Head Removal. To proceed or not to proceed

[Benz Dr.]

Yes Dan, he is catching on fast!

  So do I. Sometimes I catch on fast and sometimes I catch on slow, and sometimes I catch on half fast.

[Tyler S]

Ha! Thanks guys! Having an automotive repair background definately helps. The key is to do your research ahead of time. Every car out there has its own quirks, idiosyncrasies, and difficulties. As well as tips and tricks. Being prepared for them makes for "smoother sailing". This group does just that. We get to exchange information for the benefit of all members!

So.. Being I am so deep into this repair, My engine compartment is screaming new paint please. I knew going in this wouldn't be a simple "get in and get out" job.
Tyler

[Tyler S]

So before sending off the head to be re-worked, I decided to remove a few of the worst offending valves. Nothing is burnt but there is significant wear on the valve contact face. These may not be salvageable. The seats on the other hand look to be ok with only minor ringing on the contact area. The rotator's appear to be working correctly.The wear is very even around the circumference of the valve and seat. The guides show minimal wear but will be replaced anyway. If valves with excessive wear are re-ground and re-used, they will sit too far up into the seat, causing the valve stems to sit too high. You will run into problems with rocker arm geometry and the in-ability to adjust the valves. This will also cause the keeper grooves to sit too high, effectively reducing your valve spring tension. This could cause valve float or even worse, the keepers to come loose while running!

Tyler

[Benz Dr.]

I wonder if he needs a job?

[ja17]

Tyler,

Valves are fairly inexpensive on the aftermarket. Most like to replace them these days. If you follow MB factory specs on reconditioning the old ones, you should be fine. MB is fairly conservative on allowable wear and machining tolerances.

[Tyler S]

Joe, I'm going to leave that one up to the machine shop. If anything is questionable they will get replaced. If too much meat needs to be removed then out with the old and in with the new. I already have a set of 3.5mm thrust shims if need be. Dont want to take it down any further than that.

[ja17]

I always supply the machine shop with the factory specs and tolerances so no mistakes are made.

[Tyler S]

Joe; Scanned, Copied, Printed, and in a plastic sleeve zip tied to the head. Also written what I want done. "Check for warpage. Inspect and Advise. DO NOT MILL without authorization."
Tyler

[Benz Dr.]

We put the head in an oven and heat it up so it can be pulled straight again. This allows for minimum stock removal although the top surface of the head often needs to be touched up so that both surfaces are flat and even.

You can adjust for material removal by using cam bearing shims - I use one or two .015'' shims under each bearing. As long as you have intake valve recession at least .050 mm you won't have any clearance problems.

  You might be one of the first on here to already know about rocker geometry  - good work, young man!

[Rolf-Dieter ✝︎]

Dan, at what temperature setting and how long do you keep it in the oven. I think it is important to mention this fact.

Cheers,

Dieter

PS. How is the snow situation at your end? Any sign of spring yet?


Tyler,

Nice write up (in your posts) and photographic record. Well done!

Dieter

[Tyler S]

Thanks Guys, I dont think I will have much of an issue with warpage. I just dont want a heavy handed machinest to go ahead and mill it without letting me know. I think anything less than .003 I will leave it alone. I think I may go buy a straight edge just to confirm it myself. I can also use it to check the deck.
Tyler

[Benz Dr.]

Every head is different and there's a bit of an art to it but in general terms you would use about 400 degrees F for a 280SL head. The head is set up so that a block is placed under each end and a clamping bracket is place on top of the head in the middle ( or where the warp is ) and then the clamp is torqued down. If the head is more heavily constructed on one side as compared to the other then the heavier side would receive more torque. If you had a .005'' warp you would tighten the clamp so that it would pull straight and then a bit more to allow for elastic memory.

 The head would then be heated for about two hours and then left to cool while still under tension. In some cases a second attempt may be required if needed. Cast iron heads need 700 degrees F and often more time to pull straight. On vintage heads ( or anything valuable ) the advantages are clearly obvious.

I had a head with a .015'' warp. Yeah, it was really hot! After treatment, a .003'' cut was all it needed.

[Tyler S]

Here is a picture of the clamping setup described by Benz Dr.

[Rolf-Dieter ✝︎]

Great information for others Dan and Tyler, on the heating and clamping process prior to refurbishing the head sealing face.

Sometimes special procedures need to be developed to obtain results.

Many years ago I had issues (maintaining close tolerances) with final machining and grinding of multi stage forged and stress relieved compressor shafts (largest diameter 6" smallest [for thrust bearing sleeve and collar]1.5" diameter about 8 feet long). To overcome the issues I had the shaft only preliminary machined leaving 0.06" material for final machining and grinding in order to maintain 0.0002" TIR (Total Indicator Runout). Before this final machining and grinding took place the shaft forging was placed on the floor on V Blocks for 24 hours to self stress relieve.

[ja17]

Yes we have shops that do this kind of straightening also. Care and experience still required or you can cause a crack in the head!

I also loan my set of Mercedes original factory valve guide installation tools to the shop to use. So the valve guide installation goes smoothly. Hopefully your shop has its own.

[Tyler S]

Joe, Im sure they do. They are very experienced with these engines. How they started there business back in the 70's.
http://motorworkssd.com

When the parts driver came to pick up the head I looked in the back of his truck.
A Ferrari engine block
And 2 Rolls Royce 12 cylinder heads!

Made my little Pagoda head feel cheap.

[tel76]

Tyler,
Is there a reason why you have not gone to Metric Motors for your cylinder head re-build, I would have thought they were the go to people for Mercedes engines in the US.
I was not impressed with the different engines in the rear of there van, as far as I am aware MM only works on MB engines, that must be a plus.

[Tyler S]

Eric, three factors were involved in the decision. Not necessarily in any order.

Location: This company is located 40 minutes away from me and I will have the ability to go down there when he calls me after disassembly. I will be able to be involved in the repair. Had I decided for an "exchange" head or I lived closer to them, I would have gone with Metrics.

Shipping: It would have been expensive to ship the head and the thought of a newly refurbished head being freighted makes me nervous. All it takes is one good impact.

Experience: This group is on par with other specialists out there. I asked plenty of questions and got all the right answers. The machinest even volunteered information that I already knew but confirmed that they know the specifics of these engines. A few other members have also used them and can attest to their workmanship. Just because a company does work on other brands does not make them any less capable. The head will be rebuilt by a machinest that specializes in just MB. This guy knew all the tolerences off the top of his head! It will also be blueprinted with before and after measurments.

I guess all that really matters is the end product. Results of the work will be posted here in the coming weeks so we shall see.

Tyler

[Tyler S]

Progress Report:   The machine shop has found the head to be warped .012in. They are confident they can get this number down to .004 to .006 by straightening the head. They will then machine this amount from the head to make it flat. All machining and tolerances are being recorded during this process. The valves, guides, and seals are all going to be replaced. The seats are in good shape and will be re-ground. The end result will be a total of about .010in (.254mm) overall removed from the head height (top and bottom). This is still well within tolerance and could be actually done again down the road on its next repair. .010in cam bearing tower shims will be installed to bring the cam back up to its original height. Attention is also being made to the amount the valve seats are ground. The goal is to achieve a less than or equal to 1.0mm amount of material removed. First repair size 3.5mm valve thrust shims will be used to replace the factory 4.5mm thrust shims. Cam, crank, idler, and tensioner sprockets are all being replaced (see pic) because of wear.

Meanwhile I am making progress on cleaning the block and engine bay. The original red block paint is slowly showing its face. I think I will leave it.

Tyler

[mbzse]

.../...The original red block paint is slowly showing its face.../...

Er..  this is just the base primer glyptal red. All M-B engine blocks were finished in black. Discussed in our Forum several times previously.
/Hans in Sweden

[Tyler S]

The black must be coming off with the grease! At least I will be able to see what is clean before painting

[Benz Dr.]

I use anywhere from .015 to .030 thickness of cam shims. Some of my heads needed machining on the top and bottom surfaces so there have been times where .015'' wasn't really enough to get the rockers back into the right geometry.
 I'm aware that you can use thinner lash caps but I really prefer to use standard caps and thicker cam shims. Cam shims also have the added benefit of raising the cam which also raises the cam gear. This will bring the chain back to its original range of tension and I suppose by keeping it tight it may last longer. 

  Your mileage may vary. 

[Tyler S]

Dan, The head will be cut on the top and bottom. By how much I wont know untill the straightening process is done. My Idea is to shim the cam bearings the same (or close to) amount of material removed to bring the cam back to original height. I may also need the thinner lash caps because the seats are going to be ground, raising the valve stem height. With the head being milled on top, this will lower the ball stud bases as well. We shall see. 
Tyler

[Benz Dr.]

Understood. Two slightly different solutions to the same question. Both will work. I think that mine may address both questions but it's pretty close in either case.


Even machine shops and mechanics will agree/disagree on a whole range of subjects yet still produce very similar work. 

[Pinder]

Tyler. I painted my engine with 500 degree paint from Eastwood. So far its held up very well. it comes with a hardener so if you use it make sure you use a mask. It has a low sheen to it though they describe it as matt finish.  I used the same paint on my radiator and overflow tank.

I had my head rebuilt by MCH   (Midwest Cylinder Head). I had to ship it to them. My head needed to be welded to remove heavy pitting on two of the chambers. I think your head is in better shape. These guys did an excellent job of re creating the chambers. They straightened and machined it, and replacing all new valve guides and re cut valve seats. Total cost for  / welding and machine work was around 650.  I had my engine block bored out locally in NJ for $200. They did not deck the block as it was straight.

One thing that messed me up when I re installed the head was that when I re installed the manifold studs I did not use thread sealer. It turned out that one of the studs goes into a water passage so I had a slight leak of coolant coming out. I fixed this by removing it and using thread sealer. it fixed the problem.