black or white.

If you find in fact is the valves, you are in a best-case scenario, rather than for example a broken ring, etc.

Good luck.

Robert
Robert
W116 1977 280SEL & 1979 280SE

Berggreen

  • Newbie
  • Posts: 11
  • W116 Enthusiast
  • Location: Gentofte, Denmark
Re: Compression test on European M116.985 in 1977 350SE
« Reply #2 on: 09 August 2020, 03:17 AM »
Hi Christian,

Your description of smoke when decelerating (long downhill then accelerating again) corresponds perfectly to valve seals. Either too hard or worn.

I had an engine that did that. To test this theory back then, I added a quarter of heavy/dense/high viscosity oil additive. The one you find at any auto store. Brands vary but Winns or STP would do.

If after adding the additive blue smoke disappears or diminishes significantly, you have in fact valve seals that need to be replaced.  The additive is not a permanent solution but rather a mean to test the valves theory. It treats the seals so they can seal better, but the condition will come back eventually.

Also, I have seen engines smoking like that when too much oil is added by accident. As with the valve seals theory the smoke is bluish and not black or white.

If you find in fact is the valves, you are in a best-case scenario, rather than for example a broken ring, etc.

Good luck.

Robert

Thanks Robert, very good input and suggestion. Do you have a specific brand or type you can link to, so that I can the right stuff in my local auto-store?

About the broken ring theory: Wouldn't I see a combination of the oil-wet spark plug AND a low compression reading, if this was the case, especially when doing the compression testing with a cold engine?

Cheers,

Christian

revilla

  • Classic
  • **
  • Posts: 346
  • W116 Enthusiast
  • Location: Aix-en-Provence, France
Re: Compression test on European M116.985 in 1977 350SE
« Reply #3 on: 09 August 2020, 03:28 AM »
Yes Christian, you would see that in combination. But also, all valves seals might not be at the same level of deterioration/hardness. So your wet spark plug could be explained by just 1 bad seal.  But of course, if you end up replacing the seals (still available BTW) you want to replace them all at once.

As far as brands, I have used Wynns in the past with success. But other brands might do as well. Read the label before buying, because you want to test the seals theory, it should specifically say it reconditions rubber joints/seals.

Good luck.
« Last Edit: 09 August 2020, 03:33 AM by revilla »
Robert
W116 1977 280SEL & 1979 280SE

revilla

  • Classic
  • **
  • Posts: 346
  • W116 Enthusiast
  • Location: Aix-en-Provence, France
Robert
W116 1977 280SEL & 1979 280SE

UTn_boy

  • W116 Addict
  • ****
  • Posts: 1,305
  • Chrome Bundts & bundts with white walls are a sin!
  • Location: knoxville, tn
Re: Compression test on European M116.985 in 1977 350SE
« Reply #5 on: 09 August 2020, 12:27 PM »
Guys, don't forget that the valve stem guides are also very suspect here.  It's not always just the valve stem seals. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex

Berggreen

  • Newbie
  • Posts: 11
  • W116 Enthusiast
  • Location: Gentofte, Denmark
Re: Compression test on European M116.985 in 1977 350SE
« Reply #6 on: 09 August 2020, 12:29 PM »
https://www.misteroil.fr/fr-fr/shop/product/970/wynns-engine-oil-stop-leak-professonal-formula?gclid=EAIaIQobChMI1O3BlPON6wIVw7LVCh3ZBwNiEAQYBSABEgIK0_D_BwE

Thanks a lot!! :-)

New development this afternoon, where it was very hot (for Denmark), reaching 32C.

After a small drive at low speed and standing at idle with temp. reaching 90-95C on the meter, the oil pressure dropped down to 1.0 bar and even slightly below. Could also register a slight growling sound from the engine, when pushing on the gas in D at crawling speed. And during all this it was smoking blue smoke and smelling very badly!! :(

By thy the way, I am running a standard semi-synthetic 10W40 engine oil.

Are these bad signs for this engine, despite the high compression readings yesterday?

I am worried about pouring money into the engine to replace eg. valve stem seals or worse, if the engine is basically “a dead horse”!

Thanx,

Christian

rumb

  • W116 Addict
  • ****
  • Posts: 1,578
  • MB Enthusiast
  • Location: Fort Collins, Colorado
Re: Compression test on European M116.985 in 1977 350SE
« Reply #7 on: 09 August 2020, 02:47 PM »
Might be time to take the valve cover off and inspect. As Aarons points out it could also be a valve guide dropping. Inspect first and then perhaps remove one head.

As long as the oil pressure went back up with engine speed I would not worry about that yet.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

Berggreen

  • Newbie
  • Posts: 11
  • W116 Enthusiast
  • Location: Gentofte, Denmark
Re: Compression test on European M116.985 in 1977 350SE
« Reply #8 on: 09 August 2020, 03:14 PM »
Might be time to take the valve cover off and inspect. As Aarons points out it could also be a valve guide dropping. Inspect first and then perhaps remove one head.

As long as the oil pressure went back up with engine speed I would not worry about that yet.

Thanx for the advice. Unfortunately, I cannot do this myself and workshop charge a fortune to do any work on the engine. So just trying to get as much input from you guys, before I start spending money on that old high-mileage engine. :)

revilla

  • Classic
  • **
  • Posts: 346
  • W116 Enthusiast
  • Location: Aix-en-Provence, France
Re: Compression test on European M116.985 in 1977 350SE
« Reply #9 on: 09 August 2020, 11:08 PM »
Understandable Christian. If it was my engine I would invest 10€ in the oil additive to confirm whether it’s the valves stem seals/guides (thanks Aaron for clarifying).
Cheap, easy and non invasive.
Robert
W116 1977 280SEL & 1979 280SE

raueda1

  • Vintage
  • ***
  • Posts: 622
  • Assimilated. Resistance is futile.
  • Location: Salt Lake City, Utah
Re: Compression test on European M116.985 in 1977 350SE
« Reply #10 on: 10 August 2020, 06:09 PM »
https://www.misteroil.fr/fr-fr/shop/product/970/wynns-engine-oil-stop-leak-professonal-formula?gclid=EAIaIQobChMI1O3BlPON6wIVw7LVCh3ZBwNiEAQYBSABEgIK0_D_BwE

Thanks a lot!! :-)

New development this afternoon, where it was very hot (for Denmark), reaching 32C.

After a small drive at low speed and standing at idle with temp. reaching 90-95C on the meter, the oil pressure dropped down to 1.0 bar and even slightly below. Could also register a slight growling sound from the engine, when pushing on the gas in D at crawling speed. And during all this it was smoking blue smoke and smelling very badly!! :(
     >>>snip<<<
Thanx,

Christian
Just to be 100% clear: Are you saying that the oil pressure suddenly dropped when you were driving slowly?  Or is oil pressure of 1 bar only at idle or at slightly higher speed, say 1200 rpm?  Bad sign if it's that low during actual driving, even if slow.  As soon as you touch the gas pedal it should go up.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Lance

  • Newbie
  • Posts: 14
  • W116 Enthusiast
  • Location: Melbourne
Re: Compression test on European M116.985 in 1977 350SE
« Reply #11 on: 10 August 2020, 07:16 PM »
Plugs show that the engine is running way too lean, that is why it is overheating. Fix that first. Those compression figures are very good for a cold engine.

Lance

  • Newbie
  • Posts: 14
  • W116 Enthusiast
  • Location: Melbourne
Re: Compression test on European M116.985 in 1977 350SE
« Reply #12 on: 10 August 2020, 07:17 PM »
And 1.0 bar at 95 degrees is fine.

Lance

  • Newbie
  • Posts: 14
  • W116 Enthusiast
  • Location: Melbourne
Re: Compression test on European M116.985 in 1977 350SE
« Reply #13 on: 10 August 2020, 07:18 PM »
1.0 bar at idle that is.

Berggreen

  • Newbie
  • Posts: 11
  • W116 Enthusiast
  • Location: Gentofte, Denmark
Re: Compression test on European M116.985 in 1977 350SE
« Reply #14 on: 11 August 2020, 04:07 AM »
Quote
Just to be 100% clear: Are you saying that the oil pressure suddenly dropped when you were driving slowly?  Or is oil pressure of 1 bar only at idle or at slightly higher speed, say 1200 rpm?  Bad sign if it's that low during actual driving, even if slow.  As soon as you touch the gas pedal it should go up.

I did not really observe the oil pressure when driving, but I believe it was at max.. It was just at the end, when the temperature went up that I saw the pressure drop from the normal warm engine level of around 1.5 bars and then down to 1.0 and even a little below.
« Last Edit: 11 August 2020, 04:15 AM by Berggreen »