[W126 Coupe] UPDATE / MORE: 560SEC top-end rebuild

[Gerry Van Zandt]

All,

It turns out that that "chunk" of metal was actually 100% a non-issue! It is actually part of the cylinder head casting. I had several MB mechanics confirm this, as well as the machine shop owner (who has refurbed hundreds of M117 heads). It was also visually confirmed in Chet's photos on the process -- his head also has the same chunk out of the casting.

So, no worries there. It wasn't a problem.

Chet's guide has been a godsend as an overview of the process, and I used it EXTENSIVELY in the disassembly of the engine (as well as the very very good factory M117 5.6 engine manual).

Chet's info is here:

http://home.comcast.net/~chwilka/cylinder_head_removal_and_replac.htm
http://home.comcast.net/~chwilka/cylinder_head_r_r_Ref.htm

For those of you who are interested in much more detail, I have a MUCH more extensive, day-by-day and blow-by-blow account of the process posted on my 500E enthusiast web site at the following URL:

http://www.500espot.com/forums/viewtopic.php?f=34&t=626

To view the photographs & download the PDF attachments (and I have posted many more photos on my web site than on my Facebook page) you will have to self-register for the site. However, you can see my day by day narrative text with no problem. I think the thread is up to like 62 posts now.

There are very few special tools that are required for this job, thankfully. Again, the main props go to Chet for his write-up and photos, as that has been an invaluable process overview/reference for this process. 

A few key takeaways for people:

a) If your engine has more than 150K miles on it, your valve guides (not to mention valve seals) are living on borrowed time.If you are at 180-200K, there is no question that your heads need to be refurbished.

b) Changing valve guide seals, and NOT changing the valve guides, is only a TEMPORARY fix to the "blue smoke" problem. It will only be a matter of months until the problem re-appears. It is best just to tackle the problem and do the heads, rather than the band-aid approach of the seals only.

c) If you're going to take the time and effort to do the heads, it's HIGHLY advised that you replace all rubber, plastic and soft items under the hood. They are not particularly expensive (even collectively) and will have a HUGE impact in the overall running of your engine. This includes not only the mandatory-replace rubber parts on the intake system (slide valve, PCV, injector seals & O-rings, the O-rings that connect the intake manifold halves, etc.) but also things like clips, connectors, wire ties, motor mounts (easily accessible with heads off the car), gaskets, idle air injection hoses, EHA O-rings, and so forth. Check the fuel lines that attach to the fuel cooler - mine were beginning to show some external cracking -- something you don't want on underhood rubber fuel lines.

d) Be VERY careful about fitting the exhaust manifold gaskets. Not only should the all-metal side of the gasket face the cylinder head (fiber side to the manifold), but they MUST be oriented correctly. It is IMPERATIVE that you manually place the gasket against the exhaust manifold port so that you can see which way it should be oriented. If oriented the wrong way, then it will significantly restrict exhaust flow into the manifolds from the heads.

e) The ceramic coating of the intake and exhaust manifolds cost around $375 total, and not only will improve aesthetics but also help keep the incoming charge through the intake manifold cooler, and engine bay temps significantly lower through less radiated heat. I think it was a nice touch and not all that expensive.

f) Cam timing is one of the very most critical elements of this job, when you put things back together. It is IMPERATIVE that you document the positions of the cam timing marks when you have the engine at TDC before disassembling the cams. You need to use paint to mark the sprocket and chain on both sides, in addition to photographiing the timing mark locations on the cam towers. If you re-assemble things correctly, and things don't line up EXACTLY, you WILL grenade your motor by way of the valves hitting the pistons, necessitating another head removal and valve replacement.

g) Use PLENTY of assembly lube when re-assembling the valve train. This means that you should put the assembly lube on all metal to metal surfaces: cam bearings & journals, hydraulic compensator ball heads, rocker arm ball sockets/valve shim surface/convex cam surface, cam lobes, and so forth. This will protect everything when you turn the motor until the oil pump can get oil pressure up to everything in the head.

h) Be VERY careful when threading things into the block and heads, so as not to cross-thread. ONLY use factory torque settings if specified. NEVER over-torque anything when it comes to aluminum block or heads. Take it from me, heli-coiling is NOT fun (I had to do this once during this process).

i) Get appropriate torque wrenches. You will need a higher-torque wrench for the head bolts, hydraulic compensators, cam sprocket bolts, etc. However, get a low-torque torque wrench (say 10-50 N-m) which will far more accurately handle the many smaller torquing jobs than the larger torque wrench will. Larger torque wrenches are notoriously inaccurate at the lower 25% of their scale, so be wary of overtorquing.

The total cost of the parts (I was very comprehensive in what I replaced, and also included a new camshaft & 8 new rockers) was around $2,000. If you don't have to do a cam and rockers, and only replace a moderate amount of parts, and get them wholesale/mail order, you can probably get away with around $500-750 for everything that you need. You should expect an additional $500-600 for the refurbishment of the cylinder heads + cleaning of the intake manifold pieces by a competent machine shop.

Don't be in a hurry. Take your time. You really can do it yourself, and you will save yourself several thousands of dollars of labor costs in the process.

On a scale of 1-10, I would overall put this job at an "8" in terms of difficulty. Mainly it's patience and perseverence. This job requires a lot of time to do right. Having a lift helps significantly, although I am doing it with my car up on ramps (which I consider safer than jack stands).

Cheers,
Gerry