Unfortunately by not having the chain tensioner installed the first time when I turned the engine by hand the timing did got out of whack. Had to take of the rockers and free the cam to get the timing correct again. Hopefully in the two days I have time to install the last bits and pieces and get it running again.

I found one casualty from when I took off the head, a small plug with a single wire, the wire on bought side came off, I think it leads to the kick down switch on the transmission, correct?

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

An update since I got the head gasket installed. First off, its a much better car and it was worth the time, labor and money. I've been commuting this week for work in some heavy traffic in Hollywood and Beverly Hills and it did all hold up nicely. The temperature gauge stayed at 80*C when driving and would steadily go up to around 90*C waiting in traffic or crawling at five mph and go back to 80*C when traffic would move again. For the first 30 miles I used a thinner oil and I could hear the lifters ticking, put Castrol GTX 15W 40 in it and the ticking stopped.

It looks like the head gasket job also solved the high idle the 300SE was suffering from. The very first time I started it up it after I got everything back together the RPM went back to 1800 RPM just as it had done before the head gasket replacement. When I started the engine the next morning to take it for its first ride, the RPM went up to 1800 RPM, stayed there for 10 seconds, then I heard a loud click from the engine bay and the RPM dropped down to 800 RPM. Ater that the RPM never spiked again, and stayed always under 1000 RPM when idling. The first couple of days the idle speed would be 800RPM but now it event out to 600 RPM in D, when in P it goes up to 800 RPM. Occasionally the RPM will fluctuate a little bit, maybe new injectors are in order. The normal idle makes definitely for a more relaxed and pleasant commute.

The next three items on the list: new upper control arms and installing a 19mm rear sway bar and the glass sunroof from a W140 that's been waiting to be installed for months.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Congratulations to you Jorn.

I suspect I'll be dealing with this someday.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Very interesting thread. I have some follow up questions if you don't mind. More of a general nature than specific. I see the M102 has a single row chain. Didn't realize this. I've not heard of that being a problem on these compared to say, the single row chains on e the early 380 V8's or the 200, 230 four cylinder engines. What's different with these ones?

Also, how does a Mercedes head get to be unusable after less than 100K miles? That seems aberrant on a car of this era.

Lastly. How do you post these pic's to the forum? I need to find an alternative to photobucket.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

I read the V8 accelerates chain wear with more direction changes and the load of two cams.

Sixto
98 E320s sedan and wagon

The M103 does have a single row chain, it’s less of a problem because the chain is much shorter than in a v8. The condition of the old head is a mystery and what makes it even weirder is that the machine shop, metric motors, told me the head was rebuild before and they were not sure if there was enough left to shave the head again, not that it mattered because the head was so corroded it was junk. Another interesting part, the car passed smog a month prior to taking of the head with flying colors. And I have a car fax report to back up the mileage, but I do have a suspension something is off. There could have been catastrophic engine failure and the replaced it at some time, metric motors told me I should have the later style M103 for a 1990 300SE.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Today was the time to tie up the loose ends. Adjusted the air flow potentiometer and got the idle to pretty decent numbers I think. Finally good idle after a year and and half of ownership.

Top picture is in drive and below in park.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

And installed a 19mm rear sway bar, what a difference that makes.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Jorn, you should have the open-chamber heads and flat-top pistons.
Prior to '89 the heads had a large flat squish area opposite the spark plug, and used dished pistons. As a result, both engines had 9:1 compression. Mixing heads or pistons will result in way too much compression or way too little. Anti-freeze, even the correct stuff will eventually corrode the water passages in the head. I kept mine very clean, and still had some welding/filling to do at the first valve job, around 120k miles. So, yeah, it's possible the head was not original when you got it, especially if they used the green stuff on the radiator.
That little wire you mentioned controls the dreaded delayed 2-3 shift when the engine is cold - one of the most hated attributes of these cars. Leave it disconnected, you'll like it MUCH better when starting out in the morning.
Idle when stone cold in N should be about 1200; when warmed up, 700 with the vacuum gauge pegged left. In D idle should be 600, with the vacuum needle between the e and c on the ECONOMY gauge. This corresponds to about 16-17 in/HG manifold vacuum. Yours seems a bit low if it's fully warmed with AC off. Did you check the throttle stop switch on the linkage - Clicks when the throttle is closed.

Well, I went back and read the whole thread; you've definitely got a replacement engine in your '90 300SE. Those are the dished pistons of the earlier models. Your engine should have 981 XXXX 126 stamped on it just in front of the right motor mount. I bet it says 983, which is out of an earlier 300E. Not that it matters at this point of course.

Those old timing chains are really tough. You never hear of one failing; I have over 250k on mine and the tensioner is still on the same "notch" it was 15 years ago. All they do is run in a big oval. And someone here once remarked that the camshaft on a single-cam straight six has the lobes arranged so that for every valve that is opening there is a corresponding one that is closing, resulting in opposing forces and very little effort required of the chain to turn the cam - interesting tidbit there.

Cheers,
DG

I do have the right head installed for the older style M103. And it all makes sense now, ass the engine doesn't look like it has only 90K miles. I will check the throttle stop switch.

I'm pretty impressed with how smooth the engine is at the moment, I don't feel any vibration and hardly hear the engine when stopped at a stop light. It will need some exhaust work and it will be dead quiet.

Was already wondering about the cold shifts, what was the reason by Mercedes behind this?

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Catalyst light off probably. I do not recall the '89s having that as they had precats, my '90 does not have precats and a large cat. '90+ also received the AIR pump as well as the EGR.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Mine is a 1990 and has pre-cats, but to be honest I'm not sure what's original at this point. I does drive pretty amazing at this point, so who really cares.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

My car is a Federal version, maybe that is why? 04/90 build. Mine are mini resonators, 300E has precats.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]