Cylinder Head Discussion

[ja17]

Hello Group,
I am currently assembling a re-conditioned 280-SL cylinder head. I took a lot of photos and thought it may be a good opportunity for a discussion on the subject if anyone has any questions?


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At this point the bare cylinder head is back from the machine shop with all new valve guides pressed in place and all the valves and valve seats ground. The head was slightly warped and needed to be cut very slightly (.010") to be perfectly flat.

Joe Alexander
Blacklick, Ohio

[Cees Klumper]

Hello Joe - here's some questions/comments on this topic:

- what sort of tests can owners perform/signs should we look out for, to determine whether the cylinder head needs reconditioning? Or is this diagnostical work best left to the experts?

- I understand that rebuilding the head while the bottom-end is weak, can cause problems as a result of increased compression from the head. Would you recommend always checking the condition of the bottom-end before getting into a head rebuild?

- provided the engine is properly maintained and serviced, what sort of mileage should one be able to expect out of a head rebuild? How does that compare to the block?

- in your experience, what is the cost of the parts & labour to recondition a cylinder head - it depends on the condition of the valves, seats etc of course, but is there an average or a range that is common?

When we did my cylinder head last summer, the machine shop charges were as follows. I decided to replace all of the valves, even though this was probably not really necessary, because of the relatively small costs involved vis-a-vis the comfort of knowing now they're brand new:

1. cold tank clean head $52
2. R&R 12 valve guides + fit $96
3. machine and install 2 valve seats $72
4. valve job $88
total $308

The parts:
1. 12 valve guides $72
2. 2 valve seats $29
3. 12 valves $258
4. valve seals $10
5. head gasket set $60
6. camshaft sprocket, timing chain, rails, chain tensioner $126
total $555

Grand total $863.

It think that most owners would be able to do most of the work on a head rebuild, and without special tools like micrometers etc IF valves and guides are replaced with new anyway. The machine work would always be outsourced; the shop can determine whether the head is flat or not. Most of the labor (=cost) involved is in the dismantling and re-assembly and installation. By doing this work yourself it reduces the cost and you can allocate more money towards all-new parts such as valves and seats. Plus you become more familiar with the car and, to me at least, this is part of the fun. Of course there is some risk involved of doing everything just right.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[Benz Dr.]

I look for several things.
First is the overall thickness  of the head which must be at least 84.00 mm. After that I look at the water jaket ports to see if they're still good and then I check the head for plane. You can have a very slight warp up to about .003'' and after that you will need to mill the head or possibly have it straightened. I never worry about the top of the head and how level it is - leave it alone!
A .010'' cut is actually a fair amount of material removal and doing this three times over the life of the head will turn it into a boat anchor.

New guides are a must along with new valve springs and probably new intake valves. The exhaust are thicker and may be able to be re used. Use new seals as well.
I set the valve height by subtracting the thickness of the head and the amount the valve and seat are cut useing a depth micrometer. There must be at least .035'' clearance between the intake valve and the piston at 5 degrees ATDC.
If the head has been cut .010'' and the valves and seats are also .010 you won't have any clearance problems. You can get some thin valve spring shims and place them under the roto caps to get the proper tension on the springs. In this case you would need .010'' which is not enough to worry about.
If the valves and seats are cut too much you will run out of adjustment when setting the valves. New valves will help out a lot or you may need to install new seats. The thickness of the head is a VERY important consideration as it may not be wise to spend that kind of time and money on anything at or less than the minimum 84 mm. Thinner lash caps are available or grind them down if you only need a few to complete the job.
I use a vacuum tester to see if the valves are leaking after lapping them in. You can also use a bit of varsol and pour it into the ports. It shouldn't leak out if everything is tight. Don't lap them in any more than to just get a nice line. The valves should sit about 2/3 up from the bottom. If the line is at the top try moving the valve to a different spot - they don't have to back in the same place if you used new valve guides and valves.

Dan c
SL Barn


Daniel G Caron

[ja17]

Hello Cees,
I will work my way down your list of questions over the next few days. Others should feel free to jump in. Dan, thanks for you experiences and advice keep it coming. My comments are a result of my involvement with these engines over the last thirty-five years and may not always reflect established procedures.

Excessive oil consumption, oil smoke and possibly poor running due to low compression are first signs of head problems from normal usage. Overheating, internal engine corrosion or catastrophic mechanical failure can also require cylinder head removal.
Engine history as far as mileage and service history can provide a lot of insight into the health of the engine.
Worn valve guides, bad or loose valve seals, and worn valve stems can all contribute to engine oil usage. Compression loss does not always occure immediately.
Normally a well maintained and healthy engine may not need a valve job for 100,000 miles or more. A well  maintained healthy bottom end may go 200,000 or more. '
If the engine is basically healthy and has good oil pressure, 90% of the time reconditioning the cylinder head will cure or greatly improve oil usage and bad compression. If the engine has been previously rebuilt or suffering from very poor maintenance or years of bad storage you chances of success with just head work are greatly reduced.
Lets face it, if the head work restores your engine to good working condition you will save thousands of dollars over a total rebuild. If the head work fails to provide the expected results. You are out a head gasket and some labor. You still end up with a perfectly good reconditioned head to use during the total rebuild. Now supose you pay to have a compression test, leakdown test, and various other tests and procedures, you probably will have $200.00 to $400.00 dollars in it before you start! Spending $5.00 with your local fortune teller is often more productive. I have seen a lot money spent over the years over-testing and procrastinating before a wrong wrong diagnosis is given! Many shops will not guartantee their diagnosis or the results unless a complete engine rebuild is undertaken anyway.
If you have bottom end problems (poor oil pressure, broken or worn rings, or damaged cylinders you will have to bite the bullet.
Try to make a good decision first. Review any documentation on the engine service and maintenance. Oil pressure can be the best indicator of bottom end condition.
Document oil usage. Read the spark plugs and check the compression if the car is drivable. Engines should be warm during compression and leakdown tests.
Oil entering the cylinders will leave hard crusty deposits on the spark plugs. Do not confuse oil fouling with black wet sooty fuel fouling, or wet coolant fouling. Oil gets into the cylinders two ways past the piston rings or through the intake valve guides and then sucked into the cylinders. Oil usage from bad exhaust valve guides happens when oil passes by worn exhaust valve guides or seals and drops into the exhaust ports of the cylinder head and is drawn away from the cylinders. The oil is burned off in the exhaust. No oil fouling and no crusty deposits.
In some cases reconditioning the head may improve oil consumption and not totally illiminate it. Some ring and cylinder wear could also be present. A lot of things to consider here.
Some owners will choose to start at ground zero, when money permits, and do a total rebuild.

More to come!

Joe Alexander
Blacklick, Ohio

[ja17]

Hello,
You will need engine number on the engine block to order correct parts. The cylinder head number may be of little use but is cast on the head below the plugs on the right side. The 9.5 is the compression ratio (9.5 to 1).

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Heads after the 230-SL series had a model designation cast into the heads also. Many 250 and 280 series sedans and SLs shared the exact same heads!


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More to follow!

Joe Alexander
Blacklick, Ohio

[Joe]

Joe,
would you expand on your statement: "Oil pressure can be the best indicator of bottom end condition."?
At what oil pressure reading should one assume his bottom end needs renewal?
Can the oil pressure guage on the dash be trusted to be accurate?
I'm sure others share the gratitude I feel for your contributions to the list.
Joe Melton

[ja17]

Hello Joe,
Naturally you may not want to consider just a cylinder head rebuild if the bottom end of the engine is in poor condition. Your engine oil pressure can provide a lot of insight. To those of us who have spent many hours looking at many engines and oil pressures, what is "normal" is obvious. To the less experienced it can be a mystery.
The BBB may state that permissable minimum oil pressure is 7 psi, however this may not be "normal".
Many listers with fresh rebuilds, low mileage engines, or very heathy higher mileage engines may rarely see the oil pressure fall very far off the peg even at an idle hot. Others with high mileage engines with normal wear in good health may idle hot  around 15psi. but immediately move to the peg soon after raising rpms. Most heathy engines will cruise with the oil needle on the peg. If the ildle is at 700 rpm hot and the oil pressure is less than 10psi, I get a little concerned. If while cruising down the road you accelerate and the needle on the guage drops before rising this is may be an indication of crankshaft or bearing damage.
Now before some of you go off in a panic here take these things into consideration; lower idle rpms, elevated engine temperatures, thinner oils can decrease oil pressure readings. In addition fuel contaminated, dirty oil will also lower readings. Extended running at very high rpms will super heat engine oil causing lower readings. Get to know what is normal with your engine. Be suspicious if you notice a deteriorating oil pressure during a period of time.
Some newly rebuilt engines may only have fair oil pressure but not as good as new. This could be the result of machine work not being quite up to specs. Some rebuilders may  cut corners by and using the old oil pump (bad place to save money!)
If you have real concerns on the condition of the bottom end of your engine, the steel lower oil pan can be removed and the crankshaft, and bearings can be spot checked from below for wear or damage. Rodd may want to comment on this!
The oil pressure guages rarely fail. However they can be checked by removal and testing or hooking up an additional guage to the engine for comparison.
Happy motoring!

Joe Alexander
Blacklick, Ohio

[ja17]

Hello,
Depending on your ability, background, experience,  tool assortment, and working conditions, you may or may not ever desire to get involved in this kind of procedure yourself. Some of you may just like to be a little more educated on the matter. If you are contemplating reconditioning your head, finding a good qualified machine shop is very important. Very few repair shops do their own machine work. In most cases, after the head is removed an automotive machine shop will do the head dis-assembly, machine work and head re-assembly if desired.  Try to find one familiar and experienced with Mercedes heads. Pressing new valve guides into aluminum heads takes some expertice. Improperly installed guides can come loose after the engine is running again!
I always supply the machine shop with a copy of the correct factory specifications for the machine work and permissable wear limits on parts. Most machine shops will be glad to have you provide them with the correct new parts as needed also.
If desired you can get the head back ready to intstall. In my case I request it back dis-assembled so I can check their work and then re-assemble the valves and springs etc myself. I will try to describe some of the things to watch out for during the process. I have some photos of the basic parts for discussion also. Feel free to jump in. Stay tuned!

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Joe Alexander
Blacklick, Ohio

[Benz Dr.]

Joe,
just wondering. Why did you remove the ball stud adjusters? Are you replacing them or is this for some other reason?
 I ask because I've removed them and wished later that I had not. On a few heads the threads galled as the threaded insert came out and it would have been better to leave them alone. If I have to replace the adjusters I try using the threaded ball first and leave the base part in the head.
On 230SL heads I sometimes remove all the threaded ball parts and gring off the point on the end if they're worn a bit. This keeps the rocker from hanging up at the end and allows smooth operation. I use the valve stem grinder on my machine to do this and works quite well.

Dan c
SL Barn
113@mbz.org


Daniel G Caron

[ja17]

Hello Dan,
Those are two good points. Removal of the Ball stud bases normally is not needed and sometimes, as Dan mentioned, can lead to gaulding during removal. However in this case this head had that mysterious oil seepage around the spark plugs. It looks like the area is sweating oil. At first glance it looked like it could have been a bad valve cover gasket. A new valve cover gasket did not cure the problem. In these cases oil seeps out through the threaded ball stud holes. Photo for those unfamiliar;

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As you probably know these threaded openings exit right above the spark plugs.
With the exhaust ball stud bases the threaded opening enters the exhaust port so any oil leakage on these would go into the exhaust ports and be burned off in the exhaust(photo).

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My normal routine is only remove these if you see leakage around your spark plugs. If they seem to be gaulding during removal, I try a little heat or leave them alone. When the threads are sealed and the ball studs are torqued back in, the leaks around the spark plugs disappear.
I know what mean on those worn ball studs. They can get a crown worn on top the ball. I have also ground this crown off. It does work well. Sometimes this crown will be so bad that proper valve adjustment is impossible.

Joe Alexander
Blacklick, Ohio

[rwmastel]

What Joe is referring to (and other oil consumption discussions) can be found in these threads.

http://index.php?topic=740
http://index.php?topic=459

I'm saving money for a complete engine rebuild in 2005.

Rodd

quote:Originally posted by ja17
If you have real concerns on the condition of the bottom end of your engine, the steel lower oil pan can be removed and the crankshaft, and bearings can be spot checked from below for wear or damage. Rodd may want to comment on this!

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

[n/a]

Hello All,

Just would like to add to the Oil-pressure topic ,
i found out that when i fitted several different
oil-pressuregauges i got different idle-readings too.
So gauge to sender accuracy does matter.

Marco

[Naj ✝︎]

I have at least two oil leaks at the spark plugs. Could the ball studs be loose?
naj.

65 230SL
68 280SL

[Naj ✝︎]

I would check the water jets while the head is off. These jets divert water from the block towards the valve guides.
The 230/250 heads have six of one and three of another size while the 280 head seems to have only the three bigger ones.
Mine were so corroded that cleaning the scaling with a small screw driver made a big hole in most of them.
Part #s are

6 off  127 016 0760
3 off  127 016 0860

naj

65 230SL
68 280SL

[ja17]

Hello Naj,
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.


Joe Alexander
Blacklick, Ohio

[Benz Dr.]

If  there's corrosion around the water jacket tubes I replace them wih new ones and fill the hole up with JB weld first. It works well for these kinds of repairs as you need a good flat surface for the head gasket to seal against.

Dan c
SL Barn

Daniel G Caron

[ja17]

Hello,
Some typical problems with a cylinder head might be; worn or loose valve guides and valve seals causing, excessive oil consumption. Worn valve stems and burnt valves can contribute to low compression. Warped cylinder heads can be a result of severe overheating.

The valve guides are simply bushings (alloy bronze or copper) which are pressed into the aluminum cylinder head. The valve stems move up and down in these guides. At the top of the guide a synthetic valve seal cups around the guide and the valve stem keeping oil from seeping between the vlave stem and valve guide. Manufacturers have improved the materials used to make these valve guides and seals over the years. The newer silicone bronze valve guides should outlast the original copper and bronze valve guides. The factory has also changed to newer synthetic materials for the exhaust valve seals. Notice the black Viton valve seals for the exhaust guides (originals the white nylon. These were developed to handle the higher temperatures in today's engines.

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Worn valve guides are by far the most common point of wear. Since the exhaust valve guides are subject to much more heat than the intake they tend to wear more rapidly than the intake. As valve guide wear increases, the harder valve stems and valve seats wear also. Eventually the valve and/or seat can wear enough or burn and cause compression loss.
To be continued.

Joe Alexander
Blacklick, Ohio

[ja17]

Valve guides can come loose in the head and can end up riding up and down with the valve. This condition will cause severe oil usage and additional damage to the head. The tight hole the valve guide fits into becomes enlaraged and will no longer hold a new standard exhaust guide. Oversize (outside diameter) valve guides are available in several oversizes to correct this condition. If left un-fixed a loose valve guide may eventually cause enough damage to allow the valve to become unhooked and drop into the cylinder causing a lot of damage to the piston and cylinder head.
Ocassionally a valve seat may become damaged or loose and need replacement. This is unusual, but happens at times. The valve seat is the hard steel ring pressed into the head where the valve actually opens and closes. The engine depends on a perfect air tight seal at this seat to maintain compression.
A good automaotive machine shop can prepare the head and replace a damaged valve seat.


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Download Attachment: cyl hed combus chambers & seats.JPG
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More to come!
Joe

Joe Alexander
Blacklick, Ohio

[ja17]

Severe oveheating of the engine is the most common cause of warped heads and blown head gaskets. When an engine is overheated the aluminum cylinder head expands beyound designed limits and actually arches in the center. This allows the head gasket to fail and the aluminum head remains distorted "warped" from the heat even after cool down.
One important item that your machine shop will check when the head is removed is the "flatness" of the cylinder head. A head warped more than a couple of thousanths of an inch must be trued-up "milled".
In the old days when cylinder heads were cheap, it was common practice to automatically mill heads before any valve job, whether the head was warped or not. These days new heads are thousands of dollars to replace. You can only cut  one millimeter off of these heads before they are scrap. With this in mind milling the head should only be done when needed. This information should be conveyed to the machine shop so your head is not milled unnecessarily.
The heighth of your  cylinder head must be measured first to see if it is the stock 85mm. 84 mm is the minimum. It will have to be measured in several areas along the length of the head.

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Next cylinder head is checked for warpage using a machinist straight edge or similar.

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Feeler guages can be inserted in any gap between the head and the straight edge to determine the amount of warpage. Hopefully if your head is warped you will have enough material to mill it flat and stay within the 84mm minimum heighth. Some machine shops offer a head straightening service these days, which can re-flatten the heads somewhat before milling.

Now consider what happens when you mill a head flat, which has been  warped or arched in the center. Most of the head material is removed from the ends! Often times a used cylinder head which has been milled is much shorter at the ends than in the center! Since the combustion chambers are in the head, the compression on the outer cylinders becomes higher! The center cylinders may remain normal since little head material is removed at the center. Another bad effect of head milling is that the timing chain becomes longer as the head becomes shorter. If one milimeter is removed from the head during milling, the timing chain tensioner must take up an additional 2mm of chain, shortening the usable life of the timing chain. In severe cases the warped top deck of the cylinder head may cause camshaft bearing problems. Mill only when needed, or as Dan has said, you will have an expensive boat anchor on your hands.

Joe Alexander
Blacklick, Ohio

[Benz Dr.]

Have to question this a bit Joe.
Everything you say about head warpage I agree with but I'm not sure you would raise compression very much on the outer cylinders after milling if the head was warped. I've measured every head I've ever done and at most they were never all that much different from end to end or from middle to end.
So, what I'm saying is the whole head tends to become thinner as you cut it down but most can't even be cut 1 mm and are often less than that due to manufacturing tolerances being different from time to time. The actual amount of compression increase would be very small and often the deeper valves and seats on an old head make up for most of that.
I believe that maximum oversize pistons are not as high as standard bore ones. I've seen some with a stepped down area on one side to clear the intake valve and I guess MB decided that most engines at maxium oversize probably have cut down heads and need the extra valve clearance. These engines with stepped pistons are way down on compression even when everything is replaced with new parts. I think 140 PSI would be all you'd see in a 230SL.
 I've seen 165 on some and you can feel the difference. The only way to get the compression back up to factory specs would be to deck the block which should be considered anyway if you have a badly warped head from overheating. The block surface will stay flat almost forever but they can and will warp. When you put that nice flat head on it will leak like a dirty diaper.

I've gone to checking all the surfaces around the engine to make sure nothing is really out a long way. The block and head have to be perfectly flat or future problems will show up.

A word to the wise:
if you overheat an engine or just get it really hot you should change all the fluids. Colant, oil and trans fluid. This is recomended because you've probably exceeded the normal operating temps of these fluids and turned them into acidic junk.

Dan c
SL Barn

Daniel G Caron

[ja17]

Hello Dan,
You are probably right in most cases. However I have found that in rare severe cases the compression may be altered enough to cause problems. I had one 280-SL head warped nearly 1mm. It was planed and nearly all the material was removed from the ends to make it flat again. The compression in the middle two cylinders was about 165 lb. The end cylinders were about 190 lb. This caused numerous running problems since  100+ octane was needed for the end cylinders. The head was removed, the volume of combustion chambers were measured in cubic centimeters, the correct volume of aluminum head  material was carved out of the combustion chambers. The head was re-installed and ran just fine. This is not typical but possible. You could probably calculate the volume removed from the cylinder when one milimeter is removed and convert this into a compression figure if you needed to. Performance shops as you probably know will measure the volume of the combustion chambers to get everything equal on race cars. I guess all of this depends on where and how much the head is warped.
It would be interesting to measure the volume of a stepped piston  engine with the head installed to see if it really did vary with the earlier flat piston engines.
Speaking of acidic coolant we will discuss cylinder head corrosion next! Feel free to add some your experiences Dan. Thanks!

Joe Alexander
Blacklick, Ohio

[Joe]

Wouldn't a thicker head gasket compensate for more head milling? I know these are available for some high compression cars that needed detuned after high octane fuel became unavailable.

If the problem is the valves hitting the pistons, then couldn't the valve seats be cut deeper?

Joe

[Benz Dr.]

WOW!  1 mm is a lot for a head to be warped. I'm very surprised any machine shop would even bother, but most of them don't know the fine details , do they?
I can see where this could happen but as the saying goes '' Common things are comon ''  The stepped pistons may be all that's left in stock in some cases and I'd be tempted to mill the block to get a decent piston height. Blocks are cheaper and more plentiful than good cylinder heads. NEVER cut a head for any reason other than absolute need.
 
A good head is at least 1K or more these days. You can buy junk for less - don't do it. Always ask for the thickness of the head and if it's straight and how much the warp is. If it's right down to the 84mm minimum the valves are probably cut very deeply. This can be a source of a lot of problems like heavy oil useage and ball studs that can't be adjusted any more. I always use new intake valves unless someone says no. I usually say no as well. The intake valves are quite thin and after some wear and a few times being re ground they get way too thin and won't sit on the seat in the right position. I like them to sit mid way or maybe 2/3 of the way from the bottom of the seat. Sealing and cooling is part of how well you set the valves in place.
The whole basis of air flow through the head is determined almost entirely at the valve seat area. These engines run at about 10mm valve lift which really isn't that much. If the air can be made to flow better across the seat the engine will have more power. More power requires more fuel in most cases so careful testing must be done along the way by reading the spark plugs after a short drive.

In sumation, a 280 SL engine should have about 165 to 175 PSI and a very strong mid range power band. Idle should be dead smooth - smoother than a 230 or 250. A 230 engine should be just a bit more free reving due to the shorter stroke engine. All of them should have a nice throaty rattling sound under full throttle. There should be a high performance sound because they are high performance engines - about 1 HP per cubic inch. Even the lowly 190SL engine produces more HP per cubic inch and the 300SL produces  a lot more. This was cutting edge stuff 40 or 50 years ago when you think about it.
Don't expect too much from your engine but expect it to run like a MB.

Regards,
Dan c
SL Barn


Daniel G Caron

[Ben]

Slightly off topic but I remember reading in the Meredith book and elswhere that after a certain chassis number the 230SL recieved " Pistons for #1 cylinder with additional clearance, to prevent seizing"

Always puzzled me ?

Any comment guys?

Regards,
Ben in Ireland.
'64 230SL 4sp.
'03 CLK Kompressor

[ja17]

Hello Joe,
I have never heard of any thicker head gaskets available for these engines. The steel water distributors pressed in the heads may tend to come loose if the head is overmilled?

Hello Ben,
I never noticed different clearences on different cylinders of the 230-SL engine. I will have to look for this next time.



Joe Alexander
Blacklick, Ohio