…oh, and the brakes and all lines are brand new in the z28, which makes me happy. some one put alotof good work into the car. the 406 has a chrome breather cover w 406 printed on it, and is immaculate.
I have warned him that there is good reason you don t see these cars anymore (they were everywhere when I was a teenager) , they don t handle well, especially in the rain, and many of them were wrapped around trees, killing some of my classmates.
but at least he is off the Harley.
your spark plug getting oily may be your problem. my sons first car, an el camino had a similar problem. one plug kept getting oily and made it run rough at idle, but it ran well at speed. he just cleaned it every week, but that soon annoyed him and he, without telling me, went and bought another 350 engine and changed it by himself in one day. he left the house at dawn one morning and came home at 2 am with the new motor installed. he did a really crappy job, but I was still impressed. after I took it upon myself to fasten all the loose wires and hoses, that he left hanging every where, it looked ok.
my days of enjoying such work are sadly done, I try to convince him to take care not to destroy his body through overwork as I did.
it is nice to see someone who does enjoy it tho, and I thank you for your post, and allowing me to be a part of your joy/frustration.
After only 15 miles, it looks like you’re putting some oil on those plugs. When I look up your engine, the recommended standard NGK is the TR5. I’m surprised your existing ones aren’t BPR6EFS which I take to be resistor plugs. Perhaps TR5 is basically the same as the BPR5EFS? The “5” plugs are one heat range hotter than the “6” plugs you’re using and should reduce oil buildup but I think you still have an oil burning problem. Valve seals or piston rings; you have to decide how far to go down that road.
Mercedes originally recommended the following plugs (all nonresistor plugs) for this engine (type: 103.983, production-#: 145586):
Beru: 14 K-9 DU or 14 K-9 DUO
Bosch: H 9 DC or H 9 DCO
Champion: S 12 YC or S 12 YCC
There may be some small technical variations between the models for the US and the German market.
I asked the local Mercedes dealer and the top local auto parts dealer. Both said BP6EFS (nonresistor plugs), since the rotor arm, each distributor connector and each plug connector have a built-in resistor of 1 kOhm already.
I think the compression test with it’s high values on all cylinders (mentined in my original posting) puts emphasis on the valve stem seals too.
Regard that the first cylinder, which’s plug’s ceramic is contaminated the most, happens to have the highest compression, which takes the suspicion further away from the piston rings.
So – db4690 – I think you are the man to be asked this question: what would you do?
Of course everbody else’s opinion is welcome too!
Only:
valve stem seals
hydraulic lifters
rubber seal of upper front cover (and camshaft seal)
Or also:
head gasket
timing chain
I guess changing the valve stem seals with the head off is safer, right?
Maybe the (small) rest of the idle shakyness is caused by:
oil getting into the combustion chamber
a not completely opening intake valve because of a failing lifter
a not very correct camshaft timing because of a slightly stretched timing chain
I ask db4690 what to do, because I guess he is the one with the most experience specifically with the Mercedes M103 engine.
Of course before you go into open heart surgery you want to ask the once who have done it before.
I know from the contributions to my discussion, that many of you guys have very extensive experience and knowledge.
To experiment, I’d put in a set of Champion S12YC or S12YCC plugs and see how they look compared to the NGK’s in 15 miles. If they also show oil deposits, I’d try a set of S14YC or S14YCC (i.e., hotter) plugs. I would only drive moderately with the hotter plugs, and after 15 miles, look at them. For an Autobahn run, I’d put the cooler plugs back in. I sure hope those plugs are easy to get to.
But I know what you’re thinking: maybe the other brand with the same (lower) heat range would already sufficiently burn the oil, and could be used for any driving style then.
Well, as I already mentioned, I drive this car very moderately all the time. Even on the Autobahn I usually never exceed 3.500 rpm (which equates to 80 mph). The Italian tune-up two months ago was a singularity.
If I could be sure, that with my moderate driving style I can use the hotter plugs anyway: Okay - provided that idle shakyness would be gone then. (Although knowing that oil is getting into the combustion chamber doesn’t really feel good).
I have a gut feeling that the idle shakyness will not be cured by hotter plugs. Why? because it returned immediately with the new plugs before the fouling should have been able to cause it. I honestly don’t know now what’s causing the shakyness. Even a tapping lifter in my experience isn’t accompanied by a miss. Is it a “tap” or a louder “clack”? Certainly getting all the lifters right is a good thing to do.
That’s exactly what I think too: the new plugs were not fouled sufficiently yet to cause misfiring.
Immediately after starting the cold engine it’s a “tap”, but not each time.
When I go slightly uphill after starting the cold engine (higher load) it’s more a “clack”, but not each time either.
When the engine is warm and you keep your ear close to it it’s a “tap”, all the time.
I would replace the valve stem seals, lifters and that seal
I’d leave the chain and the head gasket alone for now
I was looking at that link I sent you some week ago, in regards to the valve stem seals. Buried in the text, it says “Valve stem seals manufactured from Viton as of 09/1989 in order to reduce oil consumption. Identification: brown colored material.”
Since your car is a 1988 model, I’d wager you have the “pre-Viton” valve stem seals.
As for the the lifters, it looks to be a major pain in the . . . because you apparently have to check the clearance and the basic setting. I suppose you could just replace the lifters, but the settings may be off.
That’s one thing that always bothered me about Mercedes-Benz. That they had hydraulic lash adjusters, but then you still had to measure clearances. To me, that’s kind of deceptive.
If you remove the head, I’m sure you’ll be tempted to send it out for a valve job . . .
Based on your symptoms, I’m not sure it’s worth it at this point
You’re sure right about me being tempted to send the removed head for a valve job.
And I would be tempted to have it faced too.
I checked my Mercedes Benz service manual CD and the link you sent me, it looks like it was 09/88 (not 89) when they started with the Viton valve stem seals (for inlet valves only).
My car was delivered in 11/88. On engine type 103.983 they made the switch up from production #134666. Mine is #145586.
So apparently I already have the Viton seals, but after 26 years and 120.000 miles maybe these are done too.
Yeah – checking the clearance of the new lifters after installation and if necessary to adjust them with washers with a different thickness is really a time consuming pain in the … But – it looks like Mercedes wants to keep it’s … covered and the residual clearance stroke of the lifters within that specific range of 0.5 – 2.4 mm (0.02 – 0.095 inch).
I think I’ll go along with what you say and just put the new lifters in and forget about checking the residual clearance, because the old lifters may also be beyond this range by now - and I don’t mind that either.
Besides I don’t have the special measuring tool for that job anyway.
So you would trust compressed air to hold the valves in place while changing the valve stem seals, right?
I’ve never done it, but I remember the compressed air trick for valve seals from every Chiltons manual over the years. Only time it wouldn’t work would seem to be if the seat is burned, but you’d see low compression.
“So you would trust compressed air to hold the valves in place while changing the valve stem seals, right?”
Yes
The only problem you may run into is that the engine may turn slighly under pressure, in which case you’d have to lock it down with a tool. However, I don’t think you’ll encounter this situation
in contrast to this somewhat louder “clacking” when I charge a little more torque from the cold engine. (See my answer to insightful’s question about the kind of (lifter) noise 2 days ago)
I hope that’s lifter related too!
In my (wishful) imagination I put it like this:
When more torque is claimed, the pressure in the combustion chamber during the combustion cycle is higher,
and the outlet valve - which starts to open before the piston reaches it’s bottom dead center - has to be opened against that higher pressure, which may cause a harder “clack” of a failing OUTLET lifter.
It’s frequency is the same as that “tapping” (half of the crankshaft’s frequency).
When the engine is warm, I can claim any torque without hearing the “clack”.
Since the idle shakyness feels a little like misfiring, I can’t get the ignition system out of my head yet.
But would ignition related problems not only emerge at idle, but also during other operating conditions, especially when accelerating from standstill?
Half a year ago - because of the idle problem - I let a Mercedes mechanic check the ignition system with his old Bosch oscillosscope (which is hardly used anymore), when the engine was hot.
He said that it doesn’t look like a brand new ignition system, but he didn’t see anything on the monitor which would cause these kicks at idle.
Did any of you guys ever experience an ignition problem that showed symptoms only at idle?
My Mini Cooper (40 years ago) behaved like that - no problem while cruising at 2000 rpm or higher, while at idle there was major misfiring (due to humidity getting into the distributor). But then getting the car moving again after a standstill without stalling it was most difficult.
Also other cars I had earlier in my life behaved like that, for instance after cleaning the engine with a high pressure gun.
But no matter how much I touch the gas pedal of my Mercedes after a traffic light turned green, the car accelerates very smoothly – while standing there at idle it was “misfiring”.
That’s why I immagine that when idle is accompanied by misfire, putting the car into motion would be accompanied by even stronger misfire !?
I remember earlier in the thread a mention of a screen , possibly in the gas tank, that could get gummed up. no chance that your fuel could have some obstruction like this?