Rebuiding Motor, Cylinder head & Gasket questions

[troctime]

Hello,

I have a charming Pagoda 230SL from 1966 for 6 years in the north of Paris.

I am on sl113.org since the purchase of my w113 and I learned a lot, thanks you all.

The car worked well all these years and I (we) spent a lot of time to restore it.

As it was my first old car I did everything upside down, the first thing I did was the upholstery ! to tell you my level of incompetence. However, it allowed me to interest 'Madame' and it is already very positive.

In a few years, everything has been redone or almost, the hoses (water, brake, gasoline), front and rear axe, brakes, bottom, wheel arches, a complete painting ...

All ... except the engine

And as everything comes to those who wait, I lost the operation of the first cylinder before Christmas

The engine was completely dismantled in November and the total rebuilding of the engine began.

Some steps are on the images ... (cylinder boring, head grinding, head warped !)

The engine block has been ground and the cylinders bored in first repair quote (82.5 mm)
I bought 6 pistons from a specialist (because MB could only sell me low compression pistons).

The cylinder head was rectified this week with a lot of material removed. I think it was warped.

After grinding the cylinder head, I'm still within the manufacturer's tolerances (84.1mm at the lowest and 84.6mm at the thickest) but the head thus bored is no longer flat on top. The 4 bearings are at different heights compared to the new surfaced head. The center of the head is thicker than the edges which have been more machined, as can be seen in the picture (the center is still black and the edges are clean).

I have two questions I would like to ask the 'old' and 'experienced' members of the forum:

1)
For the head, the guy working on the engine offers me to measure the thickness of the head where the 4 bearings are fixed. Then he will dismount the bearings and machine the 3 highest on their flat surface to find the 4 bearings at the same level. It will align the camshaft with the cylinder head side engine block.
Opinions ?

2)
I bought a head gasket at MB and I read on different forums that there could be leaks after reassembly even if we apply the 3 levels of tightening to rebuild the engine, plus a 4th tightening after driving a few hundred kilometers. The set of bolts are new of course.
I also read that it was absolutely necessary to add a sealant in addition on the gasket.
Do you have any experiences on the subject?

I thank you in advance for your constructive remarks and feedback to help me in this important step of the repair of the engine,

Regards,

Olivier

[Benz Dr.]

You will need to straighten the top of the head. This should have been done by putting it in an oven and then pulling the head until the warp was removed many years ago. Since this wasn't done, and the bottom of your head is now flat, all you can do now is machine the top of your head. This will require removing all of the valve guides, dowel pins and studs for the cam bearings. I expect you will need to remove a lot of material to get the top of your flat so you will have to add cam shims under the cam bearings to raise the cam shaft up near the correct height.

 I have to use 2 shims under each cam bearing once in a while but you may need as many as three along with thinner lash caps. All of this rocker geometry is of critical importance or you will be taking the head off again and starting over before you even drive your car. 

I'm not sure how to tell you this but you're a ways away from being done. It seems to me that someone before you didn't follow a good plan and by following their mistakes you've kind of added misery to this situation you're in.

I'm sure myself and others would be happy to guide you through this build. 

[mbzse]

In addition to what Dan states, I would suggest that you ensure that the combustion chambers in the cylinder head all have the same size (cc volume). See description for instance here: http://www.diyporting.com/cc.html
I would think that after such heavy milling, the chambers on each end of your head need significant grinding out. This is in order for all six of them to be equal volume.
M-B workshop Literature gives the volume of the combustion chamber for M127 (230SL) head to be 45,3 to 48cc, whereas M129 (250SE/SL) volume is 48,0 to 50,7cc.  Nominal compression is 9,5:1 for both engine types.

[Shvegel]

Speaking as a professional mechanic I wold never use any sealant on a cylinder head gasket.  Gasket manufacturers spend a lot of time and money developing gaskets that will allow the aluminum head to "Slide" on the iron block as it heats up.  Gluing the head to the gasket and the gasket to the block ruins all of that.   You will definately need to trim the cam bearing mount surfaces as they are now out of plane and you will be forcing yor cast iron camshaft to run in a curve which it will not like. 

[Benz Dr.]

Speaking as a professional mechanic I wold never use any sealant on a cylinder head gasket.  Gasket manufacturers spend a lot of time and money developing gaskets that will allow the aluminum head to "Slide" on the iron block as it heats up.  Gluing the head to the gasket and the gasket to the block ruins all of that.   You will definately need to trim the cam bearing mount surfaces as they are now out of plane and you will be forcing yor cast iron camshaft to run in a curve which it will not like.

I agree. If you can't turn your camshaft by hand it's likely binding.

[ja17]

All good advice. Many possibilities, the BBB states that you can shim the cam stands to resolve any binding. New head gaskets are made from improved materials with some added sealing strips. I am stuck in my old ways. I use a coat of copper gasket spray always on head gaskets and have never had any failures. As mentioned, you can remove some material from the combustion chamber of the center cylinders to equalize the compression.

[Benz Dr.]

Only time I ever see leaking is on 190SL's. They all seem to leak on the spark plug side until everything settles into place - or not.

[troctime]

Thank you for sharing some solutions with me.

I think I will shim the cam stands. Shaving the top of the cylinder head is a lot of work and I’m not certain it brings much more. Of course I will go step by step until the camshaft turns easily with 2 fingers ( a bit of work anyway ).

To compensate the room in the cylinder chambers I will try to mesure the room size but after my guy will first bore the valves seats ( mostly on the external cylinders where the shaving was most important ).

Where can I remouve some material in the combustion chamber to equilibrate the volumes ? (I think also I will have to do it on the external cyl where more material was removed) I’m sure I must be careful but if I have to find one or two cubic centimeter to remove I’d rather have some indications.

Regarding the coper spray I don’t know, some are confident with the new gasket technology and some prefer to ad some products... I really don’t want to do it all again

[Benz Dr.]

Put a straight edge on the top of your cylinder head and see how warped it really is. I think maybe I wasn't clear enough; you will need to plane the top of your head. I've tried to figure out what you intend to do and believe me, it's far more difficult than you could ever imagine. Warps can run in several different directions from different areas making it nearly impossible to shim.

[TheEngineer]

All good advice. Many possibilities, the BBB states that you can shim the cam stands to resolve any binding. New head gaskets are made from improved materials with some added sealing strips. I am stuck in my old ways. I use a coat of copper gasket spray always on head gaskets and have never had any failures. As mentioned, you can remove some material from the combustion chamber of the center cylinders to equalize the compression.

Just two cents worth from an old engineer and old mechanic: I have used copper spray on cylinder head gaskets for a long time. On my 32 year old Hilux truck I just finished doing part of the engine and had a good opportunity to inspect the headgasket which I had replaced 19 years and 80,000 miles ago: there was no indication of any leakage at all. I always hear of "improvements" and most of it is hype. I tend to stick with the proven things and sleep real well.

[troctime]

Hello
I have managed to move forward on my cyl.head.

We found a metal worker in the position to grind the surface of my cyl.head.
The result is excellent.
The top and bottom of the cylinder head are now perfectly parallel.

If I mesure the cylinder head, the thickness is 84.2 mm after processing. I'm still in (84mm) tolerances.

To facilitate the adjustment of the valves, I had made plates of 0.5 mm for the camshaft bearings.

I worked on the top and bottom of the cylinder head by almost 1 mm. The washers under the bearing should rise my camshaft from 0.5 mm.

I hope that the setting of the valve be homogenous between the ends of the cylinder head and the center of the cylinder head.

We soon begin the Assembly of the motor.

Do you have any advice? , something that we especially be careful when assembling?

I've read that the fabric sealing ring on the shaft could be a problem (this seems not to worry my colleague who has already done it).

Thank you

[mbzse]

.../...We soon begin the Assembly of the motor. Do you have any advice, something that we especially be careful when assembling?

Measure and (if needed) exchange valve guides (shaft bushings).
Look at the water dispersers; they are often corroded. Exhange as needed. (see illustration attached, three sizes are in head)
Be very careful of the freshly machined bottom surface of your engine head - no scratches or dents allowed!

[troctime]

Hi,
All valve guides are new.
So is also the entire timing chain (chain, pusher, 3xslides) and all joints.
I also redid completely the injection pump ( looks like new, a real beauty ).

You ask me to look at the water dispensers. I will go tomorrow to see my motor and try to find out.
I do not remember seeing them, where are they located on the cyl.head ?

Thanks