Head Gasket (71 w114 250), do you need to break Chain? - PeachParts Mercedes-Benz Forum

Jub · #1 04-26-2019, 02:55 PM

Hi Everyone,

Was prepping to swap out head gasket, and purchased all needed equipment (ie, spare aluminum block; gasket; chain, etc). Out of curiosity (too many projects) called my Benz expert (20years in biz) and asked how much labor would be if I gave him parts. He said that you didn't need to break chain to replace gasket...is that true?

Looking at pictures (ebay, my spare block, etc) I can see the gear attached to the aluminum block? Given he has been in biz long enough (considered a local benz legend)...what am I missing?

FYI: loaned car to wife; radiator hose came off; she ran it anyway w/out radiator fluid...heated..blew (spark plug holes flooded with radiator fluid).

Thanks in advance,

Jub

Frank Reiner · #2 04-26-2019, 05:14 PM

Quote:

Originally Posted by Jub

Hi Everyone,

Was prepping to swap out head gasket, and purchased all needed equipment (ie, spare aluminum block; gasket; chain, etc). Out of curiosity (too many projects) called my Benz expert (20years in biz) and asked how much labor would be if I gave him parts. He said that you didn't need to break chain to replace gasket...is that true?

Looking at pictures (ebay, my spare block, etc) I can see the gear attached to the aluminum block? Given he has been in biz long enough (considered a local benz legend)...what am I missing?

Would you expand on the matter of the "aluminum block"? What is it?

If you are on good terms with Dame Fortune, the chain may clear the cam gear when the tensioner is removed, or the gear may clear the end of the camshaft.

Jub · #3 04-26-2019, 06:00 PM

Hi Frank!

Good to know! I purchased a spare block years back (someone selling clean, pressure tested one dirt cheap; just in case ever needed it). Hopefully one on engine didn’t warp when engine over heated, but just in case I have a spare).

Frank Reiner · #4 04-26-2019, 06:22 PM

Quote:

Originally Posted by Jub

Hi Frank!

Good to know! I purchased a spare block years back (someone selling clean, pressure tested one dirt cheap; just in case ever needed it). Hopefully one on engine didn’t warp when engine over heated, but just in case I have a spare).

Does "spare block" = engine block? If so, it is cast iron.
The question remains: what is the "aluminum block"?

cth350 · #5 04-26-2019, 11:19 PM

ah, he means cylinder head (the part that can warp)...

On these heads, you need to check top and bottom surface for warping and total thickness.

The fun parts of this job are...
- Getting the little metal bypass line that connects the head to the water pump housing off. They are two steel banjo bolts. Meaning they are hollow and will corrode over time as they are screwed into chunks of aluminum. The ideal thing to do is torch them to get hot, then let them cool. Loosen it a fraction and add penetrating oil. Loosen it some more and oil it some more, then remove it. (unless they broke before that).
- Undoing the bolts between the exhaust manifold and exhaust. Usually you can't and you just cut the bolts.
- Disconnecting the exhaust from the manifold. There are a pair of iron+asbestos rings for seals that have probably disintegrated down to a ring of rust. A hammer helps as does wiggling it some.
- The capillary tube from the head to the gauges is a hollow fitting with a metal tube in it. You really want the tube to not turn when you unscrew the hollow fitting. It will take some penetrating oil and some back and forth action. If you twist it and break it, the alcohol inside the tube boils off and you need to find a replacement or get it fixed. Neither is cheap. Spend the time being careful instead.
- When you remove the timing chain tensioner from the head, you'll see the little idling wheel swing back a little. It uses a metal pin as a pivot. Pulling that pin out of the head is pain. You need a long 6mm x 1mm (fine thread) bolt. There are threads here that talk about how to pull the pin out. It's the same for the v8, diesel, etc motors.
- As you pull out that pin, watch the little spring between the head and the arm. It will go flying if you don't take precautions as you pull the pin out. If you loose it inside the engine, it will wind up in the pan and out of the way, forcing you to buy a new one.
- Pull the head with the intake and exhaust attached. It's heavy and an assistant sure helps. You can remove the manifold pair first, but it can be a pain to get it out of the engine compartment with the studs on the head.

Assembly is a whole other thing, including making sure that the cam turns freely. Also there's getting the exhaust manifold heat risers ready for reassembly.

HTH -CTH
PS. don't mess with the block unless you really like to work hard and spend money on this stuff, because a used motor is just simpler, faster, easier.

Jub · #6 04-27-2019, 07:43 AM

Yes, cylinder head.

I read that since block is cast iron and cylinder head is aluminum- there is a 99% chance that the iron block won’t warp under heat is is always the cylinder head (might even crack). So I’m hopeful that’s true.

I know it’s a tricky job, but I need to try. After 1 year sitting with a perfect engine and transmission simply b/c ring Gear was stripped due to defective starter. I pulled transmission and replaced ring gear and reinstalled (and was sooo happy)...then tested it for 5 days as daily driver (2 hrs/day). Signed off and on day 6 gave to my wife to go to grocery store...

Damn radiator main hose sheared off and dumped contents on freeway in seconds. This thing has become a me vs. the gods thing, and i will win or die trying! (Lol)!

Jub · #7 04-27-2019, 07:47 AM

FYI: Pic of disaster (the metal sheared off with hose still attached)

barry12345 · #8 05-02-2019, 11:47 AM

It has been decades but if I remember. Just pull the cam gear and chain. What I do absolutely remember is I never broke a chain on these engines unless required when winding a new one it.

Things to remember. That to me I learnt with some difficulty. Make sure all the valve adjusters have an adequate interference fit. Testing with a torque wrench. Check the valve clearances every 10K without fail. Or you may be dealing with a burnt exhaust valve down the road.

Depending on your experience level. Set the balancer mark. Verifying the cam mark is also in position . If not rotate the engine once to get the cam marks to align. This avoids getting the primary timing wrong. When you change or have the head off.

Overall these are not a really difficult engine to a head removal and replacement on.

I just had a look at the year yours is. I think this was after the factory upgraded the interference fit of the valve adjusters. I still would check them though but not expect to find a weak one. So many aftermarket parts are marginal today to say the least. I do not think this applies to head gaskets but I would check before buying one. These engines were not known for having any real issue with head gaskets though.

Jub · #9 05-02-2019, 02:52 PM

Thanks Barry! Never done this, but it seems so simple: remove distributor, remove manifolds, plugs, wires, get timing chain off, and don't damage cylinder head (and machine/clean aluminum at machine shop; quoted 100 for cleaning, 100 for pressure testing). The only two things that worry me are 1) Making sure I don't mess up timing marks and 2) Why people say just replace engine (vs. replace head gasket). Any comments/pics would be greatly appreciated. Can't find any step by step how to manuals (maybe because it's too easy?) But then why do people suggest to just swap out engine just b/c of blown gasket (100 bucks-ish)?

barry12345 · #10 05-16-2019, 11:33 PM

On modern engines replacement is pretty much preferable today. This is an older fashioned engine. There are two smaller bolts in the timing chain cavity as well to remember to remove.

Personally I would remove the head and using a straightedge see how much warpage is present using feeler gauges. The best place to get the head done locally wherever you are is to ask a local Mercedes dealer that has been in business for years. Where they send their local auto machine work. Plus if they are happy with it. A good shop might even put it through their contact for you to avoid the off the street prices. Unfortunatly the world seldom acts like that anymore. It is a personality thing to try to get them to do so perhaps anyways. With no markup but buying all the people in the back shop perhaps a Kentucky fried dinner.

It may very well need a few valve guides replaced. I would ask for the original Mercedes rubber valve seals as well. As there was some discussion about the quality in comparison with the aftermarket ones. Do you have any ideal of just how long the better half ran the engine after it blew it's cool?

For some reason more automotive machine shops seem to have issues than in the past today. Yet technically their equipment should be better. As a result never use one that does not have a good reputation.

There is nothing really special about that head. Other than Mercedes asks for a smaller clearance when reaming the replacement valve guides if needed.

Inspect the first cam lobe as this was about the end of the era that they had improperly hardened cams towards the front. Also number all the cam followers. I assume you already know they have to go back in the same positions.

I also have wondered if the poor work that is too common today in many places. Was caused by the drop in their volumes of incoming work. I cannot remember a friend reciently that has sent his head in for example to one. Perhaps it is several factors.

I always checked the valve seal when I got a head back with a thin liquid. Before installing it. If you know the accurate miles on the car and mention it. Generally it gives some indication of what it will probably need. You have to trust someone in the auto machining business. Checking them out helps. It may have changed but in the past I found the better places seemed to charge less as well.

Before you remove the head. I may have mentioned before. Set the damper at zero with the cam marks in place. If the cam marks are 180 degrees off just rotate the crank one more time a full 360 back to the Top dead center at the indicator. They will be on then.

Jub · #11 06-01-2019, 08:28 AM

Thanks Barry!

Update: getting a little concerned that overheating caused collateral damage to piston rings. I drained oil today (finally starting to take hard look) and found coolant in oil pan.

Question: since been sitting for a month with bad head gasket/warped aluminum head, could this just be coolant slowly leaking past piston rings over past month? Or does engine need new piston rings (ie, engine is shot)?

Thanks,

Jub

Jub · #12 06-01-2019, 08:35 AM

See attached pic

BWhitmore · #13 06-01-2019, 09:57 AM

A blown head gasket will allow coolant to leak into the oil and turn the oil the color of cream. Once the head is off look into each cylinder for signs of scrapes, etc. An over heated engine will not necessarily mean broken piston rings unless it was severely over heated for an extended period of time.

Jub · #14 06-01-2019, 10:11 AM

Thanks BWhitmore!

Benz Dr. · #15 06-01-2019, 06:45 PM

You can most certainly warp the block. This can be repaired by milling the top of the block but then you would have to pull the engine and take it all apart to do that.

Warped heads can be straightened using heat - the same way they got that way. This is done in an oven - not rocket science.