1991 300SE questions, head gasket, valves etc.

[unkl300d]

Hello my friend has this car with 157K miles on it(1991 300SE) . Previous owner has had maintainance work on it including new injectors.
However, my friend seems to have a bug up the B-Hind and wants to do preventive maintaince.

He was planning to have a mechanic replace the head gasket, replace the timing chain and adjust the valves.

Besides that he plans to replace the distribuor cap, rotor and spark plug wires etc. Tune up stuff.

He did not state any evident symptoms for wanting this work other than preventive maintainance.

He has no leak in the head gasket, and as far as I know, there is no significant oil burning.

I know the car has a bit of uneven idle but that is indemic to these cars.
My 300SE has this also. I live with it.

So, I did research in the archives and it seems the timing chain in this car is short and tough. So, perhaps it does not need to be pre-emptively replaced. ???
Does failure cause severe damage in these cars or just cause the engine to halt until part is replaced.??
Opinions?

Perhaps having the valve clearances checked may be a good idea but I told him NOT to have the head gasket relaced.

Often times you get more problems when you remove stuff than letting it be.

I told him that the timing chain could be replaced without removing the head anyway. He thought the head had to be removed for this job ergo the idea of having the head gasket done as well.

I told him that the timing chain cover half moon gasket leaks could be taken care of w/o head removal.

So, do the valves need adjusting or are they self adjusting???

He got a quote of $1800 for replacing head gasket, timing chain, replacing the stated tune up parts.
That is for labor only since he bought the parts already.

I told him to hold his horses until I got answers from this forum of noble experts !!

Anyway, please give me your opinions.

Thanks

Denis

[deanyel]

He should save his money for when something actually needs attention - and it will eventually. I see nothing wrong with changing the plugs, inspecting the cap and rotor, replacing if necessary, but the rests of it is over the top. Valves don't require adjustment. I've never heard of replacing a head gasket as preventative maintenance. A 103 motor timing chain with 157k is nothing. I once had one replaced at 280k and it was original in perfect condition. I've had two mechanics tell me since that you just don't tamper with a working factory timing chain on a 103 motor. The replacement is not likely to be as sound as the unmolested factory original. Tell him to be patient - the car will create something that actually needs to be done.

[softconsult]

A couple of thoughts.

First, since your friend does not know much about these cars, but wants to make sure it's is tip top shape I would do the following.

Ask around for the best independent MB shop in town. Take it there, and pay the shop $ 125 or so, to have it examined. It's called a Pre-Purchase inspection, only he already bought the car.

You sure don't want to start replacing things that may have been replaced recently by the former owner.

By the way, the rough idle could be the motor mounts. If the belt tensioner has never been replaced, then it is about due. The replacement of injectors at 157K sounds premature.

I just had the timing chain done on my '92 300E M103 at 218,000 miles. I was having the front engine cover resealed, so did the chain. Mechanic said it had not stretched and could have gone on and on. Mobil 1 every 5 k.

Stev

[Duke2.6]

Changing the head gasket is not PM! It's a repair and only needs to be done if/when it starts to leak.

Hydraulic lash adjusters are built into the rocker arm and do not need periodic adjustment.

The timing chains on M103 engines only need to be inspected if/when the head is removed for some other reason.

Valve guide life is probably in the 90-150K range, and if the head has to be removed to replace valve guides one should go ahead and completely overhaul the head, which may mean new valves depending on stem wear. The exhaust valve stems usually wear more than the inlet valve stems.

The bottom end of these engines should go at least 250K. Many have reported bottom ends well over this mileage and still going strong.

High oil consumption can usually be mitigated by replacing the valve stem seals, which doesn't require removing the head. If new valve stem seals don't significantly reduce oil consumption, the valve guides probably need to be replaced.

Ignition components other than the plugs are probably good for 60-120K miles, but the cap, rotor, and plug wires don't usually need to be changed unless emission testing shows very high HC with low CO or the engine develops an ignition related misfire.'

The biggest "problem" with M103 engines is probably major oil leakage at the front cover, but most have probably had this problem corrected sometime in their life.

These cars are actually not very maintenance intensive, but like any older car, they can become REPAIR intensive as they age and accumulate miles if you want to keep everything working as designed. The most important maintenance is changing the filters and fluids at the recommended intervals including the trans oil, coolant, and brake fluid. I also think the axle oil should be changed every 60-120K miles even though Mercedes never recommends axle oil changes. The recommended maintenance schedule is in the owner's manual.

Little things like shift linkage bushings and front flex discs usually need replacement at 60-90K intervals. They should be inspected every 30K and replaced if they fail visual. Otherwise you know that if the shift linkage becomes balky you need a new two dollar bushing, and if the drivetrain begins to feel like it's made out of rubber bands, the front flex disk is probably cracked. The hydraulic motor mounts can also leak and fail. One should add a motor mount inspection at the 15K maintenance interval, and if the engine becomes very "rough" the mounts are suspect.

Probably the biggest repair liability on the S-class is the climate control system. It can be expensive to repair.

Your friend should just make sure that all the Mercedes recommended PM is current. The shift linkage should work smoothly, the engine should idle with no more than a slight uneven roughness, and the drivetrain should feel tight.

Duke

[unkl300d]

Thank you all for your sound advice.

I contacted my friend with this info.

The wise thing to do is accept the opinions of this forum !!

Denis

[Lairr]

Does anyone know how often an IF the tensioner Belt needs to be changed on a Mercedes-Benz 1991 300SE with 150K?
I have been researching and lloks like the only possible concerns lie with the 380SE, which feature a Double camshaft.
Seems like the M103 Engine only has a single and timing belts not an issue even after a lot of mileage?
Please help!

p.s: I love this car!

[Ivanerrol]

The only issue with the M103 heads is the valve seals and guides and the head gasket.
If the fluids are changed as per spec with the recommended replacements the likely hood of need to repair is lessened.
Occasional use of the M103 engines leads to drying out of the rubber valve seals and guides and hence quicker replacement time.

Belt tensioners wear out. Periodic inspection should reveal when they are on the way out. A tensioner not installed correctly and adjusted as per the manual may lead to a short service life.

Duke2.6 has some very wise words in his post.

[S-Class Guru]

I agree with everything above. Especially the timing chain. It's unlikely you can even find a chain at a dealer that matches the quality of the original.
A couple of comments:
- My old '91 has 200k, and has always idled smooth as silk. But you gotta change the plugs at least every 20k, maybe sooner. Could be vacuum hose leaks, particularly to/from the IAC valve.
- The head gasket is indeed a weak point on some of the 103's, if you consider weak to be possible failure every 150K or so. The block is iron, the head aluminum. This sets up a sliding effect on the gasket as they heat and expand at different rates. Eventually the gasket will just wear down and begin to leak, most commonly coolant at the right rear of the block. It's easy to spot, certainly wouldn't do it until it indicated some symptoms.
- Valve seals are pretty notorious for creating oil usage on the highway. As stated above, they seem to fail sooner on cars that sit a lot. mine were eating oil before they were a year old.

DG