Cylinder Head Discussion

[Naj ✝︎]

Hi Joe,
The water distributors I mentioned are alli, not steel.Could you have a look at those on your head? Your picture is not very clear but one seems to be pressed in below gasket level (the picture with the red vice)
There is a low compression head gasket listed in the 230sl parts book. It was still available when I last checked (about 18 months ago)
naj

65 230SL
68 280SL

[ja17]

Hello Naj,
The low compression head gaskets are for completely different heads. These heads have lower compression and were supplied on cars to under developed  countries for use with low octane gasoline. These heads and gskets have a completely different part number from the standard compression versions.


Joe Alexander
Blacklick, Ohio

[ja17]

Hello Group,
Another very important item to look out for during cylinder head service is corrosion. Coolant eventually turns acidic as time goes on. Mercedes antifreeze is formulated for these engines and to their specifications. Off the shelf antifreeze is ok to use but shorter change intervals are reccomended if factory antifreeze is not used. When coolant turns acidic the engine will slowly start to decay from the inside out. The dissimilar metals begin to eat away at each other and expensive parts like cylinder heads can be ruined.

This picture shows a hole corroded between a coolant passage and the combustion chamber.  
Download Attachment: hole corroded in cylinder head.JPG
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The next picture shows the same head with a large portion of the head gasket sealing area gone from corrosion.

Download Attachment: gasket area eaten away.JPG
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The cyinder block of the 280-SL (M130) engine has only 1/16" sealing surface between coolant and combustion chamber! The sealing surfaces of the block and head must be precise!

Download Attachment: cylinder spacing.JPG
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If the acid level of the coolant is not checked, all engines should have coolant changes every two or three years. Engines in long term storage should be drained or checked for acid level of coolant periodically.

Re-assembly of the cylinder head to follow. Stay tuned.

Joe Alexander
Blacklick, Ohio

[Shvegel]

Joe,
 I was just wondering if the intake guides wear on these heads or just the exhaust guides?  When I did seals last summer my intakes felt like new but the exhaust guides were getting fairly sloppy.

[Benz Dr.]

I'm doing some R&D on my cylinder head and found out that these things flow quite well even in stock trim. I have a friend who has a flow bench and we put a dirty old 250SL head on it to see what the flow rate was. What we found is surprising.
The intake valve has a bout a .365'' lift and the exhaust is about .345'' lift. Both cam lobes are 40mm from cam base circle to top of lobe. It would appear that the rocker configuration has a multipling efffect due to the rocker being a fulcrum as the cam has less lift than that if it were pushing directly on the valve end.

The intake started to level off at around .300'' but the exhaust was still climbing and could indicate that if both valves had the same lift there could be improvments. I have to research this though as this design my be there for a reason and changing it could be a bad idea. One of the reasons for valve overlap ( which this engine has ) is to lower Nox readings. As the intake valve is opening the exhaust will still be opened for a short while and some exhaust gasses will be drawn back into the cylinder in due to back pressure and vacuum. This light charge of exhaust gasses actually helps to lower cylinder temps which must remain below 2000 degrees or serious damage will occour.

The intake maxed out at 148 CFM and the exhaust at about 110 CFM. If you compare these numbers to a chev 350 CID engine you would need 310 CFM at the intake valve by extrapolation. These are decent heads after all!
Now that I have a base line I'm going to see what my head will do since I have all the ports matched, intake runners polished and all new valves. If there's an improvment that's good - if not, matching everything up is a waste of time ( I doubt it though)

Dan c

Daniel G Caron

[ja17]

Hello Schvgel,
The exhaust valves and guides control the hot dirty exhaust gases. They do wear faster than the intake valves and guides. The exhaust valve stems are a larger diameter because they are sodium filled to hanldle the heat better.
The intake valves and guides control the cool, filtered intake air.
Often times the intake valves are within permissable wear even though the exhaust guides are shot.
You may have the option of just replacing  the worn exhaust valve guides. The exhaust valve guides have a groove cut in the outside of them to hold the valve seal in place. The intake guides have no groove. The outside of the  old intake guides may be worn smooth and not allow the seal to stay inplace. Later Mercedes engine designs had the grooves cut in both the intake and exhaust valve guides. In addition, replacement intake valve guides are usually a new improved alloy (silicon bronz instead of the original cooper alloy).
My point is that even if the intake valve guides are not worn on the inside diameter you should closely inspect the outside where the valve seal seats. Also realize that the original cooper alloy intake valve guides are probably inferior to new silicon bronz replacements. New valve guides are inexpensive.
The downside is that new guides MUST be installed properly or they may come loose after re-assembly, and the job must be re-done! This is why finding an experienced and competant machine shop to do the head work is so important.


Joe Alexander
Blacklick, Ohio

[ja17]

Hello Group,
In most cases the complete head along with the valves, springs etc. will be taken to the machine shop for dis-assembly and inspection. After machining it will be returned assembled, less camshaft and rockers. This is probably best, in most cases, for the non professional. I prefere to re-assemble the head myself so I can inspect the work done at the machine shop. This may not be practical for most since some special tools and experience is needed. I will quickly run through assembly so everyone can get familiar with the parts and procedures involved.

At this point the head has been returned from the machine shop cleaned, milled only if needed, new valve guides installed, valves and seats ground, etc.
Unusual problems such as replacement of valve seats, repairing of cross threaded spark plug holes, welding, replacement of broken studs etc. also has been done.

Download Attachment: cyl head with parts.JPG
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The valves have been numbered for installation after being ground at the machine shop. The valve stem is slightly oiled and installed in the head.

Download Attachment: valve being iserted into head.JPG
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 A valve rotator is placed around the valve guide. (check to make certain all valve rotators rotate freely)

Download Attachment: valve rotater installation.JPG
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 The new valve seal is installed over the valve stem and onto the new clean and dry valve guide.
Some people like to use an old valve guide to push the new seal in place.

Download Attachment: installing  exhaust valve seal.JPG
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The two valve springs are compressed with a special spring compressor and the top retainer along with the two "valve keepers" are installed. The space between the two valve keepers should be kept as equal as possible.

Repeat until all twelve valve assemblies are complete. The exhaust valve assemblies will typically be more difficult to install. The wider stems allow less room to install keepers.

I install all chain sprockets and the tensioner. The camshaft can now be installed using only the four 13mm nuts at the cam bearing bases. The head should be placed on the engine without the rocker arms.

This is the end of this "cylinder head" string except for any questions which may follow. I will try to follow up with a head installation string in the near future.



Joe Alexander
Blacklick, Ohio

[ja17]

Hello 71280-SL
Here is a photo of the early and late version M130 (280-SL) head gaskets for the 9.5 compression heads. They are not interchangable. The late version "oval" combustion chamber head gasket is on the left and the early version "square combustion chamber is on the right. Notice how close the cylinders are together! Do not oveheat these engines.

Download Attachment: Head gaskets M130 engines.JPG
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The engine breaking point for these two types of 280-SL engine was : to engine # 130.983-10-004596 or to eng #130.983-12-007229 for the early "square" chamber cylinder heads. These heads would use the head gasket # 130 016 4420. The later engines with the oval combustion chamber heads would use the head gasket #130 016 5020.


Download Attachment: cylinder head and gasket chart.jpg
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Joe Alexander
Blacklick, Ohio

[JPMOSE]

My 250SL runs like a champ and doesn't need any engine work at this point (133k miles).  However, I do use a quart of oil about every 700 miles.  I resently had new valve stem seals installed on my 560SL and the oil consumption went from a quart every 500 miles to NONE by 3000 miles when I change oil!  Hence, I would like to perform this task on my 250SL as well.

My Mercedes mechanic said that the original valve stem seals for the 250 engine are no longer available for the exhaust valves.  He stated I would have to change the exhaust valves if I wanted to renew the seals, unless I could find new old stock (NOS).  As great and honest as my mechanic is, he sometimes gets mixed up about his facts on vintage Mercedes.

Can anyone verify if this is true or not?  If it is true, does anyone have suggestions for finding NOS valve stem seals?

Thanks for your time -- this is great thread Joe...glad I found it!

Best Regards,

J. P. Mose
1968 250SL
1987 560SL

[Abbas]

Seeing is believing. I did not know how important it is to change the engine coolant every few years until I saw Joe's posting in this thread - Feb 13, 2004 - with pictures of what the coolant corrosion can do inside the cylinder head.

Posted - 13 Feb 2004 :  00:26:05      
------------------------------------------------------------------
 
Hello Group,
Another very important item to look out for during cylinder head service is corrosion. Coolant eventually turns acidic as time goes on. Mercedes antifreeze is formulated for these engines and to their specifications. Off the shelf antifreeze is ok to use but shorter change intervals are reccomended if factory antifreeze is not used. When coolant turns acidic the engine will slowly start to decay from the inside out. The dissimilar metals begin to eat away at each other and expensive parts like cylinder heads can be ruined.

This picture shows a hole corroded between a coolant passage and the combustion chamber.
Download Attachment:  hole corroded in cylinder head.JPG

The next picture shows the same head with a large portion of the head gasket sealing area gone from corrosion.

Download Attachment:  gasket area eaten away.JPG

I know now what is my next job - using MB coolant as recommended.

Thanks J.P. Mose for bringing this thread to our attention.

Abbas

280SL W113 1969 Ivory
E280 W124 1995 Silver

[JPMOSE]

NEVER MIND...it turns out the valve stem seals are available from Mercedes but had to be ordered from Germany.

Best Regards,

J. P. Mose
1968 250SL
1987 560SL

[rwmastel]

quote:Originally posted by JPMOSE

As great and honest as my mechanic is, he sometimes gets mixed up about his facts on vintage Mercedes.

It's good that you know your mechanic that well!

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Raymond]

Joe and Dan, You said don't mill the top, but if the head is bowed up in the middle, wouldn't the camshaft towers be higher in the middle too?  It would seem to be a problem as the camshaft spins.  I can't imagine you'd line bore the towers, would you?

Ray
'68 280SL 4-spd Coupe

[ja17]

Hello Raymond,

Yes you are correct, If the head warps so does the top surface. The manuals state that you must be able to turn the cam sprocket by hand after installation, (before the chain is installed). Normally some planning of the bottom surface can be done without needing to do anything on the top deck. But if the cam binds after installation you will need to shim the end cam supports or "cut the top surface" of the head also.  

Cutting the bottom and top surface of the head will result in more stock being removed from the total heighth of the head. You can only remove 1.0 mm before the head is scrap. So the alternative is if the cam binds after installation you can opt to shim the cam supports and not cut the top of the head. The other issue with cutting the top of the head is all valve guides and other protrusions would have to be removed from the hood.

Joe Alexander
Blacklick, Ohio

[Ziggy]

quote:Originally posted by ja17


Clean and dry the area around the spark plugs, make sure the valve cover gasket is good. If it begins to sweat oil again after a while it probably is leaky threads around the ball stud base. As Dan mentioned sometimes these want to gauld during removal. It seams that the leaky ones will usually remove without gaulding since they are already oiled. Also, removing them while the engine is still hot, seems to help. After removal clean everything up and put some thread sealer on the parts and torque them back into place. I made a thread chaser out of an old ball stud base, so I could restore the threads if needed.

I have this problem as well. Do I get it right that even when the ball studs are correctly torqued in, they can still leak?

[ja17]

Hello Ziggy,
Yes you may have to use some sealer on the threads of the ball stud.

[jwalk]

Hello Joe and all
Of the many pertinent threads on this site I have chosen this one for obvious reasons. My 65 230 SL runs well but I am imbarised by the smoke. With 5000 miles on a professional head job and 130 PSI on all cylinders,I had concluded that my problem may be mis located valve seals. The spark plugs indicate to me that three and four are the source oil and smoke, while the other four show clean white plugs. because of these facts, with the head on, I removed the rockers and springs on # four cylinder. Wrong, the seals are in place, the guides are tight and valves fit as new. The ball pin basses are tight , although I did not go beyond useing a breaker bar to either tighten or loose them. Now I am asking for help, what to do next? I look forward to your expert help.

Jim Walker
65 230 SL, ZF5  

[/quote]

[Benz Dr.]

The head is more important than you might think. How well it's put together will determine how well the engine will run.

We now straighten cylinder heads before any machining is done. The head is placed on two blocks and then a big clamp is placed in the center of the head or where the warp is the most. All of this is put into an oven and heated for an hour or so. If the warp is .010'' the clamp is set to pull it .005'' and then it's set to pull it a bit farther than the amount of warpage. Metal has elastic memory so you have to pull it a bit further than the amount of the warp.
Once the head cools I've found that the top of the head will be uneven. The only way to make the cam turn freely is to machine the top of the head. All the valves need to be removed so this the time to do it. Both the top and bottom surfaces need to be machined and a small cutter with a round bit is used. The surface comes back so smooth it's like a mirror.
Removing material from the top of the head will mess up your ball stud and rocker valve clearances. The best way to fix this is to use cam shims. I use .015'' shims which are the thickest I can get.
 Valve rocker gemoetry is so critical that you can ruin a valve job before the engine even gets warm the first time you start it. And, you can't fix it either. The head will have to come back off to be repaired.
 If you run out of room to adjust the rockers at the ball studs the rocker will be too low at the ball stud end and when the cam pushes the rocker down it will tend to push the valve stem sideways instead of straight down. The valve guides will wear very quickly and it will start to smoke right away. A perfectly rebuilt engine will not smoke. I can pretty much say will full confidence that any smoking problems will be in the cylinder head.
If the valve guides do get damaged small brass tubes can be installed inside of the valve guide hole. A ball that's exactly the right size is pressed through the guide and the brass tube will be swedged out to make a perfect hole. This is only effective when you have a small amount of wear on new guides.

The valve should slide easily through the guide without any binding and have a small amount of raidial play. There needs to be a little bit of clearance so the valve can move freely. If you have any doubt about your valves replace them. Measure the stem diameter and you may find that they're worn. All of this stuff has to be perfect or it will actually wear out again at a fairly high rate. Get it just right and the head will last a long time.
I use new valve springs on full rebuilds. They're cheap and I know everything will work better. All valve stem seals go on dry so they won't pop off and I use a special tool to press them on. Don't use a socket or a screw driver. Once you chew up a valve stem seal it's toast. You can't buy them seperately - you have to buy a whole set of them. After I have the seal installed I use a small amount of pre lube in the guide. If there are paint marks on the new valve springs the marks go to the bottom.
 Once I have the head put together I check the roto cap function by placing the head on two blocks of wood ( one on each end of the head ) and then I hit each valve retainer with a brass hamer. The valve should turn counter clock wise if the roto cap is working. This is an important step that's usually neglected.

[Q45Denver]

How do you measure or determine if head can be resurfaced?  Can head be mailed to you for rebuilding or would most local independent Mercedes shops or machine shops be able to do this?

[Ziggy]

quote:A perfectly rebuilt engine will not smoke. I can pretty much say will full confidence that any smoking problems will be in the cylinder head.

Do worn or broken piston rings not cause any smoke?

[Q45Denver]

I guess the bottom end on the M130 is pretty robust.  My mechanic had a hang dog look after he rebuilt my head he explained that it had been machined before and it could not be done again in the future. All was good for awhile.  A few hundred miles after the repair, my engine is smoking again. I thought it was the result of overheating but the explanation offered by Dr. Benz is more likely.

Good news is I have a spare low mile engine waiting in the wings but I would like to get it right this time. Should I just pull the engine and have the original engine completely rebuilt. Some say that just rebuilding the top end could put more stress on the bottom end and result in smoking from the rings. Will it devalue the car much to install the replacement engine? Just trying to figure out the most cost effective way to go about this?

The spare is from a manual trans car and I have an automatic. Would that present a problem?

[Benz Dr.]

I can do componet rebuilding.

A broken ring will cause the engine to smoke. What I was referring to is when you do a full rebuild and the engine smokes. Or, if it wasn't really smoking before you do a valve job but now it is after a short while. Aside from a valve stem seal popping off, the valve guides are your next suspect.

Rebuilding the head on an engine with low oil pressure and a lot of miles is pretty risky. The extra compression will pound out a bad rod bearing and the whole engine will fly apart. Only the quick and the lucky ever make the save and shut down before it goes KABOOM!.

[Q45Denver]

I guess you would need to pull the engine in order to replace the rod bearings?

[wwheeler]

My M130 motor smokes slightly for a few seconds when started cold or hot (more so when cold). Do you think the valve stem seals could be leaking? Is this amout of smoke normal?

The engine had a full documented rebuild 10 years and 12,000 miles ago and the car has 139K. Most of the miles were probably put on in the first part of that 12,000 miles and sat for the latter part and I have owned the car 8 months. The compression checked at 145 PSI. The plugs show normal whitish insulator on all cylinders. Given that the engine was a factory short block and should be OK, I think the valve stem seals may have dried out when it sat for awhile.

The slight amount of smoke it burns is normally insignificant. However, I am going to pull the valve cover off very soon anyway and thought it would be a good time to look at possible oil leaks from the head. How do you determine if the seals are bad? Is there another avenue for oil to get into the cylinders from the head?

[Benz Dr.]

A slight leak down a valve guide will give you that puff of smoke on start up and even more so when cold because the oil has had a longer time to leak into the cylinder. Even a few drops of oil will make a fair amount of smoke. When the engine is cold the oil will create more smoke than if it was warm.
In most cases the valve stem seal will be leaking. If the smoking goes away after start up and the engine really isn't using oil it's not much to worry about.

One other place where oil can leak in is at the ball studs. On the intake side you will see oil around the spark plugs but on the exhaust side you will see nothing. The oil leaks directly into the exhaust port and never really gets near the cylinder. This is why your plugs will appear to be nice and clean because everything inside of the cylinder is likely OK.