w108 280S 1971 head gasket failure

[grober]

You can check the part no in the Elring catalogue I linked to. If the core plug and head are two different metals you may be the victim of accelerated galvanic corrosion. Be careful if committing to an expensive engine rebuild for 2 reasons.
1 if the engine had ingested coolant +oil on any compression stroke the con rods may indeed be bent as previously mentioned
2 overheating this engine may lead to piston ring embrittlement leading to excessive wear/oil burning or worst still--breakage and subsequent scoring of the bores.

 

[Bellow]

OK so the cylinder head is off, and surprisingly the gasket looks intact (looks new), however 1 of the 3 screw plug on top of the cylinder head seems to have just been sitting in place. Corroded, and with half the thread missing.
This I would say was the weak point, but would not have been easy to spot unless the cylinder head was off and out of the car .

Engine block, cylinder walls, seem ok.

Has anyone seen this happen before with a screw plug on top of the cylinder head causing oil / water to mix ?

Does the plug seal(or supposed to seal) the water jacket? If so, suspect you have found the culprit - assuming as you found it, it was capable of allowing coolant to pass it in the significant quantity you have encountered.

 

[Bellow]

You can check the part no in the Elring catalogue I linked to. If the core plug and head are two different metals you may be the victim of accelerated galvanic corrosion. Be careful if committing to an expensive engine rebuild for 2 reasons.
1 if the engine had ingested coolant +oil on any compression stroke the con rods may indeed be bent as previously mentioned
2 overheating this engine may lead to piston ring embrittlement leading to excessive wear/oil burning or worst still--breakage and subsequent scoring of the bores.

To the above I add:
Re con rod bending - even if not bent, if significant amounts of water were present in any cylinder. significant side thrust will have developed during compression. Look carefully on the piston skirts for scuffing and cracking on the NS piston skirts.
If the above has occurred, check big end bearings for damage. Ditto camshaft and followers as oil/water emulsion doesn't have the film strength to cope.

 

[MercedesintheBlood]

Does the plug seal(or supposed to seal) the water jacket? If so, suspect you have found the culprit - assuming as you found it, it was capable of allowing coolant to pass it in the significant quantity you have encountered.

Yes I believe the screw plug seals the coolant . Half the thread is still in the hole...

 

[MercedesintheBlood]

Hi All

Just an update.

- Head gasket replaced
- 1 x core screw plug has been replaced (unable to unscrew the others as too tight).
- Water pump replaced.
- Exhaust + inlet manifold gasket replaced.

Been told by garage to flush coolant after approx. 80 - 100 miles twice.

Cylinder head is back on the car, car starts fine, but now have hunting at idle. Sometimes it seems to settle, but still fluctuating. I've taken it for a short drive but worried it might leave me stranded...

Any ideas what this could be related to and what I could try to resolve this ?


Also what should the operating temperature be when the car warms up ?




Thanks for all the help received so far

 

[grober]

I suspect your problem may be carb related after their coolant+oil bath. May pay you to bone up on the 2bbl ZENITH 35/40 Carb.

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[grober]

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[grober]

 

[MercedesintheBlood]

This Account Has Been Suspended

Thanks Grober, appreciate the help you have provided.

I took a photo when the head came off the car, and noticed screw 17 in the photo above was in a different position to how it is on the car now.

I'll chat with the garage, and see what adjustments were made....

So this morning the car wouldn't start, GEN light would come on, but no crank, nothing..

Moved some of the wires near the firewall, and it seems like its to do with the plug attached to the firewall that had residue in one of the holes. Car seems to start ok now after giving it a clean.

Surging idle still present, and I will read up on the links you sent me.

 

[grober]

Think 17 is the throttle arm stop screw used to adjust the idle speed referred to in the second video I posted above

 

[MercedesintheBlood]

So I have been doing a lot of reading trying to make sense of the twin Zenith carbs, but I think its best to get a specialist to balance tune them properly, and someone who understands them.

Garage adjusted them but idle seems to be running too high, and when adjusted to low, it hesitates when in park, drive, neutral and reverse.

Not sure if they will require a re-build...

 

[grober]

These carbs rely on precisely calibrated orifices and passages to flow fuel and air and derive their properties from their physical dimensions- my fear would be that some of these are now partially blocked by the oil/water residues from their emulsion "bath" putting them out of calibration/adjustment range.
Might be worth contacting these guys for a rebuild quote.

Leading Weber carburettor distributor in the UK

Southern Carburetters are the leading supplier of a carburettors and spares for the classic car market. The on-line shop offers an extensive product range and the retail outlet is based in Crawley, West Sussex.

www.southerncarbs.co.uk

 

[MercedesintheBlood]

Evening all

Just another thanks for all that responded to my original post.

I know a lot of forum posts you see on different websites, there is never an update, always left wondering did they get the car fixed and back on the road.... so thought I would provide an update.

Its funny, its only when things go wrong with cars you appreciate them even more once you get them back on the road. Even my neighbors could see I was out every day just admiring the w108 280s.

So gave Southern Carbs a call, very helpful, and did say the carbs may not need a re-build and gave me an estimate to get both carbs re-built, but then I would have to find someone to balance/adjust them, so parked that idea for now.

So instead found a Mercedes specialist not too far from where I live, and the specialist had a look and made some adjustments while I waited, and explained what he was doing. Great service !!!!

Car is running a lot better, told to give the car a good run. Did that on the weekend and drove to London, engine temp good at 175 Fahrenheit, and creeping slightly above. Will probably need some further tuning, but much better than before as once the auto choke is off the car sounds normal.

When the car is started, revs are high, but when kicking down on accelerator after say 5-10 mins to take choke off, car does idle lower. Engine temp of 175 is reached.

This is different to how the car was before the incident, but adjustments were made.

The w108 280s will need at least a few more coolant flushes, not exactly sure how many, but progress is being made. Nightmare to take out all that mixture from the radiator.

I started watching @alabbasi You Tube channel on the 300SEL 6.3 . Great viewing, and great to see the car moving...

Pics and a few vids to follow.

Next task is to find a Becker Europa radio for the car.

 

[slade1]

It is well worth fitting electronic ignition, much better cold start and smoother running. The carburettors are the same fitted to BMW E3 and early E23 should you need to get a replacement.
Congrats on getting the W108 running well.

 

[grober]

Evening all

Just another thanks for all that responded to my original post.

I know a lot of forum posts you see on different websites, there is never an update, always left wondering did they get the car fixed and back on the road.... so thought I would provide an update.

Its funny, its only when things go wrong with cars you appreciate them even more once you get them back on the road. Even my neighbors could see I was out every day just admiring the w108 280s.

So gave Southern Carbs a call, very helpful, and did say the carbs may not need a re-build and gave me an estimate to get both carbs re-built, but then I would have to find someone to balance/adjust them, so parked that idea for now.

So instead found a Mercedes specialist not too far from where I live, and the specialist had a look and made some adjustments while I waited, and explained what he was doing. Great service !!!!

Car is running a lot better, told to give the car a good run. Did that on the weekend and drove to London, engine temp good at 175 Fahrenheit, and creeping slightly above. Will probably need some further tuning, but much better than before as once the auto choke is off the car sounds normal.

When the car is started, revs are high, but when kicking down on accelerator after say 5-10 mins to take choke off, car does idle lower. Engine temp of 175 is reached.

This is different to how the car was before the incident, but adjustments were made.

The w108 280s will need at least a few more coolant flushes, not exactly sure how many, but progress is being made. Nightmare to take out all that mixture from the radiator.

I started watching @alabbasi You Tube channel on the 300SEL 6.3 . Great viewing, and great to see the car moving...

Pics and a few vids to follow.

Next task is to find a Becker Europa radio for the car.

Glad you found a specialist who is familiar with Merc carburetted engines. They are becoming increasingly rare with the passage of time!
This company is worth a look if your distributor is worn?

123/Mercedes: Immediately improve the performance of your oldtimer Mercedes with 123ignition

The 123ignition for oldtimer Mercedes 4 and 6 cylinder engines. Discover the benefits of our innovative ignition system. View our range and immediately improve the performance and reliability of your oldtimer Mercedes with the 123ignition.

www.123ignitionshop.com

 

[MercedesintheBlood]

Totally agree with you about finding someone that can work on the carburetors. Becoming more and more difficult to find someone with the knowledge on how they should run. I will look into the electronic ignition.

I was told to press the accelerator down fully twice, then hold accelerator half way, crank engine, then once car starts, press the accelerator fully down again quickly. Car is warming up. Engine temp reaches 175.

Then after 5-10 mins press accelerator fully down again quickly, revs should come right down to normal.

When starting from warm, have accelerator pressed fully down, and start car.

 

[Bellow]

What happens with carbed motors idling is that the fuel drops out of suspension in the air and 'puddles' in the manifold. The puddles then behave like a 'surface' carburettor and as fuel is pulled from the surface of the puddles the mixture richens and consequently the idle speed rises. A blip of the throttle swallows the whole lot clean in and the process begins again.

When opening the throttle for a hot/warm start, depress the pedal slowly. Prodding it quickly will cause the accelerator pump(s) to shoot fuel in possibly flooding the engine. My preferred technique would be to start cranking and while cranking, gradually depress the throttle until it fires. If it hasn't fired by full throttle (unlikely) then continue but gradually closing the throttle. When warm, the risk is always over fuelling and flooding. Start weak and go as rich as required.

 

[slade1]

BMW E3, I still have an owners hand book BMW use same carburettor.
If the engine is cold depress the accelerator pedal once before operating the starter. This will will actuate the automatic choke and bring it in the cold start position.
To start the engine -------without depressing the accelerator for second time----